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SPAX(1L) Schily´s USER COMMANDS SPAX(1L)

NAME
pax - portable archive interchange

SYNOPSIS
spax [other options] [-cdnv] [-H|-L] [-f archive]
[-o options]... [-s replstr]... [pattern...]

spax -r [other options] [-cdiknuv] [-H|-L] [-f archive]
[-o options]... [-p string]... [-s replstr]... [pattern...]

spax -w [other options] [-dituvX] [-H|-L] [-b blocksize] [-a]
[-f archive] [-o options]... [-s replstr]... [-x format]
[file...]

spax -r -w[other options] [-diklntuvX] [-H|-L] [-o options]...
[-p string]... [-s replstr]... [file...] directory

DESCRIPTION
The pax utility shall read, write, and write lists of the members of
archive files and copy directory hierarchies. A variety of archive for‐
mats shall be supported; see the -x format option.

The action to be taken depends on the presence of the -r and -w
options. The four combinations of -r and -w are referred to as the four
modes of operation: list, read, write, and copy modes, corresponding
respectively to the four forms shown in the SYNOPSIS section.

list In list mode (when neither -r nor -w are specified), pax shall
write the names of the members of the archive file read from the
standard input, with pathnames matching the specified patterns,
to standard output. If a named file is of type directory, the
file hierarchy rooted at that file shall be listed as well.

read In read mode (when -r is specified, but -w is not), pax shall
extract the members of the archive file read from the standard
input, with pathnames matching the specified patterns. If an
extracted file is of type directory, the file hierarchy rooted
at that file shall be extracted as well. The extracted files
shall be created performing pathname resolution with the direc‐
tory in which pax was invoked as the current working directory.

If an attempt is made to extract a directory when the directory
already exists, this shall not be considered an error. If an
attempt is made to extract a FIFO when the FIFO already exists,
this shall not be considered an error.

The ownership, access, and modification times, and file mode of
the restored files are discussed under the -p option.

write In write mode (when -w is specified, but -r is not), pax shall
write the contents of the file operands to the standard output
in an archive format. If no file operands are specified, a list
of files to copy, one per line, shall be read from the standard
input. A file of type directory shall include all of the files
in the file hierarchy rooted at the file.

copy In copy mode (when both -r and -w are specified), pax shall copy
the file operands to the destination directory.

If no file operands are specified, a list of files to copy, one
per line, shall be read from the standard input. A file of type
directory shall include all of the files in the file hierarchy
rooted at the file.

The effect of the copy shall be as if the copied files were
written to an archive file and then subsequently extracted,
except that there may be hard links between the original and the
copied files. If the destination directory is a subdirectory of
one of the files to be copied, the results are unspecified. If
the destination directory is a file of a type not defined by the
System Interfaces volume of IEEE Std 1003.1-2001, the results
are implementation-defined; otherwise, it shall be an error for
the file named by the directory operand not to exist, not be
writable by the user, or not be a file of type directory.

In read or copy modes, if intermediate directories are necessary to
extract an archive member, pax shall perform actions equivalent to the
mkdir() function defined in the System Interfaces volume of IEEE Std
1003.1-2001, called with the following arguments:

· The intermediate directory used as the path argument.

· The value of the bitwise-inclusive OR of S_IRWXU, S_IRWXG, and
S_IRWXO as the mode argument.

If any specified pattern or file operands are not matched by at least
one file or archive member, pax shall write a diagnostic message to
standard error for each one that did not match and exit with a non-zero
exit status.

The archive formats described in the EXTENDED DESCRIPTION section shall
be automatically detected on input. The default output archive format
shall be implementation-defined.

The spax implementation defaults to -x ustar.

A single archive can span multiple files. The pax utility shall deter‐
mine, in an implementation-defined manner, what file to read or write
as the next file.

If the selected archive format supports the specification of linked
files, it shall be an error if these files cannot be linked when the
archive is extracted, except that if the files to be linked are sym‐
bolic links and the system is not capable of making hard links to sym‐
bolic links, then separate copies of the symbolic link shall be created
instead. For archive formats that do not store file contents with each
name that causes a hard link, if the file that contains the data is not
extracted during this pax session, either the data shall be restored
from the original file, or a diagnostic message shall be displayed with
the name of a file that can be used to extract the data. In traversing
directories, pax shall detect infinite loops; that is, entering a pre‐
viously visited directory that is an ancestor of the last file visited.
When it detects an infinite loop, pax shall write a diagnostic message
to standard error and shall terminate.

OPTIONS
The pax utility shall conform to the Base Definitions volume of IEEE
Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines, except that
the order of presentation of the -o, -p, and -s options is significant.

The following options shall be supported:

-r Read an archive file from standard input.

-w Write files to the standard output in the specified archive for‐
mat.

-a Append files to the end of the archive. It is implementation-
defined which devices on the system support appending. Addi‐
tional file formats unspecified by this volume of IEEE Std
1003.1-2001 may impose restrictions on appending.

-b blocksize
Block the output at a positive decimal integer number of bytes
per write to the archive file. Devices and archive formats may
impose restrictions on blocking. Blocking shall be automatically
determined on input. Conforming applications shall not specify a
blocksize value larger than 32256. Default blocking when creat‐
ing archives depends on the archive format. (See the -x option
below.)

-c Match all file or archive members except those specified by the
pattern or file operands.

-d Cause files of type directory being copied or archived or ar‐
chive members of type directory being extracted or listed to
match only the file or archive member itself and not the file
hierarchy rooted at the file.

-f archive
Specify the pathname of the input or output archive, overriding
the default standard input (in list or read modes) or standard
output (write mode).

-H If a symbolic link referencing a file of type directory is spec‐
ified on the command line, pax shall archive the file hierarchy
rooted in the file referenced by the link, using the name of the
link as the root of the file hierarchy. Otherwise, if a sym‐
bolic link referencing a file of any other file type which pax
can normally archive is specified on the command line, then pax
shall archive the file referenced by the link, using the name of
the link. The default behavior shall be to archive the symbolic
link itself.

-i Interactively rename files or archive members. For each archive
member matching a pattern operand or file matching a file oper‐
and, a prompt shall be written to the file /dev/tty. The prompt
shall contain the name of the file or archive member, but the
format is otherwise unspecified. A line shall then be read from
/dev/tty. If this line is blank, the file or archive member
shall be skipped. If this line consists of a single period, the
file or archive member shall be processed with no modification
to its name. Otherwise, its name shall be replaced with the con‐
tents of the line. The pax utility shall immediately exit with a
non-zero exit status if end-of-file is encountered when reading
a response or if /dev/tty cannot be opened for reading and writ‐
ing.

The results of extracting a hard link to a file that has been
renamed during extraction are unspecified.

-k Prevent the overwriting of existing files.

-l (The letter ell.) In copy mode, hard links shall be made between
the source and destination file hierarchies whenever possible.
If specified in conjunction with -H or -L, when a symbolic link
is encountered, the hard link created in the destination file
hierarchy shall be to the file referenced by the symbolic link.
If specified when neither -H nor -L is specified, when a sym‐
bolic link is encountered, the implementation shall create a
hard link to the symbolic link in the source file hierarchy or
copy the symbolic link to the destination.

-L If a symbolic link referencing a file of type directory is spec‐
ified on the command line or encountered during the traversal of
a file hierarchy, pax shall archive the file hierarchy rooted in
the file referenced by the link, using the name of the link as
the root of the file hierarchy. Otherwise, if a symbolic link
referencing a file of any other file type which pax can normally
archive is specified on the command line or encountered during
the traversal of a file hierarchy, pax shall archive the file
referenced by the link, using the name of the link. The default
behavior shall be to archive the symbolic link itself.

-n Select the first archive member that matches each pattern oper‐
and. No more than one archive member shall be matched for each
pattern (although members of type directory shall still match
the file hierarchy rooted at that file).

-o options
Provide information to the implementation to modify the algo‐
rithm for extracting or writing files. The value of options
shall consist of one or more comma-separated keywords of the
form:

keyword[[:]=value][,keyword[[:]=value],...]

Some keywords apply only to certain file formats, as indicated
with each description. Use of keywords that are inapplicable to
the file format being processed produces undefined results.

Keywords in the options argument shall be a string that would be
a valid portable filename as described in the Base Definitions
volume of IEEE Std 1003.1-2001, Section 3.276, Portable Filename
Character Set.

Note: Keywords are not expected to be filenames, merely to fol‐
low the same character composition rules as portable
filenames.

Keywords can be preceded with white space. The value field shall
consist of zero or more characters; within value, the applica‐
tion shall precede any literal comma with a backslash, which
shall be ignored, but preserves the comma as part of value. A
comma as the final character, or a comma followed solely by
white space as the final characters, in options shall be
ignored. Multiple -o options can be specified; if keywords given
to these multiple -o options conflict, the keywords and values
appearing later in command line sequence shall take precedence
and the earlier shall be silently ignored. The following keyword
values of options shall be supported for the file formats as
indicated:

delete=pattern
(Applicable only to the -x pax format.) When used in
write or copy mode, pax shall omit from extended header
records that it produces any keywords matching the string
pattern. When used in read or list mode, pax shall ignore
any keywords matching the string pattern in the extended
header records. In both cases, matching shall be per‐
formed using the pattern matching notation described in
Patterns Matching a Single Character and Patterns Match‐
ing Multiple Characters. For example:

-o delete=security.*

would suppress security-related information. See pax
Extended Header for extended header record keyword usage.

When multiple -o delete=pattern options are specified,
the patterns shall be additive; all keywords matching the
specified string patterns shall be omitted from extended
header records that pax produces.

exthdr.name=string
(Applicable only to the -x pax format.) This keyword
allows user control over the name that is written into
the ustar header blocks for the extended header produced
under the circumstances described in pax Header Block.
The name shall be the contents of string, after the fol‐
lowing character substitutions have been made:

┌─────────────────┬─────────────────────────────────────────────┐
│string Includes: │ Replaced By: │
├─────────────────┼─────────────────────────────────────────────┤
│%d │ The directory name of the file, equivalent │
│ │ to the result of the dirname utility on the │
│ │ translated pathname. │
├─────────────────┼─────────────────────────────────────────────┤
│%f │ The filename of the file, equivalent to the │
│ │ result of the basename utility on the │
│ │ translated pathname. │
├─────────────────┼─────────────────────────────────────────────┤
│%p │ The process ID of the pax process. │
├─────────────────┼─────────────────────────────────────────────┤
│%% │ A '%' character. │
└─────────────────┴─────────────────────────────────────────────┘
Any other '%' characters in string produce undefined
results.

If no -o exthdr.name= string is specified, pax shall use
the following default value:

%d/PaxHeaders.%p/%f

globexthdr.name=string
(Applicable only to the -x pax format.) When used in
write or copy mode with the appropriate options, pax
shall create global extended header records with ustar
header blocks that will be treated as regular files by
previous versions of pax. This keyword allows user con‐
trol over the name that is written into the ustar header
blocks for global extended header records. The name shall
be the contents of string, after the following character
substitutions have been made:

┌─────────────────┬─────────────────────────────────────────────┐
│string Includes: │ Replaced By: │
├─────────────────┼─────────────────────────────────────────────┤
│%n │ An integer that represents the sequence │
│ │ number of the global extended header record │
│ │ in the archive, starting at 1. │
├─────────────────┼─────────────────────────────────────────────┤
│%p │ The process ID of the pax process. │
├─────────────────┼─────────────────────────────────────────────┤
│%% │ A '%' character. │
└─────────────────┴─────────────────────────────────────────────┘
Any other '%' characters in string produce undefined
results.

If no -o globexthdr.name=string is specified, pax shall
use the following default value:

$TMPDIR/GlobalHead.%p.%n

where $TMPDIR represents the value of the TMPDIR environ‐
ment variable. If TMPDIR is not set, pax shall use /tmp.

invalid=action
(Applicable only to the -x pax format.) This keyword
allows user control over the action pax takes upon
encountering values in an extended header record that, in
read or copy mode, are invalid in the destination hierar‐
chy or, in list mode, cannot be written in the codeset
and current locale of the implementation. The following
are invalid values that shall be recognized by pax:

+ In read or copy mode, a filename or link name that
contains character encodings invalid in the desti‐
nation hierarchy. (For example, the name may con‐
tain embedded NULs.)

+ In read or copy mode, a filename or link name that
is longer than the maximum allowed in the destina‐
tion hierarchy (for either a pathname component or
the entire pathname).

+ In list mode, any character string value (file‐
name, link name, user name, and so on) that cannot
be written in the codeset and current locale of
the implementation.

The following mutually-exclusive values of the action
argument are supported:

bypass In read or copy mode, pax shall bypass the file,
causing no change to the destination hierarchy. In
list mode, pax shall write all requested valid
values for the file, but its method for writing
invalid values is unspecified.

rename In read or copy mode, pax shall act as if the -i
option were in effect for each file with invalid
filename or link name values, allowing the user to
provide a replacement name interactively. In list
mode, pax shall behave identically to the bypass
action.

UTF-8 When used in read, copy, or list mode and a file‐
name, link name, owner name, or any other field in
an extended header record cannot be translated
from the pax UTF-8 codeset format to the codeset
and current locale of the implementation, pax
shall use the actual UTF-8 encoding for the name.

write In read or copy mode, pax shall write the file,
translating the name, regardless of whether this
may overwrite an existing file with a valid name.
In list mode, pax shall behave identically to the
bypass action.

If no -o invalid=option is specified, pax shall act as if
-o invalid= bypass were specified. Any overwriting of
existing files that may be allowed by the -o invalid=
actions shall be subject to permission(-p) and modifica‐
tion time (-u) restrictions, and shall be suppressed if
the -k option is also specified.

linkdata
(Applicable only to the -x pax format.) In write mode,
pax shall write the contents of a file to the archive
even when that file is merely a hard link to a file whose
contents have already been written to the archive.

listopt=format
This keyword specifies the output format of the table of
contents produced when the -v option is specified in list
mode. See List Mode Format Specifications. To avoid ambi‐
guity, the listopt= format shall be the only or final
keyword= value pair in a -o option-argument; all charac‐
ters in the remainder of the option-argument shall be
considered part of the format string. When multiple -o
listopt= format options are specified, the format strings
shall be considered a single, concatenated string, evalu‐
ated in command line order.

times (Applicable only to the -x pax format.) When used in
write or copy mode, pax shall include atime and mtime
extended header records for each file. See pax Extended
Header File Times.

In addition to these keywords, if the -x pax format is speci‐
fied, any of the keywords and values defined in pax Extended
Header, including implementation extensions, can be used in -o
option-arguments, in either of two modes:

keyword=value
When used in write or copy mode, these keyword/value
pairs shall be included at the beginning of the archive
as typeflag g global extended header records. When used
in read or list mode, these keyword/value pairs shall act
as if they had been at the beginning of the archive as
typeflag g global extended header records.

keyword:=value
When used in write or copy mode, these keyword/value
pairs shall be included as records at the beginning of a
typeflag x extended header for each file. (This shall be
equivalent to the equal-sign form except that it creates
no typeflag g global extended header records.) When used
in read or list mode, these keyword/value pairs shall act
as if they were included as records at the end of each
extended header; thus, they shall override any global or
file-specific extended header record keywords of the same
names. For example, in the command:

pax -r -o "gname:=mygroup," <archive

the group name will be forced to a new value for all
files read from the archive.

The precedence of -o keywords over various fields in the archive
is described in pax Extended Header Keyword Precedence.

-p string
Specify one or more file characteristic options (privileges).
The string option-argument shall be a string specifying file
characteristics to be retained or discarded on extraction. The
string shall consist of the specification characters a , e, m,
o, and p. Other implementation-defined characters can be
included. Multiple characteristics can be concatenated within
the same string and multiple -p options can be specified. The
meaning of the specification characters are as follows:

a Do not preserve file access times.

e Preserve the user ID, group ID, file mode bits (see the
Base Definitions volume of IEEE Std 1003.1-2001, Section
3.168, File Mode Bits), access time, modification time,
and any other implementation-defined file characteris‐
tics.

Do not preserve file modification times.

o Preserve the user ID and group ID.

p Preserve the file mode bits. Other implementation-defined
file mode attributes may be preserved.

In the preceding list, "preserve" indicates that an attribute
stored in the archive shall be given to the extracted file, sub‐
ject to the permissions of the invoking process. The access and
modification times of the file shall be preserved unless other‐
wise specified with the -p option or not stored in the archive.
All attributes that are not preserved shall be determined as
part of the normal file creation action (see File Read, Write,
and Creation).

If neither the e nor the o specification character is specified,
or the user ID and group ID are not preserved for any reason,
pax shall not set the S_ISUID and S_ISGID bits of the file mode.

If the preservation of any of these items fails for any reason,
pax shall write a diagnostic message to standard error. Failure
to preserve these items shall affect the final exit status, but
shall not cause the extracted file to be deleted.

If file characteristic letters in any of the string option-argu‐
ments are duplicated or conflict with each other, the ones given
last shall take precedence. For example, if -p eme is specified,
file modification times are preserved.

-s replstr
Modify file or archive member names named by pattern or file op‐
erands according to the substitution expression replstr, using
the syntax of the ed utility. The concepts of "address" and
"line" are meaningless in the context of the pax utility, and
shall not be supplied. The format shall be:

-s /old/new/[gp]

where as in ed, old is a basic regular expression and new can
contain an ampersand, '\n' (where n is a digit) backreferences,
or subexpression matching. The old string shall also be permit‐
ted to contain <newline>s.

Any non-null character can be used as a delimiter ( '/' shown
here). Multiple -s expressions can be specified; the expressions
shall be applied in the order specified, terminating with the
first successful substitution. The optional trailing 'g' is as
defined in the ed utility. The optional trailing 'p' shall cause
successful substitutions to be written to standard error. File
or archive member names that substitute to the empty string
shall be ignored when reading and writing archives.

-t When reading files from the file system, and if the user has the
permissions required by utime() to do so, set the access time of
each file read to the access time that it had before being read
by pax.

-u Ignore files that are older (having a less recent file modifica‐
tion time) than a pre-existing file or archive member with the
same name. In read mode, an archive member with the same name as
a file in the file system shall be extracted if the archive mem‐
ber is newer than the file. In write mode, an archive file mem‐
ber with the same name as a file in the file system shall be
superseded if the file is newer than the archive member. If -a
is also specified, this is accomplished by appending to the ar‐
chive; otherwise, it is unspecified whether this is accomplished
by actual replacement in the archive or by appending to the ar‐
chive. In copy mode, the file in the destination hierarchy shall
be replaced by the file in the source hierarchy or by a link to
the file in the source hierarchy if the file in the source hier‐
archy is newer.

-v In list mode, produce a verbose table of contents (see the STD‐
OUT section). Otherwise, write archive member pathnames to stan‐
dard error (see the STDERR section).

-x format
Specify the output archive format. The pax utility shall support
the following formats:

cpio The cpio interchange format; see the EXTENDED DESCRIPTION
section. The default blocksize for this format for char‐
acter special archive files shall be 5120. Implementa‐
tions shall support all blocksize values less than or
equal to 32256 that are multiples of 512.

pax The pax interchange format; see the EXTENDED DESCRIPTION
section. The default blocksize for this format for char‐
acter special archive files shall be 5120. Implementa‐
tions shall support all blocksize values less than or
equal to 32256 that are multiples of 512.

ustar The tar interchange format; see the EXTENDED DESCRIPTION
section. The default blocksize for this format for char‐
acter special archive files shall be 10240. Implementa‐
tions shall support all blocksize values less than or
equal to 32256 that are multiples of 512.

Implementation-defined formats shall specify a default block
size as well as any other block sizes supported for character
special archive files.

Any attempt to append to an archive file in a format different
from the existing archive format shall cause pax to exit immedi‐
ately with a non-zero exit status.

In copy mode, if no -x format is specified, pax shall behave as
if -x pax were specified.

-X When traversing the file hierarchy specified by a pathname, pax
shall not descend into directories that have a different device
ID ( st_dev; see the System Interfaces volume of IEEE Std
1003.1-2001, stat()).

Specifying more than one of the mutually-exclusive options -H and -L
shall not be considered an error and the last option specified shall
determine the behavior of the utility.

The options that operate on the names of files or archive members (-c,
-i, -n, -s, -u, and -v)shallinteractasfollows.Inread mode, the archive
members shall be selected based on the user-specified pattern operands
as modified by the -c, -n, and -u options. Then, any -s and -i options
shall modify, in that order, the names of the selected files. The -v
option shall write names resulting from these modifications.

In write mode, the files shall be selected based on the user-specified
pathnames as modified by the -n and -u options. Then, any -s and -i
options shall modify, in that order, the names of these selected files.
The -v option shall write names resulting from these modifications.

If both the -u and -n options are specified, pax shall not consider a
file selected unless it is newer than the file to which it is compared.

List Mode Format Specifications
The manual page for spax is not yet ready. The following text is a
quotation from the POSIX.1-2001 standard.

In list mode with the -o listopt=format option, the format argument
shall be applied for each selected file. The pax utility shall append a
<newline> to the listopt output for each selected file. The format
argument shall be used as the format string described in the Base Defi‐
nitions volume of IEEE Std 1003.1-2001, Chapter 5, File Format Nota‐
tion, with the exceptions 1. through 5. defined in the EXTENDED
DESCRIPTION section of printf(3), plus the following exceptions:

6. The sequence (keyword) can occur before a format conversion
specifier. The conversion argument is defined by the value of
keyword. The implementation shall support the following key‐
words:

· Any of the Field Name entries in ustar Header Block and
Octet-Oriented cpio Archive Entry. The implementation may
support the cpio keywords without the leading c_ in addi‐
tion to the form required by Values for cpio c_mode
Field.

· Any keyword defined for the extended header in pax
Extended Header.

· Any keyword provided as an implementation-defined exten‐
sion within the extended header defined in pax Extended
Header.

For example, the sequence "%(charset)s" is the string value of
the name of the character set in the extended header.

The result of the keyword conversion argument shall be the value
from the applicable header field or extended header, without any
trailing NULs.

All keyword values used as conversion arguments shall be trans‐
lated from the UTF-8 encoding to the character set appropriate
for the local file system, user database, and so on, as applica‐
ble.

7. An additional conversion specifier character, T, shall be used
to specify time formats. The T conversion specifier character
can be preceded by the sequence (keyword=subformat), where sub‐
format is a date format as defined by date operands. The default
keyword shall be mtime and the default subformat shall be:

%b %e %H:%M %Y

8. An additional conversion specifier character, M, shall be used
to specify the file mode string as defined in ls(1) Standard
Output. If (keyword) is omitted, the mode keyword shall be used.
For example, %.1M writes the single character corresponding to
the <entry type> field of the ls -l command.

9. An additional conversion specifier character, D, shall be used
to specify the device for block or special files, if applicable,
in an implementation-defined format. If not applicable, and
(keyword) is specified, then this conversion shall be equivalent
to %(keyword)u. If not applicable, and (keyword) is omitted,
then this conversion shall be equivalent to <space>.

10. An additional conversion specifier character, F, shall be used
to specify a pathname. The F conversion character can be pre‐
ceded by a sequence of comma-separated keywords:

(keyword[,keyword] ... )
The values for all the keywords that are non-null shall be con‐
catenated together, each separated by a '/'. The default shall
be (path) if the keyword path is defined; otherwise, the default
shall be (prefix, name).

11. An additional conversion specifier character, L, shall be used
to specify a symbolic line expansion. If the current file is a
symbolic link, then %L shall expand to:

"%s -> %s", <value of keyword>, <contents of link>

Otherwise, the %L conversion specification shall be the equivalent of
%F.

OPERANDS
The following operands shall be supported:

directory
The destination directory pathname for copy mode.

file A pathname of a file to be copied or archived.

pattern
A pattern matching one or more pathnames of archive members. A
pattern must be given in the name-generating notation of the
pattern matching notation in Pattern Matching Notation , includ‐
ing the filename expansion rules in Patterns Used for Filename
Expansion. The default, if no pattern is specified, is to select
all members in the archive.

STDIN
In write mode, the standard input shall be used only if no file oper‐
ands are specified. It shall be a text file containing a list of path‐
names, one per line, without leading or trailing <blank>s.

In list and read modes, if -f is not specified, the standard input
shall be an archive file.

Otherwise, the standard input shall not be used.

INPUT FILES
The input file named by the archive option-argument, or standard input
when the archive is read from there, shall be a file formatted accord‐
ing to one of the specifications in the EXTENDED DESCRIPTION section or
some other implementation-defined format.

The file /dev/tty shall be used to write prompts and read responses.

ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of pax:

LANG Provide a default value for the internationalization variables
that are unset or null. (See the Base Definitions volume of IEEE
Std 1003.1-2001, Section 8.2, Internationalization Variables for
the precedence of internationalization variables used to deter‐
mine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all
the other internationalization variables.

LC_COLLATE
Determine the locale for the behavior of ranges, equivalence
classes, and multi-character collating elements used in the pat‐
tern matching expressions for the pattern operand, the basic
regular expression for the -s option, and the extended regular
expression defined for the yesexpr locale keyword in the LC_MES‐
SAGES category.

LC_CTYPE
Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files),
the behavior of character classes used in the extended regular
expression defined for the yesexpr locale keyword in the LC_MES‐
SAGES category, and pattern matching.

LC_MESSAGES
Determine the locale for the processing of affirmative responses
that should be used to affect the format and contents of diag‐
nostic messages written to standard error.

LC_TIME
Determine the format and contents of date and time strings when
the -v option is specified.

NLSPATH
[XSI] [Option Start] Determine the location of message catalogs
for the processing of LC_MESSAGES . [Option End]

TMPDIR Determine the pathname that provides part of the default global
extended header record file, as described for the -o globexthdr=
keyword in the OPTIONS section.

TZ Determine the timezone used to calculate date and time strings
when the -v option is specified. If TZ is unset or null, an
unspecified default timezone shall be used.

ASYNCHRONOUS EVENTS
Default.

STDOUT
In write mode, if -f is not specified, the standard output shall be the
archive formatted according to one of the specifications in the
EXTENDED DESCRIPTION section, or some other implementation-defined for‐
mat (see -x format).

In list mode, when the -o listopt= format has been specified, the
selected archive members shall be written to standard output using the
format described under List Mode Format Specifications. In list mode
without the -o listopt= format option, the table of contents of the
selected archive members shall be written to standard output using the
following format:

"%s\n", <pathname>

If the -v option is specified in list mode, the table of contents of
the selected archive members shall be written to standard output using
the following formats.

For pathnames representing hard links to previous members of the ar‐
chive:

"%s == %s\n", <ls -l listing>, <linkname>

For all other pathnames:

"%s\n", <ls -l listing>

where <ls -l listing> shall be the format specified by the ls(1) util‐
ity with the -l option. When writing pathnames in this format, it is
unspecified what is written for fields for which the underlying archive
format does not have the correct information, although the correct num‐
ber of <blank>-separated fields shall be written.

In list mode, standard output shall not be buffered more than a line at
a time.

STDERR
If -v is specified in read, write, or copy modes, pax shall write the
pathnames it processes to the standard error output using the following
format:

"%s\n", <pathname>

These pathnames shall be written as soon as processing is begun on the
file or archive member, and shall be flushed to standard error. The
trailing <newline>, which shall not be buffered, is written when the
file has been read or written.

If the -s option is specified, and the replacement string has a trail‐
ing 'p', substitutions shall be written to standard error in the fol‐
lowing format:

"%s >> %s\n", <original pathname>, <new pathname>

In all operating modes of pax, optional messages of unspecified format
concerning the input archive format and volume number, the number of
files, blocks, volumes, and media parts as well as other diagnostic
messages may be written to standard error.

In all formats, for both standard output and standard error, it is
unspecified how non-printable characters in pathnames or link names are
written.

When pax is in read mode or list mode, using the -x pax archive format,
and a filename, link name, owner name, or any other field in an
extended header record cannot be translated from the pax UTF-8 codeset
format to the codeset and current locale of the implementation, pax
shall write a diagnostic message to standard error, shall process the
file as described for the -o invalid= option, and then shall process
the next file in the archive.

OUTPUT FILES
In read mode, the extracted output files shall be of the archived file
type. In copy mode, the copied output files shall be the type of the
file being copied. In either mode, existing files in the destination
hierarchy shall be overwritten only when all permission (-p), modifica‐
tion time (-u), and invalid-value (-o invalid=) tests allow it.

In write mode, the output file named by the -f option-argument shall be
a file formatted according to one of the specifications in the EXTENDED
DESCRIPTION section, or some other implementation-defined format.

EXTENDED DESCRIPTION
pax Interchange Format
A pax archive tape or file produced in the -x pax format shall contain
a series of blocks. The physical layout of the archive shall be identi‐
cal to the ustar format described in ustar Interchange Format. Each
file archived shall be represented by the following sequence:

· An optional header block with extended header records.
This header block is of the form described in pax Header
Block, with a typeflag value of x or g. The extended
header records, described in pax Extended Header, shall
be included as the data for this header block.

· A header block that describes the file. Any fields in the
preceding optional extended header shall override the
associated fields in this header block for this file.

· Zero or more blocks that contain the contents of the
file.

At the end of the archive file there shall be two 512-byte blocks
filled with binary zeros, interpreted as an end-of-archive indicator.

A schematic of an example archive with global extended header records
and two actual files is shown in pax Format Archive Example. In the
example, the second file in the archive has no extended header preced‐
ing it, presumably because it has no need for extended attributes.

Figure: pax Format Archive Example

┌──────────────────────────────┬─────────────────────────────────────────────┐
│ustar Header [typeflag = 'g'] │ │
├──────────────────────────────┤ Global Extended header │
│Global Extended Header Data │ │
├──────────────────────────────┼─────────────────────────────────────────────┤
│ustar Header [typeflag = 'x'] │ │
├──────────────────────────────┤ │
│Extended Header Data │ │
├──────────────────────────────┤ File 1: Extended Header data is included │
│ustar Header [typeflag = '0'] │ │
├──────────────────────────────┤ │
│Data for File 1 │ │
├──────────────────────────────┼─────────────────────────────────────────────┤
│ustar Header [typeflag = '0'] │ │
├──────────────────────────────┤ File 2: No Extended Header data is included │
│Data for File 2 │ │
├──────────────────────────────┼─────────────────────────────────────────────┤
│Block of binary Zeroes │ │
├──────────────────────────────┤ End of Archive Indicator │
│Block of binary Zeroes │ │
└──────────────────────────────┴─────────────────────────────────────────────┘

pax Header Block
The pax header block shall be identical to the ustar header block
described in ustar Interchange Format, except that two additional type‐
flag values are defined:

x Represents extended header records for the following file in the
archive (which shall have its own ustar header block). The for‐
mat of these extended header records shall be as described in
pax Extended Header.

g Represents global extended header records for the following
files in the archive. The format of these extended header
records shall be as described in pax Extended Header. Each
value shall affect all subsequent files that do not override
that value in their own extended header record and until another
global extended header record is reached that provides another
value for the same field. The typeflag g global headers should
not be used with interchange media that could suffer partial
data loss in transporting the archive.

For both of these types, the size field shall be the size of the
extended header records in octets. The other fields in the header block
are not meaningful to this version of the pax utility. However, if
this archive is read by a pax utility conforming to the ISO
POSIX-2:1993 standard, the header block fields are used to create a
regular file that contains the extended header records as data. There‐
fore, header block field values should be selected to provide reason‐
able file access to this regular file.

A further difference from the ustar header block is that data blocks
for files of typeflag 1 (the digit one) (hard link) may be included,
which means that the size field may be greater than zero. Archives cre‐
ated by pax -o linkdata shall include these data blocks with the hard
links.

pax Extended Header
A pax extended header contains values that are inappropriate for the
ustar header block because of limitations in that format: fields
requiring a character encoding other than that described in the ISO/IEC
646:1991 standard, fields representing file attributes not described in
the ustar header, and fields whose format or length do not fit the
requirements of the ustar header. The values in an extended header add
attributes to the following file (or files; see the description of the
typeflag g header block) or override values in the following header
block(s), as indicated in the following list of keywords.

An extended header shall consist of one or more records, each con‐
structed as follows:

"%d %s=%s\n", <length>, <keyword>, <value>

The extended header records shall be encoded according to the ISO/IEC
10646-1:2000 standard (UTF-8). The <length> field, <blank>, equals
sign, and <newline> shown shall be limited to the portable character
set, as encoded in UTF-8. The <keyword> and <value> fields can be any
UTF-8 characters. The <length> field shall be the decimal length of the
extended header record in octets, including the trailing <newline>.

The <keyword> field shall be one of the entries from the following list
or a keyword provided as an implementation extension. Keywords con‐
sisting entirely of lowercase letters, digits, and periods are reserved
for future standardization. A keyword shall not include an equals sign.
(In the following list, the notations "file(s)" or "block(s)" is used
to acknowledge that a keyword affects the following single file after a
typeflag x extended header, but possibly multiple files after typeflag
g. Any requirements in the list for pax to include a record when in
write or copy mode shall apply only when such a record has not already
been provided through the use of the -o option. When used in copy mode,
pax shall behave as if an archive had been created with applicable
extended header records and then extracted.)

atime The file access time for the following file(s), equivalent to
the value of the st_atime member of the stat structure for a
file, as described by the stat(2) function. The access time
shall be restored if the process has the appropriate privilege
required to do so. The format of the <value> shall be as
described in pax Extended Header File Times.

charset
The name of the character set used to encode the data in the
following file(s). The entries in the following table are
defined to refer to known standards; additional names may be
agreed on between the originator and recipient.

┌────────────────────────┬───────────────────────────────┐
│ <value> │ Formal Standard │
├────────────────────────┼───────────────────────────────┤
│ISO-IR 646 1990 │ ISO/IEC 646:1990 │
│ISO-IR 8859 1 1998 │ ISO/IEC 8859-1:1998 │
│ISO-IR 8859 2 1999 │ ISO/IEC 8859-2:1999 │
│ISO-IR 8859 3 1999 │ ISO/IEC 8859-3:1999 │
│ISO-IR 8859 4 1998 │ ISO/IEC 8859-4:1998 │
│ISO-IR 8859 5 1999 │ ISO/IEC 8859-5:1999 │
│ISO-IR 8859 6 1999 │ ISO/IEC 8859-6:1999 │
│ISO-IR 8859 7 1987 │ ISO/IEC 8859-7:1987 │
│ISO-IR 8859 8 1999 │ ISO/IEC 8859-8:1999 │
│ISO-IR 8859 9 1999 │ ISO/IEC 8859-9:1999 │
│ISO-IR 8859 10 1998 │ ISO/IEC 8859-10:1998 │
│ISO-IR 8859 13 1998 │ ISO/IEC 8859-13:1998 │
│ISO-IR 8859 14 1998 │ ISO/IEC 8859-14:1998 │
│ISO-IR 8859 15 1999 │ ISO/IEC 8859-15:1999 │
│ISO-IR 10646 2000 │ ISO/IEC 10646:2000 │
│ISO-IR 10646 2000 UTF-8 │ ISO/IEC 10646, UTF-8 encoding │
│BINARY │ None │
└────────────────────────┴───────────────────────────────┘
The encoding is included in an extended header for information only;
when pax is used as described in IEEE Std 1003.1-2001, it shall not
translate the file data into any other encoding. The BINARY entry indi‐
cates unencoded binary data.

When used in write or copy mode, it is implementation-defined whether
pax includes a charset extended header record for a file.

comment
A series of characters used as a comment. All characters in the
<value> field shall be ignored by pax.

gid The group ID of the group that owns the file, expressed as a
decimal number using digits from the ISO/IEC 646:1991 standard.
This record shall override the gid field in the following header
block(s). When used in write or copy mode, pax shall include a
gid extended header record for each file whose group ID is
greater than 2097151 (octal 7777777).

gname The group of the file(s), formatted as a group name in the group
database. This record shall override the gid and gname fields in
the following header block(s), and any gid extended header
record. When used in read, copy, or list mode, pax shall trans‐
late the name from the UTF-8 encoding in the header record to
the character set appropriate for the group database on the
receiving system. If any of the UTF-8 characters cannot be
translated, and if the -o invalid=UTF-8 option is not specified,
the results are implementation-defined. When used in write or
copy mode, pax shall include a gname extended header record for
each file whose group name cannot be represented entirely with
the letters and digits of the portable character set.

linkpath
The pathname of a link being created to another file, of any
type, previously archived. This record shall override the
linkname field in the following ustar header block(s). The fol‐
lowing ustar header block shall determine the type of link cre‐
ated. If typeflag of the following header block is 1, it shall
be a hard link. If typeflag is 2, it shall be a symbolic link
and the linkpath value shall be the contents of the symbolic
link. The pax utility shall translate the name of the link (con‐
tents of the symbolic link) from the UTF-8 encoding to the char‐
acter set appropriate for the local file system. When used in
write or copy mode, pax shall include a linkpath extended header
record for each link whose pathname cannot be represented
entirely with the members of the portable character set other
than NUL.

mtime The file modification time of the following file(s), equivalent
to the value of the st_mtime member of the stat structure for a
file, as described in the stat(2) function. This record shall
override the mtime field in the following header block(s). The
modification time shall be restored if the process has the
appropriate privilege required to do so. The format of the
<value> shall be as described in pax Extended Header File Times.

path The pathname of the following file(s). This record shall over‐
ride the name and prefix fields in the following header
block(s). The pax utility shall translate the pathname of the
file from the UTF-8 encoding to the character set appropriate
for the local file system.

When used in write or copy mode, pax shall include a path
extended header record for each file whose pathname cannot be
represented entirely with the members of the portable character
set other than NUL.

realtime.any
The keywords prefixed by "realtime." are reserved for future
standardization.

security.any
The keywords prefixed by "security." are reserved for future
standardization.

size The size of the file in octets, expressed as a decimal number
using digits from the ISO/IEC 646:1991 standard. This record
shall override the size field in the following header block(s).
When used in write or copy mode, pax shall include a size
extended header record for each file with a size value greater
than 8589934591 (octal 77777777777).

uid The user ID of the file owner, expressed as a decimal number
using digits from the ISO/IEC 646:1991 standard. This record
shall override the uid field in the following header block(s).
When used in write or copy mode, pax shall include a uid
extended header record for each file whose owner ID is greater
than 2097151 (octal 7777777).

uname The owner of the following file(s), formatted as a user name in
the user database. This record shall override the uid and uname
fields in the following header block(s), and any uid extended
header record. When used in read, copy, or list mode, pax shall
translate the name from the UTF-8 encoding in the header record
to the character set appropriate for the user database on the
receiving system. If any of the UTF-8 characters cannot be
translated, and if the -o invalid=UTF-8 option is not specified,
the results are implementation-defined. When used in write or
copy mode, pax shall include a uname extended header record for
each file whose user name cannot be represented entirely with
the letters and digits of the portable character set.

If the <value> field is zero length, it shall delete any header block
field, previously entered extended header value, or global extended
header value of the same name.

If a keyword in an extended header record (or in a -o option-argument)
overrides or deletes a corresponding field in the ustar header block,
pax shall ignore the contents of that header block field.

Unlike the ustar header block fields, NULs shall not delimit <value>s;
all characters within the <value> field shall be considered data for
the field. None of the length limitations of the ustar header block
fields in ustar Header Block shall apply to the extended header
records.

pax Extended Header Keyword Precedence
This section describes the precedence in which the various header
records and fields and command line options are selected to apply to a
file in the archive. When pax is used in read or list modes, it shall
determine a file attribute in the following sequence:

1. If -o delete=keyword-prefix is used, the affected
attributes shall be determined from step 7., if applica‐
ble, or ignored otherwise.

2. If -o keyword:= is used, the affected attributes shall be
ignored.

3. If -o keyword:=value is used, the affected attribute
shall be assigned the value.

4. If there is a typeflag x extended header record, the
affected attribute shall be assigned the <value>. When
extended header records conflict, the last one given in
the header shall take precedence.

5. If -o keyword=value is used, the affected attribute shall
be assigned the value.

6. If there is a typeflag g global extended header record,
the affected attribute shall be assigned the <value>.
When global extended header records conflict, the last
one given in the global header shall take precedence.

7. Otherwise, the attribute shall be determined from the
ustar header block.

pax Extended Header File Times
The pax utility shall write an mtime record for each file in write or
copy modes if the file's modification time cannot be represented
exactly in the ustar header logical record described in ustar Inter‐
change Format. This can occur if the time is out of ustar range, or if
the file system of the underlying implementation supports non-integer
time granularities and the time is not an integer. All of these time
records shall be formatted as a decimal representation of the time in
seconds since the Epoch. If a period ('.') decimal point character is
present, the digits to the right of the point shall represent the units
of a subsecond timing granularity, where the first digit is tenths of a
second and each subsequent digit is a tenth of the previous digit. In
read or copy mode, the pax utility shall truncate the time of a file to
the greatest value that is not greater than the input header file time.
In write or copy mode, the pax utility shall output a time exactly if
it can be represented exactly as a decimal number, and otherwise shall
generate only enough digits so that the same time shall be recovered if
the file is extracted on a system whose underlying implementation sup‐
ports the same time granularity.

ustar Interchange Format
A ustar archive tape or file shall contain a series of logical records.
Each logical record shall be a fixed-size logical record of 512 octets
(see below). Although this format may be thought of as being stored on
9-track industry-standard 12.7 mm (0.5 in) magnetic tape, other types
of transportable media are not excluded. Each file archived shall be
represented by a header logical record that describes the file, fol‐
lowed by zero or more logical records that give the contents of the
file. At the end of the archive file there shall be two 512-octet logi‐
cal records filled with binary zeros, interpreted as an end-of-archive
indicator.

The logical records may be grouped for physical I/O operations, as
described under the -b blocksize and -x ustar options. Each group of
logical records may be written with a single operation equivalent to
the write(2) function. On magnetic tape, the result of this write shall
be a single tape physical block. The last physical block shall always
be the full size, so logical records after the two zero logical records
may contain undefined data.

The header logical record shall be structured as shown in the following
table. All lengths and offsets are in decimal.

Table: ustar Header Block

┌───────────┬──────────────┬────────────────────┐
│Field Name │ Octet Offset │ Length (in Octets) │
├───────────┼──────────────┼────────────────────┤
│name │ 0 │ 100 │
│mode │ 100 │ 8 │
│uid │ 108 │ 8 │
│gid │ 116 │ 8 │
│size │ 124 │ 12 │
│mtime │ 136 │ 12 │
│chksum │ 148 │ 8 │
│typeflag │ 156 │ 1 │
│linkname │ 157 │ 100 │
│magic │ 257 │ 6 │
│version │ 263 │ 2 │
│uname │ 265 │ 32 │
│gname │ 297 │ 32 │
│devmajor │ 329 │ 8 │
│devminor │ 337 │ 8 │
│prefix │ 345 │ 155 │
└───────────┴──────────────┴────────────────────┘
All characters in the header logical record shall be represented in the
coded character set of the ISO/IEC 646:1991 standard. For maximum
portability between implementations, names should be selected from
characters represented by the portable filename character set as octets
with the most significant bit zero. If an implementation supports the
use of characters outside of slash and the portable filename character
set in names for files, users, and groups, one or more implementation-
defined encodings of these characters shall be provided for interchange
purposes.

However, the pax utility shall never create filenames on the local sys‐
tem that cannot be accessed via the procedures described in IEEE Std
1003.1-2001. If a filename is found on the medium that would create an
invalid filename, it is implementation-defined whether the data from
the file is stored on the file hierarchy and under what name it is
stored. The pax utility may choose to ignore these files as long as it
produces an error indicating that the file is being ignored.

Each field within the header logical record is contiguous; that is,
there is no padding used. Each character on the archive medium shall be
stored contiguously.

The fields magic, uname, and gname are character strings each termi‐
nated by a NUL character. The fields name, linkname, and prefix are
NUL-terminated character strings except when all characters in the
array contain non-NUL characters including the last character. The ver‐
sion field is two octets containing the characters "00" (zero-zero).
The typeflag contains a single character. All other fields are leading
zero-filled octal numbers using digits from the ISO/IEC 646:1991 stan‐
dard IRV. Each numeric field is terminated by one or more <space> or
NUL characters.

The name and the prefix fields shall produce the pathname of the file.
A new pathname shall be formed, if prefix is not an empty string (its
first character is not NUL), by concatenating prefix (up to the first
NUL character), a slash character, and name; otherwise, name is used
alone. In either case, name is terminated at the first NUL character.
If prefix begins with a NUL character, it shall be ignored. In this
manner, pathnames of at most 256 characters can be supported. If a
pathname does not fit in the space provided, pax shall notify the user
of the error, and shall not store any part of the file-header or data-
on the medium.

The linkname field, described below, shall not use the prefix to pro‐
duce a pathname. As such, a linkname is limited to 100 characters. If
the name does not fit in the space provided, pax shall notify the user
of the error, and shall not attempt to store the link on the medium.

The mode field provides 12 bits encoded in the ISO/IEC 646:1991 stan‐
dard octal digit representation. The encoded bits shall represent the
following values:

Table: ustar mode Field

┌──────┬─────────────────┬─────────────────────────────────────────────────┐
│ Bit │ IEEE Std │ Description │
│Value │ 1003.1-2001 Bit │ │
├──────┼─────────────────┼─────────────────────────────────────────────────┤
│04000 │ S_ISUID │ Set UID on execution. │
│02000 │ S_ISGID │ Set GID on execution. │
│01000 │ <reserved> │ Reserved for future standardization. │
│00400 │ S_IRUSR │ Read permission for file owner class. │
│00200 │ S_IWUSR │ Write permission for file owner class. │
│00100 │ S_IXUSR │ Execute/search permission for file owner class. │
│00040 │ S_IRGRP │ Read permission for file group class. │
│00020 │ S_IWGRP │ Write permission for file group class. │
│00010 │ S_IXGRP │ Execute/search permission for file group class. │
│00004 │ S_IROTH │ Read permission for file other class. │
│00002 │ S_IWOTH │ Write permission for file other class. │
│00001 │ S_IXOTH │ Execute/search permission for file other class. │
└──────┴─────────────────┴─────────────────────────────────────────────────┘
When appropriate privilege is required to set one of these mode bits,
and the user restoring the files from the archive does not have the
appropriate privilege, the mode bits for which the user does not have
appropriate privilege shall be ignored. Some of the mode bits in the
archive format are not mentioned elsewhere in this volume of IEEE Std
1003.1-2001. If the implementation does not support those bits, they
may be ignored.

The uid and gid fields are the user and group ID of the owner and group
of the file, respectively.

The size field is the size of the file in octets. If the typeflag field
is set to specify a file to be of type 1 (a link) or 2 (a symbolic
link), the size field shall be specified as zero. If the typeflag field
is set to specify a file of type 5 (directory), the size field shall be
interpreted as described under the definition of that record type. No
data logical records are stored for types 1, 2, or 5. If the typeflag
field is set to 3 (character special file), 4 (block special file), or
6 (FIFO), the meaning of the size field is unspecified by this volume
of IEEE Std 1003.1-2001, and no data logical records shall be stored on
the medium. Additionally, for type 6, the size field shall be ignored
when reading. If the typeflag field is set to any other value, the num‐
ber of logical records written following the header shall be
(size+511)/512, ignoring any fraction in the result of the division.

The mtime field shall be the modification time of the file at the time
it was archived. It is the ISO/IEC 646:1991 standard representation of
the octal value of the modification time obtained from the stat(2)
function.

The chksum field shall be the ISO/IEC 646:1991 standard IRV representa‐
tion of the octal value of the simple sum of all octets in the header
logical record. Each octet in the header shall be treated as an
unsigned value. These values shall be added to an unsigned integer,
initialized to zero, the precision of which is not less than 17 bits.
When calculating the checksum, the chksum field is treated as if it
were all spaces.

The typeflag field specifies the type of file archived. If a particular
implementation does not recognize the type, or the user does not have
appropriate privilege to create that type, the file shall be extracted
as if it were a regular file if the file type is defined to have a
meaning for the size field that could cause data logical records to be
written on the medium (see the previous description for size). If con‐
version to a regular file occurs, the pax utility shall produce an
error indicating that the conversion took place. All of the typeflag
fields shall be coded in the ISO/IEC 646:1991 standard IRV:

0 Represents a regular file. For backwards-compatibility, a type‐
flag value of binary zero ('\0') should be recognized as meaning
a regular file when extracting files from the archive. Archives
written with this version of the archive file format create reg‐
ular files with a typefla value of the ISO/IEC 646:1991 standard
IRV '0'.

1 Represents a file linked to another file, of any type, previ‐
ously archived. Such files are identified by having the same
device and file serial numbers, and pathnames that refer to dif‐
ferent directory entries. All such files shall be archived as
linked files. The linked-to name is specified in the linkname
field with a NUL-character terminator if it is less than 100
octets in length.

2 Represents a symbolic link. The contents of the symbolic link
shall be stored in the linkname field.

3,4 Represent character special files and block special files
respectively. In this case the devmajor and devminor fields
shall contain information defining the device, the format of
which is unspecified by this volume of IEEE Std 1003.1-2001.
Implementations may map the device specifications to their own
local specification or may ignore the entry.

5 Specifies a directory or subdirectory. On systems where disk
allocation is performed on a directory basis, the size field
shall contain the maximum number of octets (which may be rounded
to the nearest disk block allocation unit) that the directory
may hold. A size field of zero indicates no such limiting. Sys‐
tems that do not support limiting in this manner should ignore
the size field.

6 Specifies a FIFO special file. Note that the archiving of a FIFO
file archives the existence of this file and not its contents.

7 Reserved to represent a file to which an implementation has
associated some high-performance attribute. Implementations
without such extensions should treat this file as a regular file
(type 0).

A-Z The letters 'A' to 'Z', inclusive, are reserved for custom
implementations. All other values are reserved for future ver‐
sions of IEEE Std 1003.1-2001.

It is unspecified whether files with pathnames that refer to the same
directory entry are archived as linked files or as separate files. If
they are archived as linked files, this means that attempting to
extract both pathnames from the resulting archive will always cause an
error (unless the -u option is used) because the link cannot be cre‐
ated.

It is unspecified whether files with the same device and file serial
numbers being appended to an archive are treated as linked files to
members that were in the archive before the append.

Attempts to archive a socket using ustar interchange format shall pro‐
duce a diagnostic message. Handling of other file types is implementa‐
tion-defined.

The magic field is the specification that this archive was output in
this archive format. If this field contains ustar (the five characters
from the ISO/IEC 646:1991 standard IRV shown followed by NUL), the
uname and gname fields shall contain the ISO/IEC 646:1991 standard IRV
representation of the owner and group of the file, respectively (trun‐
cated to fit, if necessary). When the file is restored by a privi‐
leged, protection-preserving version of the utility, the user and group
databases shall be scanned for these names. If found, the user and
group IDs contained within these files shall be used rather than the
values contained within the uid and gid fields.

cpio Interchange Format
The octet-oriented cpio archive format shall be a series of entries,
each comprising a header that describes the file, the name of the file,
and then the contents of the file.

An archive may be recorded as a series of fixed-size blocks of octets.
This blocking shall be used only to make physical I/O more efficient.
The last group of blocks shall always be at the full size.

For the octet-oriented cpio archive format, the individual entry infor‐
mation shall be in the order indicated and described by the following
table; see also the <cpio.h> header.

Table: Octet-Oriented cpio Archive Entry

┌─────────────────────┬────────────────────┬─────────────────┐
│ Header Field Name │ Length (in Octets) │ Interpreted as │
├─────────────────────┼────────────────────┼─────────────────┤
│c_magic │ 6 │ Octal number │
│c_dev │ 6 │ Octal number │
│c_ino │ 6 │ Octal number │
│c_mode │ 6 │ Octal number │
│c_uid │ 6 │ Octal number │
│c_gid │ 6 │ Octal number │
│c_nlink │ 6 │ Octal number │
│c_rdev │ 6 │ Octal number │
│c_mtime │ 11 │ Octal number │
│c_namesize │ 6 │ Octal number │
│c_filesize │ 11 │ Octal number │
│ │ │ │
│Filename Field Name │ Length │ Interpreted as │
│c_name │ c_namesize │ Pathname string │
│ │ │ │
│File Data Field Name │ Length │ Interpreted as │
│c_filedata │ c_filesize │ Data │
└─────────────────────┴────────────────────┴─────────────────┘
cpio Header
For each file in the archive, a header as defined previously shall be
written. The information in the header fields is written as streams of
the ISO/IEC 646:1991 standard characters interpreted as octal numbers.
The octal numbers shall be extended to the necessary length by append‐
ing the ISO/IEC 646:1991 standard IRV zeros at the most-significant-
digit end of the number; the result is written to the most-significant
digit of the stream of octets first. The fields shall be interpreted as
follows:

c_magic
Identify the archive as being a transportable archive by con‐
taining the identifying value "070707".

c_dev, c_ino
Contains values that uniquely identify the file within the ar‐
chive (that is, no files contain the same pair of c_dev and
c_ino values unless they are links to the same file). The values
shall be determined in an unspecified manner.

c_mode Contains the file type and access permissions as defined in the
following table.

Table: Values for cpio c_mode Field

┌──────────────────────┬─────────┬────────────────────────┐
│File Permissions Name │ Value │ Indicates │
├──────────────────────┼─────────┼────────────────────────┤
│C_IRUSR │ 000400 │ Read by owner │
│C_IWUSR │ 000200 │ Write by owner │
│C_IXUSR │ 000100 │ Execute by owner │
│C_IRGRP │ 000040 │ Read by group │
│C_IWGRP │ 000020 │ Write by group │
│C_IXGRP │ 000010 │ Execute by group │
│C_IROTH │ 000004 │ Read by others │
│C_IWOTH │ 000002 │ Write by others │
│C_IXOTH │ 000001 │ Execute by others │
│C_ISUID │ 004000 │ Set uid │
│C_ISGID │ 002000 │ Set gid │
│C_ISVTX │ 001000 │ Reserved │
├──────────────────────┼─────────┼────────────────────────┤
│File Type Name │ Value │ Indicates │
├──────────────────────┼─────────┼────────────────────────┤
│C_ISDIR │ 0040000 │ Directory │
│C_ISFIFO │ 0010000 │ FIFO │
│C_ISREG │ 0100000 │ Regular file │
│C_ISLNK │ 0120000 │ Symbolic link │
│C_ISBLK │ 0060000 │ Block special file │
│C_ISCHR │ 0020000 │ Character special file │
│C_ISSOCK │ 0140000 │ Socket │
│C_ISCTG │ 0110000 │ Reserved │
└──────────────────────┴─────────┴────────────────────────┘
Directories, FIFOs, symbolic links, and regular files shall be
supported on a system conforming to this volume of IEEE Std
1003.1-2001; additional values defined previously are reserved
for compatibility with existing systems. Additional file types
may be supported; however, such files should not be written to
archives intended to be transported to other systems.

c_uid Contains the user ID of the owner.

c_gid Contains the group ID of the group.

c_nlink
Contains a number greater than or equal to the number of links
in the archive referencing the file. If the -a option is used to
append to a cpio archive, then the pax utility need not account
for the files in the existing part of the archive when calculat‐
ing the c_nlink values for the appended part of the archive, and
need not alter the c_nlink values in the existing part of the
archive if additional files with the same c_dev and c_ino values
are appended to the archive.

c_rdev Contains implementation-defined information for character or
block special files.

c_mtime
Contains the latest time of modification of the file at the time
the archive was created.

c_namesize
Contains the length of the pathname, including the terminating
NUL character.

c_filesize
Contains the length of the file in octets. This shall be the
length of the data section following the header structure.

cpio Filename
The c_name field shall contain the pathname of the file. The length of
this field in octets is the value of c_namesize.

If a filename is found on the medium that would create an invalid path‐
name, it is implementation-defined whether the data from the file is
stored on the file hierarchy and under what name it is stored.

All characters shall be represented in the ISO/IEC 646:1991 standard
IRV. For maximum portability between implementations, names should be
selected from characters represented by the portable filename character
set as octets with the most significant bit zero. If an implementation
supports the use of characters outside the portable filename character
set in names for files, users, and groups, one or more implementation-
defined encodings of these characters shall be provided for interchange
purposes. However, the pax utility shall never create filenames on the
local system that cannot be accessed via the procedures described pre‐
viously in this volume of IEEE Std 1003.1-2001. If a filename is found
on the medium that would create an invalid filename, it is implementa‐
tion-defined whether the data from the file is stored on the local file
system and under what name it is stored. The pax utility may choose to
ignore these files as long as it produces an error indicating that the
file is being ignored.

cpio File Data
Following c_name, there shall be c_filesize octets of data. Interpre‐
tation of such data occurs in a manner dependent on the file. If
c_filesize is zero, no data shall be contained in c_filedata.

When restoring from an archive:

· If the user does not have the appropriate privilege to create a
file of the specified type, pax shall ignore the entry and write
an error message to standard error.

· Only regular files have data to be restored. Presuming a regular
file meets any selection criteria that might be imposed on the
format-reading utility by the user, such data shall be restored.

· If a user does not have appropriate privilege to set a particu‐
lar mode flag, the flag shall be ignored. Some of the mode flags
in the archive format are not mentioned elsewhere in this volume
of IEEE Std 1003.1-2001. If the implementation does not support
those flags, they may be ignored.

cpio Special Entries
FIFO special files, directories, and the trailer shall be recorded with
c_filesize equal to zero. For other special files, c_filesize is
unspecified by this volume of IEEE Std 1003.1-2001. The header for the
next file entry in the archive shall be written directly after the last
octet of the file entry preceding it. A header denoting the filename
TRAILER!!! shall indicate the end of the archive; the contents of
octets in the last block of the archive following such a header are
undefined.

EXIT STATUS
The following exit values shall be returned:

0 All files were processed successfully.

>0 An error occurred.

CONSEQUENCES OF ERRORS
If pax cannot create a file or a link when reading an archive or cannot
find a file when writing an archive, or cannot preserve the user ID,
group ID, or file mode when the -p option is specified, a diagnostic
message shall be written to standard error and a non-zero exit status
shall be returned, but processing shall continue. In the case where pax
cannot create a link to a file, pax shall not, by default, create a
second copy of the file.

If the extraction of a file from an archive is prematurely terminated
by a signal or error, pax may have only partially extracted the file or
(if the -n option was not specified) may have extracted a file of the
same name as that specified by the user, but which is not the file the
user wanted. Additionally, the file modes of extracted directories may
have additional bits from the S_IRWXU mask set as well as incorrect
modification and access times.

_________________________________________________________________
The following sections are informative.

APPLICATION USAGE
Caution is advised when using the -a option to append to a cpio format
archive. If any of the files being appended happen to be given the same
c_dev and c_ino values as a file in the existing part of the archive,
then they may be treated as links to that file on extraction. Thus, it
is risky to use -a with cpio format except when it is done on the same
system that the original archive was created on, and with the same pax
utility, and in the knowledge that there has been little or no file
system activity since the original archive was created that could lead
to any of the files appended being given the same c_dev and c_ino val‐
ues as an unrelated file in the existing part of the archive. Also,
when (intentionally) appending additional links to a file in the exist‐
ing part of the archive, the c_nlink values in the modified archive can
be smaller than the number of links to the file in the archive, which
may mean that the links are not preserved on extraction.

The -p (privileges) option was invented to reconcile differences
between historical tar and cpio implementations. In particular, the two
utilities use -m in diametrically opposed ways. The -p option also pro‐
vides a consistent means of extending the ways in which future file
attributes can be addressed, such as for enhanced security systems or
high-performance files. Although it may seem complex, there are really
two modes that are most commonly used:

-p e ``Preserve everything". This would be used by the historical
superuser, someone with all the appropriate privileges, to pre‐
serve all aspects of the files as they are recorded in the ar‐
chive. The e flag is the sum of o and p, and other implementa‐
tion-defined attributes.

-p p ``Preserve" the file mode bits. This would be used by the user
with regular privileges who wished to preserve aspects of the
file other than the ownership. The file times are preserved by
default, but two other flags are offered to disable these and
use the time of extraction.

The one pathname per line format of standard input precludes pathnames
containing <newline>s. Although such pathnames violate the portable
filename guidelines, they may exist and their presence may inhibit
usage of pax within shell scripts. This problem is inherited from his‐
torical archive programs. The problem can be avoided by listing file‐
name arguments on the command line instead of on standard input.

It is almost certain that appropriate privileges are required for pax
to accomplish parts of this volume of IEEE Std 1003.1-2001. Specifi‐
cally, creating files of type block special or character special,
restoring file access times unless the files are owned by the user (the
-t option), or preserving file owner, group, and mode (the -p option)
all probably require appropriate privileges.

In read mode, implementations are permitted to overwrite files when the
archive has multiple members with the same name. This may fail if per‐
missions on the first version of the file do not permit it to be over‐
written.

The cpio and ustar formats can only support files up to 8589934592
bytes (8 * 2^30) in size.

EXAMPLES
The following command:

pax -w -f /dev/rmt/1m .

copies the contents of the current directory to tape drive 1, medium
density (assuming historical System V device naming procedures-the his‐
torical BSD device name would be /dev/rmt9).

The following commands:

mkdir newdirpax -rw olddir newdir

copy the olddir directory hierarchy to newdir.

pax -r -s ',^//*usr//*,,' -f a.pax

reads the archive a.pax, with all files rooted in /usr in the archive
extracted relative to the current directory.

Using the option:

-o listopt="%M %(atime)T %(size)D %(name)s"

overrides the default output description in Standard Output and instead
writes:

-rw-rw--- Jan 12 15:53 1492 /usr/foo/bar

Using the options:

-o listopt='%L\t%(size)D\n%.7' \
-o listopt='(name)s\n%(atime)T\n%T'

overrides the default output description in Standard Output and instead
writes:

/usr/foo/bar -> /tmp 1492
/usr/fo
Jan 12 1991
Jan 31 15:53

RATIONALE
The pax utility was new for the ISO POSIX-2:1993 standard. It repre‐
sents a peaceful compromise between advocates of the historical tar and
cpio utilities.

A fundamental difference between cpio and tar was in the way directo‐
ries were treated. The cpio utility did not treat directories differ‐
ently from other files, and to select a directory and its contents
required that each file in the hierarchy be explicitly specified. For
tar, a directory matched every file in the file hierarchy it rooted.

The pax utility offers both interfaces; by default, directories map
into the file hierarchy they root. The -d option causes pax to skip any
file not explicitly referenced, as cpio historically did. The tar -
style behavior was chosen as the default because it was believed that
this was the more common usage and because tar is the more commonly
available interface, as it was historically provided on both System V
and BSD implementations.

The data interchange format specification in this volume of IEEE Std
1003.1-2001 requires that processes with "appropriate privileges" shall
always restore the ownership and permissions of extracted files exactly
as archived. If viewed from the historic equivalence between superuser
and "appropriate privileges", there are two problems with this require‐
ment. First, users running as superusers may unknowingly set dangerous
permissions on extracted files. Second, it is needlessly limiting, in
that superusers cannot extract files and own them as superuser unless
the archive was created by the superuser. (It should be noted that
restoration of ownerships and permissions for the superuser, by
default, is historical practice in cpio, but not in tar.) In order to
avoid these two problems, the pax specification has an additional
"privilege" mechanism, the -p option. Only a pax invocation with the
privileges needed, and which has the -p option set using the e specifi‐
cation character, has the "appropriate privilege" to restore full own‐
ership and permission information.

Note also that this volume of IEEE Std 1003.1-2001 requires that the
file ownership and access permissions shall be set, on extraction, in
the same fashion as the creat(2) function when provided with the mode
stored in the archive. This means that the file creation mask of the
user is applied to the file permissions.

Users should note that directories may be created by pax while extract‐
ing files with permissions that are different from those that existed
at the time the archive was created. When extracting sensitive informa‐
tion into a directory hierarchy that no longer exists, users are
encouraged to set their file creation mask appropriately to protect
these files during extraction.

The table of contents output is written to standard output to facili‐
tate pipeline processing.

An early proposal had hard links displaying for all pathnames. This
was removed because it complicates the output of the case where -v is
not specified and does not match historical cpio usage. The hard-link
information is available in the -v display.

The description of the -l option allows implementations to make hard
links to symbolic links. IEEE Std 1003.1-2001 does not specify any way
to create a hard link to a symbolic link, but many implementations pro‐
vide this capability as an extension. If there are hard links to sym‐
bolic links when an archive is created, the implementation is required
to archive the hard link in the archive (unless -H or -L is specified).
When in read mode and in copy mode, implementations supporting hard
links to symbolic links should use them when appropriate.

The archive formats inherited from the POSIX.1-1990 standard have cer‐
tain restrictions that have been brought along from historical usage.
For example, there are restrictions on the length of pathnames stored
in the archive. When pax is used in copy (-rw) mode (copying directory
hierarchies), the ability to use extensions from the -x pax format
overcomes these restrictions.

The default blocksize value of 5120 bytes for cpio was selected because
it is one of the standard block-size values for cpio, set when the -B
option is specified. (The other default block-size value for cpio is
512 bytes, and this was considered to be too small.) The default block
value of 10240 bytes for tar was selected because that is the standard
block-size value for BSD tar. The maximum block size of 32256 bytes
(2^15-512 bytes) is the largest multiple of 512 bytes that fits into a
signed 16-bit tape controller transfer register. There are known limi‐
tations in some historical systems that would prevent larger blocks
from being accepted. Historical values were chosen to improve compati‐
bility with historical scripts using dd(1) or similar utilities to
manipulate archives. Also, default block sizes for any file type other
than character special file has been deleted from this volume of IEEE
Std 1003.1-2001 as unimportant and not likely to affect the structure
of the resulting archive.

Implementations are permitted to modify the block-size value based on
the archive format or the device to which the archive is being written.
This is to provide implementations with the opportunity to take advan‐
tage of special types of devices, and it should not be used without a
great deal of consideration as it almost certainly decreases archive
portability.

The intended use of the -n option was to permit extraction of one or
more files from the archive without processing the entire archive. This
was viewed by the standard developers as offering significant perfor‐
mance advantages over historical implementations. The -n option in
early proposals had three effects; the first was to cause special char‐
acters in patterns to not be treated specially. The second was to cause
only the first file that matched a pattern to be extracted. The third
was to cause pax to write a diagnostic message to standard error when
no file was found matching a specified pattern. Only the second behav‐
ior is retained by this volume of IEEE Std 1003.1-2001, for many rea‐
sons. First, it is in general not acceptable for a single option to
have multiple effects. Second, the ability to make pattern matching
characters act as normal characters is useful for parts of pax other
than file extraction. Third, a finer degree of control over the special
characters is useful because users may wish to normalize only a single
special character in a single filename. Fourth, given a more general
escape mechanism, the previous behavior of the -n option can be easily
obtained using the -s option or a sed script. Finally, writing a diag‐
nostic message when a pattern specified by the user is unmatched by any
file is useful behavior in all cases.

In this version, the -n was removed from the copy mode synopsis of pax;
it is inapplicable because there are no pattern operands specified in
this mode.

There is another method than pax for copying subtrees in IEEE Std
1003.1-2001 described as part of the cp(1) utility. Both methods are
historical practice: cp(1) provides a simpler, more intuitive inter‐
face, while pax offers a finer granularity of control. Each provides
additional functionality to the other; in particular, pax maintains the
hard-link structure of the hierarchy while cp(1) does not. It is the
intention of the standard developers that the results be similar (using
appropriate option combinations in both utilities). The results are not
required to be identical; there seemed insufficient gain to applica‐
tions to balance the difficulty of implementations having to guarantee
that the results would be exactly identical.

A single archive may span more than one file. It is suggested that
implementations provide informative messages to the user on standard
error whenever the archive file is changed.

The -d option (do not create intermediate directories not listed in the
archive) found in early proposals was originally provided as a comple‐
ment to the historic -d option of cpio. It has been deleted.

The -s option in early proposals specified a subset of the substitution
command from the ed utility. As there was no reason for only a subset
to be supported, the -s option is now compatible with the current ed
specification. Since the delimiter can be any non-null character, the
following usage with single spaces is valid:

pax -s " foo bar " ...

The -t description is worded so as to note that this may cause the
access time update caused by some other activity (which occurs while
the file is being read) to be overwritten.

The default behavior of pax with regard to file modification times is
the same as historical implementations of tar. It is not the histori‐
cal behavior of cpio.

Because the -i option uses /dev/tty, utilities without a controlling
terminal are not able to use this option.

The -y option, found in early proposals, has been deleted because a
line containing a single period for the -i option has equivalent func‐
tionality. The special lines for the -i option (a single period and the
empty line) are historical practice in cpio.

In early drafts, a -e charmap option was included to increase portabil‐
ity of files between systems using different coded character sets. This
option was omitted because it was apparent that consensus could not be
formed for it. In this version, the use of UTF-8 should be an adequate
substitute.

The -k option was added to address international concerns about the
dangers involved in the character set transformations of -e (if the
target character set were different from the source, the filenames
might be transformed into names matching existing files) and also was
made more general to protect files transferred between file systems
with different {NAME_MAX} values (truncating a filename on a smaller
system might also inadvertently overwrite existing files). As stated,
it prevents any overwriting, even if the target file is older than the
source. This version adds more granularity of options to solve this
problem by introducing the -o invalid=option -specifically the UTF-8
action. (Note that an existing file that is named with a UTF-8 encoding
is still subject to overwriting in this case. The -k option closes that
loophole.)

Some of the file characteristics referenced in this volume of IEEE Std
1003.1-2001 might not be supported by some archive formats. For exam‐
ple, neither the tar nor cpio formats contain the file access time. For
this reason, the e specification character has been provided, intended
to cause all file characteristics specified in the archive to be
retained.

It is required that extracted directories, by default, have their
access and modification times and permissions set to the values speci‐
fied in the archive. This has obvious problems in that the directories
are almost certainly modified after being extracted and that directory
permissions may not permit file creation. One possible solution is to
create directories with the mode specified in the archive, as modified
by the umask of the user, with sufficient permissions to allow file
creation. After all files have been extracted, pax would then reset the
access and modification times and permissions as necessary.

The list-mode formatting description borrows heavily from the one
defined by the printf(1) utility. However, since there is no separate
operand list to get conversion arguments, the format was extended to
allow specifying the name of the conversion argument as part of the
conversion specification.

The T conversion specifier allows time fields to be displayed in any of
the date formats. Unlike the ls(1) utility, pax does not adjust the
format when the date is less than six months in the past. This makes
parsing the output more predictable.

The D conversion specifier handles the ability to display the
major/minor or file size, as with ls(1), by using %-8(size)D.

The L conversion specifier handles the ls display for symbolic links.

Conversion specifiers were added to generate existing known types used
for ls(1).

pax Interchange Format
The new POSIX data interchange format was developed primarily to sat‐
isfy international concerns that the ustar and cpio formats did not
provide for file, user, and group names encoded in characters outside a
subset of the ISO/IEC 646:1991 standard. The standard developers real‐
ized that this new POSIX data interchange format should be very exten‐
sible because there were other requirements they foresaw in the near
future:

· Support international character encodings and locale information

· Support security information (ACLs, and so on)

· Support future file types, such as realtime or contiguous files

· Include data areas for implementation use

· Support systems with words larger than 32 bits and timers with
subsecond granularity

The following were not goals for this format because these are better
handled by separate utilities or are inappropriate for a portable for‐
mat:

· Encryption

· Compression

· Data translation between locales and codesets

· inode storage

The format chosen to support the goals is an extension of the ustar
format. Of the two formats previously available, only the ustar format
was selected for extensions because:

· It was easier to extend in an upwards-compatible way. It offered
version flags and header block type fields with room for future
standardization. The cpio format, while possessing a more flexi‐
ble file naming methodology, could not be extended without
breaking some theoretical implementation or using a dummy file‐
name that could be a legitimate filename.

· Industry experience since the original "tar wars" fought in
developing the ISO POSIX-1 standard has clearly been in favor of
the ustar format, which is generally the default output format
selected for pax implementations on new systems.

The new format was designed with one additional goal in mind: reason‐
able behavior when an older tar or pax utility happened to read an ar‐
chive. Since the POSIX.1-1990 standard mandated that a "format-reading
utility" had to treat unrecognized typeflag values as regular files,
this allowed the format to include all the extended information in a
pseudo-regular file that preceded each real file. An option is given
that allows the archive creator to set up reasonable names for these
files on the older systems. Also, the normative text suggests that
reasonable file access values be used for this ustar header block. Mak‐
ing these header files inaccessible for convenient reading and deleting
would not be reasonable. File permissions of 600 or 700 are suggested.

The ustar typeflag field was used to accommodate the additional func‐
tionality of the new format rather than magic or version because the
POSIX.1-1990 standard (and, by reference, the previous version of pax),
mandated the behavior of the format-reading utility when it encountered
an unknown typeflag, but was silent about the other two fields.

Early proposals of the first revision to IEEE Std 1003.1-2001 contained
a proposed archive format that was based on compatibility with the
standard for tape files (ISO 1001, similar to the format used histori‐
cally on many mainframes and minicomputers). This format was overly
complex and required considerable overhead in volume and header
records. Furthermore, the standard developers felt that it would not be
acceptable to the community of POSIX developers, so it was later
changed to be a format more closely related to historical practice on
POSIX systems.

The prefix and name split of pathnames in ustar was replaced by the
single path extended header record for simplicity.

The concept of a global extended header (typeflag g) was controversial.
If this were applied to an archive being recorded on magnetic tape, a
few unreadable blocks at the beginning of the tape could be a serious
problem; a utility attempting to extract as many files as possible from
a damaged archive could lose a large percentage of file header informa‐
tion in this case. However, if the archive were on a reliable medium,
such as a CD-ROM, the global extended header offers considerable poten‐
tial size reductions by eliminating redundant information. Thus, the
text warns against using the global method for unreliable media and
provides a method for implanting global information in the extended
header for each file, rather than in the typeflag g records.

No facility for data translation or filtering on a per-file basis is
included because the standard developers could not invent an interface
that would allow this in an efficient manner. If a filter, such as
encryption or compression, is to be applied to all the files, it is
more efficient to apply the filter to the entire archive as a single
file. The standard developers considered interfaces that would invoke a
shell script for each file going into or out of the archive, but the
system overhead in this approach was considered to be too high.

One such approach would be to have filter= records that give a pathname
for an executable. When the program is invoked, the file and archive
would be open for standard input/output and all the header fields would
be available as environment variables or command-line arguments. The
standard developers did discuss such schemes, but they were omitted
from IEEE Std 1003.1-2001 due to concerns about excessive overhead.
Also, the program itself would need to be in the archive if it were to
be used portably.

There is currently no portable means of identifying the character
set(s) used for a file in the file system. Therefore, pax has not been
given a mechanism to generate charset records automatically. The only
portable means of doing this is for the user to write the archive using
the -o charset=string command line option. This assumes that all of the
files in the archive use the same encoding. The "implementation-
defined" text is included to allow for a system that can identify the
encodings used for each of its files.

The table of standards that accompanies the charset record description
is acknowledged to be very limited. Only a limited number of character
set standards is reasonable for maximal interchange. Any character set
is, of course, possible by prior agreement. It was suggested that
EBCDIC be listed, but it was omitted because it is not defined by a
formal standard. Formal standards, and then only those with reasonably
large followings, can be included here, simply as a matter of practi‐
cality. The <value>s represent names of officially registered character
sets in the format required by the ISO 2375:1985 standard.

The normal comma or <blank>-separated list rules are not followed in
the case of keyword options to allow ease of argument parsing for
getopts.

Further information on character encodings is in pax Archive Character
Set Encoding/Decoding.

The standard developers have reserved keyword name space for vendor
extensions. It is suggested that the format to be used is:

VENDOR.keyword

where VENDOR is the name of the vendor or organization in all uppercase
letters. It is further suggested that the keyword following the period
be named differently than any of the standard keywords so that it could
be used for future standardization, if appropriate, by omitting the
VENDOR prefix.

The <length> field in the extended header record was included to make
it simpler to step through the records, even if a record contains an
unknown format (to a particular pax) with complex interactions of spe‐
cial characters. It also provides a minor integrity checkpoint within
the records to aid a program attempting to recover files from a damaged
archive.

There are no extended header versions of the devmajor and devminor
fields because the unspecified format ustar header field should be suf‐
ficient. If they are not, vendor-specific extended keywords (such as
VENDOR.devmajor) should be used.

Device and i-number labeling of files was not adopted from cpio; files
are interchanged strictly on a symbolic name basis, as in ustar.

Just as with the ustar format descriptions, the new format makes no
special arrangements for multi-volume archives. Each of the pax archive
types is assumed to be inside a single POSIX file and splitting that
file over multiple volumes (diskettes, tape cartridges, and so on),
processing their labels, and mounting each in the proper sequence are
considered to be implementation details that cannot be described
portably.

The pax format is intended for interchange, not only for backup on a
single (family of) systems. It is not as densely packed as might be
possible for backup:

· It contains information as coded characters that could be coded
in binary.

· It identifies extended records with name fields that could be
omitted in favor of a fixed-field layout.

· It translates names into a portable character set and identifies
locale-related information, both of which are probably unneces‐
sary for backup.

The requirements on restoring from an archive are slightly different
from the historical wording, allowing for non-monolithic privilege to
bring forward as much as possible. In particular, attributes such as
"high performance file" might be broadly but not universally granted
while set-user-ID or chown(2) might be much more restricted. There is
no implication in IEEE Std 1003.1-2001 that the security information be
honored after it is restored to the file hierarchy, in spite of what
might be improperly inferred by the silence on that topic. That is a
topic for another standard.

Links are recorded in the fashion described here because a link can be
to any file type. It is desirable in general to be able to restore part
of an archive selectively and restore all of those files completely. If
the data is not associated with each link, it is not possible to do
this. However, the data associated with a file can be large, and when
selective restoration is not needed, this can be a significant burden.
The archive is structured so that files that have no associated data
can always be restored by the name of any link name of any link, and
the user may choose whether data is recorded with each instance of a
file that contains data. The format permits mixing of both types of
links in a single archive; this can be done for special needs, and pax
is expected to interpret such archives on input properly, despite the
fact that there is no pax option that would force this mixed case on
output. (When -o linkdata is used, the output must contain the dupli‐
cate data, but the implementation is free to include it or omit it when
-o linkdata is not used.)

The time values are included as extended header records for those
implementations needing more than the eleven octal digits allowed by
the ustar format. Portable file timestamps cannot be negative. If pax
encounters a file with a negative timestamp in copy or write mode, it
can reject the file, substitute a non-negative timestamp, or generate a
non-portable timestamp with a leading granularities than seconds, the
normative text requires support only for seconds since the Epoch
because the ISO POSIX-1 standard states them that way. The ustar format
includes only mtime; the new format adds atime and ctime for symmetry.
The atime access time restored to the file system will be affected by
the -p a and -p e options. The ctime creation time (actually inode mod‐
ification time) is described with "appropriate privilege" so that it
can be ignored when writing to the file system. POSIX does not provide
a portable means to change file creation time. Nothing is intended to
prevent a non-portable implementation of pax from restoring the value.

The gid, size, and uid extended header records were included to allow
expansion beyond the sizes specified in the regular tar header. New
file system architectures are emerging that will exhaust the 12-digit
size field. There are probably not many systems requiring more than 8
digits for user and group IDs, but the extended header values were
included for completeness, allowing overrides for all of the decimal
values in the tar header.

The standard developers intended to describe the effective results of
pax with regard to file ownerships and permissions; implementations are
not restricted in timing or sequencing the restoration of such, pro‐
vided the results are as specified.

Much of the text describing the extended headers refers to use in
"write or copy modes". The copy mode references are due to the norma‐
tive text: "The effect of the copy shall be as if the copied files were
written to an archive file and then subsequently extracted ...". There
is certainly no way to test whether pax is actually generating the
extended headers in copy mode, but the effects must be as if it had.

pax Archive Character Set Encoding/Decoding
There is a need to exchange archives of files between systems of dif‐
ferent native codesets. Filenames, group names, and user names must be
preserved to the fullest extent possible when an archive is read on the
receiving platform. Translation of the contents of files is not within
the scope of the pax utility.

There will also be the need to represent characters that are not avail‐
able on the receiving platform. These unsupported characters cannot be
automatically folded to the local set of characters due to the chance
of collisions. This could result in overwriting previous extracted
files from the archive or pre-existing files on the system.

For these reasons, the codeset used to represent characters within the
extended header records of the pax archive must be sufficiently rich to
handle all commonly used character sets. The fields requiring transla‐
tion include, at a minimum, filenames, user names, group names, and
link pathnames. Implementations may wish to have localized extended
keywords that use non-portable characters.

The standard developers considered the following options:

· The archive creator specifies the well-defined name of the
source codeset. The receiver must then recognize the codeset
name and perform the appropriate translations to the destination
codeset.

· The archive creator includes within the archive the character
mapping table for the source codeset used to encode extended
header records. The receiver must then read the character map‐
ping table and perform the appropriate translations to the des‐
tination codeset.

· The archive creator translates the extended header records in
the source codeset into a canonical form. The receiver must then
perform the appropriate translations to the destination codeset.

The approach that incorporates the name of the source codeset poses the
problem of codeset name registration, and makes the archive useless to
pax archive decoders that do not recognize that codeset.

Because parts of an archive may be corrupted, the standard developers
felt that including the character map of the source codeset was too
fragile. The loss of this one key component could result in making the
entire archive useless. (The difference between this and the global
extended header decision was that the latter has a workaround-duplicat‐
ing extended header records on unreliable media-but this would be too
burdensome for large character set maps.)

Both of the above approaches also put an undue burden on the pax ar‐
chive receiver to handle the cross-product of all source and destina‐
tion codesets.

To simplify the translation from the source codeset to the canonical
form and from the canonical form to the destination codeset, the stan‐
dard developers decided that the internal representation should be a
stateless encoding. A stateless encoding is one where each codepoint
has the same meaning, without regard to the decoder being in a specific
state. An example of a stateful encoding would be the Japanese Shift-
JIS; an example of a stateless encoding would be the ISO/IEC 646:1991
standard (equivalent to 7-bit ASCII).

For these reasons, the standard developers decided to adopt a canonical
format for the representation of file information strings. The obvious,
well-endorsed candidate is the ISO/IEC 10646-1:2000 standard (based in
part on Unicode), which can be used to represent the characters of vir‐
tually all standardized character sets. The standard developers ini‐
tially agreed upon using UCS2 (16-bit Unicode) as the internal repre‐
sentation. This repertoire of characters provides a sufficiently rich
set to represent all commonly-used codesets.

However, the standard developers found that the 16-bit Unicode repre‐
sentation had some problems. It forced the issue of standardizing byte
ordering. The 2-byte length of each character made the extended header
records twice as long for the case of strings coded entirely from his‐
torical 7-bit ASCII. For these reasons, the standard developers chose
the UTF-8 defined in the ISO/IEC 10646-1:2000 standard. This multi-byte
representation encodes UCS2 or UCS4 characters reliably and determinis‐
tically, eliminating the need for a canonical byte ordering. In addi‐
tion, NUL octets and other characters possibly confusing to POSIX file
systems do not appear, except to represent themselves. It was realized
that certain national codesets take up more space after the encoding,
due to their placement within the UCS range; it was felt that the use‐
fulness of the encoding of the names outweighs the disadvantage of size
increase for file, user, and group names.

The encoding of UTF-8 is as follows:

UCS4 Hex Encoding UTF-8 Binary Encoding
00000000-0000007F 0xxxxxxx
00000080-000007FF 110xxxxx 10xxxxxx
00000800-0000FFFF 1110xxxx 10xxxxxx 10xxxxxx
00010000-001FFFFF 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
00200000-03FFFFFF 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
04000000-7FFFFFFF 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx

where each 'x' represents a bit value from the character being trans‐
lated.

ustar Interchange Format
The description of the ustar format reflects numerous enhancements over
pre-1988 versions of the historical tar utility. The goal of these
changes was not only to provide the functional enhancements desired,
but also to retain compatibility between new and old versions. This
compatibility has been retained. Archives written using the old archive
format are compatible with the new format.

Implementors should be aware that the previous file format did not
include a mechanism to archive directory type files. For this reason,
the convention of using a filename ending with slash was adopted to
specify a directory on the archive.

The total size of the name and prefix fields have been set to meet the
minimum requirements for {PATH_MAX} If a pathname will fit within the
name field, it is recommended that the pathname be stored there without
the use of the prefix field. Although the name field is known to be too
small to contain {PATH_MAX} characters, the value was not changed in
this version of the archive file format to retain backwards-compatibil‐
ity, and instead the prefix was introduced. Also, because of the ear‐
lier version of the format, there is no way to remove the restriction
on the linkname field being limited in size to just that of the name
field.

The size field is required to be meaningful in all implementation
extensions, although it could be zero. This is required so that the
data blocks can always be properly counted.

It is suggested that if device special files need to be represented
that cannot be represented in the standard format, that one of the
extension types (A-Z) be used, and that the additional information for
the special file be represented as data and be reflected in the size
field.

Attempting to restore a special file type, where it is converted to
ordinary data and conflicts with an existing filename, need not be spe‐
cially detected by the utility. If run as an ordinary user, pax should
not be able to overwrite the entries in, for example, /dev in any case
(whether the file is converted to another type or not). If run as a
privileged user, it should be able to do so, and it would be considered
a bug if it did not. The same is true of ordinary data files and simi‐
larly named special files; it is impossible to anticipate the needs of
the user (who could really intend to overwrite the file), so the behav‐
ior should be predictable (and thus regular) and rely on the protection
system as required.

The value 7 in the typeflag field is intended to define how contiguous
files can be stored in a ustar archive. IEEE Std 1003.1-2001 does not
require the contiguous file extension, but does define a standard way
of archiving such files so that all conforming systems can interpret
these file types in a meaningful and consistent manner. On a system
that does not support extended file types, the pax utility should do
the best it can with the file and go on to the next.

The file protection modes are those conventionally used by the ls(1)
utility. This is extended beyond the usage in the ISO POSIX-2 standard
to support the "shared text" or "sticky" bit. It is intended that the
conformance document should not document anything beyond the existence
of and support of such a mode. Further extensions are expected to
these bits, particularly with overloading the set-user-ID and set-
group-ID flags.

cpio Interchange Format
The reference to appropriate privilege in the cpio format refers to an
error on standard output; the ustar format does not make comparable
statements.

The model for this format was the historical System V cpio -c data
interchange format. This model documents the portable version of the
cpio format and not the binary version. It has the flexibility to
transfer data of any type described within IEEE Std 1003.1-2001, yet is
extensible to transfer data types specific to extensions beyond IEEE
Std 1003.1-2001 (for example, contiguous files). Because it describes
existing practice, there is no question of maintaining upwards-compati‐
bility.

cpio Header
There has been some concern that the size of the c_ino field of the
header is too small to handle those systems that have very large inode
numbers. However, the c_ino field in the header is used strictly as a
hard-link resolution mechanism for archives. It is not necessarily the
same value as the inode number of the file in the location from which
that file is extracted.

The name c_magic is based on historical usage.

cpio Filename
For most historical implementations of the cpio utility, {PATH_MAX}
octets can be used to describe the pathname without the addition of any
other header fields (the NUL character would be included in this
count). {PATH_MAX} is the minimum value for pathname size, documented
as 256 bytes. However, an implementation may use c_namesize to deter‐
mine the exact length of the pathname. With the current description of
the <cpio.h> header, this pathname size can be as large as a number
that is described in six octal digits.

Two values are documented under the c_mode field values to provide for
extensibility for known file types:

0110 000
Reserved for contiguous files. The implementation may treat the
rest of the information for this archive like a regular file. If
this file type is undefined, the implementation may create the
file as a regular file.

This provides for extensibility of the cpio format while allowing for
the ability to read old archives. Files of an unknown type may be read
as "regular files" on some implementations. On a system that does not
support extended file types, the pax utility should do the best it can
with the file and go on to the next.

FUTURE DIRECTIONS
None.

End of informative sections.
_________________________________________________________________

SEE ALSO
Shell Command Language, cp(1), ed(1), getopts(1), ls(1), printf(3), the
Base Definitions volume of IEEE Std 1003.1-2001, <cpio.h>, the System
Interfaces volume of IEEE Std 1003.1-2001, chown(2), creat(2),
mkdir(2), mkfifo(2), stat(2), utime(2), write(2).

CHANGE HISTORY
First released in Issue 4.

Issue 5
A note is added to the APPLICATION USAGE indicating that the cpio and
tar formats can only support files up to 8 gigabytes in size.

Issue 6
The pax utility is aligned with the IEEE P1003.2b draft standard:

· Support has been added for symbolic links in the options and
interchange formats.

· A new format has been devised, based on extensions to ustar.

· References to the "extended" tar and cpio formats derived from
the POSIX.1-1990 standard have been changed to remove the
"extended" adjective because this could cause confusion with the
extended tar header added in this revision. (All references to
tar are actually to ustar.)

The TZ entry is added to the ENVIRONMENT VARIABLES section.

IEEE PASC Interpretation 1003.2 #168 is applied, clarifying that
mkdir(2) and mkfifo(2) calls can ignore an [EEXIST] error when extract‐
ing an archive.

IEEE PASC Interpretation 1003.2 #180 is applied, clarifying how
extracted files are created when in read mode.

IEEE PASC Interpretation 1003.2 #181 is applied, clarifying the
description of the -t option.

IEEE PASC Interpretation 1003.2 #195 is applied.

IEEE PASC Interpretation 1003.2 #206 is applied, clarifying the han‐
dling of links for the -H, -L, and -l options.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/35 is applied, adding
the process ID of the pax process into certain fields. This change pro‐
vides a method for the implementation to ensure that different
instances of pax extracting a file named /a/b/foo will not collide when
processing the extended header information associated with foo.

IEEE Std 1003.1-2001/Cor 1-2002, item XCU/TC1/D6/36 is applied, chang‐
ing -x B to -x pax in the OPTIONS section.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/20 is applied, updat‐
ing the SYNOPSIS to be consistent with the normative text.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/21 is applied, updat‐
ing the DESCRIPTION to describe the behavior when files to be linked
are symbolic links and the system is not capable of making hard links
to symbolic links.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/22 is applied, updat‐
ing the OPTIONS section to describe the behavior for how multiple
options are to be handled.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/23 is applied, updat‐
ing the write option within the OPTIONS section.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/24 is applied, adding
a paragraph into the OPTIONS section that states that specifying more
than one of the mutually-exclusive options (-H and -L) is not consid‐
ered an error and that the last option specified will determine the
behavior of the utility.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/25 is applied, remov‐
ing the ctime paragraph within the EXTENDED DESCRIPTION. There is a
contradiction in the definition of the ctime keyword for the pax
extended header, in that the st_ctime member of the stat structure does
not refer to a file creation time. No field in the standard stat struc‐
ture from <sys/stat.h> includes a file creation time.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/26 is applied, making
it clear that typeflag 1 RB ( ustar Interchange Format) applies not
only to files that are hard-linked, but also to files that are aliased
via symlinks.

IEEE Std 1003.1-2001/Cor 2-2004, item XCU/TC2/D6/27 is applied, clari‐
fying the cpio c_nlink field.

End of quoted text from the POSIX.1-2001 standard.

OPTIONS
The following other options are implemented as extension to the POSIX
standard:

-help Prints a summary of the most important options for spax(1) and
exits.

-xhelp Prints a summary of the less important options for spax(1) and
exits.

-version
Prints the spax version number string and exists.

EXAMPLES
ENVIRONMENT
FILES
SEE ALSO
DIAGNOSTICS
NOTES
The Institute of Electrical and Electronics Engineers and The Open
Group, have given us permission to reprint portions of their documenta‐
tion. In the following statement, the phrase ``this text'' refers to
portions of the system documentation.

Portions of this text are reprinted and reproduced in electronic form
in the sfind manual, from IEEE Std 1003.1, 2004 Edition, Standard for
Information Technology -- Portable Operating System Interface (POSIX),
The Open Group Base Specifications Issue 6, Copyright (C) 2001-2004 by
the Institute of Electrical and Electronics Engineers, Inc and The Open
Group. In the event of any discrepancy between these versions and the
original IEEE and The Open Group Standard, the original IEEE and The
Open Group Standard is the referee document. The original Standard can
be obtained online at http://www.opengroup.org/unix/online.html.

BUGS
AUTHOR
Joerg Schilling
Seestr. 110
D-13353 Berlin
Germany

Mail bugs and suggestions to:

schilling@fokus.fraunhofer.de or js@cs.tu-berlin.de or
joerg@schily.isdn.cs.tu-berlin.de

Joerg Schilling 07/02/17 SPAX(1L)

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