CHATTR(1)CHATTR(1)NAMEchattr - change file attributes on a Linux file system
SYNOPSISchattr [ -RVf ] [ -v version ] [ mode ] files...
DESCRIPTIONchattr changes the file attributes on a Linux file system.
The format of a symbolic mode is +-=[acdeijstuACDST].
The operator `+' causes the selected attributes to be added to the
existing attributes of the files; `-' causes them to be removed; and
`=' causes them to be the only attributes that the files have.
The letters `acdeijstuACDST' select the new attributes for the files:
append only (a), compressed (c), no dump (d), extent format (e),
immutable (i), data journalling (j), secure deletion (s), no tail-merg‐
ing (t), undeletable (u), no atime updates (A), no copy on write (C),
synchronous directory updates (D), synchronous updates (S), and top of
directory hierarchy (T).
The following attributes are read-only, and may be listed by lsattr(1)
but not modified by chattr: huge file (h), compression error (E),
indexed directory (I), compression raw access (X), and compressed dirty
file (Z).
OPTIONS-R Recursively change attributes of directories and their contents.
-V Be verbose with chattr's output and print the program version.
-f Suppress most error messages.
-v version
Set the file's version/generation number.
ATTRIBUTES
When a file with the 'A' attribute set is accessed, its atime record is
not modified. This avoids a certain amount of disk I/O for laptop sys‐
tems.
A file with the `a' attribute set can only be open in append mode for
writing. Only the superuser or a process possessing the
CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
A file with the `c' attribute set is automatically compressed on the
disk by the kernel. A read from this file returns uncompressed data.
A write to this file compresses data before storing them on the disk.
Note: please make sure to read the bugs and limitations section at the
end of this document.
A file with the 'C' attribute set will not be subject to copy-on-write
updates. This flag is only supported on file systems which perform
copy-on-write. (Note: For btrfs, the 'C' flag should be set on new or
empty files. If it is set on a file which already has data blocks, it
is undefined when the blocks assigned to the file will be fully stable.
If the 'C' flag is set on a directory, it will have no effect on the
directory, but new files created in that directory will the No_COW
attribute.)
When a directory with the `D' attribute set is modified, the changes
are written synchronously on the disk; this is equivalent to the
`dirsync' mount option applied to a subset of the files.
A file with the `d' attribute set is not candidate for backup when the
dump(8) program is run.
The 'E' attribute is used by the experimental compression patches to
indicate that a compressed file has a compression error. It may not be
set or reset using chattr(1), although it can be displayed by
lsattr(1).
The 'e' attribute indicates that the file is using extents for mapping
the blocks on disk. It may not be removed using chattr(1).
The 'I' attribute is used by the htree code to indicate that a direc‐
tory is being indexed using hashed trees. It may not be set or reset
using chattr(1), although it can be displayed by lsattr(1).
The 'h' attribute indicates the file is storing its blocks in units of
the filesystem blocksize instead of in units of sectors, and means that
the file is (or at one time was) larger than 2TB. It may not be set or
reset using chattr(1), although it can be displayed by lsattr(1).
A file with the `i' attribute cannot be modified: it cannot be deleted
or renamed, no link can be created to this file and no data can be
written to the file. Only the superuser or a process possessing the
CAP_LINUX_IMMUTABLE capability can set or clear this attribute.
A file with the `j' attribute has all of its data written to the ext3
journal before being written to the file itself, if the filesystem is
mounted with the "data=ordered" or "data=writeback" options. When the
filesystem is mounted with the "data=journal" option all file data is
already journalled and this attribute has no effect. Only the supe‐
ruser or a process possessing the CAP_SYS_RESOURCE capability can set
or clear this attribute.
When a file with the `s' attribute set is deleted, its blocks are
zeroed and written back to the disk. Note: please make sure to read
the bugs and limitations section at the end of this document.
When a file with the `S' attribute set is modified, the changes are
written synchronously on the disk; this is equivalent to the `sync'
mount option applied to a subset of the files.
A directory with the 'T' attribute will be deemed to be the top of
directory hierarchies for the purposes of the Orlov block allocator.
This is a hint to the block allocator used by ext3 and ext4 that the
subdirectories under this directory are not related, and thus should be
spread apart for allocation purposes. For example it is a very good
idea to set the 'T' attribute on the /home directory, so that
/home/john and /home/mary are placed into separate block groups. For
directories where this attribute is not set, the Orlov block allocator
will try to group subdirectories closer together where possible.
A file with the 't' attribute will not have a partial block fragment at
the end of the file merged with other files (for those filesystems
which support tail-merging). This is necessary for applications such
as LILO which read the filesystem directly, and which don't understand
tail-merged files. Note: As of this writing, the ext2 or ext3 filesys‐
tems do not (yet, except in very experimental patches) support tail-
merging.
When a file with the `u' attribute set is deleted, its contents are
saved. This allows the user to ask for its undeletion. Note: please
make sure to read the bugs and limitations section at the end of this
document.
The 'X' attribute is used by the experimental compression patches to
indicate that a raw contents of a compressed file can be accessed
directly. It currently may not be set or reset using chattr(1),
although it can be displayed by lsattr(1).
The 'Z' attribute is used by the experimental compression patches to
indicate a compressed file is dirty. It may not be set or reset using
chattr(1), although it can be displayed by lsattr(1).
AUTHORchattr was written by Remy Card <Remy.Card@linux.org>. It is currently
being maintained by Theodore Ts'o <tytso@alum.mit.edu>.
BUGS AND LIMITATIONS
The `c', 's', and `u' attributes are not honored by the ext2, ext3,
and ext4 filesystems as implemented in the current mainline Linux ker‐
nels.
The `j' option is only useful if the filesystem is mounted as ext3.
The `D' option is only useful on Linux kernel 2.5.19 and later.
AVAILABILITYchattr is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
SEE ALSOlsattr(1)E2fsprogs version 1.42.9 February 2014 CHATTR(1)
