CHMOD(2) BSD Programmer's Manual CHMOD(2)NAME
chmod, lchmod, fchmod - change mode of a file or link
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
int
chmod(const char *path, mode_t mode);
int
lchmod(const char *path, mode_t mode);
int
fchmod(int fd, mode_t mode);
DESCRIPTION
The function chmod() sets the file permission bits of the file specified
by the pathname path to mode. lchmod() operates similarly to chmod() but
does not follow symbolic links. It allows the permission bits of a sym-
bolic link to be set. fchmod() sets the permission bits of the specified
file descriptor fd. chmod() verifies that the process owner (user) either
owns the file specified by path (or fd), or is the superuser. A mode is
created from or'd permission bit masks defined in <sys/stat.h>:
#define S_IRWXU 0000700 /* RWX mask for owner */
#define S_IRUSR 0000400 /* R for owner */
#define S_IWUSR 0000200 /* W for owner */
#define S_IXUSR 0000100 /* X for owner */
#define S_IRWXG 0000070 /* RWX mask for group */
#define S_IRGRP 0000040 /* R for group */
#define S_IWGRP 0000020 /* W for group */
#define S_IXGRP 0000010 /* X for group */
#define S_IRWXO 0000007 /* RWX mask for other */
#define S_IROTH 0000004 /* R for other */
#define S_IWOTH 0000002 /* W for other */
#define S_IXOTH 0000001 /* X for other */
#define S_ISUID 0004000 /* set user id on execution */
#define S_ISGID 0002000 /* set group id on execution */
#define S_ISVTX 0001000 /* save swapped text even after use */
If mode ISVTX (the sticky bit) is set on a file, it is ignored.
If mode ISVTX (the sticky bit) is set on a directory, an unprivileged
user may not delete or rename files of other users in that directory. The
sticky bit may be set by any user on a directory which the user owns or
has appropriate permissions. For more details of the properties of the
sticky bit, see sticky(8).
Writing or changing the owner of a file turns off the set-user-ID and
set-group-ID bits unless the user is the superuser. This makes the system
somewhat more secure by protecting set-user-ID (set-group-ID) files from
remaining set-user-ID (set-group-ID) if they are modified, at the expense
of a degree of compatibility.
RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
ERRORSchmod() or lchmod() will fail and the file mode will be unchanged if:
[ENOTDIR] A component of the path prefix is not a directory.
[ENAMETOOLONG]
A component of a pathname exceeded {NAME_MAX} characters,
or an entire path name exceeded {PATH_MAX} characters.
[ENOENT] The named file does not exist.
[EACCES] Search permission is denied for a component of the path
prefix.
[EINVAL] mode contains bits other than the file type and those
described above.
[ELOOP] Too many symbolic links were encountered in translating the
pathname.
[EPERM] The effective user ID does not match the owner of the file
and the effective user ID is not the superuser.
[EROFS] The named file resides on a read-only file system.
[EFAULT] path points outside the process's allocated address space.
[EIO] An I/O error occurred while reading from or writing to the
file system.
fchmod() will fail and the file mode will be unchanged if:
[EBADF] The descriptor is not valid.
[EINVAL] fd refers to a socket, not to a file.
[EINVAL] mode contains bits other than the file type and those
described above.
[EROFS] The file resides on a read-only file system.
[EIO] An I/O error occurred while reading from or writing to the
file system.
SEE ALSOchmod(1), chown(2), open(2), stat(2), sticky(8)STANDARDS
The chmod() function is expected to conform to IEEE Std 1003.1-1988
("POSIX").
HISTORY
The fchmod() function call appeared in 4.2BSD. The lchmod() function call
appeared in MirOS #10.
MirOS BSD #10-current May 19, 2007 1
