Section: User Commands (1)
Updated: April 2010
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chmod - change file mode bits
[OPTION]... MODE[,MODE]... FILE...
[OPTION]... OCTAL-MODE FILE...
[OPTION]... --reference=RFILE FILE...
This manual page
documents the GNU version of
changes the file mode bits of each given file according to
which can be either a symbolic representation of changes to make, or
an octal number representing the bit pattern for the new mode bits.
The format of a symbolic mode is [ugoa...][[+-=][perms...]...],
is either zero or more letters from the set
rwxXst, or a single letter from the set ugo.
modes can be given, separated by commas.
A combination of the letters ugoa controls which users' access
to the file will be changed: the user who owns it (u), other
users in the file's group (g), other users not in the file's
group (o), or all users (a). If none of these are given,
the effect is as if a were
given, but bits that are set in the umask are not affected.
The operator + causes the selected file mode bits to be added to
the existing file mode bits of each file; - causes them to be
removed; and = causes them to be added and causes unmentioned
bits to be removed except that a directory's unmentioned set user and
group ID bits are not affected.
The letters rwxXst select file mode bits for the affected users:
read (r), write (w), execute (or search for directories)
(x), execute/search only if the file is a directory or already
has execute permission for some user (X), set user or group ID
on execution (s), restricted deletion flag or sticky bit
(t). Instead of one or more of these letters, you can specify
exactly one of the letters ugo: the permissions granted to the
user who owns the file (u), the permissions granted to other
users who are members of the file's group (g),
and the permissions granted to users that are in neither of the two preceding
A numeric mode is from one to four octal digits (0-7), derived by
adding up the bits with values 4, 2, and 1. Omitted digits are
assumed to be leading zeros.
The first digit selects the set user ID (4) and set group ID (2) and
restricted deletion or sticky (1) attributes. The second digit
selects permissions for the user who owns the file: read (4), write (2),
and execute (1); the third selects permissions for other users in the
file's group, with the same values; and the fourth for other users not
in the file's group, with the same values.
never changes the permissions of symbolic links; the
system call cannot change their permissions. This is not a problem
since the permissions of symbolic links are never used.
However, for each symbolic link listed on the command line,
changes the permissions of the pointed-to file.
ignores symbolic links encountered during recursive directory
SETUID AND SETGID BITS
clears the set-group-ID bit of a
regular file if the file's group ID does not match the user's
effective group ID or one of the user's supplementary group IDs,
unless the user has appropriate privileges. Additional restrictions
may cause the set-user-ID and set-group-ID bits of
to be ignored. This behavior depends on the policy and
functionality of the underlying
system call. When in
doubt, check the underlying system behavior.
preserves a directory's set-user-ID and set-group-ID bits unless you
explicitly specify otherwise. You can set or clear the bits with
symbolic modes like
and you can set (but not clear) the bits with a numeric mode.
RESTRICTED DELETION FLAG OR STICKY BIT
The restricted deletion flag or sticky bit is a single bit, whose
interpretation depends on the file type. For directories, it prevents
unprivileged users from removing or renaming a file in the directory
unless they own the file or the directory; this is called the
restricted deletion flag
for the directory, and is commonly found on world-writable directories
like /tmp. For regular files on some older systems, the bit
saves the program's text image on the swap device so it will load more
quickly when run; this is called the
Change the mode of each FILE to MODE.
- -c, --changes
like verbose but report only when a change is made
do not treat `/' specially (the default)
fail to operate recursively on `/'
- -f, --silent, --quiet
suppress most error messages
- -v, --verbose
output a diagnostic for every file processed
use RFILE's mode instead of MODE values
- -R, --recursive
change files and directories recursively
display this help and exit
output version information and exit
Each MODE is of the form `[ugoa]*([-+=]([rwxXst]*|[ugo]))+'.
Written by David MacKenzie and Jim Meyering.
Report chmod bugs to firstname.lastname@example.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>
Report chmod translation bugs to <http://translationproject.org/team/>
Copyright © 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
The full documentation for
is maintained as a Texinfo manual. If the
programs are properly installed at your site, the command
info coreutils 'chmod invocation'
should give you access to the complete manual.
- SETUID AND SETGID BITS
- RESTRICTED DELETION FLAG OR STICKY BIT
- REPORTING BUGS
- SEE ALSO
This document was created by
using the manual pages.