chmod — change file mode bits
This manual page documents the GNU version of chmod. chmod changes the file mode
bits of each given file according to
mode, which can be either a
symbolic representation of changes to make, or an octal
number representing the bit pattern for the new mode
The format of a symbolic mode is [
perms is either zero or more
letters from the set
rwxXst, or a single letter from
symbolic 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 (
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.
+ 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.
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 (
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 categories
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.
chmod never changes the permissions of symbolic links; the chmod 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, chmod changes the permissions of the pointed-to file. In contrast, chmod ignores symbolic links encountered during recursive directory traversals.
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 chmod 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
g−s, and you can set
(but not clear) the bits with a numeric mode.
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
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 sticky bit.
Change the mode of each FILE to MODE. With
−−reference, change the mode of
each FILE to that of RFILE.
like verbose but report only when a change is made
suppress most error messages
output a diagnostic for every file processed
do not treat '/' specially (the default)
fail to operate recursively on '/'
use RFILE's mode instead of MODE values
change files and directories recursively
display this help and exit
output version information and exit
Each MODE is of the form '[ugoa]*([−+=]([rwxXst]*|[ugo]))+|[−+=][0−7]+'.
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report chmod translation bugs to <http://translationproject.org/team/>
Full documentation at: <http://www.gnu.org/software/coreutils/chmod>
or available locally via: info '(coreutils) chmod invocation'
Copyright © 2015 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.