Provided by: coreutils_9.4-3ubuntu6_amd64 
NAME
chmod - change file mode bits
SYNOPSIS
chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...
chmod [OPTION]... --reference=RFILE FILE...
DESCRIPTION
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 bits.
The format of a symbolic mode is [ugoa...][[-+=][perms...]...], where perms is either zero or more
letters from the set rwxXst, or a single letter from the set ugo. Multiple 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 (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
categories (o).
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.
SETUID AND SETGID BITS
chmod 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 MODE or RFILE 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.
For directories chmod preserves set-user-ID and set-group-ID bits unless you explicitly specify
otherwise. You can set or clear the bits with symbolic modes like u+s and g-s. To clear these bits for
directories with a numeric mode requires an additional leading zero like 00755, leading minus like -6000,
or leading equals like =755.
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 sticky bit.
OPTIONS
Change the mode of each FILE to MODE. With --reference, change the mode of each FILE to that of RFILE.
-c, --changes
like verbose but report only when a change is made
-f, --silent, --quiet
suppress most error messages
-v, --verbose
output a diagnostic for every file processed
--no-preserve-root
do not treat '/' specially (the default)
--preserve-root
fail to operate recursively on '/'
--reference=RFILE
use RFILE's mode instead of specifying MODE values. RFILE is always dereferenced if a symbolic
link.
-R, --recursive
change files and directories recursively
--help display this help and exit
--version
output version information and exit
Each MODE is of the form '[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+'.
AUTHOR
Written by David MacKenzie and Jim Meyering.
REPORTING BUGS
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report any translation bugs to <https://translationproject.org/team/>
COPYRIGHT
Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later
<https://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.
SEE ALSO
chmod(2)
Full documentation <https://www.gnu.org/software/coreutils/chmod>
or available locally via: info '(coreutils) chmod invocation'
GNU coreutils 9.4 April 2024 CHMOD(1)