CHMOD(1) User Commands CHMOD(1)
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 af‐
fected.
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 doesn't change the permissions of symbolic links; the chmod system call cannot change
their permissions on most systems, and most systems ignore permissions of symbolic links. How‐
ever, 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 direc‐
tory traversals. Options that modify this behavior are described in the OPTIONS section.
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 ap‐
propriate 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 reg‐
ular 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
--dereference
affect the referent of each symbolic link, rather than the symbolic link itself
-h, --no-dereference
affect each symbolic link, rather than the referent
--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
The following options modify how a hierarchy is traversed when the -R option is also specified.
If more than one is specified, only the final one takes effect. -H is the default.
-H if a command line argument is a symlink to a directory, traverse it
-L traverse every symbolic link to a directory encountered
-P do not traverse any symbolic links
--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
Report bugs to: bug-coreutils@gnu.org
GNU coreutils home page: <https://www.gnu.org/software/coreutils/>
General help using GNU software: <https://www.gnu.org/gethelp/>
Report any translation bugs to <https://translationproject.org/team/>
COPYRIGHT
Copyright © 2026 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 9.10 February 2026 CHMOD(1)