chmod - change access permissions of files
chmod [options] mode file...
POSIX options: [-R]
GNU options (shortest form): [-cfvR] [--help] [--version]
chmod changes the permissions 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 permissions.
The format of a symbolic mode change argument is
Such an argument is a list of symbolic mode change commands,
separated by commas. Each symbolic mode change command
starts with zero or more of the letters `ugoa'; these con-
trol 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).
Thus, `a' is here equivalent to `ugo'. 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 permissions selected to be added
to the existing permissions of each file; `-' causes them to
be removed; and `=' causes them to be the only permissions
that the file has.
The letters `rwxXstugo' select the new permissions for the
affected users: read (r), write (w), execute (or access for
directories) (x), execute only if the file is a directory or
already has execute permission for some user (X), set user
or group ID on execution (s), sticky bit (t), the permis-
sions that the user who owns the file currently has for it
(u), the permissions that other users in the file's group
have for it (g), and the permissions that other users not in
the file's group have for it (o). (Thus, `chmod g-s file'
removes the set-group-ID (sgid) bit, `chmod ug+s file' sets
both the suid and sgid bits, while `chmod o+s file' does
The `sticky bit' is not described by POSIX. The name
derives from the original meaning: keep program text on
swap device. These days, when set for a directory, it means
that only the owner of the file and the owner of that
directory may remove the file from that directory. (This is
commonly used on directories like /tmp that have general
A numeric mode is from one to four octal digits (0-7),
derived by adding up the bits with values 4, 2, and 1. Any
omitted digits are assumed to be leading zeros. The first
digit selects the set user ID (4) and set group ID (2) and
save text image (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
chmod never changes the permissions of symbolic links, since
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 encoun-
tered during recursive directory traversals.
-R Recursively change permissions of directories and their
Verbosely describe the action for each file whose per-
missions actually changes.
-f, --silent, --quiet
Do not print error messages about files whose permis-
sions cannot bechanged.
Verbosely describe the action or non-action taken for
Recursively change permissions of directories and their
GNU STANDARD OPTIONS
Print a usage message on standard output and exit suc-
Print version information on standard output, then exit
-- Terminate option list.
The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have
the usual meaning.
POSIX 1003.2 only requires the -R option. Use of other
options may not be portable. This standard does not describe
the 't' permission bit. This standard does not specify
whether chmod must preserve consistency by clearing or
refusing to set the suid and sgid bits, e.g., when all exe-
cute bits are cleared, or whether chmod honors the `s' bit
Above we described the use of the `t' bit on directories.
Various systems attach special meanings to otherwise mean-
ingless combinations of mode bits. In particular, Linux,
following System V (see System V Interface Definition (SVID)
Version 3), lets the sgid bit for files without group exe-
cute permission mark the file for mandatory locking. For
more details, see the file
This page describes chmod as found in the fileutils-3.16
package; other versions may differ slightly. Mail correc-
tions and additions to email@example.com, firstname.lastname@example.org and
email@example.com. Report bugs in the program to