chmod

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
       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 MODE values

       -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 © 2021 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 9.0                September 2021                         CHMOD(1)