chmod(1) — Linux manual page


CHMOD(1)                      User Commands                     CHMOD(1)

NAME         top

       chmod - change file mode bits

SYNOPSIS         top

       chmod [OPTION]... MODE[,MODE]... FILE...
       chmod [OPTION]... OCTAL-MODE FILE...
       chmod [OPTION]... --reference=RFILE FILE...

DESCRIPTION         top

       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 [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

       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 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.  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.
       Options that modify this behavior are described in the OPTIONS


       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.


       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         top

       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

              affect the referent of each symbolic link, rather than the
              symbolic link itself

       -h, --no-dereference
              affect each symbolic link, rather than the referent

              do not treat '/' specially (the default)

              fail to operate recursively on '/'

              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 symbolic link 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

              output version information and exit

       Each MODE is of the form

AUTHOR         top

       Written by David MacKenzie and Jim Meyering.

REPORTING BUGS         top

       GNU coreutils online help:
       Report any translation bugs to

COPYRIGHT         top

       Copyright © 2024 Free Software Foundation, Inc.  License GPLv3+:
       GNU GPL version 3 or later <>.
       This is free software: you are free to change and redistribute
       it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO         top


       Full documentation <>
       or available locally via: info '(coreutils) chmod invocation'

COLOPHON         top

       This page is part of the coreutils (basic file, shell and text
       manipulation utilities) project.  Information about the project
       can be found at ⟨⟩.  If you
       have a bug report for this manual page, see
       ⟨⟩.  This page was obtained
       from the tarball coreutils-9.5.tar.xz fetched from
       ⟨⟩ on 2024-06-14.  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

GNU coreutils 9.5              March 2024                       CHMOD(1)

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