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 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.


       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,
       or leading = like 00755 , or =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

              do not treat '/' specially (the default)

              fail to operate recursively on '/'

              use RFILE's mode instead of MODE values

       -R, --recursive
              change files and directories recursively

       --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 © 2020 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-8.32.tar.xz fetched from
       ⟨⟩ on 2020-11-01.  If you discover
       any rendering problems in this HTML version of the page, or you be‐
       lieve 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

GNU coreutils 8.32               March 2020                         CHMOD(1)

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