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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), exe‐
       cute/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  let‐
       ters  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 prob‐
       lem since the permissions of symbolic links are never used.   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.

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  appropri‐
       ate privileges.  Additional restrictions may cause the set-user-ID
       and set-group-ID bits of MODE or RFILE to be ignored.  This behav‐
       ior  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

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 pre‐
       vents  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 com‐
       monly 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/core‐
       utils/>
       Report   any   translation   bugs   to    <https://translationpro‐
       ject.org/team/>

COPYRIGHT
       Copyright  ©  2020 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 8.32              April 2020                       CHMOD(1)