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, 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 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 chmod translation bugs to <https://translationproject.org/team/>

COPYRIGHT

       Copyright  ©  2018  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 at: <https://www.gnu.org/software/coreutils/chmod>
       or available locally via: info '(coreutils) chmod invocation'