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 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 permis-
       sions 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.

       chmod  preserves  a  directory's  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, and you can set (but not clear) the bits with a numeric mode.

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: <http://www.gnu.org/software/coreutils/>
       Report chmod translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright (C) 2017 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://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: <http://www.gnu.org/software/coreutils/chmod>
       or available locally via: info '(coreutils) chmod invocation'

GNU coreutils 8.28                                                 January 2018                                                           CHMOD(1)