chmod - change access permissions of files


     chmod [options] mode file...

     POSIX options:  [-R]

     GNU options (shortest form):  [-cfvR]  [--help]  [--version]


     chmod changes the permissions 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 permissions.

     The format of a symbolic mode change argument is

     Such an argument is a list of symbolic mode change commands,
     separated  by  commas.   Each  symbolic  mode change command
     starts with zero or more of the letters `ugoa';  these  con-
     trol  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).
     Thus, `a' is here equivalent to `ugo'.  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 permissions selected to be added
     to the existing permissions of each file; `-' causes them to
     be removed; and `=' causes them to be the  only  permissions
     that the file has.

     The letters `rwxXstugo' select the new permissions  for  the
     affected  users: read (r), write (w), execute (or access for
     directories) (x), execute only if the file is a directory or
     already  has  execute permission for some user (X), set user
     or group ID on execution (s), sticky bit  (t),  the  permis-
     sions  that  the user who owns the file currently has for it
     (u), the permissions that other users in  the  file's  group
     have for it (g), and the permissions that other users not in
     the file's group have for it (o).  (Thus, `chmod  g-s  file'
     removes  the set-group-ID (sgid) bit, `chmod ug+s file' sets
     both the suid and sgid bits, while  `chmod  o+s  file'  does

     The `sticky bit'  is  not  described  by  POSIX.   The  name
     derives  from  the  original  meaning:  keep program text on
     swap device.  These days, when set for a directory, it means
     that  only  the  owner  of  the  file  and the owner of that
     directory may remove the file from that directory.  (This is
     commonly  used  on  directories  like /tmp that have general
     write permission.)

     A numeric mode is from  one  to  four  octal  digits  (0-7),
     derived  by adding up the bits with values 4, 2, and 1.  Any
     omitted digits are assumed to be leading zeros.   The  first
     digit  selects  the set user ID (4) and set group ID (2) and
     save text image (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, since
     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 encoun-
     tered during recursive directory traversals.


     -R   Recursively change permissions of directories and their


     -c, --changes
          Verbosely describe the action for each file whose  per-
          missions actually changes.

     -f, --silent, --quiet
          Do not print error messages about files  whose  permis-
          sions cannot bechanged.

     -v, --verbose
          Verbosely describe the action or non-action  taken  for
          every file.

     -R, --recursive
          Recursively change permissions of directories and their


          Print a usage message on standard output and exit  suc-

          Print version information on standard output, then exit

     --   Terminate option list.


     The variables LANG, LC_ALL, LC_CTYPE  and  LC_MESSAGES  have
     the usual meaning.


     POSIX 1003.2 only requires  the  -R  option.  Use  of  other
     options may not be portable. This standard does not describe
     the 't' permission  bit.  This  standard  does  not  specify
     whether  chmod  must  preserve  consistency  by  clearing or
     refusing to set the suid and sgid bits, e.g., when all  exe-
     cute  bits  are cleared, or whether chmod honors the `s' bit
     at all.


     Above we described the use of the `t'  bit  on  directories.
     Various  systems  attach special meanings to otherwise mean-
     ingless combinations of mode bits.   In  particular,  Linux,
     following System V (see System V Interface Definition (SVID)
     Version 3), lets the sgid bit for files without  group  exe-
     cute  permission  mark  the  file for mandatory locking. For
     more         details,         see          the          file


     This page describes chmod as  found  in  the  fileutils-3.16
     package;  other  versions  may differ slightly. Mail correc-
     tions and additions to,  and   Report  bugs  in the program to