chmod

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  ei-
       ther  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,  sepa-
       rated 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 ex-
       cept 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  dele-
       tion  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 sym-
       bolic 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.

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  un-
       less  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 directo-
       ries  with a numeric mode requires an additional leading zero, or lead-
       ing = like 00755 , or =755

RESTRICTED DELETION FLAG OR STICKY BIT
       The restricted deletion flag or sticky bit is a single bit,  whose  in-
       terpretation  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 re-
       stricted 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  (C) 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'

GNU coreutils 8.30              September 2019                        CHMOD(1)