chmod(1) - man - phpMan

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 unmen‐
       tioned 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  per‐
       missions 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.

       For directories chmod preserves set-user-ID and set-group-ID bits unless you explicitly spec‐
       ify 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  lead‐
       ing = 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 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 any translation bugs to <https://translationproject.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                          January 2026                                    CHMOD(1)