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chmod - change file modes

 

NAME

      chmod - change file modes
 

SYNOPSIS

      chmod [-fhv] [-R [-H | -L | -P]] mode file ...
 

DESCRIPTION

      The chmod utility modifies the file mode bits of the listed files as
      specified by the mode operand.
 
      The options are as follows:
 
      -f      Do not display a diagnostic message if chmod could not modify the
              mode for file, nor modify the exit status to reflect such fail‐
              ures.
 
      -H      If the -R option is specified, symbolic links on the command line
              are followed.  (Symbolic links encountered in the tree traversal
              are not followed by default.)
 
      -h      If the file is a symbolic link, change the mode of the link
              itself rather than the file that the link points to.
 
      -L      If the -R option is specified, all symbolic links are followed.
 
      -P      If the -R option is specified, no symbolic links are followed.
              This is the default.
 
      -R      Change the modes of the file hierarchies rooted in the files
              instead of just the files themselves.
 
      -v      Cause chmod to be verbose, showing filenames as the mode is modi‐
              fied.  If the -v flag is specified more than once, the old and
              new modes of the file will also be printed, in both octal and
              symbolic notation.
 
      The -H, -L and -P options are ignored unless the -R option is specified.
      In addition, these options override each other and the command’s actions
      are determined by the last one specified.
 
      Only the owner of a file or the super-user is permitted to change the
      mode of a file.
      The chmod utility exits 0 on success, and >0 if an error occurs.
 

MODES

      Modes may be absolute or symbolic.  An absolute mode is an octal number
      constructed from the sum of one or more of the following values:
 
            4000    (the setuid bit).  Executable files with this bit set will
                    run with effective uid set to the uid of the file owner.
                    Directories with this bit set will force all files and sub-
                    directories created in them to be owned by the directory
                    owner and not by the uid of the creating process, if the
                    underlying file system supports this feature: see chmod(2)
                    and the suiddir option to mount(8).
            2000    (the setgid bit).  Executable files with this bit set will
                    run with effective gid set to the gid of the file owner.
            1000    (the sticky bit).  See chmod(2) and sticky(8).
            0400    Allow read by owner.
            0200    Allow write by owner.
            0100    For files, allow execution by owner.  For directories,
                    allow the owner to search in the directory.
            0040    Allow read by group members.
            0020    Allow write by group members.
            0010    For files, allow execution by group members.  For directo‐
                    ries, allow group members to search in the directory.
            0004    Allow read by others.
            0002    Allow write by others.
            0001    For files, allow execution by others.  For directories
                    allow others to search in the directory.
 
      For example, the absolute mode that permits read, write and execute by
      the owner, read and execute by group members, read and execute by others,
      and no set-uid or set-gid behaviour is 755 (400+200+100+040+010+004+001).
 
      The symbolic mode is described by the following grammar:
 
            mode         ::= clause [, clause ...]
            clause       ::= [who ...] [action ...] action
            action       ::= op [perm ...]
            who          ::= a | u | g | o
            op           ::= + | - | =
            perm         ::= r | s | t | w | x | X | u | g | o
 
      The who symbols ‘‘u’’, ‘‘g’’, and ‘‘o’’ specify the user, group, and
      other parts of the mode bits, respectively.  The who symbol ‘‘a’’ is
      equivalent to ‘‘ugo’’.
 
      The perm symbols represent the portions of the mode bits as follows:
 
            r       The read bits.
            s       The set-user-ID-on-execution and set-group-ID-on-execution
                    bits.
            t       The sticky bit.
            w       The write bits.
            x       The execute/search bits.
            X       The execute/search bits if the file is a directory or any
                    of the execute/search bits are set in the original (unmodi‐
                    fied) mode.  Operations with the perm symbol ‘‘X’’ are only
                    meaningful in conjunction with the op symbol ‘‘+’’, and are
                    ignored in all other cases.
            u       The user permission bits in the original mode of the file.
            g       The group permission bits in the original mode of the file.
            o       The other permission bits in the original mode of the file.
 
      The op symbols represent the operation performed, as follows:
 
      +     If no value is supplied for perm, the ‘‘+’’ operation has no
            effect.  If no value is supplied for who, each permission bit spec‐
            ified in perm, for which the corresponding bit in the file mode
            creation mask (see umask(2)) is clear, is set.  Otherwise, the mode
            bits represented by the specified who and perm values are set.
 
      -     If no value is supplied for perm, the ‘‘-’’ operation has no
            effect.  If no value is supplied for who, each permission bit spec‐
            ified in perm, for which the corresponding bit in the file mode
            creation mask is clear, is cleared.  Otherwise, the mode bits rep‐
            resented by the specified who and perm values are cleared.
 
      =     The mode bits specified by the who value are cleared, or, if no who
            value is specified, the owner, group and other mode bits are
            cleared.  Then, if no value is supplied for who, each permission
            bit specified in perm, for which the corresponding bit in the file
            mode creation mask is clear, is set.  Otherwise, the mode bits rep‐
            resented by the specified who and perm values are set.
 
      Each clause specifies one or more operations to be performed on the mode
      bits, and each operation is applied to the mode bits in the order speci‐
      fied.
 
      Operations upon the other permissions only (specified by the symbol ‘‘o’’
      by itself), in combination with the perm symbols ‘‘s’’ or ‘‘t’’, are
      ignored.
 

EXAMPLES

      644           make a file readable by anyone and writable by the owner
                    only.
 
      go-w          deny write permission to group and others.
 
      =rw,+X        set the read and write permissions to the usual defaults,
                    but retain any execute permissions that are currently set.
 
      +X            make a directory or file searchable/executable by everyone
                    if it is already searchable/executable by anyone.
 
      755
      u=rwx,go=rx
      u=rwx,go=u-w  make a file readable/executable by everyone and writable by
                    the owner only.
 
      go=           clear all mode bits for group and others.
 
      g=u-w         set the group bits equal to the user bits, but clear the
                    group write bit.
 

COMPATIBILITY

      The -v option is non-standard and its use in scripts is not recommended.
      chflags(1), install(1), setfacl(1), chmod(2), stat(2), umask(2), fts(3),
      setmode(3), symlink(7), chown(8), mount(8), sticky(8)
 

STANDARDS

      The chmod utility is expected to be IEEE Std 1003.2 (“POSIX.2”) compati‐
      ble with the exception of the perm symbol “t” which is not included in
      that standard.
 

HISTORY

      A chmod command appeared in Version 1 AT&T UNIX.
 

BUGS

      There is no perm option for the naughty bits.
 

Sections

Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.