MirOS Manual: chmod(1)

CHMOD(1)                     BSD Reference Manual                     CHMOD(1)

NAME

     chmod - change file modes

SYNOPSIS

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

DESCRIPTION

     The chmod utility modifies the file mode bits of the listed files as
     specified by the mode operand. The mode of a file dictates its permis-
     sions, among other attributes.

     The options are as follows:

     -R      Recursively descend through any specified directory arguments.
             Change the modes of the file hierarchies rooted in the files in-
             stead of just the files themselves.

     -H      If the -R option is also specified, symbolic links on the command
             line are followed. (Symbolic links encountered in the tree
             traversal are not followed.)

     -L      If the -R option is also specified, all symbolic links are fol-
             lowed.

     -P      If the -R option is also specified, no symbolic links are fol-
             lowed.

     -h      If file is symbolic link, the mode of the link is changed.

     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 file's owner or the superuser is permitted to change the mode of
     a file.

     The chmod utility exits 0 on success or >0 if an error occurred.

Absolute modes

     Absolute modes are specified according to the following format:

           chmod nnnn file [...]

     An absolute mode is an octal number (specified as nnnn, where n is a
     number from 0 to 7) constructed by ORing any of the following values:

           0400    Allow read by owner.
           0200    Allow write by owner.
           0100    Allow execution (or search in directories) by owner.
           0700    Allow read, write, and execute/search by owner.
           0040    Allow read by group.
           0020    Allow write by group.
           0010    Allow execution (or search in directories) by group.
           0070    Allow read, write, and execute/search by group.
           0004    Allow read by others.
           0002    Allow write by others.
           0001    Allow execution (or search in directories) by others.
           0007    Allow read, write, and execute/search by others.

     In addition to the file permission modes, the following mode bits are
     available:

           4000    Set-user-ID on execution.
           2000    Set-group-ID on execution.
           1000    Enable sticky bit; see sticky(8) and chmod(2).

     The execute bit for a directory is often referred to as the "search" bit.
     In order to access a file, a user must have execute permission in each
     directory leading up to it in the filesystem hierarchy. For example, to
     access the file /bin/ls, execute permission is needed on /, /bin, and, of
     course, the ls binary itself.

Symbolic modes

     Symbolic modes are specified according to the following format:

           chmod <[who]op[perm]>,[[who]op[perm]],[...] file [...]

     The symbolic mode is described by the following grammar:

           mode         ::= clause [, clause ...]
           clause       ::= [who ...] [action ...] last_action
           action       ::= op [perm ...]
           last_action  ::= op [perm ...]
           who          ::= a | u | g | o
           op           ::= + | - | =
           perm         ::= r | s | t | w | x | X | u | g | o

     The who symbols indicate whose permissions are to be changed or assigned:

           u     User (owner) permissions.
           g     Group permissions.
           o     Others permissions.
           a     All of the above.

     Do not confuse the 'o' symbol with "owner". It is the user bit, 'u', that
     refers to the owner 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
                 specified in perm, for which the corresponding bit in the
                 file mode creation mask 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
                 specified in perm, for which the corresponding bit in the
                 file mode creation mask is clear, is cleared. Otherwise, the
                 mode bits represented 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 user, 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. Other-
                 wise, the mode bits represented by the specified who and perm
                 values are set.

     The perm (permission symbols) represent the portions of the mode bits as
     follows:

           r       Read bits.
           s       Set-user-ID and set-group-ID on execution bits.
           t       Sticky bit.
           w       Write bits.
           x       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       User permission bits in the mode of the original file.
           g       Group permission bits in the mode of the original file.
           o       Other permission bits in the mode of the original file.

     Each clause (given in a comma-delimited list on the command line) speci-
     fies one or more operations to be performed on the mode bits, and each
     operation is applied in the order specified.

     Operations upon the "other" permissions (specified by the symbol 'o' by
     itself), in combination with the perm symbols 's' or 't', are ignored.

EXAMPLES

     $ chmod 644 file

     Set file readable by anyone and writable by the owner only.

     $ chmod go-w file

     Deny write permission to group and others.

     $ chmod =rw,+X file

     Set the read and write permissions to the usual defaults, but retain any
     execute permissions that are currently set.

     $ chmod +X file

     Make a directory or file searchable/executable by everyone if it is al-
     ready searchable/executable by anyone.

     $ chmod 755 file
     $ chmod u=rwx,go=rx file
     $ chmod u=rwx,go=u-w file

     Any of these commands will make a file readable/executable by everyone
     and writable by the owner only.

     $ chmod go= file

     Clear all mode bits for group and others.

     $ chmod g=u-w file

     Set the group bits equal to the user bits, but clear the group write bit.

SEE ALSO

     chflags(1), chgrp(1), find(1), install(1), chmod(2), lchmod(2), stat(2),
     umask(2), fts(3), setmode(3), symlink(7), chown(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 symbols 't' and 'X' which are not in-
     cluded in that standard.

HISTORY

     A chmod command appeared in Version 1 AT&T UNIX. The -h option appeared
     in MirOS #10.

BUGS

     There's no perm option for the naughty bits.

MirOS BSD #10-current            May 20, 2007                                2

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