NAME

chmod − change the permissions mode of a file

SYNOPSIS

chmod [ −fR ] mode filename

DESCRIPTION

Change the permissions (mode) of a file or files.  Only the owner of a file (or the super-user) may change its mode. 

The mode of each named file is changed according to mode, which may be absolute or symbolic, as follows.

Absolute Modes

An absolute mode is an octal number constructed from the OR of the following modes:

 400 Read by owner. 

 200 Write by owner. 

 100 Execute (search in directory) by owner. 

 040 Read by group. 

 020 Write by group. 

 010 Execute (search) by group. 

 004 Read by others. 

 002 Write by others. 

 001 Execute (search) by others. 

4000 Set user ID on execution. 

2000 Set group ID on execution (this bit is ignored if the file is a directory; it may be set or cleared only using symbolic mode). 

1000 Sticky bit, (see chmod(2) for more information). 
 

Symbolic Modes

A symbolic mode has the form:

[ who ] op permission [ op permission ] ...

who is a combination of:

u User’s permissions. 

g Group permissions. 

o Others. 

a All, or ugo. 

If who is omitted, the default is a, but the setting of the file creation mask (see umask in sh(1) or csh(1) for more information) is taken into account.  When who is omitted, chmod will not override the restrictions of your user mask. 

op is one of:

+ To add the permission.

− To remove the permission.

= To assign the permission explicitly (all other bits for that category, owner, group, or others, will be reset). 

permission is any combination of:

r Read. 

w Write. 

x Execute. 

X Give execute permission if the file is a directory or if there is execute permission for one of the other user classes. 

s Set owner or group ID.  This is only useful with u or g.  Also, the set group ID bit of a directory may only be modified with ‘+’ or ‘−’. 

t Set the sticky bit to save program text between processes. 

The letters u, g, or o indicate that permission is to be taken from the current mode for the user-class. 

Omitting permission is only useful with ‘=’, to take away all permissions. 

Multiple symbolic modes, separated by commas, may be given.  Operations are performed in the order specified. 

SYSTEM V DESCRIPTION

If who is omitted in a symbolic mode, it does not take the file creation mask into account, but acts as if who were a. 

OPTIONS

−f Force.  chmod will not complain if it fails to change the mode of a file. 

−R Recursively descend through directory arguments, setting the mode for each file as described above.  When symbolic links are encountered, their mode is not changed and they are not traversed. 

EXAMPLES

The first example denies write permission to others, the second makes a file executable by all if it is executable by anyone:

example% chmod o−w file
example% chmod +X file

SEE ALSO

csh(1), ls(1V), sh(1), chmod(2), chown(8)

Sun Release 4.0  —  Last change: 22 March 1989