CHMOD(2) System Calls Manual CHMOD(2)NAME
chmod - change mode of file
SYNOPSIS
chmod(name, mode)
char *name;
DESCRIPTION
The file whose name is given as the null-terminated string pointed to by name has its mode changed to mode. Modes are constructed by ORing
together some combination of the following:
04000 set user ID on execution
02000 set group ID on execution
01000 save text image after execution
00400 read by owner
00200 write by owner
00100 execute (search on directory) by owner
00070 read, write, execute (search) by group
00007 read, write, execute (search) by others
If an executable file is set up for sharing (-n or -i option of ld(1)) then mode 1000 prevents the system from abandoning the swap-space
image of the program-text portion of the file when its last user terminates. Thus when the next user of the file executes it, the text
need not be read from the file system but can simply be swapped in, saving time. Ability to set this bit is restricted to the super-user
since swap space is consumed by the images; it is only worth while for heavily used commands.
Only the owner of a file (or the super-user) may change the mode. Only the super-user can set the 1000 mode.
SEE ALSO chmod(1)DIAGNOSTIC
Zero is returned if the mode is changed; -1 is returned if name cannot be found or if current user is neither the owner of the file nor the
super-user.
ASSEMBLER
(chmod = 15.)
sys chmod; name; mode
CHMOD(2)
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CHMOD(1) General Commands Manual CHMOD(1)NAME
chmod - change mode
SYNOPSIS
chmod [ -Rf ] mode file ...
DESCRIPTION
The mode of each named file is changed according to mode, which may be absolute or symbolic. An absolute mode is an octal number con-
structed from the OR of the following modes:
4000 set user ID on execution
2000 set group ID on execution
1000 sticky bit, see chmod(2)
0400 read by owner
0200 write by owner
0100 execute (search in directory) by owner
0070 read, write, execute (search) by group
0007 read, write, execute (search) by others
A symbolic mode has the form:
[who] op permission [op permission] ...
The who part is a combination of the letters u (for user's permissions), g (group) and o (other). The letter a stands for all, or ugo. If
who is omitted, the default is a but the setting of the file creation mask (see umask(2)) is taken into account.
Op can be + to add permission to the file's mode, - to take away permission and = to assign permission absolutely (all other bits will be
reset).
Permission is any combination of the letters r (read), w (write), x (execute), X (set execute only if file is a directory or some other
execute bit is set), s (set owner or group id) and t (save text - sticky). Letters u, g, or o indicate that permission is to be taken from
the current mode. Omitting permission is only useful with = to take away all permissions.
When the -R option is given, chmod recursively descends its 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.
If the -f option is given, chmod will not complain if it fails to change the mode on a file.
EXAMPLES
The first example denies write permission to others, the second makes a file executable by all if it is executable by anyone:
chmod o-w file
chmod +X file
Multiple symbolic modes separated by commas may be given. Operations are performed in the order specified. The letter s is only useful
with u or g.
Only the owner of a file (or the super-user) may change its mode.
SEE ALSO ls(1), chmod(2), stat(2), umask(2), chown(8)7th Edition May 22, 1986 CHMOD(1)