chmod

chmod [option] mode files

Change the access mode of one or more files. Only the owner of a file or a privileged user may change its mode. Create mode by concatenating the characters from who, opcode, and permission. who is optional (if omitted, default is a); choose only one opcode.

Options

-f

Suppress error message upon failure to change a file's mode.

-R

Recursively descend directory arguments while setting modes.

Who

u	User
g	Group
o	Other
a	All (default)

Opcode

+	Add permission
-	Remove permission
=	Assign permission (and remove permission of the unspecified fields)

Permission

r	Read
w	Write
x	Execute
s	Set user (or group) ID
t	Sticky bit; save text mode (file) or prevent removal of files by nonowners (directory)
u	User's present permission
g	Group's present permission
o	Other's present permission
l	Mandatory locking

Alternatively, specify permissions by a three-digit sequence. The first digit designates owner permission; the second, group permission; and the third, others permission. Permissions are calculated by adding the following octal values:

4	Read
2	Write
1	Execute

Note: a fourth digit may precede this sequence. This digit assigns the following modes:

4	Set user ID on execution
2	Set group ID on execution or set mandatory locking
1	Sticky bit

Examples

Add execute-by-user permission to file:

chmod u+x file

Either of the following assigns read-write-execute permission by owner (7), read-execute permission by group (5), and execute-only permission by others (1) to file:

chmod 751 file
chmod u=rwx,g=rx,o=x file

Any one of the following assigns read-only permission to file for everyone:

chmod =r file
chmod 444 file
chmod a-wx,a+r file

Set the user ID, assign read-write-execute permission by owner, and assign read-execute permission by group and others:

chmod 4755 file