CHMOD(1) — UNIX Programmer’s Manual

NAME

chmod − change mode

SYNOPSIS

chmod 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 constructed from the OR-ing (in effect, adding up) of the numbers 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

EXAMPLE

chmod 755 filename

changes the mode of a file you own to: read, write, execute by you and read, execute (4+1=5) for group and others.

An ls -l of filename shows [-rwxr-xr-x filename] that the requested mode is in effect.

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 of the letters "ugo". If who is omitted, the default is a but the setting of the file creation mask 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), 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.

EXAMPLES

chmod = filename

will take away all permissions from filename, including yours.

chmod o-w file

denies write permission to others.

chmod +x file

makes a file executable.

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.

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