Plan 9 /sys/man/1/chmod

NAME

chmod – change mode

SYNOPSIS

chmod mode file ...

DESCRIPTION

The mode of each named file is changed according to mode, which may be an octal number or a symbolic change to the existing mode. A mode is an octal number constructed from the OR of the following modes.
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

The who part is a combination of the letters u (for user's permissions), g (group) and o (other). The letter a stands for ugo. If who is omitted, the default is a.
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), a (append only), l (exclusive access), and t (temporary file).
Only the owner of a file or the group leader of its group may change the file's mode.

SOURCE

/sys/src/cmd/chmod.c