Mac OS X Leopard - ARCAism

Each of the permissions are either r, w, or x, signifying the ability to read, write, or execute
(these are often referred to as bits). In the case of a directory, the execute bit signifies the ability
to open the directory. The owner of any file can set these permissions as they see fit using the
chmod command. Additionally, the owner can reset the group the files belong to to any other
group the owner belongs to using the chgrp command.
The chmod command can be used one of two ways to set the permissions (also referred to as
setting the mode), either literally or symbolically. The literal way is to specify the permissions as
a string of numbers such as the following:
chmod nnnn filename
where nnnn is the combined value of permissions based on Table 18-7.
Table 18-7. chmod Literal Number Values
Value Description
Basic Permissions
400 Allows read by owner
200 Allows write by owner
100 Allows execute by owner
040 Allows read by group
020 Allows write by group
010 Allows execute by group
004 Allows read by everyone
002 Allows write by everyone
001 Allows execute by everyone
Advanced Mode Selectors (Optional, and Generally Not Recommended
to Use Unless You Really Know What You Are Doing)
4000 Sets UID on execution bit (execution of file will run with permissions of file’s owner)
2000 Sets GID on execution bit (execution of file will run with permissions of file’s group)
1000 Sets sticky bit
For example:
chmod 755 filename
would result in the filename having permissions -rwxr-xr-x.
The other, symbolic way, of setting permissions is to use chmod in the following way:
chmod [u][g][o]+/-[r][w][x] filename
where u stands for owner, g stands for group, and o stands for other (everyone); followed by
+ (for adding) or - (for denying) permissions (r, w, and x).
For example, if you had a file with the permissions -rwxr-xr-x, but you wanted to allow anyone
in its group to also write to the file, you could just use the following:
chmod g+w filename
CHAPTER 18 INTRODUCING DARWIN AND THE SHELL 321