There is a file on your system that represents each device on
your system??”printer, sound card, hard-drive partitions, monitor, and directories. Each file
has rules about who can access it and in what manner.
In this section, you will get an introduction to permissions. You??™ll learn about permissions
in more depth in Chapter 19. No matter what your skill level is, you should read the
???User Accounts and Permissions??? section of that chapter.
Linux is a multiuser operating system, with a minimum of two users on any machine: the
Root user and a generic user.
NOTE
The Root user is also the SuperUser when logged in as such, and other users can
become the SuperUser with the Root password.
Each file (again, that means everything on your system) has an owner and is assigned to a
group when it is created. Read, write, and execute permissions are set for three types of
user: Owner, Group, and Others (that is, the rest of the world).
The ls -l (long format) directory listing command displays the permissions for each file.
To see the system default permissions for a file, use the touch command to create an
empty file and then run ls -l, like this:
touch file
mikemc@linux:~> ls -l file
-rw-r--r-- 1 mikemc users 0 2004-12-08 09:43 file
TIP
touch -t will also change the access time of any existing file.
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