Page 187 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Unit 10: File System

notes

Note The VFS acts as the root level of the file-system interface.

10.3 file permissions and Directories permissions

10.3.1 ownerships and permissions

The Linux operating system differs from other computing environments in that it is not only a
multitasking system but it is also a multi-user system as well.

It means that more than one user can be operating the computer at the same time. While your
computer will only have one keyboard and monitor, it can still be used by more than one user.
For example, if your computer is attached to a network, or the Internet, remote users can log
in via telnet or ssh (secure shell) and operate the computer. In fact, remote users can execute X
applications and have the graphical output displayed on a remote computer. The X Windows
system supports this.
The multi-user capability of Linux is not a recent “innovation,” but rather a feature that is
deeply ingrained into the design of the operating system. Linux is originated from UNIX. The
environment in which UNIX was created, this makes perfect sense. Years ago before computers
were “personal;” they were large, expensive, and centralized. In order to make this practical, a
method had to be devised to protect the users from each other. After all, you could not allow the
actions of one user to crash the computer, nor could you allow one user to interfere with the files
belonging to another user.
Linux uses the same permissions scheme as Unix. Each file and directory on your system is
assigned access rights for the owner of the file, the members of a group of related users, and
everybody else. Rights can be assigned to read a file, to write a file, and to execute a file (i.e., run
the file as a program).
A typical university computer system consisted of a large mainframe computer located in some
building on campus and terminals were located throughout the campus, each connected to the
large central computer. The computer would support many users at the same time.

Did u know? What are the basic permissions to the user to access the file?

To see the permission settings for a file, we can use the ls command as follows:
$ ls -l some_file
-rw-rw-r-- 1 me me 1097374 Sep 26 18:48 some_file
We can determine a lot from examining the results of this command:
1. The file “some_file” is owned by user “me”
2. User “me” has the right to read and write this file

3. The file is owned by the group “me”
4. Members of the group “me” can also read and write this file
5. Everybody else can read this file

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