For Linux Beginners and those who want to master Linux Administration!
System Admin Concepts in GNU/Linux
source:
http://linuxcandy.com/2012/03/introduction-to-system-admin-concepts-in-gnulinux.html
Most of the GNU/Linux users may be knowing shell program. Infact
GNU/Linux Operating system has started it’s journey with command line
interface. Because of that some people even felt that GNU/Linux is only
for command line activities and not for visually attractive GUIs. FOSS
community around the globe has removed that misconception and a great
deal of improvement has made in terms of GUI (Graphical User Interface)
experience. Unlike proprietary world,
GNU/Linux offers several GUI options like GNOME, KDE, XFCE, etc. Based
on the hardware and software requirments, you can choose the appropriate
X Window System. XFCE is a light weight Interface while GNOME and KDE
are beautiful and rich GUIs.
But even when GUI is there, the world of command line is predominant
among the System Administrators. There are many reasons for the
upperhand of CLI (command line interface) over GUI . The main reason is
the availability of hundreds of powerful commands in GNU/Linux. It is
not mandatory to learn all of these commands, but a knowledge on a basic
set of 30 to 50 commands will give lot of flexibility while using
GNU/Linux Operating System. A user should understand how to go through
documentations and use it with correct syntax for his/her needs. In this
series of
articles we will try to simplify the learning of CLI and its tools.
If you are a user of one of the GNU/Linux flavoures, there will be an
option to open Terminal. In Ubuntu you can open it from Accessories. In
Fedora you can open it by right clicking on the desktop and choose
terminal. Just find out how to open terminal in your flavour. Go to the
different options in terminal and familiarize with it. You can change
the font,
background colour, open another terminal in the same window, etc. Once
you are done with these experiments, concentrate on your shell prompt.
Shell is a program between you and kernel. There are different types of
Shell Programmes like sh, bash, ksh, csh, zsh, etc.. Thanks to the
freedom of enhancement in Free Software.
*So what is your Shell?*
Shell is a programme running in the operating system, interfacing the
user. It accepts and interprets the commands and execute the same with
the help of Kernel. There are different ways to find out your shell.
Type any of the below commands and you can find your shell.
1) echo $SHELL
2) echo $0
You can choose any shell which is available in your system by just
typing the shell name. Most of the shells support all basic commands. It
may have some difference in terms of formatting, history of commands, etc.
When you opened the terminal it takes you to the home directory of your
user ID.
what is home directory ? And how will I find out where am I now?
A user’s home directory is intended to contain that user’s files;
including text documents, music, pictures or videos, etc. It may also
include their configuration files of preferred settings for any software
they have used there and might have tailored to their liking: web
browser bookmarks, favorite desktop wallpape and themes, passwords to
any external services accessed via a given software, etc. The user can
install executable software in this directory, but it will only be
available to users with permission to this directory. The home directory
can be organized further with the use of sub-directories.
Refer Wikipedia page
(https://secure.wikimedia.org/wikipedia/en/wiki/Home_directory
<https://secure.wikimedia.org/wikipedia/en/wiki/Home_d%20irectory>) for
more details.
From shell how can we find out our present working directory?
1 ) pwd (print working directory/present working directory).
Eg :-
rs@rs-ThinkPad-T400:~$ pwd
/home/rs
rs@rs-ThinkPad-T400:~$
If you are not in your home directory, just type “cd” (Change
Directory). This will take you to your home directory. Then once again
run “pwd”. Run the command “ls”. This will list all files and
directories in that directory. ls is one of the very useful commands in
a system administrators life. We will go to the nuances of this command
soon.
Type “ls -l”. It is giving lot of details. The option “l” is called long
listing. Long listing is giving the permission, link count, user and
group owning the file or directory, size of the file, modified time of
the directory/file and name of the file or directory.
From the above result how will we identify which all are directories and
files. ?
rs@rs-ThinkPad-T400:~$ ls -l
total 3375300
-rw-r–r– 1 rs rs 40 2011-09-16 17:47abc
-rw-r–r– 1 rs rs 239948 2011-06-26 13:58 bangalore_trivandrum.pdf
-rw-r–r– 1 rs rs 3455993856 2011-06-19 20:44 brasero.iso
drwxr-xr-x 3 rs rs 4096 2011-08-0718:39 Desktop
drwxr-xr-x 2 rs rs 4096 2011-04-02 11:28Documents
drwxr-xr-x 2 rs rs 4096 2011-09-18 13:40 Downloads
rs@rs-ThinkPad-T400:~$
Whatever starting with “d” is called a directory and with “-” is called
a file.
/*What is a directory and file?*/
In GNU/Linux everything is file, even a directory is a special file.
Even a printer attached to a Computer is considered as a file from the
Operating System perspective.
/*What is a file?*/
File is something which holds some content, just like the real-life
files. In the computer world there are different type of files. Text
files, Binary Files, Directories, etc. Directory is a file, which holds
the information about the files and subdirectories under that.
From the above example you can see that there are different Folders,
like Desktop, Documents, FSMK, etc. These Directory files will be
holding the information of the files and directories under that. We will
revisit this topic once we cover the concept of inode. Introducing
another command “file”.
rs@rs-ThinkPad-T400:~$ file abc
abc: POSIXshell script text executable
rs@rs-ThinkPad-T400:~$
rs@rs-ThinkPad-T400:~$ file Desktop
Desktop: directory
If we give an argument to the command “file”, it will analyse its type
and print to the standard output. I will wrap up the article for this
edition by introducing another command “man”. man command is the short
form of the word manual. It has abundant information about the commands,
tools and configuration files in GNU/Linux created by community members
across the globe. You can run the command “man man” and read about man.
To come out of the man page, just press “q” As an exercise run the
following commands, read through and find out different options of these
commands.
1) man ls
2) man pwd
3) man cd
You might have noticed that the man page of cd is missing. . Let us find
out more details about this in the next edition..
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