Learn Linux Commands The Easy Way

There are hundreds of command line tools in Linux. For a person who has just started using Linux, learning the various commands could at times, be a chore. But not any more, if you see what this website has achieved.

Playterm is a site which hosts videos of commands / tasks executed in the Linux terminal.

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Linux Commands - 10 Useful tricks for Admins

I have heard a saying - the one thing which sets apart a Linux administrator Guru from a Novice is how much more the former is able to accomplish with so few keystrokes. I do not know the veracity of that saying. But IBM Developerworks has - as usual, put together a collection of tricks which will help raise the efficiency of any system administrator by a notch or two. I am no Guru, nor am I a novice. I guess I fall somewhere in the grey areas between the two extremes, which makes reading the tricks really informative for me.

Among the tricks described are Linux commands which we seldom use such as - fuser, reset, screen, as well as invaluable tips like - resetting the root password, SSH back door entry, using VNC to SSH tunnel to a remote machine, checking your bandwidth, a couple of command line tricks, spying on the console and finally Random system information collection.

Read the article to learn more.

Linux Screen Command Revisited

Screen is a command line tool which allows you to manage several interactive shell instances within the same window. Put in simpler terms, screen command allows you to have the same functionality of tabs - but in a console. Red Hat magazine is running a very useful and informative article to installing and using GNU screen on Linux. The article is written by Steve ‘Ashcrow’ Milner and Anderson Silva. Read the article.

Power sessions with Screen

Screen is a full-screen window manager for the console, that comes with every flavour of Linux and UNIX. It is best known for multiplexing a physical terminal across several processes. By using it, you can run any number of console-based applications within a single terminal.

For example, suppose I want to run the 'top' program to keep track of the system load, edit my programming code and check my mail at the same time ... Usually, I have to open at least 3 terminals to do all this. But by using the screen utility, I can run all these programs at the same time in the same physical terminal. Another great feature of this wonderful utility is its ability to decouple the terminal emulator from the running program, which ensures your job is running even if you accidentally close your window, or in case you log out. After detaching, you can reconnect once again to the same session and regain control over the running jobs.

Here I will explain how to use this utility.
1) First open a terminal (eg: xterm if you are in X windows) and type :

$ screen

2) Screen starts and creates a new single window with a shell, pretty much like what you had before. The path name of the shell is taken from the $SHELL variable. New windows can be created within the same physical terminal using the screen commands.

3) Now that you have started screen in a terminal, suppose you want to run the 'top' program to check the System load and at the same time you want to compile a program too - Also you would like to switch between the two to see the progress made by both.

For that, first execute the first program to be run (say 'top'). now 'top' will start in the terminal.

Now open a new window in screen by pressing the '[Ctrl + a] c' - which I will state as 'C-a c' . This will create a new window in the same terminal. Here, you can give commands to compile your program.

In screen, each window is given a unique identifier. The first window is numbered 0, the next window is 1 and so on. Now to switch between your 'top' and the compiling program, you can use the key 'C-a 0' and 'C-a 1' respectively.

You can also associate names with each running window - use 'C-a A' to give a name to the current window.

Here are a few other commands that might come in handy while toggling between various running windows :

• 'C-a p' and 'C-a n' can be used to switch to the next or previous window respectively.
• 'C-a N' - where N is the number from 0 to 9, that can be used to jump to the corresponding window.
• 'C-a w' displays a list of all windows. The unique ID of each window with its name and running process is displayed, for each window. The current window is marked with an asterisk(*).
• 'C-a k' - can be used to kill the current window. You can also type 'exit' to kill the current window. If no more windows are open, then screen exits. 'C-a \' also does the same thing.
• 'C-a d' - detaches the present screen session. You can also detach by closing the terminal running your screen utility. Though, this appears to close your terminal session, in reality this does not happen. It only unbinds your session from the current terminal. All the programs started under screen will still keep running.
  

You can also log out from the machine and re-login. Then start any terminal session and type 'screen -r' to once again be connected from where you left.

In case, there were more than one screen sessions running on the machine, Screen prompts for a host.tty.pid.

For example, say I have two screen sessions. So when I type 'screen -r' command, it gives the following message:

$ screen -r
There are several suitable screens on:
 2999.pts-6.localhost  (Detached)
 1920.PTS-6.localhost  (Detached)
Type "screen [-d] -r [pid].tty.host" to resume one of them.

Choose the proper tty.host to connect to and you are controlling your program again. You can also share your screen session with others like using VNC . Imagine you are having a problem with your code and want to share it with your boss who is located in another office. You can use screen to share your session with your boss, and he can see what you are referring to. The first user starts his screen in a normal fashion and executes the following commands ...

User1:
[Ctrl-A]:multiuser on [RET]
[Ctrl-A]:acladd 

The second user starts a new screen session and connects it to the first session using ...

User2:
screen -x 

There are lots and lots of features in Screen other than those that were described here. To know more about Screen, visit the Official Screen Home Page. You can also find a very good introductory tutorial at Kuro5hin.org.

Two repositories of Linux and Unix commands and example dot files

Does your job involve writing complex bash commands ? Or perhaps you are interested in learning tips and tricks on writing versatile dotfiles. Well, here are two sites which are dedicated to collecting useful tips so as to help Linux users better.

Shell-fu - Is a great site with a growing collection of command line goodies. What makes it interesting is that there are multiple combinations of commands which achieve different tasks. And users can submit and vote for their favorite commands.

Dot files - If you precede a file with a dot, it is considered as a hidden file in Linux. There are numerous hidden files in Linux. The standard ones being .bashrc, .profile, .Xdefaults, .xinitrc and so on. But it doesn't limit to these files. Many applications create hidden files too.

Enter the following command in your terminal to see the hidden files in your home directory.

$ ls -a

This site is a repository of collections of dot files. The files are contributed by its visitors and are divided into different sections namely .vimrc, .screenrc, .bashrc, .zshrc, .Xdefaults, .conkyrc, .irbrc, .bash_profile, .xinitrc and .emacs.

10 seldom or never used GNU/Linux commands

Guess how many commands are there in GNU/Linux ? My estimate is somewhere between 1000 and 2000. And how did I arrive at this conclusion ? In my bare bones Linux installation alone, there are 1151 commands. I got this figure by running the following command :

$ ls /usr/bin /bin /sbin /usr/sbin |wc -l
1151

And each of these commands or a majority of them can be combined together to perform complex tasks, in which case, these combinations can be considered to be whole commands in their own right. Naturally, it is a humongous task to master all the 1000s of commands available in GNU/Linux. More importantly, it is easier to ignore many commands which make very good replacements of some of the commonly used commands at least for certain functions.

Brock Noland has compiled a collection of 10 commands on his site *cough* "bash cures cancer", which are seldom used by a majority of GNU/Linux users but which in his opinion are a boon for all Linux users if only they knew about them. The commands are pgrep, pstree, bc, split, nl, mkfifo, ldd, col, xmlwf and lsof . He claims that his favorite of the 10 commands is surely mkfifo. But to know why, you should read his article. He has also provided a number of examples of usage of the commands which makes it an informative read.