Running programs: Multitasking and Sessions

To run a program, type its name as you would do under DOS. If the directory where the program is stored is included in the PATH the program will start. Exception: unlike DOS, under Linux a program located in the current directory won’t run unless the directory is included in the PATH.
You can type multiple command with; as the separator like: 

$ command1; command2; ….;commandn

That’s all about running programs, but it’s easy to go a step beyond. One of the main reasons for using Linux is that it is the multitasking OS- it can run several programs (from now on, processes) at the same time. You can launch processes in background and continue working straight away.

Moreover, Linux lets you have several sessions: it’s like having many computers to work on at once!

Some wonderful tips, hope you will find useful.

To switch to session 1..6:

$ ALT-F1 …ALT-F6

To start a new session without leaving the current one:

$ su – root

This is useful, for one, when you need to mount a disk normally, only root
can do that.

To end a session:

$ exit

If there are stopped jobs (see later), you’ll be warned.

To launch a process in foreground:

$ programm [-switches] [parameter] [<input][>output]

To launch a process in background, add an ampersand ‘&’ at the end
of the command line:

$ programm [-switches] [parameter] [<input][>output]& 

[1] 123

The shell identifies the process with a job number (e.g. [1]; seebelow), and with a PID (123 in our example).

To see how many process there are:

$ ps -aux

This will output a list of currently running processes.

To find the process running

$ ps aux | grep <process name>

To kill a process:

$ kill <PID>

You may need to kill a process when you don’t know how to quit it the right way…:-). Sometimes, a process
will only be killed by either of the following:

$kill -15 <PID>

$kill -9 <PID>

In addition to this, the shell allows you to stop or temporarily suspend a process, send a process to background, and bring a process from background to foreground. In this context, process are called “jobs”.

To see how many jobs there are:

$ jobs

here jobs are identified by their job number, not by their PID

To stop a process running in foreground (it won’t always work):
$ CTRL-C

To suspend a process running in foreground (ditto):

$ CTRL-Z

To send a suspended process intothe background (it becomes a job):

$ bg <job>

To bring a job to foreground:

$ fg <job>

To kill a job:

$ kill <%job>

where job may be 1,2,3… Using these commands you can format a disk, zip a bunch of files, compiles a
program, and unzip an archive all at the same time, and still have the prompt at your disposal. Try this with DOS! And try with Windows, just to see the difference in performance.

 Running Programs on Remote Computers

To run a program on a remote machine whose Hostname (Do you know what do you mean by this:) is karnali.linuxnepal.com.np, you do:

$ telnet karnali.linuxnepal.com.np

After logging in, start your favourite program. Needless to say, you must have an account on the remote
machine. (This is bit of high tech stuff will talk about these later)

Using Directories 

Directories: Preliminary Notions

We have seen the differences between files under DOS and Linux. As for directories, under DOS the root
directory is \, under Linux / is. Similarly, nested directories are separated by \ under DOS, by / under Linux. Example of file paths:

DOS: C:\ranjan\lpora;a\MID_EOC.TEX

Linux: /home/htp/koirala/ranjan/mid_eoc.tex

As usual, .. is the parent directory, . is the current directory. Remember that the system won’t let you cd, rd, or md everywhere you want. Each user starts from his or her own directory called dir is /home/ranjan

Directory Permissions

Directories, too, have permissions, as well (user, group, and other). For a directory, rx means you can cd to that directory, and w means that you can delete a file in the directory (according to the file’s permissions, of course), or the directory itself.
For example, to prevent other users from snooping in /home/ranjan/text:

$chmod o-rwx /home/ranjan/text

Translating Commands from DOS to Linux

DIR	ls,find,du
CD	cd, pwd
MD	mkdir
RD	rmdir
DELTREE	rm -R
MOVE	mv

Notes:

1. When using rmdir, the directory to remove must be empty. To delete a directory and all of its contents, use rm -R (at your own risk).

2. The character ‘~’ is a shortcut for the name of your home directory. The commands cd or cd ~ will take
you to your home directory from wherever you are; the command cd ~/tmp will take you to /home/your_home/tmp.

3. cd – “undoes” the last cd.