A free Basic UNIX-training with muLinux

Process Management

Multi-user means that several users can operate at the same time on the same computer. This necessarily different humans do not have to be. Humans can log in also several times. This is possible with Linux over the virtual consoles. Additional users can log in also over a network.

Multitasking means however that a user can execute several programs at the same time. One can at the same time format e.g. a longer text printouts and a diskette.

A process is a program with its remark environment, in the execution. This program can be an application program or a not program visible for the user (English daemon). Each process operates in a separate, virtual address area, then no process can disturb another unknowingly knowingly (e.g. by viruses) or. Individual process successively that is permitted access to the CCU (processor). How long and in which order this occurs, by the process scheduler (English schedule) is determined. If a program " does not hang " can it, as with some primitive operation systems, which paralyze whole computer.

All processes are administered over the central process table. The processes are to each process a unique number (process number, PID) in a hierarchical order, there and the number of the parents process (producer process) with itself leads. Similarly as with the rights of access with files applies to the task management and the memory management: A process can be influenced only of its user.

Display All Current Processes with ps

/# ps
PID TTY STAT TIME:  COMMAND
...
/#
_

Each process, so each current program, is thus represented with a line. With the names of most processes we will not be able to begin up to now yet much.

PID

TTY

STAT

• D not interruptible sleep.
• R running
• S sleeping. The process waits for possibly something. Usually the processes oscillate between running and sleep back and forth.
• T interrupted process
• Z Zombie. That is a terminated process, which was not removed yet from the process table.

TIME:

COMMAND

Commands in the background &

/# find / -user craxi -print &

This instruction with a line is acknowledged. For example:

[3] 12304

The number in square brackets indicates, wievielt jobs now in the background runs. The second number is the PID.

It pay attention that jobs, which operate in the background write further on the display, and the work in the foreground substantially to disturb can. One knows however the possibility of the data bypass by means of > use, around the output into a file write. Error messages can be rerouted with > 2.

/# find / -user craxi -print 2> /dev/null > a/gefunden.txt &

Kill Processes with kill

/# bc

Now we change to the second virtual console with [Alt] [F2]. There we log ourselves as root. Around the instruction kill to apply we need the process number (PID). We determine these also ps:

/# ps
...
> _

Whom the output is too long, the output can on the processes also also with the following version "bc" filter:

/# ps | grep "bc"
26845 ? s 0:0 (bc) mawk - f / usr/bin/bc

The first number is the process number. This surely deviates with on your display. Use the number with you one displays. Additionally further lines appear also " grep " and " sed ". Those are the processes for the even used grep - instruction. These lines are uninteresting. Now we want the process with the pocket calculator bc terminate:

/# kill -9 26845

The option -9 caused that the process in any case is terminated. If this option is omitted, the program has to store still the possibility if necessary data. If we change back now to the original console, we see the following output:

/# ps
...
> Killed
/# _

The process with the pocket calculator was thus terminated. Naturally one can terminate only own processes. An exception forms here again the superuser.