Basics of Process Management
What do you do when you can’t make your process stop no matter how many times you click that little X in the corner?
Each of these different things happening on the computer is called a “process”, and your computer takes turns letting all of the processes run a little bit at a time. The computer works so fast that you usually don’t even notice.
But occasionally, a process stops responding to you. What do you do when you can’t make your process stop no matter how many times you click that little x in the corner? You try using the keyboard commands Esc and Ctrl + C. You even try Ctrl + Q, Ctrl + X, and Ctrl + Z; but they don’t work. What do you do next?
To discover the basics of how to manage processes in linux, watch and read the following tutorial.
If you can get into a terminal, you can kill any process
Well, if you can get into a terminal, you can kill any process. The command is called kill. The command name is easy enough to remember, but your problem is knowing what to kill. Each process has a different process identification number (PID) and you must use that number to kill it.
To see a list the processes currently running on your system, you can use the command ps. If I open a terminal program and type ps now, I will see this:
rosalyn@onizuka:~$ ps PID TTY TIME CMD 14036 pts/2 00:00:00 bash 14040 pts/2 00:00:00 ps
(The prompt on my system says rosalyn@onizuka:~$. Needless to say, your computer will say something different. When I show an example like this, only type the words after the dollar sign. The computer’s response will be shown on the following lines.)
The computer responds telling me what processes I am currently running in this terminal window. First, I am running the terminal window itself using the BASH shell. Then I am running the command ps. That’s not very informative. Is it?
I would really like the computer to show me all of the processes running on my system. To find that, I must use options (letters typed after the command that modify its function). In order to see all of the processes running on my system, I use the ps aux command:
rosalyn@onizuka:~$ ps aux
-
psreports a snapshot of the current processes running on your system. -
atells the computer to show all processes -
utells the user name of who owns the process, and -
xlists processes that were not started in a terminal.
This command will return a long list of processes that scrolls off my terminal screen. Somewhere in that list is the process ID that I am looking for. If I am using a terminal with a scroll bar, I can just scroll back up and read it all to find the process. Personally, however, I prefer to use a different command to get the process ID. The command called top. Top is much like a command line version of Windows “task manager”. For a more advanced Top I tend to use an application called htop. It can be easily installed in Suse via “zypper in htop” as the superuser. But for the sake of the document we’ll stick with top as it comes with all linux systems.
Tasks and processes
What’s the difference between a task and a process? Nobody knows. For the most part people use the word task when they are talking about sending things to the processor to avoid saying things like, “the processor processes the process”.
Well, actually, there is a difference between tasks and processes. The process that starts your computer is called init. It is listed by the process ID 1. This process is also called Task [0]. For the most part, however, just consider tasks and processes to be the same thing.
Top lists the processes using the most time on the computer’s processor. It prints only what will fit in your terminal window, and it refreshes every few seconds to give you an up to date picture of your system. If your program has stalled, then it is probably taking up lots of processor time, and it will be right near the top of the list. Typing top on my system shows me this:
top - 00:15:36 up 10:53, 1 user, load average: 0.79, 0.69, 0.58
Tasks: 86 total, 3 running, 83 sleeping, 0 stopped, 0 zombie
Cpu(s): 29.9% us, 6.6% sy, 0.0% ni, 62.8% id, 0.0% wa, 0.3% hi, 0.3% si
Mem: 484292k total, 361820k used, 122472k free, 25596k buffers
Swap: 1421712k total, 0k used, 1421712k free, 169384k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
13247 rosalyn 16 0 155m 67m 46m R 26.3 14.2 11:58.69 seamonkey-bin
3363 root 15 0 93448 50m 44m S 9.0 10.6 6:05.50 XFree86
14032 rosalyn 15 0 27320 14m 25m S 1.0 3.0 0:02.04 konsole
13227 rosalyn 15 0 14168 9928 11m S 0.7 2.1 0:09.65 gvim
3094 gkrellmd 15 0 18824 1340 2240 S 0.3 0.3 2:24.32 gkrellmd
13207 rosalyn 15 0 26532 14m 23m S 0.3 3.1 0:01.69 kdeinit
14196 rosalyn 16 0 2104 1084 1888 R 0.3 0.2 0:00.11 top
1 root 16 0 1516 520 1364 S 0.0 0.1 0:00.58 init
If you lengthen the terminal window, it will show more data. Now, suppose the program “seamonkey” was frozen. I could kill it by typing the command kill followed by seamonkey’s process ID 13247.
Of course, to do this I need to get a prompt again. Top will keep refreshing in the terminal window until you tell it to stop. Both the letter q for quit and typing the control button and c at the same time (Ctrl + C) will stop the program and give you back your prompt.
To kill seamonkey, I can type:
rosalyn@onizuka:~$ kill 13247
This should stop the process causing the seamonkey window to close, but sometimes it doesn’t. What do I do if seamonkey still won’t close?
Well, kill also has options. The basic command tries to be nice. It says, “Could you please stop now?” But if the process just won’t die when you ask it nicely, then use the option -9. The command kill -9 says “take no prisoners!”
So if kill alone doesn’t work, I can type:
rosalyn@onizuka:~$ kill -9 13247
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