At the heart of Unix lies the concept of a process. Understanding this concept will help you keep control of your login session as a user. If you are also a system administrator, the concept is even more important.
A process is an independently running program that has its own set of resources. For instance, we showed in an earlier section how you could direct the output of a program to a file while your shell continued to direct output to your screen. The reason that the shell and the other program can send output to different places is that they are separate processes .
On Unix, the finite resources of the system, such as the memory and the disks, are managed by one all-powerful program called the kernel. Everything else on the system is a process.
Thus, before you log in, your terminal is monitored by a getty process. After you log in, the getty process dies (a new one is started by the kernel when you log out) and your terminal is managed by your shell, which is a different process. The shell then creates a new process each time you enter a command. The creation of a new process is called forking because one process splits into two.
If you are using the X Window System , each process starts up one or more windows. Thus, the window in which you are typing commands is owned by an xterm process or a reloaded terminal program. That process forks a shell to run within the window. And that shell forks yet more processes as you enter commands.
To see the processes you are running, enter the command ps. Figure 10-2 shows some typical output and what each field means. You may be surprised how many processes you are running, especially if you are using X. One of the processes is the ps command itself, which of course dies as soon as the output is displayed.
The first field in the ps output is a unique identifier for the process. If you have a runaway process that you can’t get rid of through Ctrl-C or other means, you can kill it by going to a different virtual console or X window and entering:
$killprocess-id
The TTY field shows which
terminal the process is running on, if any. (Everything run from a
shell uses a terminal, of course, but background daemons don’t have a
terminal.)
The STAT field shows what
state the process is in. The shell is currently suspended, so this
field shows an S. An Emacs editing
session is running, but it’s suspended using Ctrl-Z. This is shown by
the T in its STAT field. The last process shown is the
ps that is generating all this
input; its state, of course, is R
because it is running.
The TIME field shows how much
CPU time the processes have used. Because both
bash and Emacs are interactive,
they actually don’t use much of the CPU.
You aren’t restricted to seeing your own processes. Look for a
minute at all the processes on the system. The a
option stands for all processes, while the x option
includes processes that have no controlling terminal (such as daemons
started at runtime):
$ ps ax | moreNow you can see the daemons that we mentioned in the previous section.
Recent versions of the ps command have a nice additional option. If you are looking for a certain process whose name (or at least parts of it) you know, you can use the option -C, followed by the name to see only the processes whose names match the name you specify:
$ ps -C httpdAnd here, with a breathtaking view of the entire Linux system at work, we end our discussion of processes (the lines are cut off at column 76; if you want to see the command lines in their full glory, add the option -w to the ps command):
kalle@owl:~ > ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.0 0.0 588 240 ? S 14:49 0:05 init [3]
root 2 0.0 0.0 0 0 ? S 14:49 0:00 [migration/0]
root 3 0.0 0.0 0 0 ? SN 14:49 0:00 [ksoftirqd/0]
root 4 0.0 0.0 0 0 ? S 14:49 0:00 [migration/1]
root 5 0.0 0.0 0 0 ? SN 14:49 0:00 [ksoftirqd/1]
root 6 0.0 0.0 0 0 ? S< 14:49 0:00 [events/0]
root 7 0.0 0.0 0 0 ? S< 14:49 0:00 [events/1]
root 8 0.0 0.0 0 0 ? S< 14:49 0:00 [kacpid]
root 9 0.0 0.0 0 0 ? S< 14:49 0:00 [kblockd/0]
root 10 0.0 0.0 0 0 ? S< 14:49 0:00 [kblockd/1]
root 11 0.0 0.0 0 0 ? S 14:49 0:00 [kirqd]
root 14 0.0 0.0 0 0 ? S< 14:49 0:00 [khelper]
root 15 0.0 0.0 0 0 ? S 14:49 0:00 [pdflush]
root 16 0.0 0.0 0 0 ? S 14:49 0:00 [pdflush]
root 17 0.0 0.0 0 0 ? S 14:49 0:00 [kswapd0]
root 18 0.0 0.0 0 0 ? S< 14:49 0:00 [aio/0]
root 19 0.0 0.0 0 0 ? S< 14:49 0:00 [aio/1]
root 689 0.0 0.0 0 0 ? S 14:49 0:00 [kseriod]
root 966 0.0 0.0 0 0 ? S 14:49 0:00 [scsi_eh_0]
root 1138 0.0 0.0 0 0 ? S 14:49 0:00 [kjournald]
root 1584 0.0 0.0 0 0 ? S 14:49 0:00 [kjournald]
root 1585 0.0 0.0 0 0 ? S 14:49 0:00 [kjournald]
root 1586 0.0 0.0 0 0 ? S 14:49 0:00 [kjournald]
root 2466 0.0 0.0 0 0 ? S 14:49 0:00 [khubd]
root 2958 0.0 0.0 1412 436 ? S 14:49 0:00 [hwscand]
root 3759 0.0 0.0 1436 612 ? Ss 14:49 0:00 /sbin/syslogd -a
root 3798 0.0 0.1 2352 1516 ? Ss 14:49 0:00 /sbin/klogd -c 1
bin 3858 0.0 0.0 1420 492 ? Ss 14:49 0:00 /sbin/portmap
root 3868 0.0 0.0 1588 652 ? Ss 14:49 0:00 /sbin/resmgrd
root 3892 0.0 0.0 1396 544 ? Ss 14:49 0:00 hcid: processing
root 3898 0.0 0.0 1420 528 ? Ss 14:49 0:00 /usr/sbin/sdpd
root 4356 0.0 0.0 0 0 ? S 14:49 0:00 [usb-storage]
root 4357 0.0 0.0 0 0 ? S 14:49 0:00 [scsi_eh_1]
root 4368 0.0 0.1 4708 1804 ? Ss 14:49 0:00 /usr/sbin/sshd -o
root 4715 0.0 0.1 2600 1240 ? S 14:49 0:00 /usr/sbin/powersa
lp 4905 0.0 0.3 6416 3392 ? Ss 14:49 0:00 /usr/sbin/cupsd
root 5103 0.0 0.1 4176 1432 ? Ss 14:49 0:00 /usr/lib/postfix/
postfix 5193 0.0 0.1 4252 1512 ? S 14:49 0:00 qmgr -l -t fifo -
root 5219 0.0 0.0 1584 704 ? Ss 14:49 0:00 /usr/sbin/cron
root 5222 0.0 0.0 42624 784 ? Ss 14:49 0:00 /usr/sbin/nscd
root 5537 0.0 0.1 2264 1216 ? Ss 14:49 0:00 login -- kalle
root 5538 0.0 0.0 1608 608 tty2 Ss+ 14:49 0:00 /sbin/mingetty tt
root 5539 0.0 0.0 1608 608 tty3 Ss+ 14:49 0:00 /sbin/mingetty tt
root 5540 0.0 0.0 1608 608 tty4 Ss+ 14:49 0:00 /sbin/mingetty tt
root 5541 0.0 0.0 1608 608 tty5 Ss+ 14:49 0:00 /sbin/mingetty tt
root 5542 0.0 0.0 1608 608 tty6 Ss+ 14:49 0:00 /sbin/mingetty tt
kalle 5556 0.0 0.1 4180 1996 tty1 Ss 14:50 0:00 -zsh
kalle 5572 0.0 0.0 3012 816 ? Ss 14:50 0:00 gpg-agent --daemo
kalle 5574 0.0 0.1 4296 1332 ? Ss 14:50 0:00 ssh-agent
kalle 5579 0.0 0.1 3708 1248 tty1 S+ 14:50 0:00 /bin/sh /usr/X11R
kalle 5580 0.0 0.0 2504 564 tty1 S+ 14:50 0:00 tee /home/kalle/.
kalle 5592 0.0 0.0 2384 652 tty1 S+ 14:50 0:00 xinit /home/kalle
root 5593 3.4 4.5 106948 46744 ? S 14:50 7:12 X :0 -auth /home/
kalle 5619 0.0 0.1 3704 1288 tty1 S 14:50 0:00 /bin/sh /usr/X11R
kalle 5658 0.0 1.0 24252 10412 ? Ss 14:50 0:00 kdeinit Running..
kalle 5661 0.0 0.8 22876 8976 ? S 14:50 0:00 kdeinit: dcopserv
kalle 5663 0.0 1.0 25340 10916 ? S 14:50 0:00 kdeinit: klaunche
akalle 5666 0.0 1.7 31316 18540 ? S 14:50 0:05 kdeinit: kded
kalle 5673 0.0 1.3 26480 14292 ? S 14:50 0:00 kdeinit: kxkb
kalle 5677 0.0 0.5 9820 5736 ? S 14:50 0:00 /opt/kde3/bin/art
kalle 5679 0.0 0.0 1372 336 tty1 S 14:50 0:00 kwrapper ksmserve
kalle 5681 0.0 1.1 24800 12116 ? S 14:50 0:00 kdeinit: ksmserve
kalle 5683 0.0 1.4 27464 15512 ? S 14:50 0:09 kdeinit: kwin -se
kalle 5686 0.0 1.8 30160 18920 ? S 14:50 0:05 kdeinit: kdesktop
kalle 5688 0.1 1.8 31748 19460 ? S 14:50 0:19 kdeinit: kicker
kalle 5689 0.0 1.0 25856 11360 ? S 14:50 0:00 kdeinit: kio_file
kalle 5692 0.0 1.3 26324 14304 ? S 14:50 0:02 kdeinit: klipper
kalle 5693 0.0 0.7 21144 7908 ? S 14:50 0:00 kpowersave
kalle 5698 0.0 1.3 25840 13804 ? S 14:50 0:00 kamix
kalle 5701 0.0 1.2 24764 12668 ? S 14:50 0:00 kpowersave
kalle 5705 0.0 1.4 29260 15260 ? S 14:50 0:01 suseplugger -capt
kalle 5706 0.0 1.2 24720 13376 ? S 14:50 0:00 susewatcher -capt
kalle 5707 0.0 1.6 28476 16564 ? S 14:50 0:00 kgpg
kalle 5713 0.0 1.2 25088 12468 ? S 14:50 0:02 kdeinit: khotkeys
kalle 5715 0.0 1.9 30296 19920 ? S 14:50 0:08 oooqs -caption Op
kalle 5717 0.0 1.5 28452 15716 ? S 14:50 0:00 kdeinit: kio_uise
kalle 5740 0.0 1.0 26040 11260 ? S 14:50 0:00 kdeinit: kio_file
kalle 5748 0.0 1.6 30084 16928 ? S 14:50 0:05 kdeinit: konsole
kalle 5750 1.8 4.0 57404 42244 ? S 14:50 3:48 kontact -session
kalle 5751 0.0 1.6 29968 16632 ? S 14:50 0:00 kdeinit: konsole
kalle 5754 0.0 0.5 14968 5976 ? S 14:50 0:00 /opt/kde3/bin/kde
kalle 5757 0.0 0.1 4188 1920 pts/2 Ss+ 14:50 0:00 /bin/zsh
kalle 5759 0.0 0.1 4188 1944 pts/3 Ss 14:50 0:00 /bin/zsh
kalle 5761 0.0 0.2 4684 2572 pts/4 Ss+ 14:50 0:00 /bin/zsh
kalle 5800 0.0 0.9 24484 9988 ? S 14:50 0:00 kalarmd --login
kalle 5803 0.0 2.6 36264 27472 ? S 14:50 0:05 xemacs
kalle 5826 0.0 0.1 3704 1172 pts/3 S+ 14:51 0:00 sh ./sshtunnel
kalle 5827 0.0 0.2 4956 2348 pts/3 S+ 14:51 0:02 ssh -X -L 23456:1
kalle 5829 0.1 1.9 31008 20204 ? S 14:51 0:20 kdeinit: ksirc -i
kalle 6086 0.0 0.1 3444 1244 ? S 15:07 0:00 /bin/sh /home/kal
kalle 6107 0.0 0.1 3704 1264 ? S 15:07 0:00 /bin/sh /home/kal
kalle 6115 0.7 4.2 71184 43512 ? S 15:07 1:29 /home/kalle/firef
kalle 6118 0.0 0.3 6460 3612 ? S 15:07 0:00 /opt/gnome/lib/GC
kalle 6137 0.0 0.5 8232 5616 ? S 15:08 0:03 perl /opt/kde3/bi
kalle 6186 0.0 2.9 42300 30384 ? S 15:10 0:03 kdeinit: konquero
kalle 6497 0.1 1.6 30592 17424 ? R 15:20 0:11 kdeinit: konsole
kalle 6498 0.0 0.2 4724 2624 pts/1 Ss+ 15:20 0:00 /bin/zsh
kalle 6511 0.9 3.0 39932 31456 pts/1 S 15:20 1:37 xemacs
kalle 6720 0.0 0.2 4584 2500 pts/5 Ss 15:32 0:00 /bin/zsh
root 6740 0.0 0.1 3480 1264 pts/5 S 15:32 0:00 su
root 6741 0.0 0.1 3608 1732 pts/5 S 15:32 0:00 bash
kalle 6818 0.0 1.6 30152 17316 ? S 15:39 0:00 kdeinit: konsole
kalle 6819 0.0 0.2 4492 2396 pts/6 Ss+ 15:39 0:00 /bin/zsh
kalle 6948 0.0 1.6 29872 16564 ? S 15:48 0:00 kdeinit: konsole
kalle 6949 0.0 0.1 4188 2040 pts/7 Ss 15:48 0:00 /bin/zsh
kalle 6982 0.0 0.1 4556 1908 pts/7 S+ 15:50 0:00 ssh cvs.kdab.net
at 8106 0.0 0.0 1432 536 ? Ss 17:24 0:00 /usr/sbin/atd
postfix 8672 0.0 0.1 4220 1448 ? S 18:09 0:00 pickup -l -t fifo
postfix 8779 0.0 0.1 4208 1396 ? S 18:15 0:00 proxymap -t unix
postfix 8796 0.0 0.1 4744 1784 ? S 18:17 0:00 trivial-rewrite -
postfix 8797 0.0 0.1 4904 1848 ? S 18:17 0:00 cleanup -z -t uni
postfix 8798 0.0 0.1 4376 1768 ? S 18:17 0:00 local -t unix
root 8807 0.0 0.0 1584 700 ? S 18:19 0:00 /USR/SBIN/CRON
kalle 8808 0.0 0.1 3112 1144 ? Ss 18:19 0:00 fetchmail
root 8822 0.0 0.0 2164 688 pts/5 R+ 18:20 0:00 ps aux