4.1.4. Displaying process information
The ps command is one of the tools for visualizing processes. This command has several options which can be combined to display different process attributes.
With no options specified, ps only gives information about the current shell and eventual processes:
theo:~> ps
PID TTY TIME CMD
4245 pts/7 00:00:00 bash
5314 pts/7 00:00:00 ps
Since this does not give enough information - generally, at least a hundred processes are running on your system - we will usually select particular processes out of the list of all processes, using the grep command in a pipe , see Section 5.1.2.1 , as in this line, which will select and display all processes owned by a particular user:
ps -ef | grep username
This example shows all processes with a process name of bash , the most common login shell on Linux systems:
theo:> ps auxw | grep bash
brenda 31970 0.0 0.3 6080 1556 tty2 S Feb23 0:00 -bash
root 32043 0.0 0.3 6112 1600 tty4 S Feb23 0:00 -bash
theo 32581 0.0 0.3 6384 1864 pts/1 S Feb23 0:00 bash
theo 32616 0.0 0.3 6396 1896 pts/2 S Feb23 0:00 bash
theo 32629 0.0 0.3 6380 1856 pts/3 S Feb23 0:00 bash
theo 2214 0.0 0.3 6412 1944 pts/5 S 16:18 0:02 bash
theo 4245 0.0 0.3 6392 1888 pts/7 S 17:26 0:00 bash
theo 5427 0.0 0.1 3720 548 pts/7 S 19:22 0:00 grep bash
In these cases, the grep command finding lines containing the string bash is often displayed as well on systems that have a lot of idletime. If you don't want this to happen, use the pgrep command.
Bash shells are a special case: this process list also shows which ones are login shells (where you have to give your username and password, such as when you log in in textmode or do a remote login, as opposed to non-login shells, started up for instance by clicking a terminal window icon). Such login shells are preceded with a dash (-).
More info can be found the usual way: ps --help or man ps . GNU ps supports different styles of option formats; the above examples don't contain errors.
Note that ps only gives a momentary state of the active processes, it is a one-time recording. The top program displays a more precise view by updating the results given by ps (with a bunch of options) once every five seconds, generating a new list of the processes causing the heaviest load periodically, meanwhile integrating more information about the swap space in use and the state of the CPU, from the proc file system:
12:40pm up 9 days, 6:00, 4 users, load average: 0.21, 0.11, 0.03
89 processes: 86 sleeping, 3 running, 0 zombie, 0 stopped
CPU states: 2.5% user, 1.7% system, 0.0% nice, 95.6% idle
Mem: 255120K av, 239412K used, 15708K free, 756K shrd, 22620K buff
Swap: 1050176K av, 76428K used, 973748K free, 82756K cached
PID USER PRI NI SIZE RSS SHARE STAT %CPU %MEM TIME COMMAND
5005 root 14 0 91572 15M 11580 R 1.9 6.0 7:53 X
19599 jeff 14 0 1024 1024 796 R 1.1 0.4 0:01 top
19100 jeff 9 0 5288 4948 3888 R 0.5 1.9 0:24 gnome-terminal
19328 jeff 9 0 37884 36M 14724 S 0.5 14.8 1:30 mozilla-bin
1 root 8 0 516 472 464 S 0.0 0.1 0:06 init
2 root 9 0 0 0 0 SW 0.0 0.0 0:02 keventd
3 root 9 0 0 0 0 SW 0.0 0.0 0:00 kapm-idled
4 root 19 19 0 0 0 SWN 0.0 0.0 0:00 ksoftirqd_CPU0
5 root 9 0 0 0 0 SW 0.0 0.0 0:33 kswapd
6 root 9 0 0 0 0 SW 0.0 0.0 0:00 kreclaimd
7 root 9 0 0 0 0 SW 0.0 0.0 0:00 bdflush
8 root 9 0 0 0 0 SW 0.0 0.0 0:05 kupdated
9 root -1-20 0 0 0 SW< 0.0 0.0 0:00 mdrecoveryd
13 root 9 0 0 0 0 SW 0.0 0.0 0:01
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