Slackware Linux Essentials
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11.3 `ps`

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So now you know how to switch back and forth between several processes that you've -started from the command line. And you also know that there are lots of processes running -all the time. So how do you list all of these programs? Well, you make use of the ps(1) command. This command has a lot of options, so we'll only -cover the most important ones here. For a complete listing, see the man page for ps. Man -pages are covered in-depth in Section 2.1.1.

- -

Simply typing ps will get you a listing of the programs -running on your terminal. This incudes the foreground processes (which include whatever -shell you are using, and of course, ps itself). Also listed are -backgrounded processes you may have running. Many times, that will be a very short -listing:

- -

Figure 11-1. Basic ps output

- - - - - -

-% ps
-   PID TTY          TIME CMD
-  7923 ttyp0    00:00:00 bash
-  8059 ttyp0    00:00:00 ps
-

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Even though this is not a lot of processes, the information is very typical. You'll -get the same columns using regular ps no matter how many processes are running. So what -does it all mean?

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Well, the PID is the process ID. All running processes are given a unique -identifier which ranges between 1 and 32767. Each process is assigned the next free PID. -When a process quits (or is killed, as you will see in the next section), it gives up its -PID. When the max PID is reached, the next free one will wrap back around to the lowest -free one.

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The TTY column indicates which terminal the process is -running on. Doing a plain ps will only list all the programs -running on the current terminal, so all the processes give the same information in the -TTY column. As you can see, both processes listed are running on ttyp0. This indicates that they are either running remotely or from -an X terminal of some variety.

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The TIME column indicated how much CPU time the process has -been running. This is different from the actual amount of time that a process runs. -Remember that Linux is a multitasking operating system. There are many processes running -all the time, and these processes each get a small portion of the processor's time. So, -the TIME column should show much less time for each process than it actually takes to -run. If you see more than several minutes in the TIME column, it could mean that -something is wrong.

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Finally, the CMD column shows what the program actually is. -It only lists the base name of the program, not any command line options or similar -information. To get that information, you'll need to use one of the many options to ps. We'll discuss that shortly.

- -

You can get a complete listing of the processes running on your system using the right -combination of options. This will probably result in a long listing of processes -(fifty-five on my laptop as I write this sentence), so I'll abbreviate the output:

- - - - - -

-% ps -ax
- PID TTY      STAT   TIME COMMAND
-   1 ?        S      0:03 init [3]
-   2 ?        SW     0:13 [kflushd]
-   3 ?        SW     0:14 [kupdate]
-   4 ?        SW     0:00 [kpiod]
-   5 ?        SW     0:17 [kswapd]
-  11 ?        S      0:00 /sbin/kerneld
-  30 ?        SW     0:01 [cardmgr]
-  50 ?        S      0:00 /sbin/rpc.portmap
-  54 ?        S      0:00 /usr/sbin/syslogd
-  57 ?        S      0:00 /usr/sbin/klogd -c 3
-  59 ?        S      0:00 /usr/sbin/inetd
-  61 ?        S      0:04 /usr/local/sbin/sshd
-  63 ?        S      0:00 /usr/sbin/rpc.mountd
-  65 ?        S      0:00 /usr/sbin/rpc.nfsd
-  67 ?        S      0:00 /usr/sbin/crond -l10
-  69 ?        S      0:00 /usr/sbin/atd -b 15 -l 1
-  77 ?        S      0:00 /usr/sbin/apmd
-  79 ?        S      0:01 gpm -m /dev/mouse -t ps2
-  94 ?        S      0:00 /usr/sbin/automount /auto file /etc/auto.misc
- 106 tty1     S      0:08 -bash
- 108 tty3     SW     0:00 [agetty]
- 109 tty4     SW     0:00 [agetty]
- 110 tty5     SW     0:00 [agetty]
- 111 tty6     SW     0:00 [agetty]
- [output cut]
-

- -

Most of these processes are started at boot time on most systems. I've made a few -modifications to my system, so your mileage will most likely vary. However, you will see -most of these processes on your system too. As you can see, these options display command -line options to the running processes. Recently, a kernel vulnerability in ptrace facilitated a fix which no longer shows command line options -for many running processes. These are now listed in brackets like PIDs 108 through 110. -It also brings up a few more columns and some other interesting output.

- -

First, you'll notice that most of these processes are listed as running on tty -“?”. Those are not attached to any particular terminal. This is most common -with daemons, which are processes which run without attaching to any particular terminal. -Common daemons are sendmail, BIND, apache, and NFS. They typically listen for some -request from a client, and return information to it upon request.

- -

Second, there is a new column: STAT. It shows the status of -the process. S stands for sleeping: the process is waiting for -something to happen. Z stands for a zombied process. A zombied -processes is one whose parent has died, leaving the child processes behind. This is not a -good thing. D stands for a process that has entered an -uninterruptible sleep. Often, these processes refuse to die even when passed a SIGKILL. -You can read more about SIGKILL later in the next section on kill . W stands for paging. A dead process is marked with an X. A process marked T is traced, or -stopped. R means that the process is runable.

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If you want to see even more information about the running processes, try this -out:

- - - - - -

-% ps -aux
- USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
- root         1  0.0  0.0   344   80 ?        S    Mar02   0:03 init [3]
- root         2  0.0  0.0     0    0 ?        SW   Mar02   0:13 [kflushd]
- root         3  0.0  0.0     0    0 ?        SW   Mar02   0:14 [kupdate]
- root         4  0.0  0.0     0    0 ?        SW   Mar02   0:00 [kpiod]
- root         5  0.0  0.0     0    0 ?        SW   Mar02   0:17 [kswapd]
- root        11  0.0  0.0  1044   44 ?        S    Mar02   0:00 /sbin/kerneld
- root        30  0.0  0.0  1160    0 ?        SW   Mar02   0:01 [cardmgr]
- bin         50  0.0  0.0  1076  120 ?        S    Mar02   0:00 /sbin/rpc.port
- root        54  0.0  0.1  1360  192 ?        S    Mar02   0:00 /usr/sbin/sysl
- root        57  0.0  0.1  1276  152 ?        S    Mar02   0:00 /usr/sbin/klog
- root        59  0.0  0.0  1332   60 ?        S    Mar02   0:00 /usr/sbin/inet
- root        61  0.0  0.2  1540  312 ?        S    Mar02   0:04 /usr/local/sbi
- root        63  0.0  0.0  1796   72 ?        S    Mar02   0:00 /usr/sbin/rpc.
- root        65  0.0  0.0  1812   68 ?        S    Mar02   0:00 /usr/sbin/rpc.
- root        67  0.0  0.2  1172  260 ?        S    Mar02   0:00 /usr/sbin/cron
- root        77  0.0  0.2  1048  316 ?        S    Mar02   0:00 /usr/sbin/apmd
- root        79  0.0  0.1  1100  152 ?        S    Mar02   0:01 gpm
- root        94  0.0  0.2  1396  280 ?        S    Mar02   0:00 /usr/sbin/auto
- chris      106  0.0  0.5  1820  680 tty1     S    Mar02   0:08 -bash
- root       108  0.0  0.0  1048    0 tty3     SW   Mar02   0:00 [agetty]
- root       109  0.0  0.0  1048    0 tty4     SW   Mar02   0:00 [agetty]
- root       110  0.0  0.0  1048    0 tty5     SW   Mar02   0:00 [agetty]
- root       111  0.0  0.0  1048    0 tty6     SW   Mar02   0:00 [agetty]
- [output cut]
-

- -

That's a whole lot of information. Basically, it adds information including what user -started the process, how much of the system resources the process is using (the %CPU, -%MEM, VSZ, and RSS columns), and on what date the process was started. Obviously, that's -a lot of information that could come in handy for a system administrator. It also brings -up another point: the information now goes off the edge of the screen so that you cannot -see it all. The -w option will force ps to wrap long lines.

- -

It's not terribly pretty, but it does the job. You've now got the complete listings -for each process. There's even more information that you can display about each process. -Check out the very in-depth man page for ps. However, the -options shown above are the most popular ones and will be the ones you need to use the -most often.

11.3 ps

11.3 `ps`