Topic: System Load and Process Monitoring

The father of all process monitoring tools must be ps. In the beginning, there was only ps and it is still the definitive tool for monitoring processes. The name is an acronym for "Process Status" as it is used to check on your own processes, or those of others using the same system

The current version of ps supports a staggering number of options in a bewildering array of styles. Typically, I use three or four options at most. Note that ps prefers BSD-style options, specified without the leading dash you may be used to.

By default ps show basic information about your own processes:

$ ps
  PID TTY          TIME CMD
19535 pts/0    00:00:00 bash
19550 pts/0    00:00:00 ps

With the addition of the u option, you'll get more information about each process. This is called the user-oriented output style:

$ ps u
USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
kgirrard 19535  0.0  0.2  1728  968 pts/0    S    08:29   0:00 -bash
kgirrard 19551  0.0  0.2  2504  880 pts/0    R    08:30   0:00 ps u

If you want to see information on processes other than just your own, add the x option:

$ ps ux
USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
dleeling 18483  0.0  0.2  1728  968 pts/1    S    08:21   0:00 -bash
kgirrard 19535  0.0  0.2  1728  968 pts/0    S    08:29   0:00 -bash
kgirrard 19579  0.0  0.2  2504  880 pts/0    R    08:33   0:00 ps ux

Many processes aren't associated with users at terminals. To show these, which include most of those that provide network services, add the a option too:

$ ps aux
USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.1  1096  472 ?        S    Jun26   0:03 init [3]
root         2  0.0  0.0     0    0 ?        SW   Jun26   0:00 [kflushd]
root         3  0.0  0.0     0    0 ?        SW   Jun26   0:00 [kpiod]
root         4  0.0  0.0     0    0 ?        SW   Jun26   0:00 [kswapd]
root         5  0.0  0.0     0    0 ?        SW<  Jun26   0:00 [mdrecoveryd]
bin        316  0.0  0.0  1088  368 ?        S    Jun26   0:00 portmap
root       351  0.0  0.1  1132  412 ?        S    Jun26   0:00 /sbin/apcupsd
root       412  0.0  0.1  1284  532 ?        S    Jun26   0:00 crond
root       430  0.0  0.1  1240  516 ?        S    Jun26   0:01 inetd
root       444  0.0  0.5  3084 2008 ?        S    Jun26   0:11 named
root       458  0.0  0.3  1324 1324 ?        SL   Jun26   0:00 xntpd
root       473  0.0  0.1  1288  516 ?        S    Jun26   0:00 lpd
root       491  0.0  0.1  1580  640 ?        S    Jun26   0:01 /usr/sbin/dhcpd
root       512  0.0  0.1  1884  716 ?        S    Jun26   0:01 sendmail
root       520  0.0  0.1  1856  752 ?        S    Jun26   0:00 /usr/sbin/httpd
root       557  0.0  0.1  3212  424 ?        S    Jun26   0:00 squid -D
...

(The complete list of processes generated by ps aux is quite long! You might want to use a pager such as more or less when looking at the full list of processes.)

There are a few pieces of information about each process that need some explanation, expecially the cyptic ones like the STAT column.

USER: The owner of the process, typically the user who started it
PID: The processes unique ID number. These are assigned sequentially as processes start. When they reach 30,000 or so, the number starts over again at 0. 0-5 are usually low-level operating system processes which never exit, however.
%CPU: Percentage of the CPU's time spent running this process.
%MEM: Percentage of total memory in use by this process
VSZ: Total virtual memory size, in 1K blocks.
RSS: Real Set Size, the actual amount of physical memory allocated to this process.
TTY: Terminal associated with this process. A ? indicates the process is not connected to a terminal.
STAT: Process state codes. Common states are S - Sleeping, R - Runnable (on run queue), N - Low priority task, Z - Zombie process
START: When the process was started, in hours and minutes, or a day if the process has been running for a while.
TIME: CPU time used by process since it started.
COMMAND: The command name. This can be modified by processes as they run, so don't rely on it abolutely!

The output from ps has many more options for different applications. Consult the manual page for complete information. Be forewarned that with three different methods to specify options, its a little overwhelming...

The Manual Page for ps

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