Determining what processes are
already running can be an important step in troubleshooting. The command 'ps' (entered on the command line in a Terminial window) with a variety of flags can give information on what is running for the user, the process id, the parent process id, and so forth.
Included in any ps display:
| PID | the process id | the number used to identify this process when halting, killing or resuming this process |
| TT | control terminal | the session that initiated this process AND when ended, typically ends this process |
| STAT | state | for example (I)dle, (S)leeping, s(T)opped |
| TIME | - | cpu time used by the process |
| COMMAND | - | which command |
Notice that shells (sh, csh, tcsh, bash, for example) show up as processes in most lists.
Following are some common examples of using ps.
ps
Issued alone, ps displays the processes running for that user. So, if you are logged in as mary and run ps, you will see the processes you, mary, are running.
[mowed:~] george% ps
PID TT STAT TIME COMMAND
1749 p1 I 0:00 -tcsh (tcsh)
ps -a
Displays all processes with terminals. Typically, a user can only view their own processes.
[mowed:~] george% ps -a
PID TT STAT TIME COMMAND
1749 p1 I 0:00 -tcsh (tcsh)
1775 p2 I 0:00 login -h 555.555.555.555 -p
1776 p2 I 0:00 -tcsh (tcsh)
1789 p2 I 0:00 -csh (csh)
1822 p2 S 0:00 -tcsh (tcsh)
1906 p2 R 0:00 ps -a
ps -l
Asks for a long listing, with fields PPID, CP, PRI, NI, ADDR, VSIZE, RSIZE and WCHAN as described below.
[mowed:~] george% ps -l
F UID PID PPID CP PRI BASE VSIZE RSIZE WCHAN STAT TT TIME COMMAND
4006 32561 1749 1730 0 10 10 2.75M 1.07M 0 I p1 0:00 -tcsh (tc
4006 32561 1776 1775 0 10 10 2.75M 1.08M 0 I p2 0:00 -tcsh (tc
4006 32561 1822 1789 0 10 10 2.75M 1.05M 0 S p2 0:00 -tcsh (tc
new items:
| F | - | flags associated with process. |
| UID | - | numerical user-id of process owner. |
| PPID | parent process id | gives the id of the process that started this process. |
| CP | - | short-term cpu utilization factor (used in scheduling). |
| PRI | - | process priority (non-positive when in non-interruptible wait). |
| VSIZE | - | virtual size of the process (in bytes). |
| RSIZE | - | real memory (resident set) size of the process (in bytes). |
| WCHAN | - | event on which process is waiting (an address in the system). |
ps -x
Asks even about processes with no terminal. The most common processes with no terminal are daemons or other processes started by the system.
The flags can be combined. For instance, 'ps -alx' is commonly used to view system processes and their parent process ids. 'ps' can be used to display percent of cpu use or memory use as well as other nifty information not covered here. For more information, consult the System Reference Manual by typing the following command at the Terminal prompt:
man ps