ch40.htm

linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

<PRE><FONT COLOR="#0066FF">$ ps -u

USER       PID %CPU %MEM SIZE  RSS TTY STAT START   TIME COMMAND

bill        41  0.1  6.8  364  472 v01 S    23:19   0:01 -bash

bill       138  0.0  3.3   72  228 v01 R    23:34   0:00 ps -u

</FONT></PRE>

<P>The most important addition to the output is the <TT>USER</TT> column, which shows

who started and owns the process. The name listed under the <TT>USER</TT> column

is the user's login name, as found in the <TT>/etc/passwd</TT> file. (<TT>ps</TT>

does a look-up in the <TT>/etc/passwd</TT> file to convert the user ID number--UID--to

the proper username.)</P>

<P>This option also adds the column labeled <TT>%CPU</TT>, which shows the percentage

of CPU time that has been used by the proce ss so far. The column <TT>%MEM</TT> shows

the percentage of your system's memory currently used by the process. These numbers

can be handy for finding processes that consume far too much CPU or memory, called

&quot;CPU hogs&quot; and &quot;memory hogs&quot; by most administrators. If you see

a user process that has very high usage, it is worth checking to make sure it is

a valid process and not a runaway that will continue to grind at your system's resources.</P>

<P>When you issue this command logged in as root, you see all the processes running

on the system. As before, you should consider paginating the output to make it readable.

With some versions of Linux's <TT>ps</TT> command, you can also use the <TT>-u</TT>

option to specify a user's processes by adding each username. For example, if you

are logged in as root and want to see only Yvonne's processes, you could issue this

command:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">ps -u yvonne

</FONT></PRE>

<P>This format of the <TT>-u</TT> option works with System V versions of <TT>ps</TT>,

but not the BSD-based version of <TT>ps</TT> included with most Linux distributions

(including the one on the CD-ROM). You can obtain other versions of <TT>ps</TT> on

FTP and BBS sites. Most users can issue this command to examine other users' processes

as well. This lets them find out who is hogging all the CPU time! It also lets the

superuser see the processes that users are running when they report problems, without

having to wade through all the system processes as well.</P>

<P>Users can also see all the processes running on the system (instead of just the

processes started by them) by using the <TT>-a</TT> option. Because the superuser

sees all the processes on the system anyway, the root login doesn't have to use this

option, although it is still legal to use it. This output doesn't change, though.

When issued by a user (not root), the <TT>-a</TT> option produces the following output:<FONT

COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">$ ps -a

 PID TTY STAT TIME COMMAND

   1 psf S   0:00 init

   6 psf S   0:00 update (sync)

  23 psf S   0:00 /usr/sbin/crond -l10

  29 psf S   0:00 /usr/sbin/syslogd

  31 psf S   0:00 /usr/sbin/klogd

  33 psf S   0:00 /usr/sbin/lpd

  40 psf S   0:00 selection -t ms

  42 v02 S   0:01 -bash

  43 v03 S   0:00 /sbin/agetty 38400 tty3

  44 v04 S   0:00 /sbin/agetty 38400 tty4

  45 v05 S   0:00 /sbin/agetty 38400 tty5

  46 v06 S   0:00 /sbin/agetty 38400 tty6

  41 v01 S   0:01 -bash

 140 v01 R   0:00 ps -a

</FONT></PRE>

<P>This is a relatively short output showing a very lightly loaded system. Most of

the entries are the Linux operating system kernel and daemons, as well as serial

port <TT>getty</TT> processes. Only the last two commands were started by the user

who issued the <TT>ps</TT> command. Of course, you can't tell who started each process

with this output, so you can combine the <TT>-u</TT> and <TT>-a</TT> options (note

that you use only one hyphen, followed by the option letters):<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">$ ps -au

USER       PID %CPU %MEM SIZE  RSS TTY STAT START   TIME COMMAND

root        64  0.0  1.5   41  224 v02 S    22:25   0:00 /sbin/agetty 38400 tty2

root        65  0.0  1.5   41  224 v03 S    22:25   0:00 /sbin/agetty 38400 tty3

root        66  0.0  1.5   41  224 v04 S    22:25   0:00 /sbin/agetty 38400 tty4

root        67  0.0  1.5   41  224 v05 S    22:25   0:00 /sbin/agetty 38400 tty5

root        68  0.0  1.5   41  224 v06 S    22:25   0:00 /sbin/agetty 38400 tty6

root        69  0.0  1.5   56  228 s00 S    22:25   0:00 gpm -t mman

root        71  0.3  3.6  388  532 pp0 S    22:26   0:02 -bash

root       155  0.0  1.5   77  220 pp0 R    22:37   0:00 ps -au

tparker    119  0.4  3.5  372  520 v01 S    22:32   0:01 -bash

tparker    132  0.1  2.2  189  324 v01 S    22:33   0:00 vi test

</FONT></PRE>

<P>The <TT>-au</TT> options produce a list with all the same columns as the <TT>-u</TT>

option, but show all the processes running on the system. The order in which you

enter the options doesn't matter, so <TT>-au</TT> is functionally the same as <TT>-ua</TT>.

When you are adding several options, this can be handy.</P>

<P>A few other <TT>ps</TT> command-line options are occasionally useful. The <TT>-l</TT>

option adds information about which processes started each process (useful when you

want to identify child processes):<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">$ ps -l

 F  UID  PID  PPID  PRI  NI  SIZE  RSS  WCHAN  STAT  TTY  TIME  COMMAND

 0  501  41   1     15   0   364   472  114d9c  S    v01  0:00  -bash

 0  501  121  41    29   0   64    208  0       R    v01  0:00  ps -l

</FONT></PRE>

<P>The <TT>PPID</TT> (Parent Process ID) column shows which process started that

particular process. You will see in the extract from the preceding output that the

<TT>ps</TT> command itself was started by a <TT>bash</TT> process, because the shell

is the entity that is the parent of all user commands. You also see that the PPID

for the login Bourne shell is PID &quot;1&quot;, which is the <TT>init</TT> process

of the operating system. (If you think about what this means, it implies that if

<TT>init</TT> ever terminates, all other processes die, too. Simply put, when <TT>init</TT>

dies, the entire system is off.)



<DL>

	<DT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading10<FONT COLOR="#000077"><B>NOTE:</B> </FONT>The Linux version

	of the <TT>ps</TT> command has a few idiosyncrasies. The hyphen before any options

	is not essential, so <TT>ps u</TT> would work in the same manner as <TT>ps -u</TT>.

	However, because UNIX convention (and most UNIX versions) requires hyphens, you should

	use them.

<HR>



</DL>



<P>For System Administrators Most system administrators get by with three versions

of the <TT>ps</TT> command (when logged in as root). To display information about

the system as a whole, the following command lines show practically everything there

is to know about processes:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">ps -ax

ps -aux

ps -le

</FONT></PRE>

<P>The meaning of the primary columns in the output from the two commands has been

mentioned earlier in this section. The rest of the columns are either evident from

their shortform or not that important. For complete information, see the <TT>ps</TT>

man page (which is not entirely accurate or complete, unfortunately).

<H3 ALIGN="CENTER"><A NAME="Heading11<FONT COLOR="#000077">Using kill</FONT></H3>

<P>Occasionally you will find a process that has locked up a terminal or isn't doing

anything, which is generally referred to as a &quot;hung&quot; process. Sometimes

a user will have a process that doesn't terminate properly (especially common with

programmers). These are &quot;runaway&quot; processes. In both cases, the only way

to get rid of the process and restore some normality to the system is to terminate

the process entirely. This is done with the <TT>kill</TT> command.</P>

<P>To use <TT>kill</TT>, you have to have access to another window or console where

you can issue commands. If your terminal is completely locked up, you have to find

another one to log in on. As a user, you can only kill your own processes--you cannot

affect any process another user on the system is running. As root, you can terminate

any process with the <TT>kill</TT> command.</P>

<P>In order to use the <TT>kill</TT> command, you need the process ID number (PID)

of the process to be terminated. You have to obtain the PID with the <TT>ps</TT>

command and note the PID. Next, use the <TT>kill</TT> command with the PID as an

argument. For example, the following terminal session shows a user process started

by Walter called <TT>bad_prog</TT>, that has hung up and needs to be killed. The

PID is obtained by displaying all of the system's processes with their usernames

(we've cut the other lines from the <TT>ps</TT> command output for simplicity's sake):<FONT

COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">$ ps -u

USER    PID %CPU %MEM SIZE RSS TTY STAT START  TIME COMMAND

walter  561 0.1  6.8  364  472 v01 S    13:19  0:01 -bash

walter  598 9.3  4.1  2736 472 v01 R    15:26  2:01 bad_prog

$ kill 598

</FONT></PRE>

<P>When you issue the <TT>kill</TT> command, you don't get any return message if

it works properly. The only way to verify that the process termination has been properly

conducted is to issue another <TT>ps</TT> command and look for the PID or process

name.

<H4 ALIGN="CENTER"><A NAME="Heading12<FONT COLOR="#000077">killing Child Processes</FONT></H4>

<P>Because some processes spawn child processes with different PIDs, you must be

sure to check that all the child processes are terminated. The best way to do this

is to watch the names of the executing processes for a few minutes to ensure the

child isn't dormant, only to return later. This problem usually happens when the

child processes are being generated by a parent. You should check the <TT>PPID</TT>

column (use the <TT>ps -l</TT> option) to see which process is the parent and terminate

that.



<DL>

	<DT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading13<FONT COLOR="#000077"><B>WARNING: </B></FONT>When you are

	killing processes and logged in as root, make sure you type the correct PID, or you

	may inadvertently terminate another process. Check the PID carefully! Also, don't

	kill any system processes unless you know what they do and why they need to be terminated.

<HR>



</DL>



<P>If the process doesn't terminate properly with the <TT>kill</TT> command, you

need to use sterner measures. The <TT>kill</TT> command actually has several levels

of operation. When issued wi



</td>
</tr>
</table>
<!-- begin footer information -->


</body></html>