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| -rw-r--r-- | chapter_06.xml | 73 |
1 files changed, 70 insertions, 3 deletions
diff --git a/chapter_06.xml b/chapter_06.xml index 785f4da..0b02a4b 100644 --- a/chapter_06.xml +++ b/chapter_06.xml @@ -94,7 +94,50 @@ is consuming when <application>ps</application> is run. </para> <para> -Finally, <application>ps</application> can also create a process tree. +To accomplish bits of this, on a per process basis, <command>ps</command> allows +one or more process IDs (PIDs) to be provided in the command line, and has the '-o' flag +to show a particular attribute of the PID. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ps -o cmd -o etime $$</userinput> +CMD ELAPSED +/bin/bash 12:22 +</screen> + +<para> +What this is displaying, is the PID's command name (cmd), and its elapsed time (etime). +The PID in this example, is a shell variable for the PID of the current shell. So you +can see, in this example, the shell process has existed for 12 minutes, 22 seconds. +</para> + +<para> +Using the <command>pgrep</command>(1) command, this can get more automatable. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ps -o cmd -o rss -o vsz $(pgrep httpd)</userinput> +CMD RSS VSZ +/usr/sbin/httpd -k restart 33456 84816 +/usr/sbin/httpd -k restart 33460 84716 +/usr/sbin/httpd -k restart 33588 84472 +/usr/sbin/httpd -k restart 30424 81608 +/usr/sbin/httpd -k restart 33104 84900 +/usr/sbin/httpd -k restart 33268 85112 +/usr/sbin/httpd -k restart 30640 82724 +/usr/sbin/httpd -k restart 15168 67396 +/usr/sbin/httpd -k restart 33180 84416 +/usr/sbin/httpd -k restart 33396 84592 +/usr/sbin/httpd -k restart 32804 84232 +</screen> + +<para> +In this example, a subshell execution, using <command>pgrep</command>, +is returning the PIDs of any process, whose command +name includes 'httpd'. Then <command>ps</command> displaying the command name, +resident memory size, and virtual memory size. +</para> + +<para> +Finally, <command>ps</command> can also create a process tree. This shows you which processes have children processes. Ending the parent of a child process also ends the child. We do this with the <arg>-ejH</arg> argument. @@ -115,12 +158,36 @@ parent of a child process also ends the child. We do this with the </screen> <para> -As you can see, <application>ps</application> is an incredibly powerful +As you can see, <command>ps</command>(1) is an incredibly powerful tool for determining not only what processes are currently active on your system, but also for learning lots of important information about them. </para> +<para> +As is the case with many of the applications, there is often several tools +for the job. Similar to the <command>ps -ejH</command> output, but more terse, +is <command>pstree</command>(1). It displays the process tree, a bit more visually. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>pstree</userinput> +init-+-atd + |-crond + |-dbus-daemon + |-httpd---10*[httpd] + |-inetd + |-klogd + |-mysqld_safe---mysqld---8*[{mysqld}] + |-screen-+-4*[bash] + | |-bash---pstree + | |-2*[bash---ssh] + | `-bash---irssi + |-2*[sendmail] + |-ssh-agent + |-sshd---sshd---sshd---bash---screen + `-syslogd +</screen> + </section> <section> @@ -130,7 +197,7 @@ them. Managing processes isn't only about knowing which ones are running, but also about communicating with them to change their behavior. The most common way of managing a program is to terminate it. Thus, the tool for -the job is named <application>kill</application>(1). Despite the name, +the job is named <command>kill</command>(1). Despite the name, <application>kill</application> doesn't actually terminate processes, but sends signals to them. The most common signal is a SIGTERM, which tells the process to finish up what it is doing and terminate. There |