diff options
| -rw-r--r-- | chapter_06.xml | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/chapter_06.xml b/chapter_06.xml index 8366fe8..5626d50 100644 --- a/chapter_06.xml +++ b/chapter_06.xml @@ -138,12 +138,103 @@ are a variety of other signals that can be sent, but the three most common are SIGTERM, SIGHUP, and SIGKILL. </para> +<para> +What a process does when it receives a signal varies. Most programs +will terminate (or attempt to terminate) whenever they receive any +signal, but there are a few important differences. For starters, the +SIGTERM signal informs the process that it should terminate itself at +its earliest convenience. This gives the process time to finish up any +important activities, such as writing information to the disk, before +it closes. In contrast, the SIGKILL signal tells the process to +terminate itself immediately, no questions asked. This is most useful +for killing processes that are not responding and is sometimes called +the "silver bullet". Some processes (particularly daemons) capture the +SIGHUP signal and reload their configuration files whenever they +receive it. +</para> + +<para> +In order to signal a process, we first need to know it's PID. You can +get this easily with <application>ps</application> as we discused. In +order to send different signals to a running process, you simply pass +the signal number and <arg>-s</arg> as an argument. The <arg>-l</arg> +argument lists all the signals you can chose and their number. You can +also send signals by their name with <arg>-s</arg>. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>kill -l</userinput> + 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL + 5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE + 9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2 +13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGSTKFLT +... many more lines ommitted ... +<prompt>darkstar:~$ </prompt><userinput>kill 1234 # SIGTERM</userinput> +<prompt>darkstar:~$ </prompt><userinput>kill -s 9 1234 # SIGKILL</userinput> +<prompt>darkstar:~$ </prompt><userinput>kill -s 1 1234 # SIGHUP</userinput> +<prompt>darkstar:~$ </prompt><userinput>kill -s HUP 1234 # SIGHUP</userinput> +</screen> + +<para> +Sometimes you may wish to terminate all running processes with a +certain name. You can kill processes by name with +<application>killall</application>(1). Just pass the same arguments to +<application>killall</application> that you would pass to +<application>kill</application>. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>killall bash # SIGTERM</userinput> +<prompt>darkstar:~$ </prompt><userinput>killall -s 9 bash # SIGKILL</userinput> +<prompt>darkstar:~$ </prompt><userinput>killall -s 1 bash # SIGHUP</userinput> +<prompt>darkstar:~$ </prompt><userinput>killall -s HUP bash # SIGHUP</userinput> +</screen> + </section> <section> <title>top</title> <para> +So far we've learned how to look at the active processes for a moment +in time, but what if we want to monitor them for an extended period? +<application>top</application>(1) allows us to do just that. It +displays an ordered list of the processes on your system, along with +vital information about them, and updates periodically. By default, +processes are ordered by their CPU percentage and updates occur every +three seconds. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>top</userinput> +top - 16:44:15 up 26 days, 5:53, 5 users, load average: 0.08, 0.03, 0.03 +Tasks: 122 total, 1 running, 119 sleeping, 0 stopped, 2 zombie +Cpu(s): 3.4%us, 0.7%sy, 0.0%ni, 95.5%id, 0.1%wa, 0.0%hi, 0.2%si, 0.0%st +Mem: 3058360k total, 2853780k used, 204580k free, 154956k buffers +Swap: 0k total, 0k used, 0k free, 2082652k cached + + PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND + 1 root 20 0 3928 632 544 S 0 0.0 0:00.99 init + 2 root 15 -5 0 0 0 S 0 0.0 0:00.00 kthreadd + 3 root RT -5 0 0 0 S 0 0.0 0:00.82 migration/0 + 4 root 15 -5 0 0 0 S 0 0.0 0:00.01 ksoftirqd/0 + 7 root 15 -5 0 0 0 S 0 0.0 0:11.22 events/0 + 9 root 15 -5 0 0 0 S 0 0.0 0:01.19 work_on_cpu/0 + 11 root 15 -5 0 0 0 S 0 0.0 0:00.01 khelper + 102 root 15 -5 0 0 0 S 0 0.0 0:02.04 kblockd/0 + 105 root 15 -5 0 0 0 S 0 0.0 1:20.08 kacpid + 106 root 15 -5 0 0 0 S 0 0.0 0:01.92 kacpi_notify + 175 root 15 -5 0 0 0 S 0 0.0 0:00.00 ata/0 + 177 root 15 -5 0 0 0 S 0 0.0 0:00.00 ata_aux + 178 root 15 -5 0 0 0 S 0 0.0 0:00.00 ksuspend_usbd + 184 root 15 -5 0 0 0 S 0 0.0 0:00.02 khubd + 187 root 15 -5 0 0 0 S 0 0.0 0:00.00 kseriod + 242 root 20 0 0 0 0 S 0 0.0 0:03.37 pdflush + 243 root 15 -5 0 0 0 S 0 0.0 0:02.65 kswapd0 +</screen> + +<para> +The man page has helpful details on how to interact with +<application>top</application> such as changing its delay interval, the +order processes are displayed, and even how to terminate processes +right from within <application>top</application> itself. </para> </section> |