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Background processes

How to administer background processes.

View and stop

Use the following commands if you want to view or stop running processes.

ps aux
USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
someuser    1170  0.0  0.0 151232  1992 ?        Sl    2019  50:29 /usr/bin/redis-server 127.0.0.1:0
someuser    1172  0.0  0.0 151232  1988 ?        Sl    2019  50:22 /usr/bin/redis-server 127.0.0.1:0
someuser    2000  0.0  0.0 1136972 10256 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2004  0.0  0.0 1136972 10256 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2010  0.0  0.0 1136972 10248 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2013  0.0  0.0 1136972 10252 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2017  0.0  0.0 1136972 10252 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2021  0.0  0.0 1136972 10252 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2030  0.0  0.0 1136972 10248 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2033  0.0  0.0 1136972 10248 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2038  0.0  0.0 1136972 10244 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2039  0.0  0.0 1136972 10244 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2043  0.0  0.0 1136972 10240 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2049  0.0  0.0 1136972 10240 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2052  0.0  0.0 1136972 10240 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2057  0.0  0.0 1136972 10240 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2063  0.0  0.0 1136972 10240 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser    2066  0.0  0.0 1136972 10240 ?       S     2019   0:00 php-fpm: pool php70-someuser-website.com
someuser  104977  0.0  0.0 780800 64508 ?        Sl   03:00   0:00 /usr/bin/hhvm -m server -c /etc/hhvm.d/someuser-website.com.ini
someuser  128392  0.0  0.0 116588  3460 pts/0    Ss+  19:09   0:00 -bash
someuser  131513  0.0  0.0 217640 12924 ?        Ss   Jan31   1:57 /usr/bin/python /usr/bin/supervisord -n -c /etc/supervisor/someuser.conf
someuser  131547  0.5  0.1 368324 160500 ?       Sl   Jan31  55:26 /usr/bin/redis-server 127.0.0.1:6385
someuser  131548  138  1.0 11902864 1443848 ?    Sl   Jan31 13629:09 /usr/bin/java -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -XX:+DisableExplicitGC -Djava.awt.headless=true -Dfile.encoding=UTF-8 -XX:
someuser  133746  0.0  0.0 116456  2960 pts/1    Ss+  19:36   0:00 -bash
someuser  147910  3.0  0.0 116456  3192 pts/2    Ss   20:14   0:00 -bash
someuser  147959  0.0  0.0 151156  1828 pts/2    R+   20:14   0:00 ps aux

A closer look tells us the process with pid 131548 is running for a long time and is showing high CPU usage. This process may be stopped by using this command:

kill 131548

If a process is really stuck and no longer responds to a SIGTERM, you may also use SIGKILL. This forces the OS to stop the process. As a result the process will not be able to stop in a planned manner and some child processes or other remnants may still be present.

kill -9 131548

Read https://linuxhandbook.com/sigterm-vs-sigkill/ to learn more about the difference between SIGTERM and SIGKILL.

If you want to stop all processes of a certain type, you may use killall. To reset PHP use the following command:

killall php-fpm

screen

If you want to start a background process you can use the screen command:

For example:

screen sleep 100

You can leave this screen by using the key combination CTRL+A, CTRL+D. To return use screen -r.