In this post by David Papkin\u00a0, will show how to create a dummy service named fake_service.<\/p>\n
In this and the following exercise, we will create a simple startup service.<\/p>\n
First we will do it for a SysVinit system.<\/strong> <\/p>\n Next we will do it for\u00a0systemd<\/strong><\/p>\n The analogous procedure is to create (as root) a file directly under <\/span>\/etc\/systemd\/system <\/span>or somewhere else in that directory tree; distributions have some varying tastes on this. For example a very minimal file named <\/span>\/etc\/systemd\/system\/fake2.service<\/span>: The original source from\u00a0https:\/\/www.linuxfoundation.org\/<\/a>\u00a0is<\/p>\n https:\/\/lms.360training.com\/scorm\/linuxfoundation\/LFS201\/Lab%204.1.pdf<\/a>. It is posted here for ease of access for students doing scripting.<\/p>\n Please support Linux<\/a> by visiting\u00a0\u00a0https:\/\/www.linuxfoundation.org\/<\/a><\/p>\n This concludes this post by David Papkin on how to create a simple startup service<\/p>\n http:\/\/davidpapkin.org\/<\/a><\/p>\n David Papkin favorite movies<\/strong><\/p>\n Robert Deniro in GoodFellas<\/a><\/p>\n
\nNote that if you are using a systemd-based system everything should still work because of the backwards compatibility\u00a0layer that all distributions utilize. However, in the next exercise we will do natively for systemd.
\nIf you are on a Debian-based system like Ubuntu, make sure you have installed the sysvinit-utils and chkconfig\u00a0packages. However, recent versions of Ubuntu no longer package chkconfig; you\u2019ll have to use the update-rc.d utility\u00a0instead.
\nFirst we have to create the service-specific script; you can create one of your own for fun, or to get the procedure down\u00a0just (as root) create a file named \/etc\/init.d\/fake_service containing the following content:
\n#!\/bin\/bash
\n# fake_service
\n# Starts up, writes to a dummy file, and exits
\n#
\n# chkconfig: 35 69 31
\n# description: This service doesn\u2019t do anything.
\n# Source function library
\n. \/etc\/sysconfig\/fake_service
\ncase “$1” in
\nstart) echo “Running fake_service in start mode…”
\ntouch \/var\/lock\/subsys\/fake_service
\necho “$0 start at $(date)” >> \/var\/log\/fake_service.log
\nif [ ${VAR1} = “true” ]
\nthen
\necho “VAR1 set to true” >> \/var\/log\/fake_service.log
\nfi
\necho
\n;;
\nstop)
\necho “Running the fake_service script in stop mode…”
\necho “$0 stop at $(date)” >> \/var\/log\/fake_service.log
\nif [ ${VAR2} = “true” ]
\nthen
\necho “VAR2 = true” >> \/var\/log\/fake_service.log
\nfi
\nrm -f \/var\/lock\/subsys\/fake_service
\necho
\n;;
\n*)
\necho “Usage: fake_service {start | stop}”
\nexit 1
\nesac
\nexit 0
\nMake the file above executable and give other proper permissions:
\n$ sudo chmod 755 \/etc\/init.d\/fake_service
\nLFS201: V 1.0 c Copyright the Linux Foundation 2015. All rights reserved.
\n2 CHAPTER 4. INIT: SYSTEMV, UPSTART, SYSTEMD
\nYou\u2019ll notice the script includes the file \/etc\/sysconfig\/fake service. (On non-RHEL systems you should change
\nthis to \/etc\/default\/fake_service.) Create it and give it the following contents:
\nVAR1=”true”
\nVAR2=”true”
\nTest to see if the script works properly by running the following commands:
\n$ sudo service fake_service
\n$ sudo service fake_service start
\n$ sudo service fake_service stop
\nLook at the file named \/var\/log\/fake service.log. What does it contain?
\nFor fun you can add additional modes like restart to the script file; look at other scripts in the directory to get examples\u00a0of what to do.
\nNext we will want to have the ability to start fake service whenever the system starts, and stop it when it shuts down.
\nIf you do:
\n$ sudo chkconfig –list fake_service
\nyou will get an error as it hasn\u2019t been set up yet for this. You can easily do this with:
\n$ sudo chkconfig –add fake_service
\nand you can turn it on or off at boot time with
\n$ sudo chkconfig fake_service on
\n$ sudo chkconfig fake_service off
\nTo test this completely you\u2019ll have to reboot the system to see if it comes on automatically. You can also try varying the\u00a0runlevels in which the service is running.<\/p>\n
\n<\/span>[Unit]
\nDescription=fake2
\nAfter=network.target
\n[Service]
\nExecStart=\/bin\/sh -c \u2019\/bin\/echo I am starting the fake2 service ; \/bin\/sleep 30\u2019
\nExecStop=\/bin\/echo I am stopping the fake2 service
\n[Install]
\nWantedBy=multi-user.target
\n<\/span>Now there are many things that can go in this <\/span>unit <\/span>file. The <\/span>After=network.target <\/span>means the service should start only after the network does, while the <\/span>WantedBy=multi-user.target <\/span>means it should start when we reach multiple-user mode. This is equivalent to runlevels 2 and 3 in <\/span>SysVinit<\/span>. Note <\/span>graphical.target <\/span>would correlate with runlevel 5.
\nNow all we have to do to start, stop and check the service status are to issue the commands:
\n<\/span>$ sudo systemctl start fake2.service
\n$ sudo systemctl status fake2.service
\n$ sudo systemctl stop fake2.service
\n<\/span>If you are fiddling with the unit file while doing this you\u2019ll need to reload things with:
\n<\/span>$ sudo systemctl daemon-reload <\/span>as the system will warn you.
\nTo keep an eye directly on the output you can do:
\n<\/span>$ sudo tail -f \/var\/log\/messages
\n<\/span>(use <\/span>\/var\/log\/syslog <\/span>on <\/span>Ubuntu<\/span>) either in background or in another windows while the service is running.
\nTo set things up so the service turns on or off on system boot:
\n<\/span>$ sudo systemctl enable fake2.service
\n$ sudo systemctl disable fake2.service<\/span><\/p>\n