How to: Set up a simple service to run in the background on a Linux machine (using daemontools)
I have just set up a new home server (a review of which will be coming soon) and have been installing various programs that I want to run on it. A number of these are servers, such as sshd, apache, samba etc. All of these have fairly easy installs under Debian and will automatically run at startup, and can be controlled by /etc/init.d scripts.
However, I also have a number of other programs I want to run as services, constantly in the background, which don’t come with nice Debian init.d scripts. After asking a question on SuperUser I found that one fairly simple solution would be to use a set of tools called daemontools. These tools provide a simple way of defining services which run constantly, and can be controlled by an administrator (in a similar way to /etc/init.d services). daemontools seem to be designed very well, and are quite easy to use, but the documentation on the website seems to lack a simple quickstart guide…so I thought I’d write my own.
At this point I should mention that I have only been using daemontools for a few hours, so I could be completely wrong about anything I say below. These instructions will be for Debian, but should be fairly easily to use with other distros (the only bit that will be significantly different is exactly how to install it with the package manager). Anyway, proceed at your own risk!
- Install daemontools In debian you will need to run apt-get install daemontools daemontools-run (both packages are important – I didn’t install the latter package and it caused me lots of frustration). This will install the tools themselves and also add the required lines to startup files to ensure that all of the required daemontools services start when the machine boots.
- Create a service directory You will probably find that the installer has created a /service directory for you. If it hasn’t then create one yourself. Then create a directory under that directory for each service that you want to run. Here we will be creating a test service, so create a directory called test. Run chmod 1755 on this directory.
- Create the service run file
daemontools needs to know what command(s) you need to run for this service, and these commands should be put inside a shell script called run in the service directory. For example, the file could contain:
#!/bin/sh echo Running service exec some-command-here
- Finished! That should be all you need to get the service running. You should probably restart the machine now as that will ensure that all of the daemontools monitoring services have started correctly. Once the machine has started the new service should have started running. If it crashes or ends for some reason it will restart after one second. Any new services you add (which you can do exactly as above) should start within five seconds. You can use the svc command to control the services you have created (see man svc for details)
I like your posting. About 15 years ago, I have used daemontools for after installing Qmail. I forgot lot of the stuff relating to this tool. Can this tool be used for user level daemons? I want to setup a user level task that will do certain checks but at random times. How can I setup daemontools for user John Doe’s task?
Extremely helpful. Thank you.