Runit program

The n1 action in the config file sets the number of old log files svlogd should maintain to 1. Resulting supervision tree when runsvdir is run as a background process in an interactive shell using this scan directory, assuming it is the working directory i. This shows that both the test-daemon and svlogd processes are supervised by the same runsv process. Forcing svlogd to perform a rotation:. This shows that a log file with a name containing a TAI64N timestamp and ending in.

Messages sent by test-service2 's run process to runsvdir 's standard output when manually started:. Resulting supervision tree:. This shows that because test-service1 has a log subdirectory, sv status shows the status of the svlogd process too, after test-daemon 's status "run: log:".

After enough seconds have elapsed:. This shows that runsv is currently executing test-service2 's finish file "finish:". This confirms that run is stopped "paused". Messages sent by test-service2 's run process to runsvdir 's standard output when manually stopped:. The sv program accepts a -v option 'verbose' that makes it wait for the action requested by the specified subcommand to be completed, and then prints the resulting process' status, as if an sv status command had been used.

If the requested action completes before the expiry of the wait period, the status line is prepended with 'ok:' followed by a space. Otherwise, the sv command exits with a nonzero code and the status line is prepended with 'timeout:' followed by a space. For the sv -v up command, and, if the supervised process is wanted up after the action i.

However, when the supervised process is executing a server program for example, it might not be ready to provide its service immediately after startup. Programs might do initialization work that could take some noticeable time before they are actually ready to serve, but it is impossible for the supervisor to know exactly how much.

If there is some program-specific way to infer that it is ready, runit is able to take advantage of it by including an executable file named check in the service directory. This file is assumed to contain code that polls for readiness , and must exit with a 0 code if it considers the supervised process to be ready, and with a nonzero code otherwise. Just like run or finish , the check file can have any format the kernel knows how to execute, and is normally a shell script.

If check determines that the process is ready, sv will print an 'ok' status line and exit, otherwise it reexecutes check after waiting milliseconds.

In other words, during the wait period sv will periodically poll for readiness using check ; if its exit code is never 0, on expiry of the wait period sv will print a 'timeout' status line and exit. In addition, the sv check command can be used to poll for readiness periodically during a wait period by executing the check file, without changing the supervised process' state. The sv status command does not use the check file. For the full description of the sv program please consult the respective man page.

Example service directory with a check file:. This service directory sets up process supervision for a hypothetical test-daemon program. It is assumed that the program can be polled for readiness using another program named test-daemon-check. For demonstration purposes, the sleep utility is used so that check does not exit too quickly. Using the sv check command after launching the supervision tree, assuming that the scan directory is the working directory:.

Because of the down file, runsv does not launch test-daemon , so it considers its supervised process to be in 'down' state, so sv check exited immediately with an 'ok' status and without executing check. Starting the supervised process using sv 's -v option:. This shows that a test-daemon process was spawned "run: test-service:" , but the test-daemon-check program determined that it was not ready. The check was executed 6 times before the expiery of the default 7 seconds wait period, so sv finally gave up with a 'timeout' status.

Polling test-daemon again:. Between both sv commands test-daemon became ready, so this time the single poll was successful, and sv exited immediately with an 'ok' status. This shows that a test-daemon process was killed and then restarted because it is supervised , but 8 polls were necessary until the test-daemon-check program determined that it was ready.

Because the process became ready during the wait period, sv exited with an 'ok' status. Stopping the test-daemon process using sv 's -v option:.

Making runsv stop and exit using sv 's -v option, assuming its supervising runsvdir parent process was already killed:. As noted in section "The check file" , the equivalences stated above imply that the start , try-restart , restart , force-reload and force-restart subcommands make sv execute the check file in the named service directories, if present, to poll for readiness.

The sv program can be invoked with the name of a service directory with any argv[0] substitution mechanism , in that case, also its exit code tries to comply with the LSB specification: it is 2 for usage errors and in the "reserved for application use" range for fatal errors, instead of in both cases, it is 0 , 3 or 4 , as appropriate, if the subcommand is status , and it is 1 on error other than fatal errors for other subcommands.

Example service directory for a hypothetical test-daemon program with a setup similar to that of section "The check file" :. Starting the supervised process using sv 's LSB-like interface:. This shows that sv start , being equivalent to sv -v up , also uses the check file. The test-daemon-check program was used to poll twice for readiness, and succeeded before the expiry of the 10 seconds wait period. Stopping the test-daemon process using sv 's LSB-like interface:.

Because test-daemon ignores the signal, the stop action didn't complete before the expiry of the wait period, so sv gives up with a "timeout" status. Stopping the test-daemon process using sv 's force-stop subcommand:.

This shows that, again, the stop action didn't complete before the expiry of the wait period, but this time a SIGKILL signal was sent to the supervised process on expiry of the wait period. The runsv program allows the customization of the effect of some sv subcommands to some degree.

This is done by providing executable files in a subdirectory of the service directory named control. The subcommands that can be customized this way are:. Just like run or finish , the files in the control subdirectory can have any format the kernel knows how to execute, and are normally shell scripts. For further details about customizing the the effect of sv , please consult runsv 's man page. Example service directory with a control subdirectory for customized control:.

This control file is executed when an sv hup command is used. A chpst -e command is used each time these control files are executed, to modify the environment according to environment directory env :. Contents of the current file in the logging directory when the supervision tree is launched, assuming that the scan directory is the working directory:. Using the sv hup command:. Using the sv -v term command:. Using the sv -v down command:. The command shows an "ok" status and a "down" state, so it successfully stopped test-daemon.

If not ensure that runit was installed properly by checking the documentation for you distro. The runsvdir utility is the first of several that we will encounter in this tutorial. The design of runit takes a very "Unixy" approach by breaking down functionality into several small utilities each responsible for a single task. This approach allows the simple components to be composed in various ways to suit you needs.

The core runit utilities are runsvdir , runsv , chpst , svlogd , and sv. Throughout this tutorial we will combine these utilities to configure and run a managed service. When runsvdir finds a new service configuration, it starts a new runsv process to manage the service. As far as runsvdir is concerned, there really is not much more to it that that. Remember that runit's philosophy is to provide simple utilities with a single responsibility.

Check out the man page for further details:. Go ahead and create your staging directory now. Before creating our first real service configuration, let's create a template. This template will illustrate the basics of using runit and can be used to quickly create new configurations in the future.

Create a directory for our template by running this command:. Next, create a script named run in the template directory with the following contents:.

This script is quite simple. First it redirects all output from stderr to stdout. The chpst utility allows us to configure how the command will be executed. Because the run script will be executed as the root user, we can use chpst to change the context to a normal user with limited permissions.

Check out the man page for more info. Take a look at the runsv man page for more details. You may have noticed that the man page for runsv mentions that it can optionally start an appendant log service. Because logging is such a critical part of monitoring an environment, let's create a template script for logging the output of our monitored process. To setup logging for our service, create a new log directory by running the following command:.

For details on logging configuration, check out the svlogd man page. Usually, a run shell script that supports a conf file has the line [ -r. If a service directory contains another directory named log , the output of the run process in the service directory will be piped to the input of the run process in the log directory.

If the log service uses svlogd , it may be configured by using the file config. How svlogd can be configured is explained in the svlogd 1 manpage.