187 lines
8 KiB
HTML
187 lines
8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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<html>
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<head>
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<title>runit - benefits</title>
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</head>
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<body>
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<a href="http://smarden.org/pape/">G. Pape</a><br>
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<a href="index.html">runit</a><br>
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<hr>
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<h1>runit - benefits</h1>
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<hr>
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<a href="#supervision">Service supervision</a><br>
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<a href="#state">Clean process state</a><br>
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<a href="#log">Reliable logging facility</a><br>
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<a href="#fast">Fast system boot up and shutdown</a><br>
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<a href="#portability">Portability</a><br>
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<a href="#packaging">Packaging friendly</a><br>
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<a href="#smallcode">Small code size</a>
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<hr>
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<a name="supervision"><h3>Service supervision</h3></a>
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Each service is associated with a <i>service directory</i>, and each
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service daemon runs as a child process of a supervising
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<a href="runsv.8.html">runsv</a> process running in this directory.
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The <a href="runsv.8.html">runsv</a> program provides a reliable interface
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for signalling the service daemon and controlling the service and
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supervisor.
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Normally the <a href="sv.8.html">sv</a> program is used to send commands
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through this interface, and to query status informations about the service.
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<p>
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The <a href="runsv.8.html">runsv</a> program supervises the corresponding
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service daemon.
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By default a service is defined to be up, that means, if the service daemon
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dies, it will be restarted.
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Of course you can <a href="sv.8.html">tell runsv</a> otherwise.
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<p>
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This reliable interface to control daemons and supervisors obsoletes
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pid-guessing programs, such as <tt>pidof</tt>, <tt>killall</tt>,
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<tt>start-stop-daemon</tt>, which, due to guessing, are prone to failures
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by design.
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It also obsoletes so called <tt>pid-files</tt>, no need for each and every
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service daemon to include code to daemonize, to write the new process id
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into a file, and to take care that the file is removed properly on shutdown,
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which might be very difficult in case of a crash.
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<hr>
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<a name="state"><h3>Clean process state</h3></a>
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<i>runit</i> guarantees each service a clean process state, no matter if the
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service is activated for the first time or automatically at boot time,
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reactivated, or simply restarted.
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This means that the service always is started with the same environment,
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resource limits, open file descriptors, and controlling terminals.
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<p>
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You don't necessarily have that with <i>sysv init</i> scripts for example.
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It requires a carefully written init script that reliably cleans up and sets
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the process state before starting the service daemon.
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This adds even more complexity to the init script in comparison with a run
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script used by <i>runit</i>.
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Many of today's init scripts don't provide a clean process state, here is
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an example on what could happen:
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<pre>
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# /etc/init.d/foo-daemon start
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Starting foo daemon: food.
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#
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</pre>
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Fine.
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Everything works, nothing to worry about.
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After rebooting the system this shows up on the screen:
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<pre>
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...
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Starting foo daemon: food: command not found
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failed.
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...
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</pre>
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The <tt>food</tt> program is installed in <tt>/opt/foo/bin/</tt>.
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When starting the service for the first time using the init script, the
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<tt>PATH</tt> environment variable contained <tt>/opt/foo/bin</tt>.
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After reboot <tt>init</tt> started the service using the init script, but
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with a different value for the <tt>PATH</tt> variable, not containing
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<tt>/opt/foo/bin</tt>.
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Of course the init script should have set <tt>PATH</tt> before starting the
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daemon; the problem is that it worked in the first place, and that the error
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didn't show up until system reboot.
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<p>
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With bad init scripts miraculous things could also happen when just doing
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<pre>
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# /etc/init.d/foo-daemon restart
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</pre>
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at the command line.
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<p>
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The clean process state includes open file descriptors, obsoleting the
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widely used hack in many service daemons to force-close all file descriptors
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that might be open, up to the limit of available file descriptors for the
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daemon process (often results in 1024 unnecessary close() system calls in a
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great number of service daemon implementations).
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<hr>
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<a name="log"><h3>Reliable logging facility</h3></a>
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The <a href="runsv.8.html">runsv</a> program provides a reliable logging
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facility for the service daemon.
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If configured, <a href="runsv.8.html">runsv</a> creates a pipe, starts and
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supervises an additional log service, redirects the log daemon's standard
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input to read from the pipe, and redirects the service daemon's standard
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output to write to the pipe.
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Restarting the service does not require restarting the log service, and vice
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versa.
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A good choice for a log daemon is <i>runit</i>'s service logging daemon
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<a href="svlogd.8.html">svlogd</a>.
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<p>
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The service daemon and the log daemon can run with different process states,
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and under different user id's.
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<i>runit</i> supports easy and reliable logging for service daemons running
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chroot'ed.
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<p>
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If <a href="runsv.8.html">runsv</a> is told to shutdown a service, e.g. at
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system shutdown, it ensures that the log service stays up as long as the
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corresponding service daemon is running and possibly writing to the log.
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<hr>
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<a name="fast"><h3>Fast system boot up and shutdown</h3></a>
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After the system's one time tasks (stage 1) are done, the system services
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are started up in parallel.
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The operating system's process scheduler takes care of having the services
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available as soon as possible.
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<p>
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On system shutdown, stage 3 uses <a href="runsv.8.html">runsv</a>'s control
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interface to wait until each service daemon is terminated and all logs are
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written.
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Again, services are taken down in parallel.
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As soon as all services are down, system halt or system reboot is initiated.
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<hr>
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<a name="portability"><h3>Portability</h3></a>
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<i>runit</i> comes ready-to-run for Debian GNU/Linux and BSD systems, and
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can easily be configured to run on other UNIX systems.
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The UNIX system's one time initialization tasks and tasks to shutdown the
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system must be identified and <i>runit</i>'s stages 1 and 3 configured
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accordingly.
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<p>
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Stages 1 and 3 handle one time tasks.
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They only run for short and exit soon.
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Stage 2 handles the system's uptime tasks (via the
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<a href="runsvdir.8.html">runsvdir</a> program) and is running the whole
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system's uptime.
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<p>
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<i>runit</i>'s stage 2 is portable across UNIX systems.
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<i>runit</i> is well suited for server systems and embedded systems, and
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also does its job well on desktop systems.
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<hr>
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<a name="packaging"><h3>Packaging friendly</h3></a>
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<i>runit</i>'s stages 1 and 3 are distribution specific.
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They normally are shell scripts, and an operating system distribution with
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software package management should adapt these scripts if they need support
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for their package management.
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The
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<a href="http://packages.debian.org/unstable/admin/runit-run.html">
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runit-run</a>
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Debian package is an attempt to integrate <i>runit</i> into
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<a href="http://www.debian.org/">Debian GNU/Linux</a> as an alternative to
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the default
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<a href="http://packages.debian.org/unstable/base/sysvinit.html">
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sysvinit</a>.
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<p>
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Stage 2 is packaging friendly:
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all a software package that provides a service needs to do is to include
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a <i>service directory</i> in the package, and to provide a symbolic link
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to this directory in <tt>/service/</tt>.
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The service will be started within five seconds, and automatically at boot
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time.
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The package's install and update scripts can use the reliable control
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interface to stop, start, restart, or send signals to the service.
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On package removal, the symbolic link simply is removed.
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The service will be taken down automatically.
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<hr>
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<a name="smallcode"><h3>Small code size</h3></a>
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One of the <i>runit</i> project's principles is to keep the code size
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small.
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As of version 1.0.0 of <i>runit</i>, the <tt>runit.c</tt> source contains
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330 lines of code; the <tt>runsvdir.c</tt> source is 274 lines of code, the
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<tt>runsv.c</tt> source 509.
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This minimizes the possibility of bugs introduced by programmer's fault,
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and makes it more easy for security related people to proofread the source
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code.
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<p>
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The <i>runit</i> core programs have a very small memory footprint and do not
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allocate memory dynamically.
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<hr>
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<address><a href="mailto:pape@smarden.org">
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Gerrit Pape <pape@smarden.org>
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</a></address>
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</body>
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</html>
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