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    <blockquote> <p>I am struggling with the best solution for system startup,</p> </blockquote> <p>You have not provided any criteria for deciding what is "best".</p> <blockquote> <p>... a simple, and robust way to take care of startup, shutdown and integrity monitoring of the embedded device?</p> </blockquote> <p>If "simple" and "best" are your criteria, then what you are looking for is already integral to the Linux OS. It uses the concept of runlevels. On start up, a runlevel is established, and a set of processes can be started. Any change to another runlevel will stop a set of processes and start a set of processes. On shutdown, which is another runlevel, all processes are terminated. </p> <p>I don't know what you mean by "integrity monitoring". If a system process terminates, then it can be "respawned" if it is so designated. The <em>proc</em> pseudo-filesystem can be used to monitor active processes. You will probably have design &amp; implement your own concept of integrity monitoring.</p> <p>BusyBox has simplified the standard (aka SysV) <em>init</em> process, presumably on the assumption that embedded processes run once or always after startup. Either <em>cron</em> or a custom daemon would have to provide process startup on events. But you argue that: </p> <blockquote> <p>It does not have a concept of run levels.<br> So we are not able to use the same startup mechanisms as a full-featured OS.</p> </blockquote> <p>Not quite. BusyBox declares:</p> <blockquote> <p>BusyBox init doesn't support multiple runlevels. The runlevels field of the /etc/inittab file is completely ignored by BusyBox init.</p> </blockquote> <p>Note the the word "multiple". BusyBox's <em>init</em> will perform process control for the runlevels equivalent to startup, shutdown and reboot. Interestingly, BusyBox even has a <code>runlevel</code> command! If you want <em>more</em> "runlevels" than BusyBox offers, then </p> <blockquote> <p>If you want runlevels, use sysvinit. </p> </blockquote> <p>SysV <em>init</em> source code is available from <a href="http://packages.qa.debian.org/s/sysvinit.html" rel="nofollow">here</a>. BusyBox is fully configurable, and its version of <em>init</em> can easily be replaced.</p> <p>A mini version of SysV <em>init</em> is released under the GPL by Axis Communications for their Etrax SoC. The Axis <code>/etc/inittab</code> is:`</p> <pre><code># The runlevels used by axis are: # 0 - Halt # 1 - Single user mode # 2 - Multiuser without network # 3 - Full multiuser mode # 4 - Upgrade # 5 - unused # 6 - Reboot id:3:initdefault: sh:1235:respawn:/bin/cttyhack /bin/sh tnet:35:once:/usr/sbin/telnetd # System initialization. si::sysinit:/etc/init.d/rc sysinit # The initscripts. l0:0:wait:/etc/init.d/rc 0 l1:1:wait:/etc/init.d/rc 1 l2:2:wait:/etc/init.d/rc 2 l3:3:wait:/etc/init.d/rc 3 l4:4:wait:/etc/init.d/rc 4 l5:5:wait:/etc/init.d/rc 5 l6:6:wait:/etc/init.d/rc 6 # Add your own stuff below </code></pre> <p>The current source is in <code>devboard-R2_20-distfiles.tar.gz</code>, which includes version 1.3.6 of <code>init.c</code> and initscript packages, and requires registration at the <a href="http://www.axis.com/products/dev_sdk/download.htm" rel="nofollow">Axis site</a>.</p>
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