this is exactly what drives people up the wall...

Posted Nov 25, 2011 11:41 UTC (Fri) by michich (guest, #17902)
In reply to: this is exactly what drives people up the wall... by khim
Parent article: That newfangled Journal thing

Can you give any example where systemd forces you to write a complex and convoluted script from scratch? I've seen cases where instead of running a program directly from the systemd unit file it made some sense to call a shell wrapper, but why would it have to be complex and convoluted?

to post comments

Because you talk about legacy code?

Posted Nov 25, 2011 12:58 UTC (Fri) by khim (subscriber, #9252) [Link] (1 responses)

One recent example: connection to Corbina.Net (I've helped my friend with that). You need start igmpproxy first (because otherwise it'll crash when L2TP disconnects), then you need to check L2TP server (some of them don't work and then you need to try again), then you connect to L2TP server and wait till everything stabilizes - and only after that you can start IPSec to connect to your real VPN network.

With SysV init you can just order all services in proper (tested and working) order while with systemd you either need to properly describe dependencies or run the whole thing as one service.

In first case you need much, much deeper understanding of the problem then "if I run igmpproxy before L2TP client then everything works, if I do it in opposite order then igmpproxy crashes when L2TP client auto-reconnects" in second case you need to write the whole script from scratch.

Because you talk about legacy code?

Posted Nov 25, 2011 13:26 UTC (Fri) by anselm (subscriber, #2796) [Link]

Yes, but which SysV init are you talking about the traditional one where you get to set all the symbolic links yourself, or the one most distributions are using these days, where the symbolic links are set automatically from dependencies in the LSB headers of the init scripts?

In the former case, any ordering you can explicitly impose on SysV init scripts through numbers in symbolic links can trivially be replicated through explicit »Before=« and »After=« dependencies in systemd. This most emphatically does not require a deeper understanding of the problem than you would need to come up with a suitable ordering for SysV init in the first place.

In the latter case, you need to specify all the dependencies in the LSB script headers for the benefit of your SysV init, and the LSB script header doesn't let you do anything that systemd dependencies don't let you do too. If anything, the systemd dependencies are a lot more expressive than the LSB script-header ones, so your job should be that much easier.

Finally, if you need to wait for something to »stabilise« after you have started a service in systemd, you can write a shell wrapper around that service which does the check, and that shell wrapper will be vastly simpler than a full SysV init script.