Linked by Dennis Heuer on Wed 25th Aug 2010 22:23 UTC
Linux I came across a news entry at Phoronix about a new init replacement, systemd, and curiously started a read into the surprisingly heavy matter. Systemd is by no means as simple as upstart. It does far more things far more straight and in more detail. The differences are so significant that they enforce quite different configuration strategies. One can argue for both, depending on the goal to reach. However, that's not what I want to write about. After having read what systemd is capable of, and how it does it, I began to put the existence of all system daemons - in their today's forms - in question.
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RE[4]: Comment by mtzmtulivu
by sorpigal on Thu 26th Aug 2010 17:33 UTC in reply to "RE[3]: Comment by mtzmtulivu"
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Linear is not 'easy' - linear is hard. Nonlinear is harder, but linear is not trivial! You have a large, unknown set of things to run which must be run in a particular order. What order? If you know you have a good order and want to insert a new item to run, where in the sequence does it go? Can you *safely* alter the order by inserting this new item and can you be sure that doing so does not break anything?

For simple things it's pretty easy to just "drop it in" and hope it will be fine, but there are many non-simple things. Does your ldap daemon need to be started before your remote filesystems are mounted? What if your /home is mounted via nfs and all users are stored in ldap? How do you know which order to load things in and how do you re-order it when it changes? Even in a purely linear situation this is not simple. If thinks work well today it's because of luck and careful engineering over many years.

It's a management nightmare which only becomes worse over time. Designing a system that works on purpose, instead of accidentally, is a worthwhile effort and a tricky problem.

Being faster is nice, sure, but that's not really a problem that needs to be solved, it's just a nice side effect. Once we can figure out sequencing properly we can get parallelism "for free" and thus some speedups. But no, it's not a goal.

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