(Apologies in advance for the length of this message -- if you don't care about order and manner in which system daemons are launched, please invoke the Delete key operator immediately.)
Everyone knows the canonical (no pun intended) unix interview question, namely Q: how many processes does the kernel start on boot? A: Only one -- init Apparently this isn't necessarily true any more, or soon won't be? I usually don't dig into random subsystems until something fails. In this case, I recently found out that my coworker had "fixed" an autofs startup timing problem in our 8.04 rollout by simply inserting a few sleep loops into the autofs init script. This hack was no longer working in 9.04, which we're testing now (not to mention dramatically increased boot times). Since autofs is a core system service, I suggested that he contact Canonical support and let them know that there is a problem; i.e. as installed by default, autofs fails to start. The support technician who got back to us made a number of comments about how processes are launched which were simply wrong. At this point, Houston: we have a problem. The Ubuntu tech staff isn't even clear on how daemons are launched at startup. So, this brings us to upstart, the init replacement. After a couple of days of looking through both the on-line documentation I could find (http://upstart.ubuntu.com/getting-started.html) and the actual installed files I find that I still have more than a number of questions about how this is supposed to work currently and in the future, as alluded to in this snippet from something posted to one of the ubuntu devel lists: ------------ > Date: Fri, 26 Jun 2009 14:55:16 -0500 > From: Robbie Williamson <rob...@ubuntu.com> > Subject: Debian/Ubuntu Boot Performance Sprint Summary <snip/>Scott James Remnant stated that he expects to have the entire Ubuntu boot sequence transitioned over to upstart by 10.04, with some work already planned for the 9.10 cycle.<snip/> ------------- Questions: 1. the previously referenced site says that jobs files are placed in /etc/init/jobs.d; actually, they seem to be in /etc/event.d -- what's up with that? 2. lizard:~~$ which init /sbin/init lizard:~~$ dpkg -S /sbin/init upstart: /sbin/init So, I'm confused: is init still being used, or what? /etc/inittab no longer exists in 9.04/9.10, and the jobs in /etc/event.d follow the event driven model outlined in the documentation, however there is still an init executable. Is this init an upstarted init? There don't appear to be any other candidate executables in the upstart package. 3. There's much discussion about improving the startup system by moving to an event driven model. The current implementation in 9.04/9.10alpha simply mimics System-V init. OK, this is transitional, but how are we going to get from A to B? Package implementers are not getting initialization scripts right now (e.g. autofs), what's the plan for rolling out a new event-driven system and how is it going to work? 4. Related: The concept of run levels is fairly useful, and the core concept in System-V init. Are run levels going to go way under full upstart implementation? If so, how will the system distinguish between, say, a maintenance single-user boot and what is currently rc2? And if run levels are not going away, how is process of startinɡ system daemons going to be event driven in any meaningful way? 5. Even after reading through the "Getting Started" page twice, the implementation under 9.04 is still confusing. For example, to quote Getting Started: "You list the events you want to start your job with start on, and the events that stop your job with stop on." OK, fair enough. However, here is /etc/event.d/rcS: ---------------- start on startup stop on runlevel console output script runlevel --set S >/dev/null || true PREVLEVEL=N RUNLEVEL=S export PREVLEVEL RUNLEVEL exec /etc/init.d/rcS end script ---------------- Doesn't this mean that rcS is stopped before /etc/init.d/rcS is ever exec'd, since the runlevel is set before the script is run? In particular, when exactly does the runlevel event stop the script? Clearly after the rcS script is exec'd (otherwise none of the goodies in /etc/rc2.d would ever get started), but this needs to be documented much more carefully, since not every case will be this clear cut. Again, package implementors can't get the timing down right now under System-V init. This is going to turn into complete pandemonium if the termination of events is ill-defined. 6. "If you're using the example jobs, you will also have runlevel X events, where X is one of 0–6 or S. Jobs will be run alongside the init scripts for that runlevel." Presumably this means in an event driven model, user-installed jobs are triggered in parallel with runlevel events? Otherwise: Um, what? 7. Finally, is there better documentation available, say something in between http://upstart.ubuntu.com/getting-started.html and slogging through the actual source code? -- Ubuntu-devel-discuss mailing list Ubuntu-devel-discuss@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-devel-discuss
