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Ubuntu To Switch To systemd
GuerillaRadio writes "Following the decision for Debian to switch to the systemd init system, Ubuntu founder and SABDFL Mark Shuttleworth has posted a blog entry indicating that Ubuntu will now follow in this decision. 'Nevertheless, the decision is for systemd, and given that Ubuntu is quite centrally a member of the Debian family, that's a decision we support. I will ask members of the Ubuntu community to help to implement this decision efficiently, bringing systemd into both Debian and Ubuntu safely and expeditiously.'"
put this line in your .bashrc file
alias service='systemctl'
Here's a pretty good treatise on the shortcomings of systemd: http://ewontfix.com/14/
System V has a scrict sense of a run level. For example, if you want a full desktop, run level 5 is often used, for a headless server, run level 3. What if you have a box that is headless most of the time, but you want to be able to run a full desktop sometimes? With System V you would change from run level 3 to run level 5 which would, depending on implimentation, stop and start services that are needed by both. Systemd instead has the concept of targets. Your full desktop target would have the headless server target as a dependency, and starting the full desktop would only run what isn't already running. You typically also have individual sevices that have dependencies. For example, you'd want your dhcp server to wait to start until the network has come online. In System V you have to define network as a number and make sure everything that depends on it has a bigger number and everything it depends on to have a smaller number. systemd's dependency model is also smart enough to start processes in parallel.
All of that is just the most exposed part of systemd (to me at least). It also supplants other processes such as xinetd and udev. Instead of having three different ways to start processes based on system events (startup, port connection, hardware event) you have a single system to manage all three. It can get complicated (wasn't udev already complicated?) but the consistency is worth it.
To keep all the consitency systemd provides a series of functions and magic variables. By magic variables I mean you set a list dependencies, which IMHO is less magic than the chkconfig comment lines in a typical System V init script. Both the magic variables and functions mean your typical service initaliation script is 10 lines instead of 100. While they may not be as obvious what's going on (a System V script is self-contained and can be ran on it's own) it is once you've become familiar with them.
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I don't think very much embedded stuff will ever use systemd..
I am using Angstrom, which uses systemd, for embedded stuff. Haven't had any problems with systemd, but haven't tried to do anything complex either. It gets stuff started at startup time, that's all I have needed.
If a daemon has problems and needs to restart itself how does it do that?
...Monit? runit? Two completely different approaches to service monitoring, one not even in an init system. And there are more (s6, daemontools, etc.).
hundreds or thousands of daemons
...What the heck are you running that puts thousands of daemons on a single server? If you're doing something this large, you might want to consider virtualization. Thousands of daemons is a gigantic attack surface to have on a single system, and a mess if something were to go wrong with one of them that takes down everything.
Indeed, journalctl is probably what I dislike the most about the current systemd stack. For one thing it is slow with full text search in large log files -- it is reasonably fast if you use the built-in column-specific search, but just running fgrep on it is not really feasible. In contrast, fgrep is ridiculously fast on modern systems as long as your log files stay below a few gigabytes in size. Also, the output of journalctl changes (mostly for the better) when you use it with pipes, which can be quite surprising.
The other major problem with systemd is how difficult it is to debug boot failures. It is quite annoying when an fstab which was correct with upstart results in silent boot failure with systemd.
Finally! A year of moderation! Ready for 2019?
In the end, yes, it's another config language you'll have to learn, but it's worth it.
Why is it worth it?
I've heard lots of "systemd is better" claims, but not one real-world example of how it took 27 hours to debug a startup issue when using SysV, but only 13 seconds using systemd. And, I really don't care about boot times, because my physical servers take 10 times as long running through BIOS checks as they do going from grub load to system ready. Even VMs don't matter much, as they don't get rebooted very often, so saving 5 seconds on a 30-second boot time isn't really a big deal.
On the other hand, I've heard lots of stories from people who have to install a custom service (i.e., not from a "apt-get" or "yum install") on a systemd system and complain about how it took hours to get the dependencies right.