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diff --git a/presentations/systemd-2016/slides.pdfpc b/presentations/systemd-2016/slides.pdfpc deleted file mode 100644 index 99326bd8bf..0000000000 --- a/presentations/systemd-2016/slides.pdfpc +++ /dev/null @@ -1,85 +0,0 @@ -[file] -slides.pdf -[notes] -### 1 -### 2 -Let's start off by looking at what an init system is, how they used to work and what systemd does different before we go into more systemd-specific details. -### 3 -system processes that are started include for example FS mounts, network settings, powertop... -system services are long-running processes such as daemons, e.g. SSH, database or web servers, session managers, udev ... - -orphans: Process whose parent has finished somehow, gets adopted by init system --> when a process terminates its parent must call wait() to get its exit() code, if there is no init system adopting orphans the process would become a zombie -### 4 -Before systemd there were simple init systems that just did the tasks listed on the previous slide. -Init scripts -> increased greatly in complexity over time, look at incomprehensible skeleton for Debian service init scripts -Runlevels -> things such as single-user mode, full multiuser mode, reboot, halt - -Init will run all the scripts, but it will not do much more than print information on success/failure of started scripts - -Init scripts run strictly sequential - -Init is unaware of inter-service dependencies, expressed through prefixing scripts with numbers etc. - -Init will not watch processes after system is booted -> crashing daemons will not automatically restart -### 5 -### 6 -How systemd came to be - -Considering the lack of process monitoring, problematic things about init scripts -> legacy init systems have drawbacks - -Apple had already built launchd, a more featured init system that monitored running processes, could automatically restart them and allowed for certain advanced features -> however it is awful to use and wrap your head around - -Lennart Poettering of Pulseaudio fame and Kay Sievers decided to implement a new init system to address these problems, while taking certain clues from Apple's design -### 7 -Systemd's design goals -### 8 -No more init scripts with opaque effects -> services are clearly defined units -Unit dependencies -> systemd can figure out what can be started in parallel -Process supervision: Unit can be configured in many ways, e.g. always restart, only restart on success etc -Service logs: We'll talk more about this later -### 9 -Units are the core component of systemd that users deal with. They define services and everything else that systemd needs to start and manage. -Note that all these are the names of the respective man page on a system with systemd installed -Types: -systemd.service - processes controlled by systemd -systemd.target - equivalent to "runlevels", grouping of units for synchronisation -systemd.timer - more powerful replacement of cron that starts other units -systemd.path - systemd equvialent of inotify, watches files/folders -> launches units -systemd.socket - expose local IPC or network sockets, launch units on connections -systemd.device - trigger units when certain devices are connected -systemd.mount - systemd equivalent of fstab entries -systemd.swap - like mount -systemd.slice - unit groups for resource management purposes -... and a few more specialised ones -### 10 -Linux cgroups are a new resource management feature added quite a long time ago, but not used much. -Cgroups can be created manually and processes can be moved into them in order to control resource utilisation -Few people used them before systemd, limits.conf was often much easier but not as fine-grained -Systemd changed this -### 11 -Systemd collects standard output and stderr from all processes into its journal system -they provide a tool for querying the log, for example grouping service logs together with correct timestamps, querying, -### 12 -Systemd tooling, most important one is systemctl for general service management -journalctl is the query and management tool for journald -systemd-analyze is used for figuring out performance issues, for example by analysing the boot process, can make cool graphs of dependencies -systemd-cgtop is like top, but not on a process level - it's on a cgroup/slice level, shows combined usage of cgroups -systemd-cgls lists contents of systemd's cgroups to see which services are in what group -there also exist a bunch of others that we'll skip for now -### 13 -### 14 -### 15 -Systemd criticism comes from many directions and usually focuses on a few points -feature-creep: systemd is absorbing a lot of different services -### 16 -explain diagram a bit -### 17 -opaque: as a result, systemd has a lot more internal complexity that people can't easily wrap your mind around. However I argue that unless you're using something like suckless' sinit with your own scripts, you probably have no idea what your init does today anyways -unstable: this was definitely true even in the first stable release, with the binary log format getting corrupted for example. I haven't personally experienced any trouble with it recently though. -Another thing is that services start depending on systemd when they shouldn't, a problem for the BSD world (who cares (hey christoph!)) -### 18 -Despite criticism, systemd was adopted rapidly by large portions of the Linux -Initially in RedHat, because Poettering and co work there and it was clear from the beginning that it would be there -ArchLinux (which I'm using) and a few others followed suit quite quickly -Eventually, the big Debian init system discussion - after a lot of flaming - led to Debian adopting it as well, which had a ripple effect for related distros such as Ubuntu which abandoned upstart for it. \ No newline at end of file |