From 8db37e39599943c33dab76e7cb390b0988e03839 Mon Sep 17 00:00:00 2001 From: Vincent Ambo Date: Sat, 21 Dec 2019 00:26:34 +0000 Subject: chore(systemd-presentation): Prepare for depot merge --- presentations/systemd-2016/slides.pdfpc | 85 +++++++++++++++++++++++++++++++++ 1 file changed, 85 insertions(+) create mode 100644 presentations/systemd-2016/slides.pdfpc (limited to 'presentations/systemd-2016/slides.pdfpc') diff --git a/presentations/systemd-2016/slides.pdfpc b/presentations/systemd-2016/slides.pdfpc new file mode 100644 index 000000000000..99326bd8bf4e --- /dev/null +++ b/presentations/systemd-2016/slides.pdfpc @@ -0,0 +1,85 @@ +[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 -- cgit 1.4.1