merge(systemd-presentation): Merge at //presentations/systemd-2016 r/256

I figured that adding old presentations in here might actually be a
useful thing to do, no matter what format they're in.

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+[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.
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