36 lines
1.9 KiB
Text
36 lines
1.9 KiB
Text
[file]
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slides.pdf
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[notes]
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### 1
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### 2
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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.
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### 3
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system processes that are started include for example FS mounts, network settings, powertop...
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system services are long-running processes such as daemons, e.g. SSH, database or web servers, session managers, udev ...
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orphans: Process whose parent has finished somehow, gets adopted by init system
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-> 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
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### 4
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Before systemd there were simple init systems that just did the tasks listed on the previous slide.
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Init scripts -> increased greatly in complexity over time, look at incomprehensible skeleton for Debian service init scripts
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Runlevels -> things such as single-user mode, full multiuser mode, reboot, halt
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Init will run all the scripts, but it will not do much more than print information on success/failure of started scripts
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Init scripts run strictly sequential
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Init is unaware of inter-service dependencies, expressed through prefixing scripts with numbers etc.
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Init will not watch processes after system is booted -> crashing daemons will not automatically restart
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### 5
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### 6
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How systemd came to be
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Considering the lack of process monitoring, problematic things about init scripts -> legacy init systems have drawbacks
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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
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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
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### 7
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Systemd's design goals
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### 8
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