forked from synit/synit
115 lines
4.5 KiB
Markdown
115 lines
4.5 KiB
Markdown
---
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title: 'What does systemd do?'
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---
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- ac-power: reports whether A/C power is connected
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- activate: do socket activation (setup sockets, exec() on activity)
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- analyze: "profile systemd", various renderings and checks of system state and config
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- ask-password: secure password entry for e.g. cryptsetup
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- backlight: saves/restores backlight brightness at shutdown/boot
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- basic
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- architecture: show some abstraction over current architecture
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- escape: string escaping for e.g. shell (blearghhh)
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- log: various kinds of logging (incl. syslog, journal, etc)
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- ratelimit: generic rate limiting datastructure and utilities
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- reboot: system call
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- util
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- in_initrd() predicate
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- virt: detects whether, and what kind of, virtualization is in effect
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- binfmt: registers binfmts with the kernel
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- boot: bootctl etc: communicate with EFI (?) about successful/failed boots
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- boot/efi: an actual EFI implementation?? can't be? maybe it's an EFI boot program. I don't know enough about this
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- busctl: introspect contents of D-Bus
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- cgls: "Recursively show control group contents"
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- cgroups-agent: sends a message to unix socket /run/systemd/cgroups-agent
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- cgtop: "Show top control groups by their resource usage"
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- core
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- automount
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- dbus-*, lots of dbus things, wonder what they all are
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- dynamic-user: dynamic user/group ID allocation for, like, temporary use?
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- efi-random: incorporate any random seed passed down from EFI
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- execute: execute programs. lots of code here!
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- job: a job/worker manager system
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- detect-virt: detect virtualization
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- firstboot
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- fsck: runs fsck
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- fstab-generator
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- getty-generator
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- hibernate-resume: a little initrd program that runs when restoring from hibernation!
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- home: manage "home areas"
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- hostname management
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- hwdb: a hardware database
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- id128: various identifiers
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- machine ID
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- boot ID
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- invocation ID
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- import: image importing for containers presumably
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- initctl: like telinit I guess
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- journal: journald, etc
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- kernel-install: when would this be used?
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- libsystemd: ?
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- libsystemd-network: implementations of network protocols?
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- dhcp, dhcp6
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- lldp
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- libudev: ?
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- login
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- machine: machined: "Manage registrations of local VMs and containers"
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- machine-id-setup: gives a machine a random persistent ID
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- modules-load: load configured modules (for explicit loading, rather than on demand)
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- mount: transient mounts
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- network: various network services e.g. dhcp, lldp, route management, wifi management
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- notify: "Notify the init system about service status updates"
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- nspawn: "Spawn a command or OS in a light-weight container"
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- nss-*
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- oom: userspace OOM killer
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- partition: partitioning tools
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- pstore: ?
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- random-seed: load/save random seed at boot/shutdown
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- resolve: a full DNS resolver
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- or? `systemd-resolved` is an interesting take on non-daemonless DNS service for processes
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on the machine: in particular it is able to do split DNS right, with ~routes advertising
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their ability to resolve specific subsets of DNS space. Apparently DBus can be used to
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get rich queries and control things, and there's a listener on a localhost address
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(127.0.0.53?) for unmodified processes to use. Tailscale makes use of the split DNS to
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get things like resolution of the private names. Presumably you can say "hey give these
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names to me and *only* me" as well as "I am able to resolve these names, but if others
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also claim to be able to, go ahead and try things in parallel"? Unclear.
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- rfkill: radio power control
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- run: "Run the specified command in a transient scope or service"
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- shared
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- shutdown
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- sleep: enter sleep, hibernate, or both (?)
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- sysctl: "Applies kernel sysctl settings"
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- sysusers: creates system user accounts
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- timedate, timesync: clock management, NTP etc
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- tmpfiles: creates hierarchy under volatile/tmpfs areas of the filesystem (!) eg /run, /tmp etc
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- udev (!!)
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- vconsole: setup virtual consoles for e.g. utf8 mode
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Unit names: "plain", "template", "instance" (of template).
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Unit files:
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- have a "scope" - "system", "global", "user". What does it mean?
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- have a "type":
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UNIT_SERVICE
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UNIT_MOUNT
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UNIT_SWAP
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UNIT_SOCKET
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UNIT_TARGET
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UNIT_DEVICE
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UNIT_AUTOMOUNT
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UNIT_TIMER
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UNIT_PATH
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UNIT_SLICE
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UNIT_SCOPE
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- have a "state":
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UNIT_ACTIVE
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UNIT_RELOADING
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UNIT_INACTIVE
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UNIT_FAILED
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UNIT_ACTIVATING
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UNIT_DEACTIVATING
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UNIT_MAINTENANCE
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Lots of code spent on argv parsing
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