synit/notes/systemd-functions.md

title
What does systemd do?

• ac-power: reports whether A/C power is connected
• activate: do socket activation (setup sockets, exec() on activity)
• analyze: "profile systemd", various renderings and checks of system state and config
• ask-password: secure password entry for e.g. cryptsetup
• backlight: saves/restores backlight brightness at shutdown/boot
• basic
  • architecture: show some abstraction over current architecture
  • escape: string escaping for e.g. shell (blearghhh)
  • log: various kinds of logging (incl. syslog, journal, etc)
  • ratelimit: generic rate limiting datastructure and utilities
  • reboot: system call
  • util
    • in_initrd() predicate
  • virt: detects whether, and what kind of, virtualization is in effect
• binfmt: registers binfmts with the kernel
• boot: bootctl etc: communicate with EFI (?) about successful/failed boots
  • boot/efi: an actual EFI implementation?? can't be? maybe it's an EFI boot program. I don't know enough about this
• busctl: introspect contents of D-Bus
• cgls: "Recursively show control group contents"
• cgroups-agent: sends a message to unix socket /run/systemd/cgroups-agent
• cgtop: "Show top control groups by their resource usage"
• core
  • automount
  • dbus-*, lots of dbus things, wonder what they all are
  • dynamic-user: dynamic user/group ID allocation for, like, temporary use?
  • efi-random: incorporate any random seed passed down from EFI
  • execute: execute programs. lots of code here!
  • job: a job/worker manager system
• detect-virt: detect virtualization
• firstboot
• fsck: runs fsck
• fstab-generator
• getty-generator
• hibernate-resume: a little initrd program that runs when restoring from hibernation!
• home: manage "home areas"
• hostname management
• hwdb: a hardware database
• id128: various identifiers
  • machine ID
  • boot ID
  • invocation ID
• import: image importing for containers presumably
• initctl: like telinit I guess
• journal: journald, etc
• kernel-install: when would this be used?
• libsystemd: ?
• libsystemd-network: implementations of network protocols?
  • dhcp, dhcp6
  • lldp
• libudev: ?
• login
• machine: machined: "Manage registrations of local VMs and containers"
• machine-id-setup: gives a machine a random persistent ID
• modules-load: load configured modules (for explicit loading, rather than on demand)
• mount: transient mounts
• network: various network services e.g. dhcp, lldp, route management, wifi management
• notify: "Notify the init system about service status updates"
• nspawn: "Spawn a command or OS in a light-weight container"
• nss-*
• oom: userspace OOM killer
• partition: partitioning tools
• pstore: ?
• random-seed: load/save random seed at boot/shutdown
• resolve: a full DNS resolver
• rfkill: radio power control
• run: "Run the specified command in a transient scope or service"
• shared
• shutdown
• sleep: enter sleep, hibernate, or both (?)
• sysctl: "Applies kernel sysctl settings"
• sysusers: creates system user accounts
• timedate, timesync: clock management, NTP etc
• tmpfiles: creates hierarchy under volatile/tmpfs areas of the filesystem (!) eg /run, /tmp etc
• udev (!!)
• vconsole: setup virtual consoles for e.g. utf8 mode

Unit names: "plain", "template", "instance" (of template).

Unit files:

• have a "scope" - "system", "global", "user". What does it mean?
• have a "type": UNIT_SERVICE UNIT_MOUNT UNIT_SWAP UNIT_SOCKET UNIT_TARGET UNIT_DEVICE UNIT_AUTOMOUNT UNIT_TIMER UNIT_PATH UNIT_SLICE UNIT_SCOPE
• have a "state": UNIT_ACTIVE UNIT_RELOADING UNIT_INACTIVE UNIT_FAILED UNIT_ACTIVATING UNIT_DEACTIVATING UNIT_MAINTENANCE

Lots of code spent on argv parsing