---
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