Boot process
systemd
systemd is the default init system for the major Linux distributions. Previous was SysV init
- cron
- syslog
Boot process
Once kernel is set up, it begins the systemd initialization system and systemd takes over and continues to mount the host’s file systems and start services.
systemd Units
Types:
- service unit
- mount unit
- socket unit
- slice unit
Unit files in:
/usr/lib/systemd/user/Runtime for unit files in:
/run/systemd/system/Unit files that extend a service (take precedence)
/etc/systemd/system/| Unit Type | File Extension | Description |
|---|---|---|
| Service unit | .service | A system service. |
| Target unit | .target | A group of systemd units. |
| Automount unit | .automount | A file system automount point. |
| Device unit | .device | A device file recognized by the kernel. |
| Mount unit | .mount | A file system mount point. |
| Path unit | .path | A file or directory in a file system. |
| Scope unit | .scope | An externally created process. |
| Slice unit | .slice | A group of hierarchically organized units that manage system processes. |
| Snapshot unit | .snapshot | A saved state of the systemd manager. |
| Socket unit | .socket | An inter-process communication socket. |
| Swap unit | .swap | A swap device or a swap file. |
| Timer unit | .timer | A systemd timer. |