Introduction to systemdOGAWA Yusaku

What is systemd● Init daemon● It is designed to be backwards compatible with System

V init

● Strength○ Parallel startup (Dependency-based startup)○ On-demand service activation○ Replacements for various daemons and

utilities such as syslog, cron, etc.

● Encapsulate information about system services, listening sockets, device files, and other objects that are relevant to the init system

● Unit types○ Service unit: A system service○ Device unit: A device file○ Mount unit: A fs mount point○ Target unit: A group of units○ etc.

What is unit

Target

Unit

System V boot process

Read inittab

rc.sysinit

init

BIOS/UEFI

GRUB/LILO

Kernel

Run level 3

Run level 2

Run level 4

Run level 1

Run level 5

sysinit.targetbasic.targetmulti-user.target

systemd boot process

default.target

systemd

BIOS/UEFI

GRUB/LILO

Kernel

symlink

rescue.target

Unit Unit Unit

symlink Unit

On-demand activation● Socket-based activation● Bus-based activation● Device-based activation● Path-based activation