Introduction to systemd
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Systemd is an init system that replaces traditional init daemons. It allows for parallel startup of services through dependency-based activation of units which encapsulate system objects like services, devices, and mounts. Systemd also provides on-demand activation of services through sockets, buses, devices, and file paths. It aims to be backwards compatible with System V while offering improvements like parallel startup and centralized logging.
Introduction to systemd
- 1. Introduction to systemd OGAWA Yusaku
- 2. 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.
- 3. What is unit ● 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. Target Unit
- 4. System V boot process init Read inittab rc.sysinit BIOS/UEFI GRUB/LILO Kernel Run level 1 Run level 2 Run level 3 Run level 4 Run level 5
- 5. systemd boot process systemd default.target symlink Unit multi-user.target basic.target sysinit.target BIOS/UEFI GRUB/LILO Kernel symlink rescue.target Unit Unit Unit
- 6. On-demand activation ● Socket-based activation ● Bus-based activation ● Device-based activation ● Path-based activation