为什么linux系统中init被systemd替换了

Linux init 进程是系统初始化进程，比较古老了，所以出现了一些新的替代方案：

Upstart – A init replacement daemon implemented in Ubuntu GNU/Linux and designed to start process asynchronously.
Epoch – A init replacement daemon built around simplicity and service management, designed to start process single-threaded.
Mudar – A init replacement daemon written in Python, implemented on Pardus GNU/Linux and designed to start process asynchronously.
systemd – A init replacement daemon designed to start process in parallel, implemented in a number of standard distribution – Fedora, OpenSuSE, Arch, RHEL, CentOS, etc.

比较出名的就是 systemd，他的优缺点如下：

Features of systemd

1. Clean, stateforward and efficient design.
2. Simpler boot process.
3. Concurrent and parallel processing at boot.
4. Better API.
5. Simple Unit Syntax.
6. Ability to remove optional components.
7. Low memory footprints.
8. Improved technique to express dependencies.
9. Initialization instruction written in config file and not in shell script.
10. Make use of Unix Domain Socket.
11. Job Scheduling using systemd Calendar Timers.
12. Event Logging with journald.
13. Choice of logging System events with systemd as well as syslog.
14. Logs are stored in binary file.
15. systemd state can be preserved to be called later in future.
16. Track process using kernel’s cgroup and not PID.
17. Users login managed by systemd-logind.
18. Better integration with Gnome for interoperability.

Bottlenecks systemd

1. Everything at one place.
2. Not POSIX standard.

英文好的筒子可以直接去看原文，很好很强大：

https://www.tecmint.com/systemd-replaces-init-in-linux/