写完才找到自己之前写过的一篇 SystemV, Upstart和SystemD的简单比较
历史概览
历史上有3中开启自启的相关程序，分别是 system v (update-rc.d/chkconfig(CentOS), service), upstart(initctl), sytemd(systemctl)。很多发行版提供多种选择，或允许安装备用方案。
- System V: the older init system:
/etc/init.d/,/etc/rcN.d/- Debian 6 and earlier
- Ubuntu 9.04 and earlier
- CentOS 5 and earlier
- Upstart:
/etc/init/- Ubuntu 9.10 to Ubuntu 14.10, including Ubuntu 14.04
- CentOS 6
- systemd: the init system for the most recent distributions featured here:
/etc/sytem/- Debian 7 and Debian 8
- Ubuntu 15.04 and newer
- CentOS 7
实操查看有哪些目录和文件
root@tx:~# echo $SHELL
/bin/bash
root@tx:~# cat /etc/issue
Debian GNU/Linux 9 \n \l
root@tx:~# ls -lh /etc/ | grep profile
-rw-r--r-- 1 root root 767 Mar 4 2016 profile
drwxr-xr-x 2 root root 4.0K Nov 20 2019 profile.d
root@tx:~# ls -lh /etc/ | grep init
drwxr-xr-x 2 root root 4.0K Oct 13 2018 init
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 init.d
drwxr-xr-x 5 root root 4.0K Jul 15 2017 initramfs-tools
root@tx:~# ls -lh /etc/ | grep rc
-rw-r--r-- 1 root root 2.0K Jul 26 2018 bash.bashrc
-rw-r--r-- 1 root root 1.8K May 16 2017 inputrc
-rw-r--r-- 1 root root 8.6K Jan 11 2017 nanorc
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc0.d
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc1.d
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc2.d
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc3.d
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc4.d
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc5.d
drwxr-xr-x 2 root root 4.0K Mar 16 12:38 rc6.d
-rwxr-xr-x 1 root root 262 Mar 10 17:39 rc.local
drwxr-xr-x 2 root root 4.0K Oct 13 2018 rcS.d
-rw-r--r-- 1 root root 4.9K Mar 18 2017 wgetrc
Detail of these directories:
root@tx:~# ls -lh /etc/profile.d
total 8.0K
-rw-r--r-- 1 root root 663 Apr 12 2016 bash_completion.sh
-rw-r--r-- 1 root root 161 Nov 20 2019 nix.sh
-rw-r--r-- 1 root root 0 Nov 20 2019 nix.sh.backup-before-nix
root@tx:~# ls -lh /etc/rcS.d/
total 0
lrwxrwxrwx 1 root root 20 Oct 13 2018 S01hwclock.sh -> ../init.d/hwclock.sh
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01kmod -> ../init.d/kmod
lrwxrwxrwx 1 root root 20 Jul 15 2017 S01networking -> ../init.d/networking
lrwxrwxrwx 1 root root 16 Jul 15 2017 S01procps -> ../init.d/procps
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01udev -> ../init.d/udev
root@tx:~# ls -lh /etc/rc0.d/
total 0
lrwxrwxrwx 1 root root 16 Jul 26 2018 K01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 K01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 20 Oct 13 2018 K01hwclock.sh -> ../init.d/hwclock.sh
lrwxrwxrwx 1 root root 20 Jul 15 2017 K01networking -> ../init.d/networking
lrwxrwxrwx 1 root root 15 Jul 27 2018 K01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 K01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 17 Jul 15 2017 K01rsyslog -> ../init.d/rsyslog
root@tx:~# ls -lh /etc/rc1.d/
total 0
lrwxrwxrwx 1 root root 16 Jul 26 2018 K01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 K01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 15 Jul 27 2018 K01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 K01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 17 Jul 15 2017 K01rsyslog -> ../init.d/rsyslog
root@tx:~# ls -lh /etc/rc2.d/
total 0
lrwxrwxrwx 1 root root 15 Jul 15 2017 S01acpid -> ../init.d/acpid
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01cron -> ../init.d/cron
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01dbus -> ../init.d/dbus
lrwxrwxrwx 1 root root 16 Jul 26 2018 S01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 S01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 21 Jul 17 2017 S01kdump-tools -> ../init.d/kdump-tools
lrwxrwxrwx 1 root root 15 Jul 17 2017 S01kexec -> ../init.d/kexec
lrwxrwxrwx 1 root root 20 Jul 17 2017 S01kexec-load -> ../init.d/kexec-load
lrwxrwxrwx 1 root root 15 Jul 27 2018 S01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 S01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 15 Jul 26 2018 S01rsync -> ../init.d/rsync
lrwxrwxrwx 1 root root 17 Jul 15 2017 S01rsyslog -> ../init.d/rsyslog
lrwxrwxrwx 1 root root 13 Jul 15 2017 S01ssh -> ../init.d/ssh
lrwxrwxrwx 1 root root 17 Jan 23 2019 S01sysstat -> ../init.d/sysstat
root@tx:~# ls -lh /etc/rc3.d/
total 0
lrwxrwxrwx 1 root root 15 Jul 15 2017 S01acpid -> ../init.d/acpid
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01cron -> ../init.d/cron
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01dbus -> ../init.d/dbus
lrwxrwxrwx 1 root root 16 Jul 26 2018 S01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 S01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 21 Jul 17 2017 S01kdump-tools -> ../init.d/kdump-tools
lrwxrwxrwx 1 root root 15 Jul 17 2017 S01kexec -> ../init.d/kexec
lrwxrwxrwx 1 root root 20 Jul 17 2017 S01kexec-load -> ../init.d/kexec-load
lrwxrwxrwx 1 root root 15 Jul 27 2018 S01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 S01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 15 Jul 26 2018 S01rsync -> ../init.d/rsync
lrwxrwxrwx 1 root root 17 Jul 15 2017 S01rsyslog -> ../init.d/rsyslog
lrwxrwxrwx 1 root root 13 Jul 15 2017 S01ssh -> ../init.d/ssh
lrwxrwxrwx 1 root root 17 Jan 23 2019 S01sysstat -> ../init.d/sysstat
root@tx:~# ls -lh /etc/rc4.d/
total 0
lrwxrwxrwx 1 root root 15 Jul 15 2017 S01acpid -> ../init.d/acpid
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01cron -> ../init.d/cron
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01dbus -> ../init.d/dbus
lrwxrwxrwx 1 root root 16 Jul 26 2018 S01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 S01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 21 Jul 17 2017 S01kdump-tools -> ../init.d/kdump-tools
lrwxrwxrwx 1 root root 15 Jul 17 2017 S01kexec -> ../init.d/kexec
lrwxrwxrwx 1 root root 20 Jul 17 2017 S01kexec-load -> ../init.d/kexec-load
lrwxrwxrwx 1 root root 15 Jul 27 2018 S01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 S01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 15 Jul 26 2018 S01rsync -> ../init.d/rsync
lrwxrwxrwx 1 root root 17 Jul 15 2017 S01rsyslog -> ../init.d/rsyslog
lrwxrwxrwx 1 root root 13 Jul 15 2017 S01ssh -> ../init.d/ssh
lrwxrwxrwx 1 root root 17 Jan 23 2019 S01sysstat -> ../init.d/sysstat
root@tx:~# ls -lh /etc/rc5.d/
total 0
lrwxrwxrwx 1 root root 15 Jul 15 2017 S01acpid -> ../init.d/acpid
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01cron -> ../init.d/cron
lrwxrwxrwx 1 root root 14 Jul 15 2017 S01dbus -> ../init.d/dbus
lrwxrwxrwx 1 root root 16 Jul 26 2018 S01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 S01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 21 Jul 17 2017 S01kdump-tools -> ../init.d/kdump-tools
lrwxrwxrwx 1 root root 15 Jul 17 2017 S01kexec -> ../init.d/kexec
lrwxrwxrwx 1 root root 20 Jul 17 2017 S01kexec-load -> ../init.d/kexec-load
lrwxrwxrwx 1 root root 15 Jul 27 2018 S01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 S01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 15 Jul 26 2018 S01rsync -> ../init.d/rsync
lrwxrwxrwx 1 root root 17 Jul 15 2017 S01rsyslog -> ../init.d/rsyslog
lrwxrwxrwx 1 root root 13 Jul 15 2017 S01ssh -> ../init.d/ssh
lrwxrwxrwx 1 root root 17 Jan 23 2019 S01sysstat -> ../init.d/sysstat
root@tx:~# ls -lh /etc/rc6.d/
total 0
lrwxrwxrwx 1 root root 16 Jul 26 2018 K01docker -> ../init.d/docker
lrwxrwxrwx 1 root root 17 Mar 16 12:38 K01haproxy -> ../init.d/haproxy
lrwxrwxrwx 1 root root 20 Oct 13 2018 K01hwclock.sh -> ../init.d/hwclock.sh
lrwxrwxrwx 1 root root 15 Jul 17 2017 K01kexec -> ../init.d/kexec
lrwxrwxrwx 1 root root 20 Jul 17 2017 K01kexec-load -> ../init.d/kexec-load
lrwxrwxrwx 1 root root 20 Jul 15 2017 K01networking -> ../init.d/networking
lrwxrwxrwx 1 root root 15 Jul 27 2018 K01nginx -> ../init.d/nginx
lrwxrwxrwx 1 root root 20 Jan 23 2019 K01postgresql -> ../init.d/postgresql
lrwxrwxrwx 1 root root 17 Jul 15 2017 K01rsyslog -> ../init.d/rsyslog
root@tx:~# ls -lh /etc/init.d
total 96K
-rwxr-xr-x 1 root root 2.3K Sep 20 2016 acpid
-rwxr-xr-x 1 root root 3.0K May 3 2015 cron
-rwxr-xr-x 1 root root 2.8K Apr 6 2017 dbus
-rwxr-xr-x 1 root root 3.8K Jul 19 2018 docker
-rwxr-xr-x 1 root root 3.4K Apr 4 2017 haproxy
-rwxr-xr-x 1 root root 3.8K Mar 22 2017 hwclock.sh
-rwxr-xr-x 1 root root 1.5K Jan 5 2017 kdump-tools
-rwxr-xr-x 1 root root 1.1K Jun 29 2016 kexec
-rwxr-xr-x 1 root root 3.3K Jun 29 2016 kexec-load
-rwxr-xr-x 1 root root 2.0K Dec 26 2016 kmod
-rwxr-xr-x 1 root root 4.5K Sep 16 2016 networking
-rwxr-xr-x 1 root root 4.5K Jul 12 2017 nginx
-rwxr-xr-x 1 root root 1.5K Jun 8 2018 postgresql
-rwxr-xr-x 1 root root 1.2K Nov 22 2016 procps
-rwxr-xr-x 1 root root 4.3K Dec 10 2017 rsync
-rwxr-xr-x 1 root root 2.9K Jan 19 2017 rsyslog
-rwxr-xr-x 1 root root 4.0K Mar 30 2017 ssh
-rwxr-xr-x 1 root root 731 Jun 5 2017 sudo
-rwxr-xr-x 1 root root 1.6K May 26 2017 sysstat
-rwxr-xr-x 1 root root 6.0K Jun 5 2017 udev
root@tx:~# ls -lh /etc/init
total 44K
-rw-r--r-- 1 root root 1.9K Jul 19 2018 docker.conf
-rw-r--r-- 1 root root 977 Jan 5 2017 kdump-tools.conf
-rw-r--r-- 1 root root 2.5K Jun 2 2015 networking.conf
-rw-r--r-- 1 root root 933 Jun 2 2015 network-interface.conf
-rw-r--r-- 1 root root 530 Jun 2 2015 network-interface-container.conf
-rw-r--r-- 1 root root 1.8K Jun 2 2015 network-interface-security.conf
-rw-r--r-- 1 root root 401 Jul 12 2017 nginx.conf
-rw-r--r-- 1 root root 637 Mar 30 2017 ssh.conf
-rw-r--r-- 1 root root 337 Jun 5 2017 udev.conf
-rw-r--r-- 1 root root 360 Jun 5 2017 udevmonitor.conf
-rw-r--r-- 1 root root 352 Jun 5 2017 udevtrigger.conf
root@tx:~# ls -lh /etc/systemd/
total 36K
-rw-r--r-- 1 root root 1014 Jun 5 2017 journald.conf
-rw-r--r-- 1 root root 1022 Jun 5 2017 logind.conf
drwxr-xr-x 2 root root 4.0K Jun 5 2017 network
-rw-r--r-- 1 root root 642 Jun 5 2017 resolved.conf
drwxr-xr-x 10 root root 4.0K Nov 20 2019 system
-rw-r--r-- 1 root root 1.6K Jul 20 2017 system.conf
-rw-r--r-- 1 root root 607 Jun 5 2017 timesyncd.conf
drwxr-xr-x 2 root root 4.0K Jun 5 2017 user
-rw-r--r-- 1 root root 1.2K Jun 5 2017 user.conf
/etc/rc.d/rc文件定义了服务启动的顺序是先K后S，而具体的每个运行级别的服务状态是放在/etc/rc.d/rc*.d（*=0~6）目录下，所有的文件均是指向/etc/init.d下相应文件的符号链接。
S表示的是启动时需要start的服务内容，K表示关机时需要关闭的服务内容。
如果我们需要自己增加启动的内容，可以在init.d目录中增加相关的shell脚本，然后在rc*.d目录中建立链接文件指向该shell脚本。这些shell脚本的启动或结束顺序是由S或K字母后面的数字决定，数字越小的脚本越先执行。
运行级别的含义：
1 Single user (super user)
2 multi user
3 multi user + network
4 not used / user definable
5 multi user, network + X11
/etc/init.d里的shell脚本能够响应start，stop，restart，reload命令来管理某个具体的应用。
root@tx:~# /etc/init.d/docker
Usage: service docker {start|stop|restart|status}
root@tx:~# /etc/init.d/nginx
Usage: nginx {start|stop|restart|reload|force-reload|status|configtest|rotate|upgrade}
root@tx:~# /etc/init.d/procps
Usage: /etc/init.d/procps {start|stop|restart|reload|force-reload|status}
root@tx:~# /etc/init.d/cron
[info] Usage: /etc/init.d/cron {start|stop|status|restart|reload|force-reload}.
root@tx:~# /etc/init.d/sudo
Usage: /etc/init.d/sudo {start|stop|restart|force-reload|status}
root@tx:~# /etc/init.d/networking
Usage: /etc/init.d/networking {start|stop|reload|restart|force-reload}
root@tx:~# /etc/init.d/sysstat
[FAIL] Usage: /etc/init.d/sysstat {start|stop|restart|reload|force-reload|status} ... failed!
root@tx:~# /etc/init.d/udev
Usage: /etc/init.d/udev {start|stop|restart|reload|force-reload|status}
/etc/init.d/就是旧时代liunx的用法，/etc/init/是现在Ubuntu的提倡并一步步转型的用法。为了平缓过渡，便让service命令可以同时寻找到两个文件夹。
如何添加脚本到开机启动项
添加到 /etc/rc.local
放置脚本到 /etc/profile.d/
通过 chkconfig / update-rc.d 命令
将启动文件cp到 /etc/init.d/或者/etc/rc.d/init.d/（前者是后者的软连接）下
vim 启动文件，文件前面务必添加如下三行代码，否侧会提示chkconfig不支持
#!/bin/sh 告诉系统使用的shell
# chkconfig: 35 20 80 分别代表运行级别分别是3和5（一共0到6），启动优先权，关闭优先权，此行代码必须
# description: http server（自己随便发挥），此行代码必须
chkconfig --add 脚本文件名，操作后就已经添加了