systemctl 命令

systemctl命令控制：启动、停止、开机自启能够被syatemctl管理的软件，一般也称之为服务

语法：systemctl start ｜ stop｜ status ｜enable ｜disable 服务名

（启动/停止/查看状态/开启开机自启/关闭开机自启）

NetworkManager 主网络服务

network 副网络

firewalld 防火墙

sshd，ssh服务（Xshell远程都玩Linux使用的就是这个服务）

# systemctl list-units --type=service --state=running 查看当前正在运行中的服务
root@hcss-ecs-c2b8:~# systemctl list-units --type=service --state=runningUNIT                             LOAD   ACTIVE SUB     DESCRIPTION                                   atd.service                      loaded active running Deferred execution schedulerchrony.service                   loaded active running chrony, an NTP client/servercloudResetPwdUpdateAgent.service loaded active running cloudResetPwdUpdateAgentcontainerd.service               loaded active running containerd container runtimecron.service                     loaded active running Regular background program processing daemondbus.service                     loaded active running D-Bus System Message Busdocker.service                   loaded active running Docker Application Container Enginefwupd.service                    loaded active running Firmware update daemongetty@tty1.service               loaded active running Getty on tty1irqbalance.service               loaded active running irqbalance daemonModemManager.service             loaded active running Modem Managermultipathd.service               loaded active running Device-Mapper Multipath Device Controllermysqld.service                   loaded active running LSB: start and stop MySQLNetworkManager.service           loaded active running Network Managernginx.service                    loaded active running nginx - high performance web serverpackagekit.service               loaded active running PackageKit Daemonpolkit.service                   loaded active running Authorization Managerrsyslog.service                  loaded active running System Logging Serviceserial-getty@ttyS0.service       loaded active running Serial Getty on ttyS0snapd.service                    loaded active running Snap Daemonssh.service                      loaded active running OpenBSD Secure Shell serversystemd-journald.service         loaded active running Journal Servicesystemd-logind.service           loaded active running User Login Managementsystemd-resolved.service         loaded active running Network Name Resolutionsystemd-udevd.service            loaded active running Rule-based Manager for Device Events and Filesudisks2.service                  loaded active running Disk Managerunattended-upgrades.service      loaded active running Unattended Upgrades Shutdownuniagent.service                 loaded active running Unified Agentupower.service                   loaded active running Daemon for power managementuser@0.service                   loaded active running User Manager for UID 0uuidd.service                    loaded active running Daemon for generating UUIDswpa_supplicant.service           loaded active running WPA supplicantLOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.
32 loaded units listed.

这里我在服务器上安装了一个mysql数据,mysql数据库安装完成后他会自己注册为系统的一个服务,这样我们能直接通过systemctl命令对mysql的状态进行管理

# 先查看服务列表是否有mysql的相关服务
root@hcss-ecs-c2b8:~# systemctl list-units --type=service | grep mysqlmysqld.service                     loaded active running LSB: start and stop MySQL
# systemctl status mysql 查看mysql的状态
root@hcss-ecs-c2b8:~# systemctl status mysql
● mysqld.service - LSB: start and stop MySQLLoaded: loaded (/etc/init.d/mysqld; generated)Active: active (running) since Sat 2024-09-28 10:12:41 CST; 1min 53s agoDocs: man:systemd-sysv-generator(8)Process: 96068 ExecStart=/etc/init.d/mysqld start (code=exited, status=0/SUCCESS)Tasks: 34 (limit: 2006)Memory: 362.1MCPU: 1.198sCGroup: /system.slice/mysqld.service├─96081 /bin/sh /www/server/mysql/bin/mysqld_safe --datadir=/www/server/data --pid-file=/www/server/data/hcss-ecs-c2b8.pid└─96706 /www/server/mysql/bin/mysqld --basedir=/www/server/mysql --datadir=/www/server/data --plugin-dir=/www/server/mysql/lib/plugin ->Sep 28 10:12:40 hcss-ecs-c2b8 systemd[1]: Starting LSB: start and stop MySQL...
Sep 28 10:12:41 hcss-ecs-c2b8 mysqld[96068]: Starting MySQL. *
Sep 28 10:12:41 hcss-ecs-c2b8 systemd[1]: Started LSB: start and stop MySQL.
lines 1-15/15 (END)

现在我们去吧运行中的mysqld服务停止掉,并查看其状态

root@hcss-ecs-c2b8:~# systemctl stop mysqld
root@hcss-ecs-c2b8:~# systemctl status mysqld
○ mysqld.service - LSB: start and stop MySQLLoaded: loaded (/etc/init.d/mysqld; generated)Active: inactive (dead) #这由原来的running 变成了 deadDocs: man:systemd-sysv-generator(8)

对于这种服务,我们希望他永远不要停止,就算是服务器重启,我们也希望他能在服务器重启后也能自己启动,这是我们就需要用enable和disable这个命令来关闭和开启服务的开机自启

root@hcss-ecs-c2b8:~# systemctl enable mysqld
# 这里提示的很清楚,我们这个mysqld不是本地服务所以需要使用重定向到systemd-sysv-install这里去开启
# 我们直接复制下面这个executing:后面的命令就好了,本地服务就能直接成功,disable命令也是这样的
mysqld.service is not a native service, redirecting to systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable mysqld
root@hcss-ecs-c2b8:~# /lib/systemd/systemd-sysv-install enable mysqld
root@hcss-ecs-c2b8:~# systemctl disable mysqld
mysqld.service is not a native service, redirecting to systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install disable mysqld
root@hcss-ecs-c2b8:~# /lib/systemd/systemd-sysv-install disable mysqld

这里我们重启一下无服务器,立马查看服务状态就能知道他是否开机自启

目前介绍了本地服务和第三方服务的状态和开机自启管理

这里我们来实现以下,如何让我们自己编写的脚本开机自启

首先我们编写一个测试脚本

[Unit]Description=Run a Custom Script at Startup[Service]ExecStart=/var/test/auto_start.sh
ExecStop=/var/test/auto_start.sh[Install]WantedBy=multi-user.target                        

在上面的配置文件中，为了演示起见，我将一些本测试脚本不需要但是比较重要的配置项也写了出来，其实如果不需要可以删除，但是[Unit]/[Service]/[Install]这三个标签需要保留。
我们来一个个简单介绍一下配置项：

Description：运行软件描述
Documentation：软件的文档
After：因为软件的启动通常依赖于其他软件，这里是指定在哪个服务被启动之后再启动，设置优先级
Wants：弱依赖于某个服务，目标服务的运行状态可以影响到本软件但不会决定本软件运行状态
Requires：强依赖某个服务，目标服务的状态可以决定本软件运行。
ExecStart：执行命令
ExecStop：停止执行命令
ExecReload：重启时的命令
Type：软件运行方式，默认为simple
WantedBy：这里相当于设置软件，选择运行在linux的哪个运行级别，只是在systemd中不在有运行级别概念，但是这里权当这么理解。 

如果有多项，用逗号作为分隔。