Systemctl和Unit file的常见用法与区别
Systemctl基础
1、首先检查你的系统中是否安装有systemd并确定当前安装的版本
[root@servergroup ~]# systemctl --version
systemd 239
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN2 -IDN +PCRE2 default-hierarchy=legacy
2、检查systemd和systemctl的二进制文件和库文件的安装位置
[root@servergroup ~]# whereis systemd
systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz
3、 分析启动时各个进程花费的时间
[root@servergroup ~]# systemd-analyze blame
22.243s dnf-makecache.service
6.324s NetworkManager-wait-online.service
4.585s tuned.service
1.881s php-fpm.service
1.611s vdo.service
1.563s sssd.service
1.536s firewalld.service
1.434s dracut-initqueue.service
1.399s lvm2-monitor.service
1.023s httpd.service
950ms polkit.service
785ms initrd-switch-root.service
549ms systemd-udev-trigger.service
498ms chronyd.service
426ms zabbix-agent.service
423ms lvm2-pvscan@8:2.service
341ms systemd-vconsole-setup.service
270ms systemd-user-sessions.service
246ms user@0.service
232ms sshd.service
206ms NetworkManager.service
203ms boot.mount
198ms kmod-static-nodes.service
193ms systemd-journald.service
183ms dev-mapper-cl/x2dswap.swap
182ms nis-domainname.service
177ms dev-mqueue.mount
172ms plymouth-quit-wait.servic4 分析启动时的关键链
[root@servergroup ~]# systemd-analyze critical-chain
The time after the unit is active or started is printed after the "@" character.
The time the unit takes to start is printed after the "+" character.
multi-user.target @11.968s
└─rsyslog.service @11.872s +96ms
└─network-online.target @11.861s
└─NetworkManager-wait-online.service @5.536s +6.324s
└─NetworkManager.service @5.325s +206ms
└─network-pre.target @5.322s
└─firewalld.service @3.784s +1.536s
└─polkit.service @2.829s +950ms
└─basic.target @2.724s
└─sockets.target @2.724s
└─dbus.socket @2.724s
└─sysinit.target @2.721s
└─systemd-update-utmp.service @2.711s +9ms
└─auditd.service @2.652s +57ms
└─systemd-tmpfiles-setup.service @2.609s +42ms
└─import-state.service @2.550s +56ms
└─local-fs.target @2.549s
└─boot.mount @2.346s +203ms
└─systemd-fsck@dev-disk-by/x2duuid-709a568a/x2d6be7/x2d4f96/x2da343/x2d2cad0cdbf3>
└─local-fs-pre.target @2.204s
└─lvm2-monitor.service @804ms +1.399s
└─dm-event.socket @752ms
└─-.mount
└─system.slice
└─-.slice
重要：Systemctl接受服务（.service），挂载点（.mount），套接口（.socket）和设备（.device）作为单元。
5. 列出所有可用单元
[root@servergroup ~]# systemctl list-unit-files
UNIT FILE STATE
proc-sys-fs-binfmt_misc.automount static
-.mount generated
boot.mount generated
dev-hugepages.mount static
dev-mqueue.mount static
home.mount generated
proc-sys-fs-binfmt_misc.mount static
sys-fs-fuse-connections.mount static
sys-kernel-config.mount static
sys-kernel-debug.mount static
tmp.mount static
systemd-ask-password-console.path static
systemd-ask-password-plymouth.path static
systemd-ask-password-wall.path static
session-1.scope transient
arp-ethers.service disabled
atd.service enabled
auditd.service enabled
autovt@.service enabled
blk-availability.service disabled
chrony-dn***v@.service static
chrony-wait.service disabled
chronyd.service enabled
…………………………6. 列出所有运行中单元
[root@servergroup ~]# systemctl list-units UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File> sys-devices-pci0000:00-0000:00:07.1-ata2-host1-target1:0:0-1:0:0:0-block-sr0.device loaded active plugged > sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda-sda1.device loaded active plugged > sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda-sda2.device loaded active plugged > sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda.device loaded active plugged VMw> sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:1-2:0:1:0-block-sdb-sdb1.device loaded active plugged > sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:1-2:0:1:0-block-sdb-sdb2.device loaded active plugged > sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:1-2:0:1:0-block-sdb.device loaded active plugged VMw> sys-devices-pci0000:00-0000:00:11.0-0000:02:00.0-net-ens32.device loaded active plugged 82545EM Gigabit > sys-devices-platform-serial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/ser> sys-devices-platform-serial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/ser> sys-devices-platform-serial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/ser> sys-devices-platform-serial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/ser> sys-devices-virtual-block-dm/x2d0.device loaded active plugged /sys/devices/virtual/bloc> sys-devices-virtual-block-dm/x2d1.device loaded active plugged /sys/devices/virtual/bloc> sys-devices-virtual-block-dm/x2d2.device loaded active plugged /sys/devices/virtual/bloc> sys-module-configfs.device loaded active plugged /sys/module/configfs sys-subsystem-net-devices-ens32.device loaded active plugged 82545EM Gigabit Ethernet- 1.
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7. 列出所有失败单元
[root@servergroup ~]# systemctl --failed
UNIT LOAD ACTIVE SUB DESCRIPTION
● kdump.service loaded failed failed Crash recovery kernel arming
LOAD = 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.
1 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
8. 检查某个单元（如 sshd.service）是否启用
[root@servergroup ~]# systemctl is-enabled sshd.service
enabled
使用Systemctl控制并管理服务
9. 列出所有服务（包括启用的和禁用的）
To show all installed unit files use 'systemctl list-unit-files'.
[root@servergroup ~]# systemctl list-unit-files --type=service
UNIT FILE STATE
arp-ethers.service disabled
atd.service enabled
auditd.service enabled
autovt@.service enabled
blk-availability.service disabled
chrony-dn***v@.service static
chrony-wait.service disabled
chronyd.service enabled
cockpit-motd.service static
cockpit.service static
console-getty.service disabled
container-getty@.service static
cpupower.service disabled
crond.service enabled
dbus-org.fedoraproject.FirewallD1.service enabled
dbus-org.freedesktop.hostname1.service static
dbus-org.freedesktop.locale1.service static
dbus-org.freedesktop.login1.service static
dbus-org.freedesktop.NetworkManager.service enabled
dbus-org.freedesktop.nm-dispatcher.service enabled
dbus-org.freedesktop.portable1.service static
dbus-org.freedesktop.timedate1.service enabled
dbus.service static
10. Linux中如何启动、重启、停止、重载服务以及检查服务（如chronyd.service）状态
[root@servergroup ~]# systemctl start chronyd.service
[root@servergroup ~]# systemctl restart chronyd.service
[root@servergroup ~]# systemctl stop chronyd.service
[root@servergroup ~]# systemctl status chronyd.service
● chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled; vendor preset: enabled)
Active: inactive (dead) since Sat 2021-07-17 22:49:25 CST; 5s ago
Docs: man:chronyd(8)
man:chrony.conf(5)
Process: 3379 ExecStartPost=/usr/libexec/chrony-helper update-daemon (code=exited, status=0/SUCCESS)
Process: 3375 ExecStart=/usr/sbin/chronyd $OPTIONS (code=exited, status=0/SUCCESS)
Main PID: 3377 (code=exited, status=0/SUCCESS)
Jul 17 22:49:19 servergroup systemd[1]: Stopped NTP client/server.
Jul 17 22:49:19 servergroup systemd[1]: Starting NTP client/server...
Jul 17 22:49:19 servergroup chronyd[3377]: chronyd version 3.3 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCF>
Jul 17 22:49:19 servergroup chronyd[3377]: Frequency 4.010 +/- 1.814 ppm read from /var/lib/chrony/drift
Jul 17 22:49:19 servergroup chronyd[3377]: Using right/UTC timezone to obtain leap second data
Jul 17 22:49:19 servergroup systemd[1]: Started NTP client/server.
Jul 17 22:49:25 servergroup systemd[1]: Stopping NTP client/server...
Jul 17 22:49:25 servergroup systemd[1]: Stopped NTP client/server.
注意：当我们使用systemctl的start，restart，stop和reload命令时，我们不会从终端获取到任何输出内容，只有status命令可以打印输出。
11. 如何激活服务并在启动时启用或禁用服务（即系统启动时自动启动服务）
[root@servergroup ~]# systemctl is-active chronyd.service
active
[root@servergroup ~]# systemctl disable chronyd.service
Removed /etc/systemd/system/multi-user.target.wants/chronyd.service.
[root@servergroup ~]# systemctl enable chronyd.service
Created symlink /etc/systemd/system/multi-user.target.wants/chronyd.service → /usr/lib/systemd/system/chronyd.service.
12. 如何屏蔽（让它不能启动）或显示服务（如 chronyd.service）
[root@servergroup ~]# systemctl mask chronyd.service
Created symlink /etc/systemd/system/chronyd.service → /dev/null.
[root@servergroup ~]# systemctl unmask chronyd.service
Removed /etc/systemd/system/chronyd.service.13. 使用systemctl命令杀死服务
[root@servergroup ~]# systemctl kill chronyd
[root@servergroup ~]# systemctl status chronyd.service
● chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled; vendor preset: enabled)
Active: inactive (dead) since Sat 2021-07-17 22:51:55 CST; 5s ago
Docs: man:chronyd(8)
man:chrony.conf(5)
Main PID: 3413 (code=exited, status=0/SUCCESS)
Jul 17 22:49:49 servergroup systemd[1]: Starting NTP client/server...
Jul 17 22:49:49 servergroup chronyd[3413]: chronyd version 3.3 starting (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP +SCF>
Jul 17 22:49:49 servergroup chronyd[3413]: Frequency 4.010 +/- 1.814 ppm read from /var/lib/chrony/drift
Jul 17 22:49:49 servergroup chronyd[3413]: Using right/UTC timezone to obtain leap second data
Jul 17 22:49:49 servergroup systemd[1]: Started NTP client/server.
Jul 17 22:49:58 servergroup chronyd[3413]: Selected source 69.89.207.199
Jul 17 22:49:58 servergroup chronyd[3413]: System clock TAI offset set to 37 seconds
使用Systemctl控制并管理挂载点
14. 列出所有系统挂载点
[root@servergroup ~]# systemctl list-unit-files --type=mount
UNIT FILE STATE
-.mount generated
boot.mount generated
dev-hugepages.mount static
dev-mqueue.mount static
home.mount generated
proc-sys-fs-binfmt_misc.mount static
sys-fs-fuse-connections.mount static
sys-kernel-config.mount static
sys-kernel-debug.mount static
tmp.mount static 15. 在启动时激活、启用或禁用挂载点（系统启动时自动挂载）
systemctl is-active tmp.mount
systemctl enable tmp.mount
systemctl disable tmp.mount使用Systemctl控制并管理套接口
16. 列出所有可用系统套接口
[root@servergroup ~]# systemctl list-unit-files --type=socket
UNIT FILE STATE
cockpit.socket disabled
dbus.socket static
dm-event.socket enabled
httpd.socket disabled
lvm2-lvmpolld.socket enabled
sshd.socket disabled
sssd-autofs.socket disabled
sssd-kcm.socket enabled
sssd-nss.socket disabled
sssd-pac.socket disabled
sssd-pam-priv.socket disabled
sssd-pam.socket disabled
sssd-ssh.socket disabled
sssd-sudo.socket disabled
syslog.socket static
systemd-coredump.socket static
systemd-initctl.socket static
systemd-journald-dev-log.socket static
systemd-journald.socket static
systemd-rfkill.socket static
systemd-udevd-control.socket static
systemd-udevd-kernel.socket static
17. 在Linux中启动、重启、停止、重载套接口并检查其状态
[root@servergroup ~]#systemctl start cups.socket
[root@servergroup ~]#systemctl restart cups.socket
[root@servergroup ~]#systemctl stop cups.socket
[root@servergroup ~]#systemctl reload cups.socket
[root@servergroup ~]#systemctl status cups.socket18. 在启动时激活套接口，并启用或禁用它（系统启动时自启动）
[root@servergroup ~]#systemctl is-active cockpit.socket
[root@servergroup ~]#systemctl enable cockpit.socket
[root@servergroup ~]#systemctl disable cockpit.socket服务的CPU利用率（分配额）
19. 获取当前某个服务的CPU分配额（如chronyd）
[root@servergroup ~]# systemctl show -p CPUShares chronyd.service
CPUShares=[not set]
注意：各个服务的默认CPU分配份额=1024，你可以增加/减少某个进程的CPU分配份额。
20. 将某个服务（chronyd.service）的CPU分配份额限制为2000 CPUShares
[root@servergroup ~]# systemctl set-property chronyd.service CPUShares=2000
[root@servergroup ~]#
[root@servergroup ~]# systemctl show -p CPUShares chronyd.service
CPUShares=2000
21. 检查某个服务的所有配置细节
[root@servergroup ~]# systemctl show chrondy
Restart=no
NotifyAccess=none
RestartUSec=100ms
TimeoutStartUSec=1min 30s
TimeoutStopUSec=1min 30s
RuntimeMaxUSec=infinity
WatchdogUSec=0
WatchdogTimestampMonotonic=0
PermissionsStartOnly=no
RootDirectoryStartOnly=no
RemainAfterExit=no
GuessMainPID=yes
MainPID=0
ControlPID=0
FileDescriptorStoreMax=0
NFileDescriptorStore=0
StatusErrno=0
Result=success
UID=[not set]
GID=[not set]
NRestarts=0
ExecMainStartTimestampMonotonic=0
ExecMainExitTimestampMonotonic=0
ExecMainPID=0
22. 分析某个服务（chronyd）的关键链
[root@servergroup ~]# systemd-analyze critical-chain chronyd.service
The time after the unit is active or started is printed after the "@" character.
The time the unit takes to start is printed after the "+" character.
chronyd.service +32ms
└─basic.target @2.724s
└─sockets.target @2.724s
└─dbus.socket @2.724s
└─sysinit.target @2.721s
└─systemd-update-utmp.service @2.711s +9ms
└─auditd.service @2.652s +57ms
└─systemd-tmpfiles-setup.service @2.609s +42ms
└─import-state.service @2.550s +56ms
└─local-fs.target @2.549s
└─boot.mount @2.346s +203ms
└─systemd-fsck@dev-disk-by/x2duuid-709a568a/x2d6be7/x2d4f96/x2da343/x2d2cad0cdbf399.service @2.>
└─local-fs-pre.target @2.204s
└─lvm2-monitor.service @804ms +1.399s
└─dm-event.socket @752ms
└─-.mount
└─system.slice
└─-.slice
23. 获取某个服务（chronyd）的依赖性列表
[root@servergroup ~]# systemctl list-dependencies chronyd.service
chronyd.service
● ├─-.mount
● ├─system.slice
● └─sysinit.target
● ├─dev-hugepages.mount
● ├─dev-mqueue.mount
● ├─dracut-shutdown.service
● ├─import-state.service
● ├─kmod-static-nodes.service
● ├─ldconfig.service
● ├─loadmodules.service
● ├─lvm2-lvmpolld.socket
● ├─lvm2-monitor.service
● ├─nis-domainname.service
● ├─plymouth-read-write.service
● ├─plymouth-start.service
● ├─proc-sys-fs-binfmt_misc.automount
● ├─rngd.service
24. 按等级列出控制组
root@servergroup ~]# systemd-cgls
Control group /:
-.slice
├─user.slice
│ └─user-0.slice
│ ├─session-1.scope
│ │ ├─1696 sshd: root [priv]
│ │ ├─1722 sshd: root@pts/0,pts/1
│ │ ├─1723 -bash
│ │ ├─1744 man systemctl
│ │ ├─1754 less
│ │ ├─2184 -bash
│ │ ├─4484 systemd-cgls
│ │ └─4485 systemd-cgls
│ └─user@0.service
│ └─init.scope
│ ├─1706 /usr/lib/systemd/systemd --user
│ └─1713 (sd-pam)
├─init.scope
│ └─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 17
└─system.slice
控制系统运行等级
25. 启动系统救援模式
[root@servergroup ~]#systemctl rescue26. 进入紧急模式
[root@servergroup ~]# systemctl emergency27 列出当前使用的运行等级
[root@servergroup ~]# systemctl get-default
multi-user.target
28. 启动运行等级3，即多用户模式（命令行）
[root@servergroup ~]# systemctl isolate multi-user.target 29. 设置多用户模式或图形模式为默认运行等级
[root@servergroup ~]# systemctl set-default multi-user.target 30. 重启、停止、挂起、休眠系统或使系统进入混合睡眠
[root@servergroup ~]# systemctl reboot
[root@servergroup ~]# systemctl halt
[root@servergroup ~]# systemctl suspend
[root@servergroup ~]# systemctl hibernate
[root@servergroup ~]# systemctl hybrid-sleepUnit file的介绍
Service 段
主要字段如下：
【启动类型】
Type： 定义启动时的进程行为。它有以下几种值。
Type=simple： 默认值，ExecStart字段启动的进程为主进程服务进程不会 fork，如果该服务要启动其他服务，不要使用此类型启动，除非该服务是 socket 激活型
Type=forking： ExecStart字段将以fork()方式从父进程创建子进程启动，创建后父进程会立即退出，子进程成为主进程。通常需要指定PIDFile字段，以便 Systemd 能够跟踪服务的主进程对于常规的守护进程（daemon），除非你确定此启动方式无法满足需求，使用此类型启动即可
Type=oneshot： 只执行一次，Systemd 会等当前服务退出，再继续往下执行适用于只执行一项任务、随后立即退出的服务通常需要指定RemainAfterExit=yes字段，使得 Systemd 在服务进程退出之后仍然认为服务处于激活状态
Type=dbus： 当前服务通过 D-Bus 信号启动。当指定的 BusName 出现在 DBus 系统总线上时，Systemd认为服务就绪
Type=notify： 当前服务启动完毕会发出通知信号，通知 Systemd，然后 Systemd 再启动其他服务
Type=idle： Systemd 会等到其他任务都执行完，才会启动该服务。一种使用场合是：让该服务的输出，不与其他服务的输出相混合
【启动行为】
ExecStart： 启动当前服务的命令
ExecStart=/bin/echo execstart1
ExecStart=
ExecStart=/bin/echo execstart2
顺序执行设定的命令，把字段置空，表示清除之前的值
ExecStartPre： 启动当前服务之前执行的命令
ExecStartPost： 启动当前服务之后执行的命令
ExecReload： 重启当前服务时执行的命令
ExecStop： 停止当前服务时执行的命令
ExecStopPost： 停止当前服务之后执行的命令
RemainAfterExit：当前服务的所有进程都退出的时候，Systemd 仍认为该服务是激活状态
参考文献：
©著作权归作者所有：来自51CTO博客作者Happy_Future的原创作品
Systemctl和Unit file
https://blog.51cto.com/u_15131458/3119541
