Systemctl是一个systemd工具，主要负责控制systemd系统和服务管理器。
Systemd是一个系统管理守护进程、工具和库的集合，用于取代System V初始进程。Systemd的功能是用于集中管理和配置类UNIX系统。
在Linux生态系统中，Systemd被部署到了大多数的标准Linux发行版中，只有为数不多的几个发行版尚未部署。Systemd通常是所有其它守护进程的父进程，但并非总是如此。
使用Systemctl管理Linux服务
本文旨在阐明在运行systemd的系统上“如何控制系统和服务”。
Systemd初体验和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
# systemd --version@H_403_25@systemd215@H_403_25@+PAM+AUDIT+SELINUX+IMA+SYSVINIT+LIBCRYPTSETUP+GCRYPT+ACL+XZ-SECCOMP-APPARMOR@H_403_25@
上例中很清楚地表明，我们安装了215版本的systemd。
2. 检查systemd和systemctl的二进制文件和库文件的安装位置
# whereis systemd@H_403_25@systemd:/usr/lib/systemd/etc/systemd/usr/share/systemd/usr/share/man/man1/systemd.1.gz@H_403_25@# whereis systemctl@H_403_25@systemctl:/usr/bin/systemctl/usr/share/man/man1/systemctl.1.gz@H_403_25@
3. 检查systemd是否运行
# ps -eaf | grep [s]ystemd@H_403_25@root10016:27?00:00:00/usr/lib/systemd/systemd--switched-root--system--deserialize23@H_403_25@root4441016:27?00:00:00/usr/lib/systemd/systemd-journald@H_403_25@root4691016:27?00:00:00/usr/lib/systemd/systemd-udevd@H_403_25@root5551016:27?00:00:00/usr/lib/systemd/systemd-logind@H_403_25@dbus5561016:27?00:00:00/bin/dbus-daemon--system--address=systemd:--nofork--nopidfile--systemd-activation@H_403_25@
注意：systemd是作为父进程（PID=1）运行的。在上面带（-e）参数的ps命令输出中，选择所有进程，（-a）选择除会话前导外的所有进程，并使用（-f）参数输出完整格式列表（即 -eaf）。
也请注意上例中后随的方括号和例子中剩余部分。方括号表达式是grep的字符类表达式的一部分。
4. 分析systemd启动进程
# systemd-analyze@H_403_25@Startupfinishedin487ms(kernel)+2.776s(initrd)+20.229s(userspace)=23.493s@H_403_25@
5. 分析启动时各个进程花费的时间
# systemd-analyze blame@H_403_25@8.565smariadb.service@H_403_25@7.991swebmin.service@H_403_25@6.095spostfix.service@H_403_25@4.311shttpd.service@H_403_25@3.926sfirewalld.service@H_403_25@3.780skdump.service@H_403_25@3.238stuned.service@H_403_25@1.712snetwork.service@H_403_25@1.394slvm2-monitor.service@H_403_25@1.126ssystemd-logind.service@H_403_25@....@H_403_25@
6. 分析启动时的关键链
# systemd-analyze critical-chain@H_403_25@Thetime after the unitisactiveorstartedisprinted after the"@"character.@H_403_25@Thetime the unit takes to startisprinted after the"+"character.@H_403_25@multi-user.target@20.222s@H_403_25@└─mariadb.service@11.657s+8.565s@H_403_25@└─network.target@11.168s@H_403_25@└─network.service@9.456s+1.712s@H_403_25@└─NetworkManager.service@8.858s+596ms@H_403_25@└─firewalld.service@4.931s+3.926s@H_403_25@└─basic.target@4.916s@H_403_25@└─sockets.target@4.916s@H_403_25@└─dbus.socket@4.916s@H_403_25@└─sysinit.target@4.905s@H_403_25@└─systemd-update-utmp.service@4.864s+39ms@H_403_25@└─auditd.service@4.563s+301ms@H_403_25@└─systemd-tmpfiles-setup.service@4.485s+69ms@H_403_25@└─rhel-import-state.service@4.342s+142ms@H_403_25@└─local-fs.target@4.324s@H_403_25@└─boot.mount@4.286s+31ms@H_403_25@└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d19608096@H_403_25@└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device@4@H_403_25@
重要：Systemctl接受服务（.service），挂载点（.mount），套接口（.socket）和设备（.device）作为单元。
7. 列出所有可用单元
# systemctl list-unit-files@H_403_25@UNIT FILE STATE@H_403_25@proc-sys-fs-binfmt_misc.automountstatic@H_403_25@dev-hugepages.mountstatic@H_403_25@dev-mqueue.mountstatic@H_403_25@proc-sys-fs-binfmt_misc.mountstatic@H_403_25@sys-fs-fuse-connections.mountstatic@H_403_25@sys-kernel-config.mountstatic@H_403_25@sys-kernel-debug.mountstatic@H_403_25@tmp.mount disabled@H_403_25@brandbot.path disabled@H_403_25@.....@H_403_25@
8. 列出所有运行中单元
# systemctl list-units@H_403_25@UNIT LOAD ACTIVE SUB DESCRIPTION@H_403_25@proc-sys-fs-binfmt_misc.automount loaded active waitingArbitraryExecutableFileFormatsFileSyste@H_403_25@sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged VBox_CD-ROM@H_403_25@sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged PRO/1000MTDesktopAdapter@H_403_25@sys-devices-pc...00:05.0-sound-card0.device loaded active plugged82801AAAC'97 Audio Controller@H_403_25@sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged VBox_HARDDISK@H_403_25@sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8@H_403_25@sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged VBox_HARDDISK@H_403_25@sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0@H_403_25@sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1@H_403_25@sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2@H_403_25@sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3@H_403_25@sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0@H_403_25@sys-devices-virtual-block-dm\x2d1.device loaded active plugged /sys/devices/virtual/block/dm-1@H_403_25@sys-module-configfs.device loaded active plugged /sys/module/configfs@H_403_25@...@H_403_25@
9. 列出所有失败单元
# systemctl --Failed@H_403_25@UNIT LOAD ACTIVE SUB DESCRIPTION@H_403_25@kdump.service loaded Failed FailedCrashrecovery kernel arming@H_403_25@LOAD=Reflectswhether the unit definition was properly loaded.@H_403_25@ACTIVE=Thehigh-level unit activation state,i.e.generalization of SUB.@H_403_25@SUB=Thelow-level unit activation state,values depend on unit type.@H_403_25@1loaded units listed.Pass--all to see loaded but inactive units,too.@H_403_25@Toshow all installed unit filesuse'systemctl list-unit-files'.@H_403_25@
10. 检查某个单元（如 cron.service）是否启用
11. 检查某个单元或服务是否运行
# systemctl status firewalld.service@H_403_25@firewalld.service-firewalld-dynamicfirewall daemon@H_403_25@Loaded:loaded(/usr/lib/systemd/system/firewalld.service;enabled)@H_403_25@Active:active(running)sinceTue2015-04-2816:27:55IST;34minago@H_403_25@MainPID:549(firewalld)@H_403_25@CGroup:/system.slice/firewalld.service@H_403_25@└─549/usr/bin/python-Es/usr/sbin/firewalld--nofork--nopid@H_403_25@Apr2816:27:51tecmint systemd[1]:Startingfirewalld-dynamicfirewall daemon...@H_403_25@Apr2816:27:55tecmint systemd[1]:Startedfirewalld-dynamicfirewall daemon.@H_403_25@
使用Systemctl控制并管理服务
12. 列出所有服务（包括启用的和禁用的）
# systemctl list-unit-files --type=service@H_403_25@UNIT FILE STATE@H_403_25@arp-ethers.service disabled@H_403_25@auditd.service enabled@H_403_25@autovt@.service disabled@H_403_25@blk-availability.service disabled@H_403_25@brandbot.servicestatic@H_403_25@collectd.service disabled@H_403_25@console-getty.service disabled@H_403_25@console-shell.service disabled@H_403_25@cpupower.service disabled@H_403_25@crond.service enabled@H_403_25@dbus-org.Fedoraproject.FirewallD1.service enabled@H_403_25@....@H_403_25@
13. Linux中如何启动、重启、停止、重载服务以及检查服务（如 httpd.service）状态
# systemctl start httpd.service@H_403_25@# systemctl restart httpd.service@H_403_25@# systemctl stop httpd.service@H_403_25@# systemctl reload httpd.service@H_403_25@# systemctl status httpd.service@H_403_25@httpd.service-TheApacheHTTPServer@H_403_25@Loaded:loaded(/usr/lib/systemd/system/httpd.service;enabled)@H_403_25@Active:active(running)sinceTue2015-04-2817:21:30IST;6sago@H_403_25@Process:2876ExecStop=/bin/kill-WINCH ${MAINPID}(code=exited,status=0/SUCCESS)@H_403_25@MainPID:2881(httpd)@H_403_25@Status:"Processing requests..."@H_403_25@CGroup:/system.slice/httpd.service@H_403_25@├─2881/usr/sbin/httpd-DFOREGROUND@H_403_25@├─2884/usr/sbin/httpd-DFOREGROUND@H_403_25@├─2885/usr/sbin/httpd-DFOREGROUND@H_403_25@├─2886/usr/sbin/httpd-DFOREGROUND@H_403_25@├─2887/usr/sbin/httpd-DFOREGROUND@H_403_25@└─2888/usr/sbin/httpd-DFOREGROUND@H_403_25@Apr2817:21:30tecmint systemd[1]:StartingTheApacheHTTPServer...@H_403_25@Apr2817:21:30tecmint httpd[2881]:AH00558:httpd:Couldnotreliably determine the server's fully q...ssage@H_403_25@Apr 28 17:21:30 tecmint systemd[1]: Started The Apache HTTP Server.@H_403_25@Hint: Some lines were ellipsized,use -l to show in full.@H_403_25@
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。
14. 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）
# systemctl is-active httpd.service@H_403_25@# systemctl enable httpd.service@H_403_25@# systemctl disable httpd.service@H_403_25@
15. 如何屏蔽（让它不能启动）或显示服务（如 httpd.service）
# systemctl mask httpd.service@H_403_25@ln-s'/dev/null''/etc/systemd/system/httpd.service'@H_403_25@# systemctl unmask httpd.service@H_403_25@rm'/etc/systemd/system/httpd.service'@H_403_25@
16. 使用systemctl命令杀死服务
# systemctl kill httpd@H_403_25@# systemctl status httpd@H_403_25@httpd.service-TheApacheHTTPServer@H_403_25@Loaded:loaded(/usr/lib/systemd/system/httpd.service;enabled)@H_403_25@Active:Failed(Result:exit-code)sinceTue2015-04-2818:01:42IST;28minago@H_403_25@MainPID:2881(code=exited,status=0/SUCCESS)@H_403_25@Status:"Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"@H_403_25@Apr2817:37:29tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:29tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:39tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:39tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:49tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:49tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:59tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2817:37:59tecmint systemd[1]:httpd.service:Gotnotification messagefromPID2881,but recepti...bled.@H_403_25@Apr2818:01:42tecmint systemd[1]:httpd.service:control process exited,code=exited status=226@H_403_25@Apr2818:01:42tecmint systemd[1]:Unithttpd.service entered Failed state.@H_403_25@Hint:Somelines were ellipsized,use-l to showinfull.@H_403_25@
使用Systemctl控制并管理挂载点
17. 列出所有系统挂载点
# systemctl list-unit-files --type=mount@H_403_25@UNIT FILE STATE@H_403_25@dev-hugepages.mountstatic@H_403_25@dev-mqueue.mountstatic@H_403_25@proc-sys-fs-binfmt_misc.mountstatic@H_403_25@sys-fs-fuse-connections.mountstatic@H_403_25@sys-kernel-config.mountstatic@H_403_25@sys-kernel-debug.mountstatic@H_403_25@tmp.mount disabled@H_403_25@
18. 挂载、卸载、重新挂载、重载系统挂载点并检查系统中挂载点状态
# systemctl start tmp.mount@H_403_25@# systemctl stop tmp.mount@H_403_25@# systemctl restart tmp.mount@H_403_25@# systemctl reload tmp.mount@H_403_25@# systemctl status tmp.mount@H_403_25@tmp.mount-TemporaryDirectory@H_403_25@Loaded:loaded(/usr/lib/systemd/system/tmp.mount;disabled)@H_403_25@Active:active(mounted)sinceTue2015-04-2817:46:06IST;2min48sago@H_403_25@Where:/tmp@H_403_25@What:tmpfs@H_403_25@Docs:man:hier(7)@H_403_25@http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems@H_403_25@Process:3908ExecMount=/bin/mount tmpfs/tmp-t tmpfs-o mode=1777,strictatime(code=exited,status=0/SUCCESS)@H_403_25@Apr2817:46:06tecmint systemd[1]:MountingTemporaryDirectory...@H_403_25@Apr2817:46:06tecmint systemd[1]:tmp.mount:Directory/tmp to mount overisnotempty,mounting anyway.@H_403_25@Apr2817:46:06tecmint systemd[1]:MountedTemporaryDirectory.@H_403_25@
19. 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@H_403_25@# systemctl enable tmp.mount@H_403_25@# systemctl disable tmp.mount@H_403_25@
20. 在Linux中屏蔽（让它不能启用）或可见挂载点
# systemctl mask tmp.mount@H_403_25@ln-s'/dev/null''/etc/systemd/system/tmp.mount'@H_403_25@# systemctl unmask tmp.mount@H_403_25@rm'/etc/systemd/system/tmp.mount'@H_403_25@
使用Systemctl控制并管理套接口
21. 列出所有可用系统套接口
# systemctl list-unit-files --type=socket@H_403_25@UNIT FILE STATE@H_403_25@dbus.socketstatic@H_403_25@dm-event.socket enabled@H_403_25@lvm2-lvMetad.socket enabled@H_403_25@rsyncd.socket disabled@H_403_25@sshd.socket disabled@H_403_25@syslog.socketstatic@H_403_25@systemd-initctl.socketstatic@H_403_25@systemd-journald.socketstatic@H_403_25@systemd-shutdownd.socketstatic@H_403_25@systemd-udevd-control.socketstatic@H_403_25@systemd-udevd-kernel.socketstatic@H_403_25@11unit files listed.@H_403_25@
22. 在Linux中启动、重启、停止、重载套接口并检查其状态
# systemctl start cups.socket@H_403_25@# systemctl restart cups.socket@H_403_25@# systemctl stop cups.socket@H_403_25@# systemctl reload cups.socket@H_403_25@# systemctl status cups.socket@H_403_25@cups.socket-CUPSPrintingServiceSockets@H_403_25@Loaded:loaded(/usr/lib/systemd/system/cups.socket;enabled)@H_403_25@Active:active(listening)sinceTue2015-04-2818:10:59IST;8sago@H_403_25@Listen:/var/run/cups/cups.sock(Stream)@H_403_25@Apr2818:10:59tecmint systemd[1]:StartingCUPSPrintingServiceSockets.@H_403_25@Apr2818:10:59tecmint systemd[1]:Listeningon CUPSPrintingServiceSockets.@H_403_25@
23. 在启动时激活套接口，并启用或禁用它（系统启动时自启动）
# systemctl is-active cups.socket@H_403_25@# systemctl enable cups.socket@H_403_25@# systemctl disable cups.socket@H_403_25@
24. 屏蔽（使它不能启动）或显示套接口
# systemctl mask cups.socket@H_403_25@ln-s'/dev/null''/etc/systemd/system/cups.socket'@H_403_25@# systemctl unmask cups.socket@H_403_25@rm'/etc/systemd/system/cups.socket'@H_403_25@
服务的cpu利用率（分配额）
25. 获取当前某个服务的cpu分配额（如httpd）
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。
26. 将某个服务（httpd.service）的cpu分配份额限制为2000 cpuShares/
# systemctl set-property httpd.service cpuShares=2000@H_403_25@# systemctl show -p cpuShares httpd.service@H_403_25@cpuShares=2000@H_403_25@
注意：当你为某个服务设置cpuShares，会自动创建一个以服务名命名的目录（如 httpd.service），里面包含了一个名为90-cpuShares.conf的文件，该文件含有cpuShare限制信息，你可以通过以下方式查看该文件：
# vi /etc/systemd/system/httpd.service.d/90-cpuShares.conf@H_403_25@[Service]@H_403_25@cpuShares=2000@H_403_25@
27. 检查某个服务的所有配置细节
# systemctl show httpd@H_403_25@Id=httpd.service@H_403_25@Names=httpd.service@H_403_25@Requires=basic.target@H_403_25@Wants=system.slice@H_403_25@WantedBy=multi-user.target@H_403_25@Conflicts=shutdown.target@H_403_25@Before=shutdown.target multi-user.target@H_403_25@After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice@H_403_25@Description=TheApacheHTTPServer@H_403_25@LoadState=loaded@H_403_25@ActiveState=active@H_403_25@SubState=running@H_403_25@FragmentPath=/usr/lib/systemd/system/httpd.service@H_403_25@....@H_403_25@
28. 分析某个服务（httpd）的关键链
# systemd-analyze critical-chain httpd.service@H_403_25@Thetime after the unitisactiveorstartedisprinted after the"@"character.@H_403_25@Thetime the unit takes to startisprinted after the"+"character.@H_403_25@httpd.service+142ms@H_403_25@└─network.target@11.168s@H_403_25@└─network.service@9.456s+1.712s@H_403_25@└─NetworkManager.service@8.858s+596ms@H_403_25@└─firewalld.service@4.931s+3.926s@H_403_25@└─basic.target@4.916s@H_403_25@└─sockets.target@4.916s@H_403_25@└─dbus.socket@4.916s@H_403_25@└─sysinit.target@4.905s@H_403_25@└─systemd-update-utmp.service@4.864s+39ms@H_403_25@└─auditd.service@4.563s+301ms@H_403_25@└─systemd-tmpfiles-setup.service@4.485s+69ms@H_403_25@└─rhel-import-state.service@4.342s+142ms@H_403_25@└─local-fs.target@4.324s@H_403_25@└─boot.mount@4.286s+31ms@H_403_25@└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.service@4.092s+149ms@H_403_25@└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device@4.092s@H_403_25@
29. 获取某个服务（httpd）的依赖性列表
# systemctl list-dependencies httpd.service@H_403_25@httpd.service@H_403_25@├─system.slice@H_403_25@└─basic.target@H_403_25@├─firewalld.service@H_403_25@├─microcode.service@H_403_25@├─rhel-autorelabel-mark.service@H_403_25@├─rhel-autorelabel.service@H_403_25@├─rhel-configure.service@H_403_25@├─rhel-dmesg.service@H_403_25@├─rhel-loadmodules.service@H_403_25@├─paths.target@H_403_25@├─slices.target@H_403_25@│├─-.slice@H_403_25@│└─system.slice@H_403_25@├─sockets.target@H_403_25@│├─dbus.socket@H_403_25@....@H_403_25@
30. 按等级列出控制组
# systemd-cgls@H_403_25@├─1/usr/lib/systemd/systemd--switched-root--system--deserialize23@H_403_25@├─user.slice@H_403_25@│└─user-0.slice@H_403_25@│└─session-1.scope@H_403_25@│├─2498sshd:root@pts/0@H_403_25@│├─2500-bash@H_403_25@│├─4521systemd-cgls@H_403_25@│└─4522systemd-cgls@H_403_25@└─system.slice@H_403_25@├─httpd.service@H_403_25@│├─4440/usr/sbin/httpd-DFOREGROUND@H_403_25@│├─4442/usr/sbin/httpd-DFOREGROUND@H_403_25@│├─4443/usr/sbin/httpd-DFOREGROUND@H_403_25@│├─4444/usr/sbin/httpd-DFOREGROUND@H_403_25@│├─4445/usr/sbin/httpd-DFOREGROUND@H_403_25@│└─4446/usr/sbin/httpd-DFOREGROUND@H_403_25@├─polkit.service@H_403_25@│└─721/usr/lib/polkit-1/polkitd--no-debug@H_403_25@....@H_403_25@
31. 按cpu、内存、输入和输出列出控制组
# systemd-cgtop@H_403_25@PathTasks%cpuMemoryInput/sOutput/s@H_403_25@/831.0437.8M--@H_403_25@/system.slice-0.1---@H_403_25@/system.slice/mariadb.service20.1---@H_403_25@/system.slice/tuned.service10.0---@H_403_25@/system.slice/httpd.service60.0---@H_403_25@/system.slice/NetworkManager.service1----@H_403_25@/system.slice/atop.service1----@H_403_25@/system.slice/atopacct.service1----@H_403_25@/system.slice/auditd.service1----@H_403_25@/system.slice/crond.service1----@H_403_25@/system.slice/dbus.service1----@H_403_25@/system.slice/firewalld.service1----@H_403_25@/system.slice/lvm2-lvMetad.service1----@H_403_25@/system.slice/polkit.service1----@H_403_25@/system.slice/postfix.service3----@H_403_25@/system.slice/rsyslog.service1----@H_403_25@/system.slice/system-getty.slice/getty@tty1.service1----@H_403_25@/system.slice/systemd-journald.service1----@H_403_25@/system.slice/systemd-logind.service1----@H_403_25@/system.slice/systemd-udevd.service1----@H_403_25@/system.slice/webmin.service1----@H_403_25@/user.slice/user-0.slice/session-1.scope3----@H_403_25@
控制系统运行等级
32. 启动系统救援模式
# systemctl rescue@H_403_25@Broadcastmessagefromroot@tecmint on pts/0(Wed2015-04-2911:31:18IST):@H_403_25@Thesystemisgoing down torescuemode NOW!@H_403_25@
33. 进入紧急模式
# systemctl emergency@H_403_25@Welcometo emergency mode!Afterloggingin,type"journalctl -xb"to view@H_403_25@system logs,"systemctl reboot"to reboot,"systemctl default"totryagain@H_403_25@to bootintodefaultmode.@H_403_25@
34. 列出当前使用的运行等级
35. 启动运行等级5，即图形模式
# systemctl isolate runlevel5.target@H_403_25@或@H_403_25@# systemctl isolate graphical.target@H_403_25@
36. 启动运行等级3，即多用户模式（命令行）
# systemctl isolate runlevel3.target@H_403_25@或@H_403_25@# systemctl isolate multiuser.target@H_403_25@
36. 设置多用户模式或图形模式为默认运行等级
# systemctl set-default runlevel3.target@H_403_25@# systemctl set-default runlevel5.target@H_403_25@
37. 重启、停止、挂起、休眠系统或使系统进入混合睡眠
# systemctl reboot@H_403_25@# systemctl halt@H_403_25@# systemctl suspend@H_403_25@# systemctl hibernate@H_403_25@# systemctl hybrid-sleep@H_403_25@
对于不知运行等级为何物的人，说明如下。
- Runlevel 0 : 关闭系统
- Runlevel 1 : 救援？维护模式
- Runlevel 3 : 多用户，无图形系统
- Runlevel 4 : 多用户，无图形系统
- Runlevel 5 : 多用户，图形化系统
- Runlevel 6 : 关闭并重启机器
