在本教程中,我们将向您介绍在运行systemd的linux系统上如何使用systemctl命令工具有效的控制系统和服务.
Systemctl 介绍
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。
开始Systemd和Systemctl 基础工具之旅
01、首先检查系统上是否安装了systemd以及当前安装的Systemd的版本是什么？
# systemd --versionsystemd 215+PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR从上面的例子可以清楚地看出，我们已经安装了systemd 215版本。
02.检查systemd和systemctl的二进制文件和库的安装位置。
# whereis systemd systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz# whereis systemctlsystemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
03.检查systemd是否正在运行。
# ps -eaf | grep [s]ystemdroot 1 0 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd --switched-root --system --deserialize 23root 444 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-journaldroot 469 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-udevdroot 555 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-loginddbus 556 1 0 16:27 ? 00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation注意：systemd作为父守护进程运行（PID = 1）。 在上面的命令ps中使用（-e）选择所有进程，（ – a）选择除会话前导之外的所有进程和（-f）选择完整格式列表（即-eaf）。
另请注意上面示例中的方括号以及其他示例。 Square Bracket表达式是grep的字符类模式匹配的一部分。
04.分析systemd启动过程
# systemd-analyzeStartup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s
05.分析每个进程在引导时花费的时间
# systemd-analyze blame8.565s mariadb.service7.991s webmin.service6.095s postfix.service4.311s httpd.service3.926s firewalld.service3.780s kdump.service3.238s tuned.service1.712s network.service1.394s lvm2-monitor.service1.126s systemd-logind.service....
06.分析启动时的关键链
# systemd-analyze critical-chainThe 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 @20.222s└─mariadb.service @11.657s +8.565s└─network.target @11.168s└─network.service @9.456s +1.712s└─NetworkManager.service @8.858s +596ms└─firewalld.service @4.931s +3.926s└─basic.target @4.916s└─sockets.target @4.916s└─dbus.socket @4.916s└─sysinit.target @4.905s└─systemd-update-utmp.service @4.864s +39ms└─auditd.service @4.563s +301ms└─systemd-tmpfiles-setup.service @4.485s +69ms└─rhel-import-state.service @4.342s +142ms└─local-fs.target @4.324s└─boot.mount @4.286s +31ms└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d19608096└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4重要：Systemctl接受服务（.service），挂载点（.mount），套接字（.socket）和设备（.device）作为单位。
07、列出所有可用的单位
# systemctl list-unit-files
UNIT FILE STATE proc-sys-fs-binfmt_misc.automount static dev-hugepages.mount static dev-mqueue.mount static 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 disabledbrandbot.path disabled.....
08、列出所有运行单元
# systemctl list-unitsUNIT LOAD ACTIVE SUB DESCRIPTIONproc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File Systesys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROMsys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged PRO/1000 MT Desktop Adaptersys-devices-pc...00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controllersys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISKsys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISKsys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0sys-devices-virtual-block-dm\x2d1.device loaded active plugged /sys/devices/virtual/block/dm-1sys-module-configfs.device loaded active plugged /sys/module/configfs...
09、列出所有失败的单元
# systemctl --failed UNIT LOAD ACTIVE SUB DESCRIPTIONkdump.service loaded failed failed Crash recovery kernel armingLOAD = 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'.
10、检查单元(cron.service)是否启用?
# systemctl is-enabled crond.serviceenabled
11.检查单元或服务是否正在运行？
systemctl status firewalld.servicefirewalld.service - firewalld - dynamic firewall daemonLoaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)Active: active (running) since Tue 2018-04-28 16:27:55 IST; 34min agoMain PID: 549 (firewalld)CGroup: /system.slice/firewalld.service└─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopidApr 28 16:27:51 tecmint systemd[1]: Starting firewalld - dynamic firewall daemon...Apr 28 16:27:55 tecmint systemd[1]: Started firewalld - dynamic firewall daemon.
使用Systemctl控制和管理服务
12.列出所有服务（包括启用和禁用）
# systemctl list-unit-files --type=serviceUNIT FILE STATE arp-ethers.service disabledauditd.service enabled autovt@.service disabledblk-availability.service disabledbrandbot.service static collectd.service disabledconsole-getty.service disabledconsole-shell.service disabledcpupower.service disabledcrond.service enabled dbus-org.fedoraproject.FirewallD1.service enabled ....
13.如何在Linux中启动，重新启动，停止，重新加载和检查服务（httpd.service）的状态
# systemctl start httpd.service# systemctl restart httpd.service# systemctl stop httpd.service# systemctl reload httpd.service# systemctl status httpd.servicehttpd.service - The Apache HTTP ServerLoaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)Active: active (running) since Tue 2018-04-28 17:21:30 IST; 6s agoProcess: 2876 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS)Main PID: 2881 (httpd)Status: "Processing requests..."CGroup: /system.slice/httpd.service├─2881 /usr/sbin/httpd -DFOREGROUND├─2884 /usr/sbin/httpd -DFOREGROUND├─2885 /usr/sbin/httpd -DFOREGROUND├─2886 /usr/sbin/httpd -DFOREGROUND├─2887 /usr/sbin/httpd -DFOREGROUND└─2888 /usr/sbin/httpd -DFOREGROUNDApr 28 17:21:30 tecmint systemd[1]: Starting The Apache HTTP Server...Apr 28 17:21:30 tecmint httpd[2881]: AH00558: httpd: Could not reliably determine the server's fully q...ssageApr 28 17:21:30 tecmint systemd[1]: Started The Apache HTTP Server.Hint: Some lines were ellipsized, use -l to show in full.注意：当我们使用systemctl等启动，重启，停止和重载等命令时，我们将不会在终端上获得任何输出，只有status命令会打印输出。
14.如何在引导时激活服务并启用或禁用服务（系统引导时自动启动服务）
# systemctl is-active httpd.service# systemctl enable httpd.service# systemctl disable httpd.service
15.如何屏蔽（使其无法启动）或取消屏蔽服务（httpd.service)
ln -s '/dev/null' '/etc/systemd/system/httpd.service'# systemctl unmask httpd.servicerm '/etc/systemd/system/httpd.service'
16.如何使用systemctl命令终止服务
# systemctl kill httpd# systemctl status httpdhttpd.service - The Apache HTTP ServerLoaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)Active: failed (Result: exit-code) since Tue 2018-04-28 18:01:42 IST; 28min agoMain PID: 2881 (code=exited, status=0/SUCCESS)Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec"Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled.Apr 28 18:01:42 tecmint systemd[1]: httpd.service: control process exited, code=exited status=226Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state.Hint: Some lines were ellipsized, use -l to show in full.
使用Systemctl控制和管理挂载点
17.列出所有系统安装点
# systemctl list-unit-files --type=mountUNIT FILE STATE dev-hugepages.mount static dev-mqueue.mount static 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 disabled
18.如何装载，卸载，重新装载，重新装载系统装载点，以及检查系统上装载点的状态
# systemctl start tmp.mount# systemctl stop tmp.mount# systemctl restart tmp.mount# systemctl reload tmp.mount# systemctl status tmp.mounttmp.mount - Temporary DirectoryLoaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled)Active: active (mounted) since Tue 2018-04-28 17:46:06 IST; 2min 48s agoWhere: /tmpWhat: tmpfsDocs: man:hier(7)http://www.freedesktop.org/wiki/Software/systemd/APIFileSystemsProcess: 3908 ExecMount=/bin/mount tmpfs /tmp -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS)Apr 28 17:46:06 tecmint systemd[1]: Mounting Temporary Directory...Apr 28 17:46:06 tecmint systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway.Apr 28 17:46:06 tecmint systemd[1]: Mounted Temporary Directory.
19.如何在引导时激活，启用或禁用装入点（在系统引导时自动装入）
# systemctl is-active tmp.mount# systemctl enable tmp.mount# systemctl disable tmp.mount
20.如何在Linux中屏蔽（使其无法启动）或取消屏蔽挂载点
# systemctl mask tmp.mountln -s '/dev/null' '/etc/systemd/system/tmp.mount'# systemctl unmask tmp.mountrm '/etc/systemd/system/tmp.mount'
使用Systemctl控制和管理套接字
21.列出所有可用的系统套接字。
# systemctl list-unit-files --type=socketUNIT FILE STATE dbus.socket static dm-event.socket enabled lvm2-lvmetad.socket enabled rsyncd.socket disabledsshd.socket disabledsyslog.socket static systemd-initctl.socket static systemd-journald.socket static systemd-shutdownd.socket static systemd-udevd-control.socket static systemd-udevd-kernel.socket static 11 unit files listed.
22.如何在Linux中启动，重新启动，停止，重新加载和检查套接字的状态（例如：cups.socket）
# systemctl start cups.socket# systemctl restart cups.socket# systemctl stop cups.socket# systemctl reload cups.socket# systemctl status cups.socketcups.socket - CUPS Printing Service SocketsLoaded: loaded (/usr/lib/systemd/system/cups.socket; enabled)Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s agoListen: /var/run/cups/cups.sock (Stream)Apr 28 18:10:59 tecmint systemd[1]: Starting CUPS Printing Service Sockets.Apr 28 18:10:59 tecmint systemd[1]: Listening on CUPS Printing Service Sockets.
23.如何激活套接字并在引导时启用或禁用（在系统引导时自动启动套接字）
# systemctl is-active cups.socket# systemctl enable cups.socket# systemctl disable cups.socket
24.如何屏蔽（使其无法启动）或取消屏蔽插座（cups.socket）
# systemctl mask cups.socketln -s '/dev/null' '/etc/systemd/system/cups.socket'# systemctl unmask cups.socketrm '/etc/systemd/system/cups.socket'
服务的CPU利用率（份额）
25.获取服务的当前CPU份额（比如httpd）
# systemctl show -p CPUShares httpd.serviceCPUShares=1024注意：每个服务的默认值都为CPUShare = 1024.您可以增加/减少进程的CPU份额。
26.将服务的CPU份额（httpd.service）限制为2000 CPUShares /
# systemctl set-property httpd.service CPUShares=2000# systemctl show -p CPUShares httpd.serviceCPUShares=2000注意：为服务设置CPUShare时，会创建一个名为service的目录（httpd.service.d），其中包含一个包含CPUShare Limit信息的文件90-CPUShares.conf。 您可以将文件视为：
# vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf [Service]CPUShares=2000
27.检查服务的所有配置详细信息
# systemctl show httpdId=httpd.serviceNames=httpd.serviceRequires=basic.targetWants=system.sliceWantedBy=multi-user.targetConflicts=shutdown.targetBefore=shutdown.target multi-user.targetAfter=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.sliceDescription=The Apache HTTP ServerLoadState=loadedActiveState=activeSubState=runningFragmentPath=/usr/lib/systemd/system/httpd.service....
28.分析服务的关键链（httpd）
# systemd-analyze critical-chain httpd.serviceThe 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.httpd.service +142ms└─network.target @11.168s└─network.service @9.456s +1.712s└─NetworkManager.service @8.858s +596ms└─firewalld.service @4.931s +3.926s└─basic.target @4.916s└─sockets.target @4.916s└─dbus.socket @4.916s└─sysinit.target @4.905s└─systemd-update-utmp.service @4.864s +39ms└─auditd.service @4.563s +301ms└─systemd-tmpfiles-setup.service @4.485s +69ms└─rhel-import-state.service @4.342s +142ms└─local-fs.target @4.324s└─boot.mount @4.286s +31ms└─systemd-fsck@dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.service @4.092s +149ms└─dev-disk-by\x2duuid-79f594ad\x2da332\x2d4730\x2dbb5f\x2d85d196080964.device @4.092s
29.获取服务的依赖项列表（httpd）
# systemctl list-dependencies httpd.servicehttpd.service├─system.slice└─basic.target├─firewalld.service├─microcode.service├─rhel-autorelabel-mark.service├─rhel-autorelabel.service├─rhel-configure.service├─rhel-dmesg.service├─rhel-loadmodules.service├─paths.target├─slices.target│ ├─-.slice│ └─system.slice├─sockets.target│ ├─dbus.socket....
30.按层次列出控制组
# systemd-cgls├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 23├─user.slice│ └─user-0.slice│ └─session-1.scope│ ├─2498 sshd: root@pts/0 │ ├─2500 -bash│ ├─4521 systemd-cgls│ └─4522 systemd-cgls└─system.slice├─httpd.service│ ├─4440 /usr/sbin/httpd -DFOREGROUND│ ├─4442 /usr/sbin/httpd -DFOREGROUND│ ├─4443 /usr/sbin/httpd -DFOREGROUND│ ├─4444 /usr/sbin/httpd -DFOREGROUND│ ├─4445 /usr/sbin/httpd -DFOREGROUND│ └─4446 /usr/sbin/httpd -DFOREGROUND├─polkit.service│ └─721 /usr/lib/polkit-1/polkitd --no-debug....
31.根据CPU，内存，输入和输出列出控制组
# systemd-cgtopPath Tasks %CPU Memory Input/s Output/s/ 83 1.0 437.8M - -/system.slice - 0.1 - - -/system.slice/mariadb.service 2 0.1 - - -/system.slice/tuned.service 1 0.0 - - -/system.slice/httpd.service 6 0.0 - - -/system.slice/NetworkManager.service 1 - - - -/system.slice/atop.service 1 - - - -/system.slice/atopacct.service 1 - - - -/system.slice/auditd.service 1 - - - -/system.slice/crond.service 1 - - - -/system.slice/dbus.service 1 - - - -/system.slice/firewalld.service 1 - - - -/system.slice/lvm2-lvmetad.service 1 - - - -/system.slice/polkit.service 1 - - - -/system.slice/postfix.service 3 - - - -/system.slice/rsyslog.service 1 - - - -/system.slice/system-getty.slice/getty@tty1.service 1 - - - -/system.slice/systemd-journald.service 1 - - - -/system.slice/systemd-logind.service 1 - - - -/system.slice/systemd-udevd.service 1 - - - -/system.slice/webmin.service 1 - - - -/user.slice/user-0.slice/session-1.scope 3 - - - -
控制系统运行级别
32.如何启动系统救援模式
# systemctl rescueBroadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST):The system is going down to rescue mode NOW!33.如何进入紧急模式。
# systemctl emergencyWelcome to emergency mode! After logging in, type "journalctl -xb" to viewsystem logs, "systemctl reboot" to reboot, "systemctl default" to try againto boot into default mode.
34.列出当前使用的运行级别
# systemctl get-defaultmulti-user.target5.如何启动Runlevel 5 aka图形模式。
# systemctl isolate runlevel5.targetOR# systemctl isolate graphical.target
36.如何启动Runlevel 3又称多用户模式（命令行）
# systemctl isolate runlevel3.targetOR# systemctl isolate multiuser.target
36.如何将多用户模式或图形模式设置为默认运行级别
# systemctl set-default runlevel3.target# systemctl set-default runlevel5.target
37.如何重启，暂停，暂停，休眠或将系统置于混合睡眠状态
# systemctl reboot# systemctl halt# systemctl suspend# systemctl hibernate# systemctl hybrid-sleep对于那些可能不了解跑步水平及其作用的人。
- 运行级别0：关闭并关闭系统电源。
- 运行级别1：救援？维护模式。
- 运行级别3：多用户，无图形系统。
- 运行级别4：多用户，无图形系统。
- 运行级别5：多用户，图形系统。
- 运行级别6：关闭并重新启动机器。
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