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
1 # systemctl --version 2 systemd 215 3 +PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR
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
1 # whereis systemd 2 systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz 3 # whereis systemctl 4 systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
3. 检查systemd是否运行
1 # ps -eaf | grep [s]ystemd 2 root 1 0 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd --switched-root --system --deserialize 23 3 root 444 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-journald 4 root 469 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-udevd 5 root 555 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-logind 6 dbus 556 1 0 16:27 ? 00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
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
1 # systemd-analyze 2 Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s
5. 分析启动时各个进程花费的时间
# systemd-analyze blame 8.565s mariadb.service 7.991s webmin.service 6.095s postfix.service 4.311s httpd.service 3.926s firewalld.service 3.780s kdump.service 3.238s tuned.service 1.712s network.service 1.394s lvm2-monitor.service 1.126s systemd-logind.service ....
6. 分析启动时的关键链
1 # systemd-analyze critical-chain 2 The time after the unit is active or started is printed after the "@" character. 3 The time the unit takes to start is printed after the "+" character. 4 multi-user.target @20.222s 5 └─mariadb.service @11.657s +8.565s 6 └─network.target @11.168s 7 └─network.service @9.456s +1.712s 8 └─NetworkManager.service @8.858s +596ms 9 └─firewalld.service @4.931s +3.926s 10 └─basic.target @4.916s 11 └─sockets.target @4.916s 12 └─dbus.socket @4.916s 13 └─sysinit.target @4.905s 14 └─systemd-update-utmp.service @4.864s +39ms 15 └─auditd.service @4.563s +301ms 16 └─systemd-tmpfiles-setup.service @4.485s +69ms 17 └─rhel-import-state.service @4.342s +142ms 18 └─local-fs.target @4.324s 19 └─boot.mount @4.286s +31ms 20 └─systemd-fsck@dev-disk-byx2duuid-79f594adx2da332x2d4730x2dbb5fx2d85d19608096 21 └─dev-disk-byx2duuid-79f594adx2da332x2d4730x2dbb5fx2d85d196080964.device @4
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
-
1 # systemctl list-unit-files 2 UNIT FILE STATE 3 proc-sys-fs-binfmt_misc.automount static 4 dev-hugepages.mount static 5 dev-mqueue.mount static 6 proc-sys-fs-binfmt_misc.mount static 7 sys-fs-fuse-connections.mount static 8 sys-kernel-config.mount static 9 sys-kernel-debug.mount static 10 tmp.mount disabled 11 brandbot.path disabled 12 .....
8. 列出所有运行中单元
1 # systemctl list-units 2 UNIT LOAD ACTIVE SUB DESCRIPTION 3 proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File Syste 4 sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROM 5 sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged PRO/1000 MT Desktop Adapter 6 sys-devices-pc...00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controller 7 sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISK 8 sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8 9 sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISK 10 sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0 11 sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1 12 sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 13 sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3 14 sys-devices-virtual-block-dmx2d0.device loaded active plugged /sys/devices/virtual/block/dm-0 15 sys-devices-virtual-block-dmx2d1.device loaded active plugged /sys/devices/virtual/block/dm-1 16 sys-module-configfs.device loaded active plugged /sys/module/configfs 17 ...
9. 列出所有失败单元
1 # systemctl --failed 2 UNIT LOAD ACTIVE SUB DESCRIPTION 3 kdump.service loaded failed failed Crash recovery kernel arming 4 LOAD = Reflects whether the unit definition was properly loaded. 5 ACTIVE = The high-level unit activation state, i.e. generalization of SUB. 6 SUB = The low-level unit activation state, values depend on unit type. 7 1 loaded units listed. Pass --all to see loaded but inactive units, too. 8 To show all installed unit files use 'systemctl list-unit-files'.
10. 检查某个单元（如 cron.service）是否启用
1 # systemctl is-enabled crond.service 2 enabled
11. 检查某个单元或服务是否运行
1 # systemctl status firewalld.service 2 firewalld.service - firewalld - dynamic firewall daemon 3 Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled) 4 Active: active (running) since Tue 2015-04-28 16:27:55 IST; 34min ago 5 Main PID: 549 (firewalld) 6 CGroup: /system.slice/firewalld.service 7 └─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid 8 Apr 28 16:27:51 tecmint systemd[1]: Starting firewalld - dynamic firewall daemon... 9 Apr 28 16:27:55 tecmint systemd[1]: Started firewalld - dynamic firewall daemon.
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）
1 # systemctl list-unit-files --type=service 2 UNIT FILE STATE 3 arp-ethers.service disabled 4 auditd.service enabled 5 autovt@.service disabled 6 blk-availability.service disabled 7 brandbot.service static 8 collectd.service disabled 9 console-getty.service disabled 10 console-shell.service disabled 11 cpupower.service disabled 12 crond.service enabled 13 dbus-org.fedoraproject.FirewallD1.service enabled 14 ....
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
1 # systemctl start httpd.service 2 # systemctl restart httpd.service 3 # systemctl stop httpd.service 4 # systemctl reload httpd.service 5 # systemctl status httpd.service 6 httpd.service - The Apache HTTP Server 7 Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled) 8 Active: active (running) since Tue 2015-04-28 17:21:30 IST; 6s ago 9 Process: 2876 ExecStop=/bin/kill -WINCH ${MAINPID} (code=exited, status=0/SUCCESS) 10 Main PID: 2881 (httpd) 11 Status: "Processing requests..." 12 CGroup: /system.slice/httpd.service 13 ├─2881 /usr/sbin/httpd -DFOREGROUND 14 ├─2884 /usr/sbin/httpd -DFOREGROUND 15 ├─2885 /usr/sbin/httpd -DFOREGROUND 16 ├─2886 /usr/sbin/httpd -DFOREGROUND 17 ├─2887 /usr/sbin/httpd -DFOREGROUND 18 └─2888 /usr/sbin/httpd -DFOREGROUND 19 Apr 28 17:21:30 tecmint systemd[1]: Starting The Apache HTTP Server... 20 Apr 28 17:21:30 tecmint httpd[2881]: AH00558: httpd: Could not reliably determine the server's fully q...ssage 21 Apr 28 17:21:30 tecmint systemd[1]: Started The Apache HTTP Server. 22 Hint: Some lines were ellipsized, use -l to show in full.
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）
1 # systemctl is-active httpd.service 2 # systemctl enable httpd.service 3 # systemctl disable httpd.service
15. 如何屏蔽（让它不能启动）或显示服务（如 httpd.service）
1 # systemctl mask httpd.service 2 ln -s '/dev/null' '/etc/systemd/system/httpd.service' 3 # systemctl unmask httpd.service 4 rm '/etc/systemd/system/httpd.service'
16. 使用systemctl命令杀死服务
1 # systemctl kill httpd 2 # systemctl status httpd 3 httpd.service - The Apache HTTP Server 4 Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled) 5 Active: failed (Result: exit-code) since Tue 2015-04-28 18:01:42 IST; 28min ago 6 Main PID: 2881 (code=exited, status=0/SUCCESS) 7 Status: "Total requests: 0; Current requests/sec: 0; Current traffic: 0 B/sec" 8 Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 9 Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 10 Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 11 Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 12 Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 13 Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 14 Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 15 Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. 16 Apr 28 18:01:42 tecmint systemd[1]: httpd.service: control process exited, code=exited status=226 17 Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state. 18 Hint: Some lines were ellipsized, use -l to show in full.
使用Systemctl控制并管理挂载点
17. 列出所有系统挂载点
1 # systemctl list-unit-files --type=mount 2 UNIT FILE STATE 3 dev-hugepages.mount static 4 dev-mqueue.mount static 5 proc-sys-fs-binfmt_misc.mount static 6 sys-fs-fuse-connections.mount static 7 sys-kernel-config.mount static 8 sys-kernel-debug.mount static 9 tmp.mount disabled
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
1 # systemctl start tmp.mount 2 # systemctl stop tmp.mount 3 # systemctl restart tmp.mount 4 # systemctl reload tmp.mount 5 # systemctl status tmp.mount 6 tmp.mount - Temporary Directory 7 Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled) 8 Active: active (mounted) since Tue 2015-04-28 17:46:06 IST; 2min 48s ago 9 Where: /tmp 10 What: tmpfs 11 Docs: man:hier(7) 12 http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems 13 Process: 3908 ExecMount=/bin/mount tmpfs /tmp -t tmpfs -o mode=1777,strictatime (code=exited, status=0/SUCCESS) 14 Apr 28 17:46:06 tecmint systemd[1]: Mounting Temporary Directory... 15 Apr 28 17:46:06 tecmint systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway. 16 Apr 28 17:46:06 tecmint systemd[1]: Mounted Temporary Directory.
19. 在启动时激活、启用或禁用挂载点（系统启动时自动挂载）
1 # systemctl is-active tmp.mount 2 # systemctl enable tmp.mount 3 # systemctl disable tmp.mount
20. 在Linux中屏蔽（让它不能启用）或可见挂载点
1 # systemctl mask tmp.mount 2 ln -s '/dev/null' '/etc/systemd/system/tmp.mount' 3 # systemctl unmask tmp.mount 4 rm '/etc/systemd/system/tmp.mount'
使用Systemctl控制并管理套接口
21. 列出所有可用系统套接口
1 # systemctl list-unit-files --type=socket 2 UNIT FILE STATE 3 dbus.socket static 4 dm-event.socket enabled 5 lvm2-lvmetad.socket enabled 6 rsyncd.socket disabled 7 sshd.socket disabled 8 syslog.socket static 9 systemd-initctl.socket static 10 systemd-journald.socket static 11 systemd-shutdownd.socket static 12 systemd-udevd-control.socket static 13 systemd-udevd-kernel.socket static 14 11 unit files listed.
22. 在Linux中启动、重启、停止、重载套接口并检查其状态
1 # systemctl start cups.socket 2 # systemctl restart cups.socket 3 # systemctl stop cups.socket 4 # systemctl reload cups.socket 5 # systemctl status cups.socket 6 cups.socket - CUPS Printing Service Sockets 7 Loaded: loaded (/usr/lib/systemd/system/cups.socket; enabled) 8 Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s ago 9 Listen: /var/run/cups/cups.sock (Stream) 10 Apr 28 18:10:59 tecmint systemd[1]: Starting CUPS Printing Service Sockets. 11 Apr 28 18:10:59 tecmint systemd[1]: Listening on CUPS Printing Service Sockets.
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）
1 # systemctl is-active cups.socket 2 # systemctl enable cups.socket 3 # systemctl disable cups.socket
24. 屏蔽（使它不能启动）或显示套接口
1 # systemctl mask cups.socket 2 ln -s '/dev/null' '/etc/systemd/system/cups.socket' 3 # systemctl unmask cups.socket 4 rm '/etc/systemd/system/cups.socket'
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）
1 # systemctl show -p CPUShares httpd.service 2 CPUShares=1024
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/
1 # systemctl set-property httpd.service CPUShares=2000 2 # systemctl show -p CPUShares httpd.service 3 CPUShares=2000
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：
1 # vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf 2 [Service] 3 CPUShares=2000
27. 检查某个服务的所有配置细节
1 # systemctl show httpd 2 Id=httpd.service 3 Names=httpd.service 4 Requires=basic.target 5 Wants=system.slice 6 WantedBy=multi-user.target 7 Conflicts=shutdown.target 8 Before=shutdown.target multi-user.target 9 After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice 10 Description=The Apache HTTP Server 11 LoadState=loaded 12 ActiveState=active 13 SubState=running 14 FragmentPath=/usr/lib/systemd/system/httpd.service 15 ....
28. 分析某个服务（httpd）的关键链
1 # systemd-analyze critical-chain httpd.service 2 The time after the unit is active or started is printed after the "@" character. 3 The time the unit takes to start is printed after the "+" character. 4 httpd.service +142ms 5 └─network.target @11.168s 6 └─network.service @9.456s +1.712s 7 └─NetworkManager.service @8.858s +596ms 8 └─firewalld.service @4.931s +3.926s 9 └─basic.target @4.916s 10 └─sockets.target @4.916s 11 └─dbus.socket @4.916s 12 └─sysinit.target @4.905s 13 └─systemd-update-utmp.service @4.864s +39ms 14 └─auditd.service @4.563s +301ms 15 └─systemd-tmpfiles-setup.service @4.485s +69ms 16 └─rhel-import-state.service @4.342s +142ms 17 └─local-fs.target @4.324s 18 └─boot.mount @4.286s +31ms 19 └─systemd-fsck@dev-disk-byx2duuid-79f594adx2da332x2d4730x2dbb5fx2d85d196080964.service @4.092s +149ms 20 └─dev-disk-byx2duuid-79f594adx2da332x2d4730x2dbb5fx2d85d196080964.device @4.092s
29. 获取某个服务（httpd）的依赖性列表
1 # systemctl list-dependencies httpd.service 2 httpd.service 3 ├─system.slice 4 └─basic.target 5 ├─firewalld.service 6 ├─microcode.service 7 ├─rhel-autorelabel-mark.service 8 ├─rhel-autorelabel.service 9 ├─rhel-configure.service 10 ├─rhel-dmesg.service 11 ├─rhel-loadmodules.service 12 ├─paths.target 13 ├─slices.target 14 │ ├─-.slice 15 │ └─system.slice 16 ├─sockets.target 17 │ ├─dbus.socket 18 ....
30. 按等级列出控制组
1 # systemd-cgls 2 ├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 23 3 ├─user.slice 4 │ └─user-0.slice 5 │ └─session-1.scope 6 │ ├─2498 sshd: root@pts/0 7 │ ├─2500 -bash 8 │ ├─4521 systemd-cgls 9 │ └─4522 systemd-cgls 10 └─system.slice 11 ├─httpd.service 12 │ ├─4440 /usr/sbin/httpd -DFOREGROUND 13 │ ├─4442 /usr/sbin/httpd -DFOREGROUND 14 │ ├─4443 /usr/sbin/httpd -DFOREGROUND 15 │ ├─4444 /usr/sbin/httpd -DFOREGROUND 16 │ ├─4445 /usr/sbin/httpd -DFOREGROUND 17 │ └─4446 /usr/sbin/httpd -DFOREGROUND 18 ├─polkit.service 19 │ └─721 /usr/lib/polkit-1/polkitd --no-debug 20 ....
31. 按CPU、内存、输入和输出列出控制组
1 # systemd-cgtop 2 Path Tasks %CPU Memory Input/s Output/s 3 / 83 1.0 437.8M - - 4 /system.slice - 0.1 - - - 5 /system.slice/mariadb.service 2 0.1 - - - 6 /system.slice/tuned.service 1 0.0 - - - 7 /system.slice/httpd.service 6 0.0 - - - 8 /system.slice/NetworkManager.service 1 - - - - 9 /system.slice/atop.service 1 - - - - 10 /system.slice/atopacct.service 1 - - - - 11 /system.slice/auditd.service 1 - - - - 12 /system.slice/crond.service 1 - - - - 13 /system.slice/dbus.service 1 - - - - 14 /system.slice/firewalld.service 1 - - - - 15 /system.slice/lvm2-lvmetad.service 1 - - - - 16 /system.slice/polkit.service 1 - - - - 17 /system.slice/postfix.service 3 - - - - 18 /system.slice/rsyslog.service 1 - - - - 19 /system.slice/system-getty.slice/getty@tty1.service 1 - - - - 20 /system.slice/systemd-journald.service 1 - - - - 21 /system.slice/systemd-logind.service 1 - - - - 22 /system.slice/systemd-udevd.service 1 - - - - 23 /system.slice/webmin.service 1 - - - - 24 /user.slice/user-0.slice/session-1.scope 3 - - - -
控制系统运行等级
32. 启动系统救援模式
1 # systemctl rescue 2 Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST): 3 The system is going down to rescue mode NOW!
33. 进入紧急模式
1 # systemctl emergency 2 Welcome to emergency mode! After logging in, type "journalctl -xb" to view 3 system logs, "systemctl reboot" to reboot, "systemctl default" to try again 4 to boot into default mode.
34. 列出当前使用的运行等级
1 # systemctl get-default 2 multi-user.target
35. 启动运行等级5，即图形模式
1 # systemctl isolate runlevel5.target 2 或 3 # systemctl isolate graphical.target
36. 启动运行等级3，即多用户模式（命令行）
1 # systemctl isolate runlevel3.target 2 或 3 # systemctl isolate multiuser.target
36. 设置多用户模式或图形模式为默认运行等级
1 # systemctl set-default runlevel3.target 2 # systemctl set-default runlevel5.target
37. 重启、停止、挂起、休眠系统或使系统进入混合睡眠
1 # systemctl reboot 2 # systemctl halt 3 # systemctl suspend 4 # systemctl hibernate 5 # systemctl hybrid-sleep
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
via: http://www.tecmint.com/manage-services-using-systemd-and-systemctl-in-linux/
作者：Avishek Kumar 译者：GOLinux 校对：wxy