#1. 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。
2. systemctl 基本功能：
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分析systemd启动过程
$ systemd-analyze Startup finished in 767ms (kernel) + 6.540s (initrd) + 20.174s (userspace) = 27.483s -
分析每个进程在引导时花费的时间
$ systemd-analyze Startup finished in 767ms (kernel) + 6.540s (initrd) + 20.174s (userspace) = 27.483s systemd-analyze blame 7.301s tuned.service 5.075s systemd-vconsole-setup.service 4.984s network.service 3.829s etcd.service 3.806s postfix.service 1.512s docker.service .... -
分析启动时的关键链
$ 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 @20.163s └─tuned.service @7.413s +7.301s └─network.target @7.395s └─network.service @2.410s +4.984s └─basic.target @2.359s └─sockets.target @2.359s └─dbus.socket @2.357s └─sysinit.target @2.357s └─systemd-update-utmp.service @2.343s +13ms └─auditd.service @2.145s +196ms └─systemd-tmpfiles-setup.service @2.138s +5ms └─rhel-import-state.service @2.103s +33ms └─local-fs.target @2.102s └─boot.mount @1.836s +266ms └─local-fs-pre.target @1.835s └─lvm2-monitor.service @849ms +985ms └─lvm2-lvmetad.service @906ms └─lvm2-lvmetad.socket @831ms └─-.slice重要：Systemctl接受服务（.service），挂载点（.mount），套接字（.socket）和设备（.device）作为单位。
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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 ... -
列出所有运行单元
$ systemctl list-units UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File Syste sys-devices-pc...0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROM sys-devices-pc...:00:03.0-net-enp0s3.device loaded active plugged PRO/1000 MT Desktop Adapter sys-devices-pc...00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controller sys-devices-pc...:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISK sys-devices-pc...:0:0-block-sda-sda2.device loaded active plugged LVM PV Qzyo3l-qYaL-uRUa-Cjuk-pljo-qKtX-VgBQ8 sys-devices-pc...0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISK sys-devices-pl...erial8250-tty-ttyS0.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS0 sys-devices-pl...erial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1 sys-devices-pl...erial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 sys-devices-pl...erial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3 sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0 sys-devices-virtual-block-dm\x2d1.device loaded active plugged /sys/devices/virtual/block/dm-1 sys-module-configfs.device loaded active plugged /sys/module/configfs ... -
列出所有失败的单元
$ 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'. -
检查单元(cron.service)是否启用?
$ systemctl is-enabled crond.service enabled -
检查单元或服务是否正在运行？
$ systemctl status firewalld.service firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled) Active: active (running) since Tue 2018-04-28 16:27:55 IST; 34min ago Main PID: 549 (firewalld) CGroup: /system.slice/firewalld.service └─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid Apr 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. -
列出所有服务（包括启用和禁用）
$ systemctl list-unit-files --type=service UNIT FILE STATE arp-ethers.service disabled auditd.service enabled autovt@.service disabled blk-availability.service disabled brandbot.service static collectd.service disabled console-getty.service disabled console-shell.service disabled cpupower.service disabled crond.service enabled dbus-org.fedoraproject.FirewallD1.service enabled .... -
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.service httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled) Active: active (running) since Tue 2018-04-28 17:21:30 IST; 6s ago Process: 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 -DFOREGROUND Apr 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...ssage Apr 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。
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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 -
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.service rm '/etc/systemd/system/httpd.service' -
如何使用systemctl命令终止服务
# systemctl kill httpd # systemctl status httpd httpd.service - The Apache HTTP Server Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled) Active: failed (Result: exit-code) since Tue 2018-04-28 18:01:42 IST; 28min ago Main 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=226 Apr 28 18:01:42 tecmint systemd[1]: Unit httpd.service entered failed state. Hint: Some lines were ellipsized, use -l to show in full. -
列出所有系统安装点
# systemctl list-unit-files --type=mount UNIT 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 -
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.mount tmp.mount - Temporary Directory Loaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled) Active: active (mounted) since Tue 2018-04-28 17:46:06 IST; 2min 48s ago Where: /tmp What: tmpfs Docs: man:hier(7) http://www.freedesktop.org/wiki/Software/systemd/APIFileSystems Process: 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. -
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 -
如何在Linux中屏蔽（使其无法启动）或取消屏蔽挂载点
# systemctl mask tmp.mount ln -s '/dev/null' '/etc/systemd/system/tmp.mount' # systemctl unmask tmp.mount rm '/etc/systemd/system/tmp.mount' -
列出所有可用的系统套接字。
# systemctl list-unit-files --type=socket UNIT FILE STATE dbus.socket static dm-event.socket enabled lvm2-lvmetad.socket enabled rsyncd.socket disabled sshd.socket disabled syslog.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. -
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.socket cups.socket - CUPS Printing Service Sockets Loaded: loaded (/usr/lib/systemd/system/cups.socket; enabled) Active: active (listening) since Tue 2015-04-28 18:10:59 IST; 8s ago Listen: /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. -
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 -
如何屏蔽（使其无法启动）或取消屏蔽插座（cups.socket）
# systemctl mask cups.socket ln -s '/dev/null' '/etc/systemd/system/cups.socket' # systemctl unmask cups.socket rm '/etc/systemd/system/cups.socket' -
获取服务的当前CPU份额（比如httpd）
# systemctl show -p CPUShares httpd.service CPUShares=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。
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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.service CPUShares=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 -
检查服务的所有配置详细信息
# systemctl show httpd Id=httpd.service Names=httpd.service Requires=basic.target Wants=system.slice WantedBy=multi-user.target Conflicts=shutdown.target Before=shutdown.target multi-user.target After=network.target remote-fs.target nss-lookup.target systemd-journald.socket basic.target system.slice Description=The Apache HTTP Server LoadState=loaded ActiveState=active SubState=running FragmentPath=/usr/lib/systemd/system/httpd.service .... -
分析服务的关键链（httpd）
# systemd-analyze critical-chain httpd.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. 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 -
获取服务的依赖项列表（httpd）
# systemctl list-dependencies httpd.service httpd.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 .... -
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 .... -
根据CPU，内存，输入和输出列出控制组
# systemd-cgtop Path 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 - - - - -
如何启动系统救援模式
# systemctl rescue Broadcast message from root@tecmint on pts/0 (Wed 2015-04-29 11:31:18 IST): The system is going down to rescue mode NOW! -
如何进入紧急模式。
# systemctl emergency Welcome to emergency mode! After logging in, type "journalctl -xb" to view system logs, "systemctl reboot" to reboot, "systemctl default" to try again to boot into default mode. -
列出当前使用的运行级别
# systemctl get-default multi-user.target -
如何启动Runlevel 5 aka图形模式。
# systemctl isolate runlevel5.target OR # systemctl isolate graphical.target -
如何启动Runlevel 3又称多用户模式（命令行）
# systemctl isolate runlevel3.target OR # systemctl isolate multiuser.target -
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 -
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