Systemctl是systemd工具，它是负责控制systemd系统和服务经理。
Systemd是系统管理后台程序，工具和库用作替换System V启动守护进程的集合。 Systemd作为UNIX系统的集中管理和配置平台。
在Linux生态系统Systemd已实施的大部分标准的Linux发行版有一些例外。 Systemd是所有其他守护程序的父进程，通常但不总是。
使用Systemctl管理Linux服务
本文旨在运行systemd系统中的“ 如何控制体系和服务 ”扔光。
从Systemtd和Systemctl基础开始
1.首先检查是否是systemd在系统上安装与否，什么是当前安装Systemd的版本？
# systemd --version systemd 215 +PAM +AUDIT +SELINUX +IMA +SYSVINIT +LIBCRYPTSETUP +GCRYPT +ACL +XZ -SECCOMP -APPARMOR
这是从上面的例子清楚，我们已经systemd 215版本安装。
2.检查哪里systemd和systemctl的二进制文件和库安装。
# whereis systemd systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz # whereis systemctl systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
3.检查是否systemd运行与否。
# ps -eaf | grep [s]ystemd root 1 0 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd --switched-root --system --deserialize 23 root 444 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-journald root 469 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-udevd root 555 1 0 16:27 ? 00:00:00 /usr/lib/systemd/systemd-logind dbus 556 1 0 16:27 ? 00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
注意 ：systemd运行父进程（PID = 1）。 在上面的命令ps与（-e）选择所有进程，（-A）选择所有的进程除了会议的领导人和（-f）全格式列表（即-eaf）。
还要注意上面示例中的方括号和其余的示例。 方括号表达式是grep的字符类模式匹配的一部分。
4.分析systemd启动过程。
# systemd-analyze Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s
5.分析每个进程在引导所用的时间。
# 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.在开机分析关键链。
# 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 @20.222s └─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
重要提示 ：Systemctl接受服务（。服务 ），挂载点（.mount），socket（.socket）和设备（.device）为单位。
7.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 disabled brandbot.path disabled .....
8.列出所有正在运行的单位。
# 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 ...
9.列出所有失败的单位。
# 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'.
10.检查如果一个单位（cron.service）或不启用？
# systemctl is-enabled crond.service enabled
11.检查是否单位或服务的运行或不？
# systemctl status firewalld.service firewalld.service - firewalld - dynamic firewall daemon Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled) Active: active (running) since Tue 2015-04-28 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 youcl systemd[1]: Starting firewalld - dynamic firewall daemon... Apr 28 16:27:55 youcl systemd[1]: Started firewalld - dynamic firewall daemon.
使用Systemctl控制和管理服务
12.清单（包括启用和禁用）的所有服务。
# 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 ....
13.我如何启动，重新启动，停止，刷新和检查的Linux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 2015-04-28 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 youcl systemd[1]: Starting The Apache HTTP Server...
Apr 28 17:21:30 youcl httpd[2881]: AH00558: httpd: Could not reliably determine the server's fully q...ssage
Apr 28 17:21:30 youcl systemd[1]: Started The Apache HTTP Server.
Hint: Some lines were ellipsized, use -l to show in full.
注意：当我们使用的命令，例如启动 ， 重新启动 ， 停止和重新加载 systemctl，我们不会在终端上的任何输出，只有命令会将打印输出。
14.如何为主动服务，并启用或禁用在引导时即服务（在系统启动时自动启动服务）。
# systemctl is-active httpd.service # systemctl enable httpd.service # systemctl disable httpd.service
15.如何屏蔽（使得不可能启动）或揭露服务（httpd.service）。
# systemctl mask httpd.service ln -s '/dev/null' '/etc/systemd/system/httpd.service' # systemctl unmask httpd.service rm '/etc/systemd/system/httpd.service'
16.如何将使用systemctl命令杀死的服务。
# 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 2015-04-28 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 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:29 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:39 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:39 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:49 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:49 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:59 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 17:37:59 youcl systemd[1]: httpd.service: Got notification message from PID 2881, but recepti...bled. Apr 28 18:01:42 youcl systemd[1]: httpd.service: control process exited, code=exited status=226 Apr 28 18:01:42 youcl systemd[1]: Unit httpd.service entered failed state. Hint: Some lines were ellipsized, use -l to show in full.
使用Systemctl控制和管理挂接点
17.列出所有系统挂载点。
# 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
18，怎样安装，卸载，重新装入，重装系统挂载点，并检查在系统上安装点的状态。
# 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 2015-04-28 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 youcl systemd[1]: Mounting Temporary Directory... Apr 28 17:46:06 youcl systemd[1]: tmp.mount: Directory /tmp to mount over is not empty, mounting anyway. Apr 28 17:46:06 youcl systemd[1]: Mounted Temporary Directory.
19.如何活跃，启用或禁用在引导时（自动安装在系统启动时）挂载点。
# systemctl is-active tmp.mount # systemctl enable tmp.mount # systemctl disable tmp.mount
20.如何屏蔽（使其无法启动），或在Linux中揭露一个安装点。
# systemctl mask tmp.mount ln -s '/dev/null' '/etc/systemd/system/tmp.mount' # systemctl unmask tmp.mount rm '/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socket。
# 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.
22.如何启动，重新启动，停止，刷新，检查socket的状态：在Linux中（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 youcl systemd[1]: Starting CUPS Printing Service Sockets. Apr 28 18:10:59 youcl systemd[1]: Listening on CUPS Printing Service Sockets.
23.如何主动套接字，并启用或在系统启动时关闭（在系统启动时自动启动socket）。
# systemctl is-active cups.socket # systemctl enable cups.socket # systemctl disable cups.socket
24.如何屏蔽（使得不可能启动）或揭露的socket（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'
