systemctl命令详解及使⽤教程
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 --version
systemd 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/
# whereis systemctl
systemctl: /usr/bin/systemctl /usr/share/man/man1/
03.检查systemd是否正在运⾏。
# 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-analyze
Startup 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 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
....
06.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 @20.222s
└─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
└─unt @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
unt static
brandbot.path disabled
.....
08、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
<0-1:0:0:0-block-sr0.device loaded active plugged VBOX_CD-ROM
<:00:03.0-net-enp0s3.device loaded active plugged PRO/1000 MT Desktop Adapter
<00:05.0-sound-card0.device loaded active plugged 82801AA AC'97 Audio Controller
<:0:0-block-sda-sda1.device loaded active plugged VBOX_HARDDISK
<:0:0-block-sda-sda2.device loaded active plugged LVM PV 0-2:0:0:0-block-sda.device loaded active plugged VBOX_HARDDISK
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
...
09、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'.
10、检查单元(cron.service)是否启⽤?
# systemctl is-enabled crond.service
enabled
11.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
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=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.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: ""
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
Apr 28 17:21:30 tecmint httpd[2881]: AH00558: httpd: Could not reliably determine the server's 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。
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.service
rm '/etc/systemd/system/httpd.service'
16.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, bled.
Apr 28 17:37:29 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, bled.
Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, bled.
Apr 28 17:37:39 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, bled.
Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, bled.
Apr 28 17:37:49 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, bled.
Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, bled.
Apr 28 17:37:59 tecmint systemd[1]: httpd.service: Got notification message from PID 2881, 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.
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=mount
UNIT FILE STATE
unt static
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 unt
# systemctl unt
# systemctl unt
# systemctl unt
# systemctl unt
exitedLoaded: loaded (/usr/lib/systemd/unt; disabled)
Active: active (mounted) since Tue 2018-04-28 17:46:06 IST; 2min 48s ago
Where: /tmp
What: tmpfs
Docs: man:hier(7)
/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
Apr 28 17:46:06 tecmint systemd[1]: unt: 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）
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