From:https://linux.cn/article-5926-1.html
systemctl命令是系统服务管理器指令，它实际上将 service 和 chkconfig 这两个命令组合到一起。
| 任务 | 旧指令 | 新指令 |
| 使某服务自动启动 | chkconfig --level 3 httpd on | systemctl enable httpd.service |
| 使某服务不自动启动 | chkconfig --level 3 httpd off | systemctl disable httpd.service |
| 检查服务状态 | service httpd status | systemctl status httpd.service （服务详细信息） systemctl is-active httpd.service（仅显示是否 Active) |
| 显示所有已启动的服务 | chkconfig --list | systemctl list-units --type=service |
| 启动某服务 | service httpd start | systemctl start httpd.service |
| 停止某服务 | service httpd stop | systemctl stop httpd.service |
| 重启某服务 | service httpd restart | systemctl restart httpd.service |
1.启动nfs服务 systemctl start nfs-server.service
2.设置开机自启动 systemctl enable nfs-server.service
3.停止开机自启动 systemctl disable nfs-server.service
4.查看服务当前状态 systemctl status nfs-server.service
5.重新启动某服务 systemctl restart nfs-server.service
6.查看所有已启动的服务 systemctl list -units --type=service
7.开启防火墙22端口 iptables -I INPUT -p tcp --dport 22 -j accept 如果仍然有问题，就可能是SELinux导致的 关闭SElinux：
修改/etc/selinux/config文件中的SELINUX=””为disabled，然后重启。 彻底关闭防火墙：
sudo systemctl status firewalld.service
sudo systemctl stop firewalld.service
sudo systemctl disable firewalld.service
简单总结
启动一个服务：systemctl start postfix.service
关闭一个服务：systemctl stop postfix.service
重启一个服务：systemctl restart postfix.service
显示一个服务的状态：systemctl status postfix.service
在开机时启用一个服务：systemctl enable postfix.service
在开机时禁用一个服务：systemctl disable postfix.service
查看服务是否开机启动：systemctl is-enabled postfix.service;echo $?
查看已启动的服务列表：systemctl list-unit-files|grep enabled说明：启用服务就是在当前“runlevel”的配置文件目录/etc/systemd/system/multi-user.target.wants/里，建立/usr/lib/systemd/system里面对应服务配置文件的软链接；禁用服务就是删除此软链接。
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。
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
# systemctl --version
systemd 215
+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
# 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.gz3. 检查systemd是否运行
# 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
# systemd-analyze
Startup finished in 487ms (kernel) + 2.776s (initrd) + 20.229s (userspace) = 23.493s5. 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
# 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：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
# 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. 列出所有运行中单元
# 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
...9. 列出所有失败单元
# 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. 检查某个单元（如 cron.service）是否启用
# systemctl is-enabled crond.service
enabled11. 检查某个单元或服务是否运行
# systemctl status firewalld.service
firewalld.service - firewalld - dynamic firewall daemonLoaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)Active: active (running) since Tue 2015-04-28 16:27:55 IST; 34min agoMain PID: 549 (firewalld)CGroup: /system.slice/firewalld.service└─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --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.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）
# 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. 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
# 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 ServerLoaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)Active: active (running) since Tue 2015-04-28 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 -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）
# systemctl is-active httpd.service
# systemctl enable httpd.service
# systemctl disable httpd.service15. 如何屏蔽（让它不能启动）或显示服务（如 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. 使用systemctl命令杀死服务
# systemctl kill httpd
# systemctl status httpd
httpd.service - The Apache HTTP ServerLoaded: loaded (/usr/lib/systemd/system/httpd.service; enabled)Active: failed (Result: exit-code) since Tue 2015-04-28 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=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控制并管理挂载点
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 disabled18. 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
# systemctl start tmp.mount
# systemctl stop tmp.mount
# systemctl restart tmp.mount
# systemctl reload tmp.mount
# systemctl status tmp.mount
tmp.mount - Temporary DirectoryLoaded: loaded (/usr/lib/systemd/system/tmp.mount; disabled)Active: active (mounted) since Tue 2015-04-28 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. 在启动时激活、启用或禁用挂载点（系统启动时自动挂载）
# systemctl is-active tmp.mount
# systemctl enable tmp.mount
# systemctl disable tmp.mount20. 在Linux中屏蔽（让它不能启用）或可见挂载点
# systemctl mask tmp.mount
ln -s '/dev/null' '/etc/systemd/system/tmp.mount'
# systemctl unmask tmp.mount
rm '/etc/systemd/system/tmp.mount'使用Systemctl控制并管理套接口
21. 列出所有可用系统套接口
# 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. 在Linux中启动、重启、停止、重载套接口并检查其状态
# 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 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. 在启动时激活套接口，并启用或禁用它（系统启动时自启动）
# systemctl is-active cups.socket
# systemctl enable cups.socket
# systemctl disable cups.socket24. 屏蔽（使它不能启动）或显示套接口
# systemctl mask cups.socket
ln -s '/dev/null' '/etc/systemd/system/cups.socket'
# systemctl unmask cups.socket
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）
# systemctl show -p CPUShares httpd.service
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/
# systemctl set-property httpd.service CPUShares=2000
# systemctl show -p CPUShares httpd.service
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：
# vi /etc/systemd/system/httpd.service.d/90-CPUShares.conf
[Service]
CPUShares=200027. 检查某个服务的所有配置细节
# 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
....28. 分析某个服务（httpd）的关键链
# 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 @4.092s29. 获取某个服务（httpd）的依赖性列表
# 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
....30. 按等级列出控制组
# 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. 按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 - - - -控制系统运行等级
32. 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!33. 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.34. 列出当前使用的运行等级
# systemctl get-default
multi-user.target35. 启动运行等级5，即图形模式
# systemctl isolate runlevel5.target
或
# systemctl isolate graphical.target36. 启动运行等级3，即多用户模式（命令行）
# systemctl isolate runlevel3.target
或
# systemctl isolate multiuser.target36. 设置多用户模式或图形模式为默认运行等级
# systemctl set-default runlevel3.target
# systemctl set-default runlevel5.target37. 重启、停止、挂起、休眠系统或使系统进入混合睡眠
# systemctl reboot
# systemctl halt
# systemctl suspend
# systemctl hibernate
# 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
)
