linux下如何使用systemctl管理systemd服务与单元

先来个简单总结（后面才是from的链接的内容）：

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。

1. 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.gz 
3. 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。

1. 分析systemd启动进程

systemd-analyze

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

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。

1. 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

enabled 
11. 检查某个单元或服务是否运行

systemctl status firewalld.service

firewalld.service - firewalld - dynamic firewall daemon 
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled) 
Active: active (running) since Tue 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 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 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 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。

1. 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.service

1. 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 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 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 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

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 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.mount

1. 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 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. 
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.socket

1. 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。

1. 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=2000 
27. 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 @4.092s 
29. 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/[e-mail] 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