systemctl使用详解

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。

systemd 和 systemctl

01.检查安装版本

# 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/systemd.1.gz

# whereis systemctl
systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz

03.检查是否正在运行

# 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
└─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  
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
.....

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
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
...

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 firewall daemon...
Apr 28 16:27:55 tecmint systemd[1]: Started firewalld - dynamic firewall daemon.

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        #启动服务
# systemctl restart httpd.service      #重启服务
# systemctl stop httpd.service         #停止服务
# systemctl reload httpd.service       #重载服务
# systemctl status httpd.service       #服务状态
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.

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-开机自启）

# systemctl is-active httpd.service   #是否开机自启
# systemctl enable httpd.service      #设置开机自启
# systemctl disable httpd.service     #禁用开机自启

在 CentOS 服务器上，单独设置自定义脚本的开机自启：

一、创建脚本

首先创建你要在重启时执行的脚本文件，例如my_script.sh，确保该脚本具有可执行权限。如果脚本需要特定的解释器（如bash），在脚本的开头添加相应的解释器声明，例如：

#!/bin/bash
# 你的脚本内容

二、使用systemd配置

1. 创建一个

   systemd

   服务单元文件：

   • 以 root 用户身份创建一个服务单元文件，例如/etc/systemd/system/my_script.service，内容如下：

[Unit]
Description=My Script on Boot
After=network.target

[Service]
Type=simple
ExecStart=/path/to/my_script.sh
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

• 将/path/to/my_script.sh替换为你的脚本的实际路径。

1. 启用并启动服务：
   • 重新加载systemd配置：

sudo systemctl daemon-reload

• 启用服务，使其在系统启动时自动启动：

sudo systemctl enable my_script.service

• 可以启动服务以立即测试：

sudo systemctl start my_script.service

这样配置后，每次 CentOS 服务器重启时，my_script.sh脚本将会自动执行。

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, 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.

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   
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.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.

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）

# systemctl is-active tmp.mount
# systemctl enable tmp.mount
# systemctl disable  tmp.mount

20.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'

控制和管理套接字

21.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.

22.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.

23.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

24.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'

服务的CPU利用率（份额）

25.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。

26.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  

27.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
....

28.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

29.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
....

30.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
....

31.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        -        -        -
...

控制系统运行级别

32.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!

33.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.

34.列出当前使用的运行级别

# systemctl get-default
multi-user.target

5.如何启动Runlevel 5 aka图形模式。

# systemctl isolate runlevel5.target
OR
# systemctl isolate graphical.target

36.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

36.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

• 运行级别0：关闭并关闭系统电源。
• 运行级别1：救援？维护模式。
• 运行级别3：多用户，无图形系统。
• 运行级别4：多用户，无图形系统。
• 运行级别5：多用户，图形系统。
• 运行级别6：关闭并重新启动机器。

37.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