centos 7 systemctl 命令总结

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。

案例：
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

[root@web-01-110 ~]# systemctl --version
systemd 219
+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID +ELFUTILS +KMOD +IDN

2. 检查systemd和systemctl的二进制文件和库文件的安装位置
[root@web-01-110 ~]# whereis systemctl
systemctl: /usr/bin/systemctl /usr/share/man/man1/systemctl.1.gz
[root@web-01-110 ~]# whereis systemd
systemd: /usr/lib/systemd /etc/systemd /usr/share/systemd /usr/share/man/man1/systemd.1.gz

3. 检查systemd是否运行
[root@web-01-110 ~]# ps -ef|grep systemd
root          1      0  0 03:06 ?        00:00:01 /usr/lib/systemd/systemd --switched-root --system --deserialize 21
root        353      1  0 03:06 ?        00:00:00 /usr/lib/systemd/systemd-journald
root        386      1  0 03:06 ?        00:00:00 /usr/lib/systemd/systemd-udevd
root        924      1  0 03:06 ?        00:00:00 /usr/lib/systemd/systemd-logind
dbus        935      1  0 03:06 ?        00:00:00 /bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
root       4008   2666  0 04:07 pts/0    00:00:00 grep --color=auto systemd

注意：systemd是作为父进程（PID=1）运行的

4. 分析systemd启动进程
[root@web-01-110 ~]# systemd-analyze
Startup finished in 615ms (kernel) + 3.729s (initrd) + 26.040s (userspace) = 30.385s

5. 分析启动时各个进程花费的时间
[root@web-01-110 ~]# systemd-analyze blame
          5.657s kdump.service
          5.366s NetworkManager-wait-online.service
          5.350s abrt-ccpp.service
          5.043s sysstat.service
          4.191s systemd-logind.service
          3.905s rhel-dmesg.service
          3.875s tuned.service


6. 分析启动时的关键链
[root@web-01-110 ~]# 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 @26.029s
`-tuned.service @20.345s +3.875s
  `-network.target @20.314s
    `-network.service @19.689s +622ms
      `-NetworkManager-wait-online.service @14.309s +5.366s

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
[root@web-01-110 ~]# systemctl list-unit-files
UNIT FILE                                     STATE   
proc-sys-fs-binfmt_misc.automount             static  
dev-hugepages.mount                           static  
dev-mqueue.mount                              static  
proc-fs-nfsd.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
var-lib-nfs-rpc_pipefs.mount                  static  
brandbot.path                                 disabled

说明： static 它是指对应的 Unit 文件中没有定义[Install]区域，因此无法配置为开机启动服务;disabled关闭开机启动；enable开启开机启动

8. 列出所有运行中单元
[root@web-01-110 ~]# 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-pci0000:00-0000:00:07.1-ata2-host2-target2:0:0-2:0:0:0-block-sr0.device loaded active plugged   VMwar
  sys-devices-pci0000:00-0000:00:10.0-host0-target0:0:0-0:0:0:0-block-sda-sda1.device loaded active plugged   VMwar
  sys-devices-pci0000:00-0000:00:10.0-host0-target0:0:0-0:0:0:0-block-sda-sda2.device loaded active plugged   VMwa


9. 列出所有失败单元
[root@web-01-110 ~]# 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 ty


10. 检查某个单元（如 cron.service）是否启用
查看crond定时任务是否启动服务
[root@web-01-110 ~]# systemctl is-enabled crond
enabled

11. 检查某个单元或服务是否运行
查看firewalld防火墙是否运行，Active: inactive (dead) 说明关闭状态
[root@web-01-110 ~]# systemctl status firewalld
* firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; disabled; vendor preset: enabled)
   Active: inactive (dead)  活动：无效（死亡）
     Docs: man:firewalld(1)


12. 列出所有服务（包括启用的和禁用的）
[root@web-01-110 ~]# systemctl list-unit-files --type=service
UNIT FILE                                     STATE   
abrt-ccpp.service                             enabled
abrt-oops.service                             enabled
abrt-pstoreoops.service                       disabled
abrt-vmcore.service                           enabled
abrt-xorg.service                             enabled
abrtd.service                                 enabled
arp-ethers.service                            disabled
atd.service                                   enabled
auditd.service                                enabled

说明：enabled 开启，disabled 关闭       


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

[root@web-01-110 ~]# systemctl start httpd.service
[root@web-01-110 ~]# systemctl restart httpd.service
[root@web-01-110 ~]# systemctl stop httpd.service
[root@web-01-110 ~]# systemctl reload httpd.service
[root@web-01-110 ~]# 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。


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）

[root@web-01-110 ~]# systemctl is-active httpd.service
[root@web-01-110 ~]# systemctl enable httpd.service
[root@web-01-110 ~]# systemctl disable httpd.service


15. 如何屏蔽（让它不能启动）或显示服务（如 httpd.service）

[root@web-01-110 ~]# systemctl mask crond.service
Created symlink from /etc/systemd/system/crond.service to /dev/null.
[root@web-01-110 ~]# systemctl unmask crond.service
Removed symlink /etc/systemd/system/crond.service.

16. 在启动时激活、启用或禁用挂载点（系统启动时自动挂载）

[root@web-01-110 ~]# systemctl is-active tmp.mount
[root@web-01-110 ~]# systemctl enable tmp.mount
[root@web-01-110 ~]# systemctl disable  tmp.mount


17. 获取当前某个服务的CPU分配额（如httpd）

[root@web-01-110 ~]# 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。

18. 检查某个服务的所有配置细节

    [root@web-01-110 ~]# 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

    ....

参考资料：https://www.tecmint.com/manage-services-using-systemd-and-systemctl-in-linux/