識別自動啟動的系統程序

系統啟動的伺服器程序由systemd系統和伺服器管理器進行管理
systemctl可以縮寫或者省略單元名稱、進度數條目和單元說明

• 服務單元具有.service副檔名，代表系統服務
• 套接字單元具有.socket副檔名，代表程序之間通訊

• 路徑單元具有.path副檔名，用於將服務的啟用推遲到特定檔案系統更改發生之後

  服務狀態

[[email protected] 桌面]$ systemctl status sshd
sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service
 
; enabled)
   Active: active (running) since 日 2017-07-30 22:38:24 CST; 2h 11min ago
  Process: 6723 ExecStartPre=/usr/sbin/sshd-keygen (code=exited, status=0/SUCCESS)
 Main PID: 6724 (sshd)
   CGroup: /system.slice/sshd.service
           └─6724 /usr/sbin/sshd -D

使用systemctl列出單元檔案

1. 查詢所有單元的狀態，以驗證系統啟動

[[email protected] 桌面]$ systemctl
UNIT                        LOAD   ACTIVE SUB       DESCRIPTION
proc-sys...t_misc.automount loaded active waiting   Arbitrary Executable File Fo
sys-devi...-sda-sda1.device loaded active plugged   VMware_Virtual_S
...
 

1. 僅查詢服務單元的狀態

[[email protected] 桌面]$ systemctl --type=service
UNIT                         LOAD   ACTIVE SUB     DESCRIPTION
abrt-ccpp.service            loaded active exited  Install ABRT coredump hook
abrt-oops.service            loaded active running ABRT kernel log watcher
abrt-xorg.service            loaded active running ABRT Xorg log watcher
...

1. 查詢處於失敗或者維護的任何單元

[[email protected] 桌面]$ systemctl status rngd.service 
rngd.service - Hardware RNG Entropy Gatherer Daemon
   Loaded: loaded (/usr/lib/systemd/system/rngd.service; enabled)
   Active: active (running) since 日 2017-07-30 21:01:49 CST; 4h 14min ago
 Main PID: 911 (rngd)
   CGroup: /system.slice/rngd.service
           └─911 /sbin/rngd -f

1. 顯示特定單元的活動和啟用

[student@localhost 桌面]$ systemctl is-active sshd
active
[student@localhost 桌面]$ systemctl is-enabled sshd
enabled

1. 列出所有已載入單元的活動狀態

[[email protected]st 桌面]$ systemctl list-units --type=service
UNIT                         LOAD   ACTIVE SUB     DESCRIPTION
abrt-ccpp.service            loaded active exited  Install ABRT coredump hook
abrt-oops.service            loaded active running ABRT kernel log watcher
abrt-xorg.service            loaded active running ABRT Xorg log watcher

1. 檢視所有單元已啟用和已禁用設定

[[email protected] 桌面]$ 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 
accounts-daemon.service                     enabled 
alsa-restore.service                        static  
...

1. 僅檢視失敗的服務

[[email protected] 桌面]$ systemctl --failed --type=service
UNIT          LOAD   ACTIVE SUB    DESCRIPTION
kdump.service loaded failed failed Crash recovery kernel arming
rhnsd.service loaded failed failed LSB: Starts the Spacewalk Daemon

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.

2 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.

控制系統服務

1.驗證程序正在執行

[student@localhost 桌面]$ ps -up 6724
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root      6724  0.0  0.0  82956   104 ?        Ss   7月30   0:00 /usr/sbin/sshd

[[email protected] 桌面]$ ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.5  53912  5672 ?        Ss   7月30   0:04 /usr/lib/syste
root         2  0.0  0.0      0     0 ?        S    7月30   0:00 [kthreadd]
...

2.停止服務(注意許可權問題)

[root@localhost ~]# systemctl stop sshd.service 

3.啟動服務（程序ID已經改變）

[root@localhost ~]# systemctl start sshd.service 

4.重啟服務

[root@localhost ~]# systemctl restart sshd.service 

5.重新載入配置檔案（程序ID不變）

[root@localhost ~]# systemctl reload sshd.service

5.遮蔽服務

系統中裝了相互衝突的服務
遮蔽將在配置目錄中建立連線，使得啟動服務時什麼都不會發生

[root@localhost ~]# systemctl mask sshd.service 
ln -s '/dev/null' '/etc/systemd/system/sshd.service'
[root@localhost ~]# systemctl unmask sshd.service 
rm '/etc/systemd/system/sshd.service'

使系統守護程序在系統啟動時啟動或停止

1.禁用服務，禁用服務並不會iu停止服務。

[root@localhost ~]# systemctl disable sshd.service 
rm '/etc/systemd/system/multi-user.target.wants/sshd.service'

2.啟用服務

[root@localhost ~]# systemctl enable sshd.service 
ln -s '/usr/lib/systemd/system/sshd.service' '/etc/systemd/system/multi-user.target.wants/sshd.service'
[root@localhost ~]# systemctl is-enabled sshd.service 
enabled

systemctl命令摘要