systemd

centos7 編寫測試服務
bak.sh腳本內容：

cp -a /etc/sysconfig /app/sysconfig-bak >> /dev/null

bak腳本要加執行權限

服務Unit文件示例

[Unit]
Description=backup /etc
Requires=atd.service
[Service]
Type=simple
ExecStart=/bin/bash -c "echo /lib/systemd/system/bak.sh|at now"
[Install]
WantedBy=multi-user.target

運行級別

ls /usr/lib/systemd/system/*.target

`運行級別：
    0 ==> runlevel0.target, poweroff.target
    1 ==> runlevel1.target, rescue.target
    2 ==> runlevel2.target, multi-user.target
    3 ==> runlevel3.target, multi-user.target
    4 ==> runlevel4.target, multi-user.target
    5 ==> runlevel5.target, graphical.target
    6 ==> runlevel6.target, reboot.target
    `

設置默認運行級別

systemctl set-default multi-user.target    
等同於建立軟連接：
ln  -s  /usr/lib/systemd/system/multi-user.target   /etc/systemd/system/default.target

刪除軟連接使用原來默認運行級別
rm  -f   /etc/systemd/system/default.target