linux systemd 多种启动方案

背景

此篇文章以nginx服务为例，如果检查nginx服务启动异常（一般语法有误），则启动备选方案。

方案一：定义systemd OnFailure参数

查看systemd 关于nginx的配置文件

编辑文件，添加OnFailure参数，如果nginx启动失败，则启动备选服务nginx.failure.service

vim /lib/systemd/system/nginx.service

[Unit]
Description=nginx - high performance web server
Documentation=https://nginx.org/en/docs/
After=network-online.target remote-fs.target nss-lookup.target
Wants=network-online.target
OnFailure=nginx.failure.service

[Service]
Type=forking
PIDFile=/var/run/nginx.pid
ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"

[Install]
WantedBy=multi-user.target

创建服务nginx.failure.service

vim /lib/systemd/system/nginx.failure.service

[Unit]
Description=nginx backup


[Service]
Type=forking
PIDFile=/var/run/nginx.pid
ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.bak.conf
ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"

[Install]
WantedBy=multi-user.target

重新加载systemd服务

systemctl daemon-reload

方案二：自定义启动shell

查看systemd 关于nginx的配置文件

编辑文件，修改ExecStart启动命令

vim /lib/systemd/system/nginx.service

[Unit]
Description=nginx - high performance web server
Documentation=https://nginx.org/en/docs/
After=network-online.target remote-fs.target nss-lookup.target
Wants=network-online.target

[Service]
Type=forking
PIDFile=/var/run/nginx.pid
#ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
ExecStart=/bin/sh -c '/usr/sbin/nginx -t &&  /usr/sbin/nginx -c /etc/nginx/nginx.conf  || /usr/sbin/nginx -c /etc/nginx/nginx.bak.conf'
ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"

[Install]
WantedBy=multi-user.target

ExecStart启动命令介绍
第一步：检查nginx语法/usr/sbin/nginx -t（默认检查/etc/nginx/nginx.conf）
第二步：nginx语法检查通过，则启动/usr/sbin/nginx -c /etc/nginx/nginx.conf
第三步：nginx语法检查不通过，则启动/usr/sbin/nginx -c /etc/nginx/nginx.bak.conf

重新加载systemd服务

systemctl daemon-reload