在Serivce单元文件中使用管道
#!/bin/sh # 在指令ExecStart的参数中，命令后的内容会被视为参数，所以对于管道应该使用如下形式： ExecStart=/bin/sh -c '/apppath/appname > /filepath/filename 2>&1' # 下面是一种错误的用法： ExecStart=/apppath/appname > /filepath/filename 2>&1 # 则systemd会将/apppath/appname视为参数，而“>”、“/filepath/filename”、“2>&1”则会被视为命令参数。
“运行级别”
在 systemd 中，已经没有了以往“运行级别”的概念了，而是“目标（Target）”。下面是“运行级别”和“目标”的对应关系：
Run level 0 is matched by poweroff.target (and runlevel0.target is a symbolic link to poweroff.target).
Run level 1 is matched by rescue.target (and runlevel1.target is a symbolic link to rescue.target).
Run level 3 is emulated by multi-user.target (and runlevel3.target is a symbolic link to multi-user.target).
Run level 5 is emulated by graphical.target (and runlevel5.target is a symbolic link to graphical.target).
Run level 6 is emulated by reboot.target (and runlevel6.target is a symbolic link to reboot.target).
Emergency is matched by emergency.target.
Run level 1 is matched by rescue.target (and runlevel1.target is a symbolic link to rescue.target).
Run level 3 is emulated by multi-user.target (and runlevel3.target is a symbolic link to multi-user.target).
Run level 5 is emulated by graphical.target (and runlevel5.target is a symbolic link to graphical.target).
Run level 6 is emulated by reboot.target (and runlevel6.target is a symbolic link to reboot.target).
Emergency is matched by emergency.target.
查看默认“目标”：systemctl get-default
设置默认“目标”：systemctl set-default multi-user.target
变更“运行级别”：systemctl isolate multi-user.target
How to Change Runlevels (targets) in SystemD
参考文献
How to Pipe Output to a File When Running as a Systemd Service?