systemctl enable 不起作用

Question

为什么在以下所有尝试启用或重新启用时，systemctl 都没有给出错误消息[电子邮件保护]明显失败

~ $ systemctl list-unit-files | grep enabled  
[email protected]                            enabled          
[email protected]                             enabled          
systemd-fsck-root.service                  enabled-runtime  
remote-fs.target                           enabled          
~ $ sudo systemctl enable [email protected]   
~ $ systemctl list-unit-files | grep enabled  
[email protected]                            enabled          
[email protected]                             enabled          
systemd-fsck-root.service                  enabled-runtime  
remote-fs.target                           enabled          
~ $   sudo systemctl unmask [email protected]   
~ $   sudo systemctl reenable [email protected]   
Removed /etc/systemd/system/multi-user.target.wants/[email protected].  
Created symlink /etc/systemd/system/multi-user.target.wants/[email protected] → /usr/lib/systemd/system/[email protected].  
~ $ systemctl list-unit-files | grep enabled  
[email protected]                            enabled          
[email protected]                             enabled          
systemd-fsck-root.service                  enabled-runtime  
remote-fs.target                           enabled          
~ $   sudo systemctl start [email protected]   
~ $ systemctl list-unit-files | grep enabled  
[email protected]                            enabled          
[email protected]                             enabled          
systemd-fsck-root.service                  enabled-runtime  
remote-fs.target                           enabled          

上面创建的符号链接指向 /usr/lib/systemd/system/[电子邮件保护]，它具有这些特点。

~ $ systemctl -a list-unit-files|grep [email protected]  
[email protected]                            static           
~ $ systemctl status [email protected]  
Failed to get properties: Unit name [email protected] is neither a valid invocati>  
~ $ sudo systemctl enable [email protected]  
The unit files have no installation config (WantedBy, RequiredBy, Also, Alias  
settings in the [Install] section, and DefaultInstance for template units).  
**This means they are not meant to be enabled using systemctl.**  
Possible reasons for having this kind of units are:  
1) A unit may be statically enabled by being symlinked from another unit's  
   .wants/ or .requires/ directory.  
2) A unit's purpose may be to act as a helper for some other unit which has  
   a requirement dependency on it.  
3) A unit may be started when needed via activation (socket, path, timer,  
   D-Bus, udev, scripted systemctl call, ...).  
4) In case of template units, the unit is meant to be enabled with some  
   instance name specified.