在红帽7我看到
-session optional pam_systemd.so 在/etc/pam.d/system-session 。
我还看到在LFS文档中提到了-前缀： http : //www.linuxfromscratch.org/blfs/view/7.6-systemd/general/systemd.html
请帮我理解这里的情况是什么意思，而不是简单的session 。
引用man pam.conf ：
If the type value from the list above is prepended with a - character the PAM library will not log to the system log if it is not possible to load the module because it is missing in the system. This can be useful especially for modules which are not always installed on the system and are not required for correct authentication and authorization of the login session.