http://blog.51cto.com/11975865/2308030
https://www.jianshu.com/p/247cdbabf389
https://baijiahao.baidu.com/s?id=1617176098301027885&wfr=spider&for=pc
http://blog.chinaunix.net/uid-29792372-id-5767174.html
https://blog.csdn.net/y87329396/article/details/48264731
https://www.nb-fk.com/1032.html
https://blog.csdn.net/Dyminas/article/details/80729574
sudo ocserv -c /etc/ocserv/ocserv.conf -f -d 1
note: setting 'plain' as primary authentication method
note: setting 'file' as supplemental config option
listening (TCP) on 0.0.0.0:4433...
listening (UDP) on 0.0.0.0:4433...
ocserv[2756]: main: initialized ocserv 0.12.1
ocserv[2757]: sec-mod: reading supplemental config from files
ocserv[2757]: sec-mod: error loading file '/etc/ssl/private/server-key.pem'
ocserv[2757]: GnuTLS error (at sec-mod.c:832): Error while reading file.
ocserv[2756]: main: main.c:947: ocserv-secmod died unexpectedly
ocserv[2756]: main: termination request received; waiting for children to die
ocserv[2756]: main: main-sec-mod-cmd.c:106: command socket for sec-mod closed
ocserv[2756]: main: main.c:1203: error in command from sec-mod
ocserv[2756]: main: termination request received; waiting for children to die
[root@izj6cicoumyvpswiuhxb66z CA]#