syslog错误：
May 8 09:54:21 pptpteste-VirtualBox pppd[2367]: LCP: timeout sending Config-Requests
May 8 09:54:21 pptpteste-VirtualBox NetworkManager[2367]: LCP: timeout sending Config-Requests
May 8 09:54:21 pptpteste-VirtualBox NetworkManager[2367]: Connection terminated.
May 8 09:54:21 pptpteste-VirtualBox pppd[2367]: Connection terminated.
May 8 09:54:21 pptpteste-VirtualBox pppd[2367]: Terminating on signal 15
May 8 09:54:21 pptpteste-VirtualBox pptp[2375]: nm-pptp-service-2351 warn[decaps_hdlc:pptp_gre.c:226]: short read (-1): Input/output error
May 8 09:54:21 pptpteste-VirtualBox pptp[2375]: nm-pptp-service-2351 warn[decaps_hdlc:pptp_gre.c:238]: pppd may have shutdown, see pppd log
May 8 09:54:21 pptpteste-VirtualBox pptp[2382]: nm-pptp-service-2351 log[callmgr_main:pptp_callmgr.c:245]: Closing connection (unhandled)
May 8 09:54:21 pptpteste-VirtualBox pptp[2382]: nm-pptp-service-2351 log[ctrlp_rep:pptp_ctrl.c:258]: Sent control packet type is 12 'Call-Clear-Request'
May 8 09:54:21 pptpteste-VirtualBox pptp[2382]: nm-pptp-service-2351 log[call_callback:pptp_callmgr.c:84]: Closing connection (call state)
May 8 09:54:21 pptpteste-VirtualBox NetworkManager[2367]: Terminating on signal 15
May 8 09:54:21 pptpteste-VirtualBox pppd[2367]: Child process /sbin/pptp 150.161.70.99 --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-2351 (pid 2370) terminated with signal 15
May 8 09:54:21 pptpteste-VirtualBox NetworkManager[2367]: Child process /sbin/pptp 150.161.70.99 --nolaunchpppd --loglevel 0 --logstring nm-pptp-service-2351 (pid 2370) terminated with signal 15
May 8 09:54:21 pptpteste-VirtualBox pppd[2367]: Modem hangup
May 8 09:54:21 pptpteste-VirtualBox NetworkManager[2367]: Modem hangup
May 8 09:54:21 pptpteste-VirtualBox pppd[2367]: Exit.
May 8 09:54:22 pptpteste-VirtualBox NetworkManager[553]: <info> [1588942461.5657] vpn-connection[0x560f4da78590,9cfb61ed-0a2a-4e49-b47c-63ba8b5132b0,"CIN",0]: VPN service disappeared