Write a short debugging guide

[dguido]

This would be a section at the bottom of the Troubleshooting guide to help people who want to investigate on their own.

Algo server

ipsec statusall
ipsec leases | head -1
journalctl -f -u strongswan
journalctl -f SYSLOG_IDENTIFIER=charon

macOS

Console: search for nesessionmanager
log show --predicate 'subsystem == "com.apple.networkextension"' --info --last 1h
/var/log/racoon.log
Increase logging: https://forums.developer.apple.com/thread/31375
https://developer.apple.com/bug-reporting/profiles-and-logs/?name=vpn

Ubuntu 17.04

Windows 10

[TC1977]

Other useful commands to run on the Algo server:

service strongswan status to check the ipsec status
service dnscrypt-proxy status to check on dns resolution
service dnsmasq status for adblocking
dmesg for apparmor or memory-related errors
grep "charon.*IKE_SA.*established.*username" /var/log/syslog to find connection times and IP addresses for username
journalctl -u strongswan|grep unable to find the "unable to install policy" error with iOS/macOS clients as in #963
tail -f /var/log/syslog|grep charon to keep a running log

[TC1977]

Also useful to remind people to check their cloud firewall (e.g. #1215) and their router settings (esp port forwarding or ESP forwarding #520, #727). And check IP settings as in #1130.