This is a document that assists with the troubleshooting of an Asterisk based PABX that is not working properly.
It was done based on a FreePBX installation, but it could work with most Asterisk installations as Asterisk is command line driven. The only problem you may encouter here is that some of these commands to not work on some versions of Asterisk, e.g. MikoPBX.
Core Show Channels
Check if the service is running
Do this using SSH
service asterisk status
Check if a SIP trunk is registered
First log in to the command line utility
asterisk -rv sip show peers
Check which extensions are registered
asterisk -rv core show hints
Look for `State:Idle`