Question
Why do I receive "PTY allocation request failed on channel 0" when attempting to use SSH or Terminal?
Answer
The error can occur for a number of reasons and has been noted to be fixed upon rebooting the server or remounting /dev/pts.
The following third-party article provides more discussion and possible resolutions:
https://stackoverflow.com/questions/27021641/how-to-fix-request-failed-on-channel-0/30191214