PTY allocation request failed on channel 0
There is a limit of 256 pseudo terminals on a system. Maybe you have an application that is leaking pseudo terminals. Use
lsof /dev/pts/*
to see what processes have open pseudo-terminals
shell request failed on channel 0
I was getting this error (without PTY allocation error). It turns out that one of my applications (QtCreator 3.0.?) was leaking Zombie processes. Other users were able to log in so I might have been hitting my per user process quota (if there is such a thing). I’ve updated to QtCreator 3.3. So far so good.