Linux – Debugging frozen Gnu screen session

debiangnu-screenlinux

We've been using GNU screen on our jump box to have ssh sessions open to multiple hosts within our private network. One window per host.

Recently we've built a new environment and are experiencing frequent screen hangs.
Most often when a lot of terminal output is being spooled to the screen (cat'ing a file for instance), screen becomes unresponsive. The terminal stops updating mid-command, and I can't switch to any other screen window.

I can log into the jump box again, and do a screen -dr , and it attaches like nothing was the matter.
The .screenrc we use is:

bindkey -k k2 screen
bindkey -k k3 prev
bindkey -k k4 next
bindkey -k k7 copy
bindkey -k k8 title
bindkey -k k9 windows
startup_message off
hardstatus alwayslastline
hardstatus string "%-w%{= BW}%50>%n %t%{-}%+w%<"
nonblock on

While a screen session is frozen like this, can you suggest what I should be looking at to work out what the cause is because I'm fairly stumped?

This is under debian wheezy, screen=4.1.0~20120320gitdb59704-7, and these are EC2 instances in case that's relevant.

Best Answer

On occasion, the xterm you're using gets a Ctrl-S from whatever output is being parsed. This causes the session to "lock" in place (like a "pause"), and you can hit Ctrl-Q to resume. There have been several instances where this happens.

History: Ctrl-S sends a "Software Flow Control Off (XOFF)" to the remote host, Ctrl-Q sends the XON.

SSH Tip: If the above doesn't work; Next time the SSH session hangs on you, type ~. (that's "Tilde" and "dot". That should axe the hung SSH session and get you back to screen.

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