openssh PTY allocation

Darren Tucker dtucker at
Sun Jul 24 11:24:45 EST 2011

On Sun, Jul 24, 2011 at 4:47 AM, Mordechai T. Abzug <morty at> wrote:
> We recently upgraded to openss 5.8p2 from a somewhat older version.
> This broke openssh login to ScreenOS devices.  These devices don't
> support PTY allocation.  Apparently, ssh now reacts to PTY allocation
> failure by failing the login.  This is a change from the previous
> behavior.  The simple workaround is ssh -T $device.
> There don't seem to be any ssh_config options that control PTY
> allocation behavior.  Any way we can get some options?  There should
> be at least one, maybe two ssh_config options to control PTY behavior:
> one to control the PTY failure behavior, something like
> ExitOnPTYFailure yes|no|no-warn, and one to give the equivalent of -T
> or -t, i.e. something like PTYEnable: yes|no|force-yes|yes-if-login.

Damien already added a config option ("RequestTTY") but there hasn't
been a release since then (this problem didn't become apparent until
after the 5.8 release when people used it with the problem devices).

             Specifies whether to request a pseudo-tty for the session.  The
             argument may be one of: ``no'' (never request a TTY), ``yes''
             (always request a TTY when standard input is a TTY), ``force''
             (always request a TTY) or ``auto'' (request a TTY when opening a
             login session).  This option mirrors the -t and -T flags for

Darren Tucker (dtucker at
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.

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