Maximum ptys

Andy Koppe
Sat Dec 18 16:12:00 GMT 2010

On 18 December 2010 02:58, Rob B wrote:
> I seem to be hitting my maximum pty limit after running my cygwin
> machine for about a week.  I open rxvt terminals and have an openssh
> server.  rxvt on the machine and connections via ssh work fine after
> reboot.  After about 1 week goes by I get messages about failure to
> allocate a pty.
> Once this happens, I can't open an rxvt at the machine anymore (get
> error message: can't open pseudo-tty), or ssh in (get error message:
> PTY allocation request failed on channel 0).
> If I shut down an existing rxvt window on my machine, I can create one
> more rxvt (or connect via ssh one more time), but then I hit the limit
> again (get the failure messages) when I try to open another one.  I
> don't have many windows open, but I think ptys may not be getting
> freed when ssh connections shut down in a not so nice way.
> In cygwin, how do I determine how many ptys are in use?
> How do I determine which processes are using a pty?

The TTY column in the output of 'ps' shows that.

> I found the following link with Google, but the procedure does not
> work for cygwin:

The limit is hard-coded to 128 tty devices in Cygwin, which means
there can be up to 64 pty master/slave pairs. You'd have to rebuild
the Cygwin DLL to change it.


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