Work around 'ControlPath too long' on Mac OS X

Mac OS X sets TMPDIR to a very long path within /var, so long
that a socket created in that location is too big for a struct
sockaddr_un on the platform, resulting in OpenSSH being unable
to create or bind to a socket in that location.

Instead we try to use the very short and very common /tmp, but
fall back to the guessed default if /tmp does not exist.

Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed