经过多年的稳定登录后，在 Windows 10 下在 cygwin 上执行 ssh 最近开始失败。来自 Xwindows 的 mintty 下 ssh 的相关输出：
% ssh -tt -vvv <user@host>
debug3: Failed to open file:C:\\ProgramData\\ssh/ssh_known_hosts error:2
debug3: Failed to open file:C:\\ProgramData\\ssh/ssh_known_hosts2 error:2
debug3: failed to open file:/dev/tty error:3
debug1: read_passphrase: can't open /dev/tty: No such file or directory
debug3: spawning /usr/X11R6/bin/ssh-askpass
CreateProcessW failed error:2
ssh_askpass: posix_spawn: No such file or directory
Host key verification failed.
特殊文件 /dev/tty 在那里：
% ls -la /dev/tty
crw-rw-rw- 1 jpmattia None 5, 0 May 22 15:04 …