Make sure that it's configured to forward the X connection. If DISPLAY isn't set at all, check your Xshell settings. If DISPLAY is set to a bad value, check your initialization file: make sure that they don't set DISPLAY. OpenSSH uses the first free display number starting at 10 (you'll get a higher number if there are other remote X connections already). It is designed to be uncomplicated for beginners and powerful for professionals.
Xshell Free is a very fast, small, compact and innovative Freeware File Transfer and Networking for Windows PC.
#Xshell 5 terminal backgrounds download
The first thing to check is echo $DISPLAY: does it look reasonable? It would typically be something like localhost:10.0, with the host part localhost because the SSH server is relaying connections the SSH server machine where the X clients will be running to the SSH client machine which is running the X server. Xshell Free application is free to download and offers easy-to-install, easy-to-use, secure, and reliable File Transfer and Networking applications. Then, if xclock doesn't work, you can begin to investigate why. Under a normal SSH connection, either SSH sets DISPLAY automatically, and everything works, or SSH doesn't set DISPLAY, and then setting it manually cannot work because that means SSH isn't relaying the X11 connection. Unless Xshell (which I'm not familiar with) is doing something unusual, you must not set DISPLAY.