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I'm able to connect using Rexec with X11 forwarding from a Windows PC using Mocha, however I need to find a method of achieving the same from a Mac.

I doubt it makes any difference, but the remote host runs VMS.

Can anyone offer any pointers to get me up and running?

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up vote 3 down vote accepted

Well I'm not familiar with Rexec, but if it's a standard x11 program then this should hopefully work.

First you'll need to install X11 on your Mac. I don't think there's a stand alone installer available for download, but you should be able to install it from your Mac OS X Installation disk. Should say something like Optional Extras.

I personally just install the full Xcode developer tools package which installs a bunch of required software for installing software from source code.

Next you'll need to to ssh to the box that will be running the X11 app. Open Terminal (in Application > Utilities) and run the ssh command with the -Y flag (I used -Y instead of -X for security reasons. If this doesn't seem to work you can use ssh -X instead, but it's not recommended. See the man page on ssh.):

ssh -Y username@hostname

Once logged in you can run the app from the command line (if it's in your $PATH):


Hopefully that's all you need to do. You might have better luck doing those two commands from xterm (instead of Terminal). For more information on X11 forwarding from/to a Mac check out Configuring and Running X11 Applications on Mac OS X from Apple's website.

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Thanks. I've added X11 from my install disk, unfortunately SSH isn't an option on the remote host. I can telnet into the host, but that won't give me X forwarding. I'm told the way to connect to get X forwarding to work is via rexec (512/TCP). Much like yourself, I'm not familiar with rexec at all. – Bryan Feb 27 '10 at 16:12
Why is SSH not an option? – grawity Feb 27 '10 at 17:47
@Grawity: The host is a part of a industrial control system. We can't simply make changes without going through lengthy approval processes and testing. If there was a requirement for a change, it isn't a problem, but asking to add SSH just so I can connect from my mac isn't going to be approved. I can connect via a windows PC, so it isn't a problem, it would just be nice not to have to use a Virtual Machine or to have to dig my laptop out. – Bryan Feb 28 '10 at 11:53
Bryan: You could try pushing SSH as a "security improvement" (which it is; rexec and the like are quite insecure)... Anyway. In Unix-like server systems, you could set the remote $DISPLAY variable to, say,, where was your own external IP -- then X11 connections would be made directly over TCP. On VMS, seems to have the answer. Don't forget to configure your X server (Mocha) and your router to accept X11 connections. – grawity Feb 28 '10 at 14:11

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