Using Tramp with Cygwin and GNU Emacs on Windows

I use GNU Emacs 21.2 (aka "NT-Emacs") with Cygwin on Microsoft Windows. With the emacs-lisp package TRAMP, you can use numerous methods for remote editing, similar to how ange-ftp uses ftp. Where security requires it, you can use ssh (specifically, the Cygwin version of OpenSSH), instead of ftp.

If you are familiar with Emacs, Cygwin and OpenSSH, it's not complicated at all. The only major problem is that the elisp packages tramp and cygwin-mount cannot be used together.

Pre-requisites

• GNU Emacs 20.7 or later. You must not be using the cygwin-mount package — it is not compatible with tramp.

• Cygwin, including the openssh package. (The openssh package is not installed by default, you must deliberately select it.)

• You must already be able to connect to the remote host from your Cygwin bash shell, without typing your ssh passphrase or remote password. This means running ssh-agent and ssh-add, and having your public keys installed properly at the remote site. If this is new to you, read the ssh man pages and the local documentation file "C:\cygwin\usr\doc\Cygwin\openssh-<version>.README" (depending on where you installed Cygwin).

• There are some further requirements for the remote host, but if it's a modern UNIX system, it should work fine.

Procedure

1. Install TRAMP. See the resources below for download information. It is sufficient to unpack the tramp/lisp/*.el files into Emacs' site-lisp directory.

2. Put the following statements in your ~/.emacs file:

       (require 'tramp)
       (setq tramp-default-method "smx")
       (setq tramp-debug-buffer t) 

   The last line is optional, but certainly a good idea when trying something new like this with tramp.

3. Ensure that your emacs "bin" directory is in your Cygwin bash shell PATH. For example, in my ~/.bashrc file, I set my PATH as follows:

       export PATH="/usr/local/bin:/bin:/c/gnu/emacs-21.2/bin:/c/WINDOWS/COMMAND:/c/WINDOWS" 

   (I have mounted C: as /c/. You can do likewise or use /cygdrive/c/ instead.)

4. In the Cygwin bash shell, authenticate yourself with ssh-agent and ssh-add. Something like:

       bash$ eval `ssh-agent`
       bash$ ssh-add
       [type your passphrase when prompted] 

5. Start Emacs by typing runemacs in the Cygwin bash shell:

       bash$ runemacs 

6. In Emacs, visit your remote home directory with:

       C-x C-f /[user@remotehost]

   Success! (Right?)

Discussion

• You need the Emacs bin directory in your Cygwin PATH not just to find runemacs.exe, but also so that runemacs can find emacs.exe.

• Invoking runemacs from the Cygwin bash shell does two things. First, it puts C:/cygwin/bin and other Cygwin-related directories in Emacs' exec-path. This is necessary to find ssh.exe and cygwin1.dll, as well as other DLLs required by ssh.exe. Second, it allows ssh to communicate with ssh-agent, through the SSH_AGENT_PID and SSH_AUTH_SOCK environment variables.

References

GNU Emacs

GNU Emacs
GNU Emacs FAQ for Windows

Cygwin

Cygwin Project home page
Cygwin FAQ

Emacs-lisp packages

Tramp home page
cygwin-mount.el from emacswiki.org

OpenSSH

OpenSSH home page

Back to David's Home Page