Pushing with Magit from Windows

Chris Smith edited this page Jan 3, 2017 · 13 revisions

Table of Contents

Introduction

Windows does not have the concept of a PTY, so there is no way for Emacs to intercept password prompts from Git. You will get an error message like

bash: /dev/tty: No such device or address
error: failed to execute prompt script (exit code 1)
fatal: could not read Username for 'https://github.com': No error

NOTE: Git for Windows 1.x simply hangs indefinitely.

It's possible to work around this by configuring Git so that Magit doesn't need to send it a password, there are several methods to do this.

The following assumes native Emacs and Git for Windows (version 2 or greater is highly recommended).

Before starting: set HOME

If you haven't explicitly set the HOME environment variable, do so now. Not doing this means git (and ssh) will use a different HOME depending on whether or not they were called from Emacs. For https remotes this will only have the effect of ignoring any .gitconfig you may have set. But if OpenSSH can't find it's config files (especially known_hosts), you won't be able to use it from magit at all.

The easiest way is to run setx HOME C:/path/to/home from a cmd.exe console. See What are PATH and other environment variables, and how can I set or use them? for more information.

Note that you should move your config files from whichever HOME you didn't choose to the new common one.

git-gui--askpass

If you access the remote over https, the GIT_ASKPASS environment variable can be used to tell git to use a gui prompt for the password. Add the following to your init file:

(setenv "GIT_ASKPASS" "git-gui--askpass")

It will be quite annoying to enter your username and password every time, so you should also use password caching: run git config --global credential.helper wincred to enable it (requires Git for Windows 1.8.1 or greater)

Pros:

  • No additional installation needed: the "git-gui--askpass" program comes builtin with git.

Cons:

  • The GUI prompt doesn't mesh so nicely with Emacs

NOTE: In Git for Windows 1.x, if you press cancel at the prompt Magit will still hang.

Troubleshooting

Check that your remote is using an https url.

This should work from cmd.exe (assuming you have git.exe in %PATH%). First run set GIT_ASKPASS=git-gui--askpass to simulate the Emacs setup given above.

Passphrase-less OpenSSH key

If git uses a passphrase-less SSH key, then there is no need to type in anything. The procedure for installing keys depends on the remote, for Github see https://help.github.com/articles/generating-ssh-keys/.

Pros:

  • No additional installation needed: OpenSSH comes installed with Git for Windows.
  • Don't need to type anything after the 1 time setup.

Cons:

  • It's not secure to use a passphrase-less key: read access to the private key file on your dev machine now gives write access to any remotes!

Troubleshooting

Check that your remote is using an SSH url.

Make sure you have explictly set HOME (see above).

Check that you can run git push from the command line without entering any password/passphrase.

OpenSSH passphrase caching, via ssh-agent

If an OpenSSH key is protected by a passphrase, it can be used with Magit by caching the passphrase with ssh-agent. Install the ssh-agency package to manage this for you.

Also add

(setenv "SSH_ASKPASS" "git-gui--askpass")

to your init file to get a graphical prompt on the first where you need to enter your passphrase (the alternative is ssh-agency pops up a console cmd.exe style window).

Pros:

  • No additional installation (apart from a small Emacs package) needed: OpenSSH comes installed with Git for Windows.
  • Don't need to type anything after entering the passphrase on startup.
  • Secure: your SSH keys cannot be used without entering the passphrase.

Cons:

  • One more package to install.

Note: The SSH_ASKPASS setting does not work with Git for Windows 1.x (see https://stackoverflow.com/questions/10960269/git-ssh-askpass-on-windows). If you have a reference to where/when/how this was fixed in Git for Windows 2.x please edit it in.

Troubleshooting

Check that using a passphrase-less key works first.

Check the result of evaluating:

(list ssh-agency-add-executable (file-executable-p ssh-agency-add-executable)
      ssh-agency-agent-executable (file-executable-p ssh-agency-agent-executable))

You should get something like ("c:/Program Files (x86)/Git/bin/ssh-add.exe" t "c:/Program Files (x86)/Git/bin/ssh-agent.exe" t)

If you get nil instead of t, customize ssh-agency-add-executable and ssh-agency-agent-executable to the correct paths (this should only be necessary if you installed ssh in a non-standard place).

If it still doesn't work, try running:

(call-process-shell-command
  (concat "start \"ssh-add\" cmd /K" (shell-quote-argument ssh-agency-add-executable)))

This will open a console. If you didn't get prompted to input your passphrase, try running the following commands at the console (adjusting the ssh-add.exe paths if needed):

"c:/Program Files (x86)/Git/bin/ssh-add.exe" -l
"c:/Program Files (x86)/Git/bin/ssh-add.exe" path/to/your/ssh/key/

Customize ssh-agency-keys so ssh-agency will find your keys automatically from now on.

Using SSH keys with PuTTY

It's possible to use PuTTY to manage SSH keys instead of OpenSSH. This is similar to using ssh-agent, the main difference is that PuTTY's pagent (its ssh-agent equivalent) is GUI based, and is accessible from an icon in the system tray.

  1. Download plink.exe, pagent.exe, and puttygen.exe from https://www.chiark.greenend.org.uk/~sgtatham/putty/download.html.
  2. Set the GIT_SSH variable to the full path of plink.exe. On a Windows 10 system configured with MSys2 for Bash usage, /C/Program\\ Files\\ \\(x86\\)/PuTTY/plink.exe worked with the eLisp expression below.
  3. Generate (or import an existing OpenSSH) private key using puttygen.exe.
  4. Install the public key on the remote (as for OpenSSH the exact procedure here depends on the server).
  5. Start pagent.exe and add the key.
  6. 1st time connecting to a host only: execute plink <user>@<hostname> and answer yes to add the host's key to the list of known hosts.

See also: http://gitolite.com/gitolite/putty.html - general instructions for using PuTTY with git.

Pros:

  • Don't need to type anything after entering the passphrase on startup.
  • Secure: your SSH keys cannot be used without entering the passphrase.

Cons:

  • Need to install additional software.

Troubleshooting

  • Check that your remote is using an SSH url.

  • Check that (getenv "GIT_SSH") returns the full path to plink.exe, so you should get something like plink: Release 0.64 when evaluating the code below:

(shell-command-to-string (concat (getenv "GIT_SSH") " -V"))
  • Check the output from running plink <user>@<hostname> from cmd.exe.
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