# SSH Agent

## 1. Configuration

SSH requires no configuration, but you may put common command line options in `~/.ssh/agent.conf` to avoid repeating them in every invocation.

See `(trezor|keepkey|ledger)-agent -h` for details on the configuration file format.

## 2. Usage

To get your public key so you can add it to `authorized_hosts` or allow
ssh access to a service that supports it, run:

```
(trezor|keepkey|ledger)-agent identity@myhost
```

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<br/>

There are two main ways to use invoke SSH:

##### 1. Run your command with the agent's environment

If you run:

```
$ (trezor|keepkey|ledger)-agent _ COMMAND --WITH --ARGUMENTS
```

the agent is started in the background and the command is executed with environment variables set up to use the SSH agent.  The `_` is an ignored parameter.  The agent will exit after the command completes.

As a shortcut you can run

```
$ (trezor|keepkey|ledger)-agent _ -s
```

to start a shell with the proper environment.

##### 2. Connect to a server directly via `(trezor|keepkey|ledger)-agent`

If you just want to connect to a server this is the simplest way to do it:

```
$ (trezor|keepkey|ledger)-agent user@remotehost -c ARGS FOR SSH
```

## 3. Common Use Cases

### Start a single SSH session
[![Demo](https://asciinema.org/a/22959.png)](https://asciinema.org/a/22959)

### Start multiple SSH sessions from a sub-shell
This feature allows using regular SSH-related commands within a subprocess running user's shell.
`SSH_AUTH_SOCK` environment variable is defined for the subprocess (pointing to the SSH agent, running as a parent process).
This way the user can use SSH-related commands (e.g. `ssh`, `ssh-add`, `sshfs`, `git`, `hg`), while authenticating via the hardware device.
[![Subshell](https://asciinema.org/a/33240.png)](https://asciinema.org/a/33240)

### Load different SSH identities from configuration file
[![Config](https://asciinema.org/a/bdxxtgctk5syu56yfz8lcp7ny.png)](https://asciinema.org/a/bdxxtgctk5syu56yfz8lcp7ny)

### Implement passwordless login

Run:

	/tmp $ trezor-agent user@ssh.hostname.com -v > hostname.pub
	2015-09-02 15:03:18,929 INFO         getting "ssh://user@ssh.hostname.com" public key from Trezor...
	2015-09-02 15:03:23,342 INFO         disconnected from Trezor
	/tmp $ cat hostname.pub
	ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBGSevcDwmT+QaZPUEWUUjTeZRBICChxMKuJ7dRpBSF8+qt+8S1GBK5Zj8Xicc8SHG/SE/EXKUL2UU3kcUzE7ADQ= ssh://user@ssh.hostname.com

Append `hostname.pub` contents to `/home/user/.ssh/authorized_keys`
configuration file at `ssh.hostname.com`, so the remote server
would allow you to login using the corresponding private key signature.

### Access remote Git/Mercurial repositories

Copy your public key and register it in your repository web interface (e.g. [GitHub](https://help.github.com/articles/adding-a-new-ssh-key-to-your-github-account/)):

	$ trezor-agent -v -e ed25519 git@github.com | xclip

Use the following Bash alias for convenient Git operations:

	$ alias git_hub='trezor-agent -v -e ed25519 git@github.com -- git'

Replace `git` with `git_hub` for remote operations:

	$ git_hub push origin master

The same works for Mercurial (e.g. on [BitBucket](https://confluence.atlassian.com/bitbucket/set-up-ssh-for-mercurial-728138122.html)):

	$ trezor-agent -v -e ed25519 git@bitbucket.org -- hg push


## 4. Troubleshooting

If SSH connection fails to work, please open an [issue](https://github.com/romanz/trezor-agent/issues)
with a verbose log attached (by running `trezor-agent -vv`) .

##### Incompatible SSH options

Note that your local SSH configuration may ignore `trezor-agent`, if it has `IdentitiesOnly` option set to `yes`.

     IdentitiesOnly
             Specifies that ssh(1) should only use the authentication identity files configured in
             the ssh_config files, even if ssh-agent(1) or a PKCS11Provider offers more identities.
             The argument to this keyword must be “yes” or “no”.
             This option is intended for situations where ssh-agent offers many different identities.
             The default is “no”.

If you are failing to connect, try running:

    $ trezor-agent -vv user@host -- ssh -vv -oIdentitiesOnly=no user@host