ssh-key-sync

Command ssh-key-sync is a tool for managing authorized_key files, by synchronizing the contents with public keys managed by accounts on GitHub.

Project Overview

Module github.com/shoenig/ssh-key-sync provides the command ssh-key-sync.

Getting Started

The ssh-key-sync command can be downloaded from the releases page.

Alternatively, you can use Go directly.

go install github.com/shoenig/ssh-key-sync@latest

Example Usage

There are a few arguments, but typically you should only need to specify --github-user. The Linux user and authorized_key file are by default assumed to be of the user running the command.

ssh-key-sync --github-user <user>

Configuration

ssh-key-sync -help
Usage of ./ssh-key-sync:
  -authorized-keys string
    	override the output authorized_keys file (default "/home/$USER/.ssh/authorized_keys")
  -github-api string
    	specify the GitHub API endpoint (default "https://api.github.com")
  -github-user string
    	specify the github user
  -system-user string
    	specify the unix system user (default "$USER")
  -prune
        delete all keys not found in github
  -verbose
    	print verbose logging

Install

The following steps should get ssh-key-sync running as a systemd-timer on any system with systemd. You could also use cron or some other periodic task runner, but these instructions work with most major Linux distrobutions.

These examples use linux and amd64 - be sure to use the correct version for your operating system and architecture.

Download Archive

$ wget https://github.com/shoenig/ssh-key-sync/releases/download/v1.7.2/ssh-key-sync_1.7.2_linux_amd64.tar.gz

Extract Archive

$ sudo tar -C /usr/local/bin -xf ssh-key-sync_1.7.2_linux_amd64.tar.gz

Create `authorized_keys`

$ mkdir ~/.ssh && chmod 700 ~/.ssh
$ touch ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys

Setup Systemd Timer

A great way to keep your authorized_key file up-to-date is to run ssh-key-sync periodically via a systemd timer. To set this up, we will need two files - one service file which represents execution of ssh-key-sync, and a timer file which represents the schedule on which the service should be executed. Use the example below, modifying paths to suite your needs.

The service file `/etc/systemd/system/ssh-key-sync.service`

[Unit]
Description=Synchronize ssh authorized keys with public keys from github.

[Service]
ExecStart=/usr/local/bin/ssh-key-sync -verbose -system-user <user> -github-user <user>

The timer file `/etc/systemd/system/ssh-key-sync.timer`

[Unit]
Description=Run ssk-key-sync every 6 hours

[Timer]
OnBootSec=5min
OnUnitActiveSec=6h
Unit=ssh-key-sync.service

[Install]
WantedBy=timers.target

Enable the timer

$ sudo systemctl daemon-reload
$ sudo systemctl enable ssh-key-sync.timer

See if it works

The timer will run in the background on its schedule, but it's nice to run the service immediately so we can see that it is working correctly. To do that, just start the service.

$ sudo systemctl start ssh-key-sync.service

And now we can view the status to make sure it ran correctly.

$ sudo systemctl status ssh-key-sync

You should see some output like,

○ ssh-key-sync.service - Synchronize ssh authorized keys with public keys from github.
     Loaded: loaded (/etc/systemd/system/ssh-key-sync.service; static)
     Active: inactive (dead) since Tue 2023-04-11 15:29:32 CDT; 2s ago
   Duration: 236ms
TriggeredBy: ○ ssh-key-sync.timer
    Process: 2104 ExecStart=/usr/local/bin/ssh-key-sync -verbose -system-user shoenig -github-user shoenig (code=exited>
   Main PID: 2104 (code=exited, status=0/SUCCESS)
        CPU: 22ms

Apr 11 15:29:32 localhost.localdomain systemd[1]: Started Synchronize ssh authorized keys with public keys from github..
Apr 11 15:29:32 localhost.localdomain ssh-key-sync[2104]: 2023/04/11 15:29:32 using default output authorized_keys file>
Apr 11 15:29:32 localhost.localdomain ssh-key-sync[2104]: 2023/04/11 15:29:32 process local user shoenig from shoenig@g>
Apr 11 15:29:32 localhost.localdomain ssh-key-sync[2104]: 2023/04/11 15:29:32 loaded 0 existing keys for user "shoenig"
Apr 11 15:29:32 localhost.localdomain ssh-key-sync[2104]: 2023/04/11 15:29:32 acquire github keys from "https://api.git>
Apr 11 15:29:32 localhost.localdomain ssh-key-sync[2104]: 2023/04/11 15:29:32 retrieved 10 keys for github user: shoenig
Apr 11 15:29:32 localhost.localdomain systemd[1]: ssh-key-sync.service: Deactivated successfully.

It works! And inspecting the ~/.ssh/authorized_keys file should reveal it contains your public keys from GitHub.

Contributing

The github.com/shoenig/ssh-key-sync tool is always improving with new features and error corrections. For contributing bug fixes and new features please file an issue.

License

MIT

shoenig/ssh-key-sync