MacOS LaunchDaemon plist for TCP service thats launched on demand when socket is connected to

1-README.md

MacOS LaunchDaemon plist for TCP service thats launched on demand when socket is connected to

This service isn't started at launch, which is by design. The command being launched establishes a tunnel to a virtual machine running on the host using UTM.app. I created a LoginItem that launches the virtual machine at startup using UTM's registered URI handlers. By starting these tunnels lazily, we are able to connect at a time after the virtual machine has already booted and able to be reached on the network. Trying to do this at startup would result in a failure to connect.

Instructions

1. Ensure ssh is configured on the remote machine, you've generated an ssh key and you've copied that ssh key to the remote host.
2. Replace {{ path_to_public_key }} with the full path to the ssh key you generated in step 1.
3. Replace {{ remote_user }} with your username on the remote machine.
4. Replace {{ remote_host }} with the remote hostname or ip address (for virtual machines this will probably be an ip address reachable by your local machine).
5. Replace {{ your_username }} with your username, ex: $ whoami
6. Replace {{ your_groupname }} with an appropriate group name, select from groups returned by $ id -Gn $(whoami), ex: staff.
7. Replace {{ port }} with the remote port you'd like to tunnel locally.
8. Rename the template to remove the prefix and replace template with the port number you want to tunnel: $ mv 2-com.ssh.tunnel.port.template.plist com.ssh.tunnel.port.8080.plist
9. Install the plist: $ sudo install -o root -g wheel -m 644 com.ssh.tunnel.port.8080.plist /Library/LaunchDaemons
10. Load the plist to activate it: $ sudo launchd load -w /Library/LaunchDaemons/com.ssh.tunnel.port.8080.plist

2-com.ssh.tunnel.port.template.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.ssh.tunnel.port.{{ port }}</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/bin/ssh</string>
        <string>-C</string>
        <string>-i</string>
        <string>{{ path_to_public_key }}</string>
        <string>-o</string>
        <string>ControlMaster=auto</string>
        <string>-o</string>
        <string>ControlPersist=16</string>
        <string>-o</string>
        <string>ServerAliveCountMax=2</string>
        <string>-o</string>
        <string>ServerAliveInterval=5</string>
        <string>-W</string>
        <string>localhost:{{ port }}</string>
        <string>{{ remote_user }}@{{ remote_host }}</string>
    </array>
    <key>OnDemand</key>
    <true/>
    <key>UserName</key>
    <string>{{ your_username }}</string>
    <key>GroupName</key>
    <string>{{ your_groupname }}</string>
    <key>inetdCompatibility</key>
    <dict>
        <key>Wait</key>
        <false/>
    </dict>
    <key>Sockets</key>
    <dict>
        <key>Listeners</key>
        <dict>
            <key>SockServiceName</key>
            <string>{{ port }}</string>
        </dict>
    </dict>
</dict>
</plist>