Lack of network access after disconnecting from a VPN can be a symptom of a routing issue. If your VPN client doesn't disconnect cleanly, the gateway that directs your traffic to the virtual network can sometimes be left in place, effectively routing your traffic to a dead end.

I'd suggest bringing your interfaces down, flushing the routing table of gateway entries, and bringing them up again:

1. Bring your network interfaces down:

   for i in $(ifconfig | egrep -o "^[a-z].+\d{1}:" | sed 's/://'); do sudo ifconfig "$i" down; done
   

2. Flush the routing table: sudo route -n flush.

3. Bring your interfaces back up again: (repeat step 1 with up instead of down).

If you want a reusable Bash function for this that you can drop into your .bashrc (or wherever), you could save the following:

resetroute () {
    echo "Flushing routes...";
    for i in $(ifconfig | egrep -o "^[a-z].+\d{1}:" | sed 's/://');
    do
        sudo ifconfig "$i" down;
    done;
    sudo route -n flush;
    for i in $(ifconfig | egrep -o "^[a-z].+\d{1}:" | sed 's/://');
    do
        sudo ifconfig "$i" up;
    done
}

You can tear down and start up the network interface using:

sudo ifconfig en0 down
sudo ifconfig en0 up

launchctl(8) is your friend. Just keep in mind that some of the services (sshd for example) are disabled in the configuration file so you will need to use the -w switch when loading them. Here is a sshd example:

$ sudo launchctl load -w /System/Library/LaunchDaemons/ssh.plist

You can stop the service using the unload subcommand.

$ sudo launchctl unload  /System/Library/LaunchDaemons/ssh.plist

To list the services, as you might have already guessed use the 'list' subcommand ;)

The standard Reboot UI has the checkbox that could be toggled programmatically:

$ defaults write com.apple.loginwindow TALLogoutSavesState -bool false

You can use scutil interactively from the terminal. Run sudo scutil and run these commands, swapping your DNS servers in where appropriate:

> open
> d.init
> d.add ServerAddresses * 8.8.8.8 9.9.9.9
> set State:/Network/Service/PRIMARY_SERVICE_ID/DNS
> quit

Instead of using 8.8.8.8 and 9.9.9.9 use your DNS servers.

The only problem is this is not persistent across reboots. If you want permanent changes, you'll want ncutil. The reason editing /etc/resolv.conf isn't sufficient in newer versions of OS X is because configd now uses a database to store information of current settings, which other applications read. Certain applications will still read /etc/resolv.conf (host for example), although that is not the case for all applications.

Once you've logged in via ssh then you need to use shutdown with the -r flag (for restart):

$ ssh username@ip-address
$ sudo /sbin/shutdown -r now

Or, to do it all in one command:

$ ssh username@ip-address sudo /sbin/shutdown -r now

You could easily achieve this using mount_smbfs (which is, actually, a wrapper for mount -t smbfs) :

mount_smbfs //user@SERVER/folder ./mntpoint

Optionally, add the workgroup :

mount_smbfs -W workgroup //user@SERVER/folder ./mntpoint

You could, of course, change the ./mntpoint (for something like /Volumes/smb).

After doing this, simply go to ./mntpoint to browse your data.

To unmount, using the following command :

umount ./mntpoint

Specifically for Docker for Mac, because it's a "GUI" app, there's a workaround:

osascript -e 'quit app "Docker"'

Since you'd want to restart, here's the way to open it from the command line:

open -a Docker

There's probably a more symmetrical command to open using osascript, but the open command seems more common than the osascript one.