I have two network interfaces in my Ubuntu guest (on OS X 10.4 host), one NAT, one host-only.

Sometimes one of them doesn’t get an IP address — in ifconfig it has an inet6 address but not an inet address.

Today I tried

sudo dhclient eth1

and it worked — all it needed to do was re-query VirtualBox’s built-in DHCP server.

I would have thought this would do that automatically:

sudo /etc/init.d/networking restart

However that didn’t help… But dhclient did.

Another recurring problem is that when I move between different networks, DNS resolution gets screwed up. There’s a description of this with a suggested work around (using VBox’s DNS Proxy) here:

http://forums.virtualbox.org/viewtopic.php?f=1&t=28332

However, while this seemed to help with two of the networks I use frequently, it didn’t with a third, even after rebooting.

So, as suggested on one or two threads, I’ve removed the DNSProxy setting, and set the Ubuntu guest to use Google’s public DNS servers instead of those provided by the DHCP server for the NATted virtual NIC. (Blah blah blah.) Follow example here (more or less):

http://grumpymole.posterous.com/how-to-use-google-public-dns-or-opendns-in-ub

Seems to be working so far… But only tested on one of the offending networks, and without rebooting yet. Updates to come later.

… Nope, after upgrading to Snow Leopard and the latest VirtualBox (it’s now from Oracle — scary), random problems persist.

Sometimes I’ll lose guest-host connectivity in the middle of a session, without any sleep or other interruptions, but will still be able to see the internet from the NAT adaptor.

One possible solution here involving using OS X itself as the NAT router:

http://akutz.wordpress.com/2009/08/20/building-a-better-os-x-firewall-or-how-i-solved-the-nat-problem-for-virtualbox/

… but it’ll take work.

Or maybe a simpler version of the same approach: have a single host-only adaptor, use OS X’s internet sharing to share the AirPort card, and manually tell the vbox to use 192.168.56.1 as the default gateway:

http://forum.virtualbox.org/viewtopic.php?f=1&t=26544

If all else fails, try using a different ethernet hardware emulator.

This is fine in native desktop apps, but less fine in some text-mode programs (e.g. vim), when for some reason this often produces a superscript ³ instead.

So I’ve set up a custom keyboard mapping in iTerm to map F3 to #, which works nicely. However!

If I’m SSHed in to a remote Linux machine (or even my local Ubuntu VirtualBox) neither of these keys work in X apps. But, xmodmap (via the config file ~/.Xmodmap) can help. For some reason, Macs all have a dedicated key for these characters — § and ± — which no-one ever uses. But with this line in ~/.Xmodmap we can remap it to produce #:

keycode 18=numbersign

UPDATE: I’ve found a better way which works pretty much globally…

Using Ukelele you can copy the British keyboard layout and then remap keys to your heart’s content. I’ve moved the § character to the alt-§ key combination, in case I ever need it, and moved the # character to the raw § key. This seems to be respected almost everywhere so I don’t need to mess around with alt-3 or F3 any more. Joy. It also works over JollysFastVNC to a remote RealVNC server, which none of the other methods did.

Unfortunately, things still aren’t perfect. If I actually open a VirtualBox console session into GNOME on the local Ubuntu VM, the pointless § and ± key actually produces < and > so neither of these tricks work. In fact, I can’t get anything to generate a # even though I have the MacBook Pro Intl keyboard layout selected in GNOME. Any ideas?

UPDATE 2: YES!! I’ve finally cracked it for VirtualBox. With the help of the xkeycaps command, I discovered that X the keycodes coming into Ubuntu weren’t what I thought they were — somewhere the Mac-ness of the keyboard layout was getting lost. It turned out that the § key was generating keycode 94 instead. So I set up this in .Xmodmap on the Ubuntu VM:

keycode 94=numbersign

Now it works in VirtualBox too. Leave gifts of thanks below :-)