crond runs /bin/sh not /bin/bash

Got caught by this today. Cron jobs normally run /bin/sh, not /bin/bash. It's probably required POSIX behaviour.

Normally most commands run out of cron are not affected because they are not dependent on bash, or the shell script starts with #!/bin/bash. However commands like vncserver which start up desktops (e.g. with the @reboot time spec) can be sensitive to the shell used because of environment scripts in /etc/profile.d.

Therefore if you want to ensure that the cron job works the same whether run interactively or from a crontab, specify the shell. E.g.

@reboot SHELL=/bin/bash /usr/bin/vncserver ...

VM in VirtualBox using unbound WiFi interface on host

I have a Linux host with 2 interfaces, a wired gigabit Ethernet and WiFi. Currently only the wired interface is connected. I wanted to experiment using WiFi interface by a VM guest in VirtualBox. There are various scenarios for this. I might want to test network routing by using the WiFi in conjunction with a smartphone offering tethering. Or access the Internet using from a VM on the desktop using the smartphone when the broadband connection is down.

The short answer is yes, this is eminently possible. The key points to take away are that, 1. the host has to configure the WiFi interface, i.e. load the appropriate driver and authenticate to the access point but not assign an IP address to it, and 2. the guest has to use bridging to access the host's WiFi interface. In fact it will appear to be a wired interface to the guest. All the usual IP configuration methods are available, static or DHCP, depending on what the access point allows. Also note that the MAC address seen by the gateway will be the MAC of the guest, not the MAC of the WiFi interface.