Tethering a Linux machine inside VirtualBox

Yes you can.


Today I needed to test an openconnect VPN connection while inside a LAN. At this site my desktop is Windows but I needed to check connectivity from outside for Linux users, using the openconnect and NetworkManager-openconnect packages.


Let's see, I could plug my smartphone into the USB port of the desktop, forward the USB connection to Fedora 16 inside VirtualBox and I should be able to connect to usb0 and I would have a WAN connection from outside. Right?


To cut to the chase, it just works.


In the VirtualBox, make sure USB forwarding is enabled in the VM settings. Plug in the smartphone and turn on USB tethering. Ignore Windows suggestions to install hardware drivers for your smartphone. When the VM is running, there will be a USB icon on the bottom bar. Choose the USB device that is your smartphone. Windows will suggest installing a VirtualBox USB driver. Do that. On Linux a usb0 device should appear in the network manager and after disabling the eth0 device which forwards to Windows, you can connect to it. You should then get a DHCP lease from your smartphone and be connected to the outside world.


It seems you have to install the VirtualBox USB driver every time the VM is started, not sure why.


This should work on other distros. For example I know openconnect works on Debian and Ubuntu. It should also work for other VPN technologies, such as openvpn. The USB network driver is called cdc-ether, by the way.

Two gotchas with Postfix, Dovecot, Amavis and Clamav on Debian Squeeze

1. The first problem was when this error appeared in /var/log/mail.log:


Mar 10 16:56:39 mailhost amavis[2877]: (02877-01) (!)ClamAV-clamd av-scanner FAILED: CODE(0x358cef8) unexpected , output="/var/lib/amavis/tmp/amavis-20120310T165639-02877/parts: lstat() failed: Permission denied. ERROR\n" at (eval 103) line 594.


The problem is that clamav requires access to files created by amavis. We fix this by putting amavis and clamav in each other's group.



usermod -a -G clamav amavis

usermod -a -G amavis clamav

Then restart amavis and clamav-daemon.

2. The second problem was when postfix could not authenticate incoming SMTP connections by chaining to dovecot's auth process, resulting in this message in /var/log/mail.log:

Mar 10 18:28:14 mailhost postfix/smtpd[7217]: warning: SASL: Connect to /var/run/dovecot/auth-client failed: No such file or directory

The problem is that postfix runs chrooted by default in Squeeze and this named pipe is outside of the chroot tree. To fix it we tell dovecot to use this path instead:

/var/spool/postfix/private/auth-client


Then in /etc/postfix/main.cf we specify the path to the named pipe with:



smtpd_sasl_path = private/auth-client


It's a path relative to $queue_directory which is /var/spool/postfix.