Mount usb-hdd/usb-flash disk to Ubuntu Server:
1, plug the hardware
2, run below command, see which maybe the device name
tail -f /var/log/messages
3, mount it
sudo mount -t <file system type|vfat> <device name|/dev/sdb2> <path to mount|/mnt>
Install Linux header files (maybe for vmware server):
1, run
uname -r
2, run
sudo apt-get install linux-headers-<output from the last command>
Removed your only account out of sodoers:
1, reboot machine.
2, press esc when grub loading
3, select "recovery mode (single root)" mode
4, run
usermod -g admin <username>
5, exit