Some tips about ubuntu server | or it may works on other linux distributions too

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