Command line auto complete tab key not work in terminal for Ubuntu

I had this problem using XFCE and TigerVNC: pressing tab just switched between the terminals I had open. It was solved by following the directions given in the link @Jonas provided: http://how-to.cc/fix-bash-command-line-completion. I will copy a few pieces in here in case the link should ever be broken.

Step 1:

Make sure that your .bashrc file contains something like

if [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
fi

so that a file containing bash completion info is actually sourced. In my case, /etc/bash_completion pointed to /usr/share/bash-completion/bash_completion which contained the stuff to set up. For reference, the end of my .bashrc looked like this:

if ! shopt -oq posix; then
  if [ -f /usr/share/bash-completion/bash_completion ]; then
    . /usr/share/bash-completion/bash_completion
  elif [ -f /etc/bash_completion ]; then
    . /etc/bash_completion
  fi
fi

Step 2:

Disable the behaviour of tab changing windows. This is done in the file ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-keyboard-shortcuts.xml by changing the line

<property name="&lt;Super&gt;Tab" type="string" value="switch_window_key"/>

to

<property name="&lt;Super&gt;Tab" type="empty"/>

Step 3:

Reboot or restart your VNC server (XFCE).

Try this,

1. Open the Xfce Application Menu > Settings > Window Manager
2. Click on the Keyboard Tab
3. Clear the Switch window for same application setting

Refer here.

The XFCE Terminal has kidnapped the tab key for a feature of it's own, tab/windows switching. Instead the normal tab is sent if you press CTRL-tab.

I say this is a mistake on the design of XFCE Terminal emulator, but theres no way I know to get rid of the kidnapping of tab!