How to clear bash history completely?

The file ~/.bash_history holds the history.

To clear the bash history completely on the server, open terminal and type

cat /dev/null > ~/.bash_history

Other alternate way is to link ~/.bash_history to /dev/null

However,

One annoying side-effect is that the history entries has a copy in the memory and it will flush back to the file when you log out.

To workaround this, use the following command (worked for me):

cat /dev/null > ~/.bash_history && history -c && exit

What to do:

In every open bash shell (you may have multiple terminals open):

history -c
history -w

Why: As noted above, history -c empties the file ~/.bash_history. It is important to note that bash shell does not immediately flush history to the bash_history file. So, it is important to (1) flush the history to the file, and (2) clear the history, in all terminals. That's what the commands above do.

Reference: http://www.giannistsakiris.com/index.php/2007/09/13/how-to-clear-bash-history-and-what-to-watch-out-for/

execute the following commands to clear history forever

history -c && history -w

good luck!