Add Timestamps to Your Bash History

Put this in your profile script (.bashrc):

export HISTTIMEFORMAT="%d/%m/%y %T "

I also find it helpful to increase the size of my command-line history:

export HISTFILESIZE=10000
export HISTSIZE=10000

The first controls how many are stored. The second controls how many are kept in memory. You can also tweak it to hold an actual unlimited number if you so wish.