I want to know the time that a long process was started.
How can I see the time when each bash command was given?

I don't know exactly how to do this, but date is a programme that will print out the date and time of when you called it, so if you had a programme called some_programme, entering date && some_programe will print out the date and time, then execute the programme. If the programme had a lot of input/output it could be a pain.

Bringing this to the next level if you entered WHEN=`date` && some_programme && echo $WHEN then it'd execute the programme then print out when that programme was executed. You could put this all in a bash script to make it easier.

suguru, I do not think it is possible. bash saves its commands into ~/.bash_history with one command per line. It does not save the time of each command. So, although you cannot see when you executed a particular command, you can follow Ebel's instructions for seeing how long a process has been running.

Alternately, you can change your bash prompt via the PS1 variable (see this page) to display the time for the PROMPT. So for example like this:
In this case, you can implicitly see how long each command took to execute before exiting and returning to the prompt.