Possible Duplicate: Avoid to keep command in history
Is there a facility to skip history for some commands in Linux?
How can I skip history for a login?
When I login as user abc, I don't want my machine to save commands history for user abc.
abc
You can use export the HISTIGNORE variable for this user. Have a look at this. To make it permanent, you need to export it in a file like ~/.bashrc.
HISTIGNORE
~/.bashrc