Be advised that the location of the history file for both Kshell and bash is controlled with the
HISTFILE environment variable. If a user sets this, (I do, and most people I work with do), you might not find anything or everything that you expect. Further, history won't have any details about commands that were executed from scripts started from the command line, nor will it have any information about what users are executing from at or cron.
Depending on what your goal is, you might consider using system accounting to track how your systems are being used. See the man pages for
accton which turns accounting on/off,
sa which summarises accounting information and
lastcomm which lists the accounting information by user and/or by command and shows execution time and elapsed time (information you'll not get by looking at the history).
System accounting will show all commands run by all users, not just what was run from the command line.
Link to lastcomm manpage which should reference other related pages:
Man Page for lastcomm (All Section 1) - The UNIX and Linux Forums