Process accounting allows you to keep detailed logs of every command a user runs, including CPU time and memory used. From a security standpoint, this means the system administrator can gather information about what user ran which command and at what time. This is not only very useful in assessing a break-in or local root compromise, but can also be used to spot attempted malicious behavior by normal users of the system. (Remember that intrusions don’t always come from the outside.)

To enable process accounting, run these commands:

# mkdir /var/account

# touch /var/account/pacct && chmod 660 /var/account/pacct

# /sbin/accton /var/account/pacct

Alternatively, if you are running Red Hat or SuSE Linux and have the process accounting package installed, you can run a startup script to enable process accounting. On Red Hat, try this:

# chkconfig psacct on

# /sbin/service psacct start

On SuSE, use these commands:

# chkconfig acct on

# /sbin/service acct start

The process accounting package provides several programs to make use of the data that is being logged. The ac program analyzes total connect time for users on the system.

Running it without any arguments prints out the number of hours logged by the current user.

If you want to display connect time for all users who have logged onto the system, use the -p switch.

The lastcomm command lets you search the accounting logs by username, command name, or terminal:

To summarize the accounting information, you can use the sa command. By default it will list all the commands found in the accounting logs and print the number of times that each one has been executed.

You can also use the -u flag to output per-user statistics:

You can peruse the output of these commands every so often to look for suspicious activity, such as increases in CPU usage or commands that are known to be used for mischief.