EYE ON CHANGE

If an intruder is loose on your system, it is important to learn about the attack as soon as possible. Several tools in the Linux environment check individual directories, and files send notice of changes. You can run one of these tools as a cronjob or write a script that runs in a loop and regularly performs file checks. In both cases, however, you are forced to either run the tool frequently (at high cost to system resources) or else settle for long intervals between checks, which could potentially open a window for an intruder.

The Linux 2.6.13 kernel introduced a solution to this dilemma. The kernel’s Inotify interface provides a means for monitoring files and directories in realtime. Users need only tell the kernel which files they are interested in, and the kernel notifies the user whenever a change occurs.