epoch
also: Unix epoch, POSIX epoch, Unix time, POSIX time
The epoch is the reference point (January 1, 1970, 00:00:00 UTC) from which Unix timestamps measure elapsed seconds. All time on Unix-like systems is calculated as the number of seconds since this moment.
The Unix epoch is a fundamental concept in computing that standardizes how time is represented on Linux and other Unix-like systems. Rather than storing dates and times in human-readable format, the system tracks time as a single number—the count of seconds (or milliseconds) elapsed since midnight UTC on January 1, 1970.
For example, the timestamp 1704067200 represents January 1, 2024 at midnight UTC. You can see your system's current Unix timestamp using date +%s.
This approach simplifies time calculations, comparisons, and storage. File modification times, log entries, and scheduled tasks all use epoch-based timestamps internally, though tools typically display them in human-readable format.