E.2.28. /proc/uptime

This file contains information detailing how long the system has been on since its last restart. The output of /proc/uptime is quite minimal:
350735.47 234388.90
The first value represents the total number of seconds the system has been up. The second value is the sum of how much time each core has spent idle, in seconds. Consequently, the second value may be greater than the overall system uptime on systems with multiple cores.