This question already has an answer here:
/proc/uptime shows how long the system has been running since the last time I turned it on. Is there a way to determine the total amount of time the system has ever been on since I first installed it? For example, if I setup the system, run it for 20 minutes, turn it off, and turn it on again for 10 minutes, I'm looking for something that tells me the system has been run for 30 minutes total. Is there a command that does this? What about one for finding the date the system was installed?