If I run a docker image and call uptime, I always get a longer value than the real one.
docker run -it 1d2dfb3a35ab
root@7efb3e947f73:/# uptime
23:41:57 up 16 min, 0 users, load average: 0.06, 0.02, 0.00
It hasn't been running for 16 minutes, not even 16 seconds. =:-O
Is this a known issue or what?
The first process start time could be used as container start time:
stat /proc/1/cmdline
/proc/1/cmdline is a virtual file in the procfs, whose creation date is the same as the container creation date. The stat command shows its filesystem-level attributes, its creation date between them.
The displayed uptime is that of the host. The kernel does not track uptime for individual containers in this way (though Docker does).