Linux boot time

Issue

This article discusses how to determine when a Linux machine was last restarted or rebooted.

Environment

RHEL 7 & 8

Resolution

It is reasonable to expect all of these commands to give very nearly the same answer:

• who -b
• uptime -s
• ls -ld /proc/1
• last reboot | head -1

However, sometimes they don't. The difference is most likely the delta between local time and UTC. The best answer (in UTC) will be from uptime -s.

For example, on a server last booted at 6:24am EST (UTC-0400) on December 17, 2018:

% who -b
         system boot  Dec 17 06:24
% uptime -s
2018-12-17 10:24:11
% ls -ld /proc/1
dr-xr-xr-x. 9 root root 0 Dec 17 06:24 /proc/1
% last reboot | head -1
reboot   system boot  3.10.0-957.1.3.e Mon Dec 17 06:24 - 10:19 (49+03:55)  

Please note: If there is a discrepancy between the times shown by various methods, run the command  sudo timedatectl set-local-rtc 0.