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Old 12-02-2013, 06:29 PM   #1
devUnix
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Registered: Oct 2010
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Distribution: RHEL 5.1 on My PC, & SunOS / Sun Solaris, RHEL, SuSe, Debian, FreeBSD and other Linux flavors @ Work
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Last Boot Time


Why does the last boot time differ in each output below? For example: uptime and "who -b" do not sound in sync.

Code:
$ date
Mon Dec  2 19:25:29 EST 2013


$ uptime
 19:25:03 up 20 days,  4:41,  3 users,  load average: 0.10, 0.08, 0.02

$ who -b
         system boot  2013-11-12 14:43

$ last boot

wtmp begins Fri Sep  7 14:12:08 2012

$ last | grep boot
reboot   system boot  2.6.32-279.el6.x Tue Nov 12 14:43 - 19:25 (20+04:41)
reboot   system boot  2.6.32-279.el6.x Tue Nov 12 14:30 - 14:40  (00:10)
reboot   system boot  2.6.32-279.el6.x Tue Nov 12 14:15 - 14:27  (00:12)
reboot   system boot  2.6.32-279.el6.x Wed May 22 17:04 - 14:12 (173+22:07)
reboot   system boot  2.6.32-279.el6.x Mon Jan 28 14:44 - 17:00 (114+01:16)


Also... how do we figure out if the system has been warm (soft) rebooted or cold (hard) rebooted?

Last edited by devUnix; 12-02-2013 at 06:34 PM.
 
Old 12-02-2013, 06:56 PM   #2
Ser Olmy
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These seem to match up perfectly:
Quote:
Originally Posted by devUnix View Post
Code:
$ date
Mon Dec  2 19:25:29 EST 2013


$ uptime
 19:25:03 up 20 days,  4:41,  3 users,  load average: 0.10, 0.08, 0.02

$ who -b
         system boot  2013-11-12 14:43
Subtracting 20 days and 4:41 as reported by uptime from the current date/time (Dec 2 19:25) gives you Nov 12 14:44, and the one minute difference between that and who -b is probably just due to the seconds getting truncated or rounded.

Quote:
Originally Posted by devUnix View Post
Code:
$ last boot

wtmp begins Fri Sep  7 14:12:08 2012

$ last | grep boot
reboot   system boot  2.6.32-279.el6.x Tue Nov 12 14:43 - 19:25 (20+04:41)
reboot   system boot  2.6.32-279.el6.x Tue Nov 12 14:30 - 14:40  (00:10)
reboot   system boot  2.6.32-279.el6.x Tue Nov 12 14:15 - 14:27  (00:12)
reboot   system boot  2.6.32-279.el6.x Wed May 22 17:04 - 14:12 (173+22:07)
reboot   system boot  2.6.32-279.el6.x Mon Jan 28 14:44 - 17:00 (114+01:16)
The top entry seems to match uptime/who -b.

The start of wtmp does not match the system boot time on any of my systems either. Should it? I have one starting back in June 2010 when the system in question was first installed. FWIW, last | grep boot returns nothing on one of my systems, even though that system has surely been rebooted a number of times.
Quote:
Originally Posted by devUnix View Post
Also... how do we figure out if the system has been warm (soft) rebooted or cold (hard) rebooted?
A hard reboot due to power failure, system lockup or a kernel panic will leave no trace of a shutdown event in the logs. If you see log entries indicating the system has booted without entries for a corresponding shutdown immediately preceding them, there's been a crash of some kind.

Last edited by Ser Olmy; 12-02-2013 at 06:59 PM.
 
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