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How to get the boot time of Ubuntu?

rated 0 times [ 2] [ 0] / answers: 1 / hits: 367 / 2 Years ago, sat, october 8, 2022, 4:55:20

I am trying to find the boot time of Ubuntu.

The following tells me that my last reboot took 1 minutes 39 second.

$ last reboot

reboot   system boot  3.8.0-29-generic Wed Jan  8 14:55 - 16:35  (01:39)    

reboot   system boot  3.8.0-29-generic Wed Jan  8 14:38 - 14:55  (00:16)    

reboot   system boot  3.8.0-29-generic Wed Jan  8 14:27 - 14:38  (00:10)    

reboot   system boot  3.8.0-29-generic Wed Jan  8 11:07 - 14:27  (03:19)    

reboot   system boot  3.8.0-29-generic Wed Jan  8 00:03 - 00:31  (00:27)    

reboot   system boot  3.8.0-29-generic Tue Jan  7 10:39 - 14:22  (03:43)    

reboot   system boot  3.8.0-29-generic Mon Jan  6 10:51 - 18:42  (07:50)    

reboot   system boot  3.8.0-29-generic Sun Jan  5 22:08 - 00:19  (02:11)    

reboot   system boot  3.8.0-29-generic Sat Jan  4 11:34 - 15:47  (04:12)

While when I looked at dmesg:

[   14.707210] type=1400 audit(1389173157.301:11): apparmor="STATUS" operation="profile_replace" name="/usr/lib/NetworkManager/nm-dhcp-client.action" pid=1018 comm="apparmor_parser"

This shows that the total boot time is 14.707210. So as per the above two methods which is the actual boot time?

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4 Years ago

answered 2 Years ago attagjump · Accepted Answer

The first command, last reboot, does not tell you the boot time. It tells you at what times your system was running. For example, the first entry tells you that your system has been running from 14:55 to 16:35 on Wed 8. That's 1 hour and 39 minutes. It did not take your system 1 hour and 39 minutes to boot - hopefully ;)

The second command, dmesg, brings you closer to what you want to know, but since dmesg will continually output more system events while your system is running, it's not the tool of choice to measure boot time either.

If you really want to reliably measure your system boot time, I would recommend a tool such as bootchart.

See here:
https://wiki.ubuntu.com/BootCharting