[I caught some misconceptions here which I think will this post clear off eventually]
There should not be any difference since both refer to /var/run/utmp
file, which has its own format to store the records. If at all there is any difference, then your utmp file is busted. uptime shows the amount of time that has passed since the system has been booted or how long the system has been running. It does not tell you the system clock or system boot time . System boot time information is stored /var/run/wtmp
file.
[centos@centos temp]$ date; uptime; who -b
Fri Dec 9 20:41:40 IST 2011
20:41:40 up 1:32, 2 users, load average: 0.50, 0.37, 0.29
system boot 2011-12-09 19:11
uptime refers as well /proc/uptime, which essentially keeps the counters in kernel.
[centos@centos temp]$ sleep 1; cat /proc/uptime; uptime; sleep 5; cat /proc/uptime ; uptime
5914.79 5271.83
20:47:39 up 1:38, 2 users, load average: 0.29, 0.31, 0.27
5920.07 5276.80
20:47:44 up 1:38, 2 users, load average: 0.56, 0.36, 0.29
/var/run/wtmp
is referred by last/lastb commands. who
& w
refers /var/run/utmp
file. last reboot
will show a log of all reboots since the log file was created.
Additionally, if you are having /proc filesystem, then tool such as procinfo
can give you bootup time as well.
Example:
bash$ procinfo | grep Bootup
Bootup: Wed Mar 21 15:15:50 2001 Load average: 0.04 0.21 0.34 3/47 6829
who -b
still show the same date (2009-07-09 20:51
) or does it change ? The manpage of mywho
suggests that it is using/var/run/utmp
if no file is specified. Are the write permissions for this file reasonable (userroot
and grouputmp
on my system) ? Is/var
full ? – Andre Holzner Aug 9 '11 at 21:52uptime
reads/proc/uptime
.who
reads/var/run/utmp
, which doesn't seem to be updated correctly. What distribution are you using? – Gilles 'SO- stop being evil' Aug 9 '11 at 22:55