Ubuntu – What counts towards uptime

On one hand this answer is six years late, on the other hand it's a blink of the eye if the internet is eternal!

You can get the real uptime with this little bash script:

$ suspendtime

Apr 07 05:53:34 to Apr 07 17:07:17 suspended 11 hours, 13 minutes, 43 seconds
Apr 07 21:56:34 to Apr 08 04:20:57 suspended 6 hours, 24 minutes, 23 seconds
      (... SNIP ...)
May 08 05:55:20 to May 08 16:32:37 suspended 10 hours, 37 minutes, 17 seconds
May 08 23:21:00 to May 09 07:02:05 suspended 7 hours, 41 minutes, 5 seconds

Linux uptime 2,813,939 seconds (4 weeks, 4 days, 13 hours, 38 minutes, 59 seconds)
64 Suspends 1,715,196 seconds (2 weeks, 5 days, 20 hours, 26 minutes, 36 seconds)
Real uptime 1,098,743 seconds (1 week, 5 days, 17 hours, 12 minutes, 23 seconds)

Linux will report uptime as 8 days and 40 minutes. The real uptime (after subtracting suspend time) is about 2 days and 18 hours.

suspendtime bash script

Here's the code you can copy to your system:

#!/bin/bash

# NAME: suspendtime
# PATH: $HOME/askubuntu/
# DESC: For: https://askubuntu.com/questions/321855/how-to-get-real-uptime
# DATE: November 6, 2019.

# NOTE: Calculate suspend time from systemd's journalctl

# UPDT: 2019-11-07 Fine-tune removing 0 Units in DaysMinutesStr
#       2020-05-09 Add "weeks" unit measure to DaysMinutes() function

# Duplicate DaysMinutes from ~/.bashrc for Ask Ubuntu
DaysMinutes () {

    local w d h m s
    (( w = ${1} / 604800 ))
    (( d = ${1}%604800 / 86400 ))
    (( h = (${1}%86400) / 3600 ))
    (( m = (${1}%3600) / 60 ))
    (( s = ${1}%60 ))
    DaysMinutesStr="$w weeks, $d days, $h hours, $m minutes, $s seconds"
    
    # Convert 1's to singular
    [[ ${DaysMinutesStr:0:2} = "1 " ]] && \
        DaysMinutesStr="${DaysMinutesStr/weeks/week}"
    DaysMinutesStr="${DaysMinutesStr/ 1 days/ 1 day}"
    DaysMinutesStr="${DaysMinutesStr/ 1 hours/ 1 hour}"
    DaysMinutesStr="${DaysMinutesStr/ 1 minutes/ 1 minute}"
    DaysMinutesStr="${DaysMinutesStr/ 1 seconds/ 1 second}"

    # Suppress zero strings
    [[ ${DaysMinutesStr:0:1} = "0" ]] &&
        DaysMinutesStr="${DaysMinutesStr/0 weeks, / }"
    DaysMinutesStr="${DaysMinutesStr/ 0 days, / }"
    DaysMinutesStr="${DaysMinutesStr/ 0 hours, / }"
    DaysMinutesStr="${DaysMinutesStr/ 0 minutes, / }"
    DaysMinutesStr="${DaysMinutesStr/, 0 seconds/}"
} # DaysMinutes

# Build array of suspend cycles from Systemd
IFS=$'\n' Arr=( $(journalctl -b-0 | \
                grep -E 'systemd\[1]: Start.*Suspend' | cut -c1-15) )

[[ ${#Arr[@]} -gt 0 ]] && upper=$(( ${#Arr[@]} - 1 ))
[[ $upper -gt 0 ]] && for (( i=0; i<upper; i=i+2 )) ; do
    (( SuspendCount++ ))
    Time=$(( $(date +%s -d "${Arr[i+1]}") - $(date +%s -d "${Arr[i]}") ))
    SuspendTime=$(( SuspendTime + Time ))
    DaysMinutes "$Time"
    printf "%s to %s suspended%s\n" "${Arr[i]}" "${Arr[i+1]}" \
          "$DaysMinutesStr"
done

echo
LinuxTime=$(( $(date +%s -d "Now") - $(date +%s -d "$(uptime -s)") ))
DaysMinutes "$LinuxTime"
printf "Linux uptime %'d seconds (%s)\n" "$LinuxTime" "$DaysMinutesStr"
DaysMinutes "$SuspendTime"
printf "%s Suspends %'d seconds (%s)\n" \
        "$SuspendCount" "$SuspendTime" "$DaysMinutesStr"
RealTime=$(( LinuxTime - SuspendTime ))
DaysMinutes "$RealTime"
printf "Real uptime %'d seconds (%s)\n" "$RealTime" "$DaysMinutesStr"

About half the program is converting seconds to human readable format in weeks, days, hours, minutes and seconds. The function DaysMinutes does this and was copied from my ~/.bashrc file where you may want to put that function yourself.

How it works

The key component is getting suspend start and end times from journalctl:

$ journalctl -b-0 | grep -E 'systemd\[1]: Start.*Suspend'
Oct 31 05:55:19 alien systemd[1]: Starting Suspend...
Oct 31 16:54:26 alien systemd[1]: Started Suspend.
 (... SNIP ...)
Nov 07 21:07:28 alien systemd[1]: Starting Suspend...
Nov 08 05:08:52 alien systemd[1]: Started Suspend.

• The journalctl -b-0 command reads all the system messages for the current boot. You could enhance the function to look at the previous boot using -b-1 the boot before that with -b-2, etc.
• The grep command with regex does the heavy lifting returning 32 system messages pertaining to suspend from the 19,330 system messages recorded (on my system)

shouldn't uptime be resetting to zero if the 'the system is fully powered off'

• suspend/hibernate are not considered "off". The last "wake up time" is stored in /var/log/pm-suspend.log.

or pausing because the system is hibernated

• now that would be odd. How would one then know what the actual uptime is?

or is this a bug?

Uptime is the time since last (re)boot. Basically the system stores at boot time what the time is and "now" -/- that time is the uptime. So in that regard: no, not a bug. The command predates notebooks and hibernate/suspend so maybe if you create a feature request someone decides it is a good feature to have. It probably is a very easy addition:just update the time stored on disk. And I can not imagine it is a lot more than adding a call to the hibernation/suspend script. But it will also be difficult to get it happen :)