Bsrgvty

Check the time stamp of /var/lib/apt/periodic/update-success-stamp.

$ ls -l /var/lib/apt/periodic/update-success-stamp
-rw-r--r-- 1 root root 0 Jan 25 01:41 /var/lib/apt/periodic/update-success-stamp

Here the time is Jan 25 01:41 when apt-get last executed. To get the time only, use the following command in terminal,

$ ls -l /var/lib/apt/periodic/update-success-stamp | awk 'print $6" "$7" "$8'
Jan 25 01:41

It is the best place to check the last update time. If you found /var/lib/apt/periodic/ to be empty you can try,

ls -l /var/log/apt/history.log

Update

It is found that due to some reasons above files update-success-stamp or history.log remain unavailable in some systems. There is a new proposal from derobert to look into the file /var/cache/apt/pkgcache.bin.

pkgcache.bin is Apt's memory mapped package cache location. It get renewed after each update. So it is the perfect candidate to know the last time when apt was updated.

One can use the following command to know the exact time,

ls -l /var/cache/apt/pkgcache.bin | cut -d' ' -f6,7,8

or

stat /var/cache/apt/pkgcache.bin

I use /var/cache/apt to determine if I need to run apt-get update. By default, if the difference between the current time and cache time of /var/cache/apt is less than 24 hr, I don't need to run apt-get update. The default update interval can be overridden by passing a number to function runAptGetUpdate()

function trimString()

 local -r string="$1"

 sed -e 's/^ *//g' -e 's/ *$//g' <<< "$string"


function isEmptyString()

 local -r string="$1"

 if [[ "$(trimString "$string")" = '' ]]
 then
 echo 'true'
 else
 echo 'false'
 fi


function info()

 local -r message="$1"

 echo -e "33[1;36m$message33[0m" 2>&1


function getLastAptGetUpdate()

 local aptDate="$(stat -c %Y '/var/cache/apt')"
 local nowDate="$(date +'%s')"

 echo $((nowDate - aptDate))


function runAptGetUpdate()

 local updateInterval="$1"

 local lastAptGetUpdate="$(getLastAptGetUpdate)"

 if [[ "$(isEmptyString "$updateInterval")" = 'true' ]]
 then
 # Default To 24 hours
 updateInterval="$((24 * 60 * 60))"
 fi

 if [[ "$lastAptGetUpdate" -gt "$updateInterval" ]]
 then
 info "apt-get update"
 apt-get update -m
 else
 local lastUpdate="$(date -u -d @"$lastAptGetUpdate" +'%-Hh %-Mm %-Ss')"

 info "nSkip apt-get update because its last run was '$lastUpdate' ago"
 fi

Sample Output:

<root@ubuntu><~/ubuntu-cookbooks/libraries>
# runAptGetUpdate 

Skip apt-get update because its last run was '0h 37m 43s' ago

I extracted these functions from my personal github: https://github.com/gdbtek/ubuntu-cookbooks/blob/master/libraries/util.bash

You may also interested about the file:

/var/log/apt/term.log

Open it with less or cat as root.

I use this command

stat /var/cache/apt/ | grep -i -e access -e modify

to show last time it was accessed ie. running 'apt-get update' also last time it was actually updated.

note if the times are different there may not have been an update available. Since I have my updates and upgrades running by crontab at specific times I can tell if my updates ran or not.

Combining @ssokolow's last comment with the answer from here, this command will run apt-get update if it hasn't run in the last 7 days:

[ -z "$(find -H /var/lib/apt/lists -maxdepth 0 -mtime -7)" ] && sudo apt-get update

Explanation:

• 
  -mtime -7 finds files that have a change time in the last 7 days. You can use -mmin if you care about shorter times.


• 
  -maxdepth 0 ensures find won't go into the contents of the directory.


• 
  -H dereferences /var/lib/apt/lists if it's a soft link


• If for some reason find fails, then the command would run. This seems to me like the safe default. If you want to flip the default, use -n in the test and -mtime +7 in the find command.

I just posted an answer to this question on following topic

Where can I look up my update history?

The answer may be less appropriate for this topic, as it specifically looks for "apt-get upgrade". Here's sample output.

xenial% 9: ./linuxpatchdate 
2016-07-19 54
2017-02-24 363
2017-03-08 7
2017-03-09 2

See the other topic for source code and more explanation.

LAST_UPDATED=$( stat --format="%X" /var/cache/apt/pkgcache.bin )
UNIX_TIME=$( date +%s )
TIME_DIFF=$(( UNIX_TIME - LAST_UPDATED ))

if [[ "$TIME_DIFF" -gt 43200 ]]
then
 # It's been 12 hours since apt-get update was ran.
fi