We can solve it in reverse way.
List out users who have logged into the system in last 180 days :
Code:
lastlog -b 0 -t 180
Except these users, no user has been logged into the system in last 180 days.
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Users who did not loginto system in last 180 days
But it lists the users who never logged in.... so do not print the users who never logged in...
Code:
lastlog -b 180 | grep -iv "never"