Question

If use bash script how to record the number of logged in users every 5 minutes. Each measurement needs to be appended to a text file. There should be one line of text for each measurement, formatted as follows.

Fri Oct 11 13:12:04 EDT 2011 8 users

Answer 1

This will count multiple logins of a single user as multiple matches i.e if you ssh into a machine 3 times with the same account this will show 3 users

echo $(date) $(who | awk '{print $1}' | wc -l) users >> log.txt

To treat multiple logins from one username as one match this is what you want:

echo $(date) $(who | awk '{print $1}' | uniq | wc -l) users >> log.txt