Level Goal
The password for the next level is stored in the file data.txt and is the only line of text that occurs only once

Commands you may need to solve this level: grep, sort, uniq, strings, base64, tr, tar, gzip, bzip2, xxd

Lets see wich files there are in the home directory by doing an ‘ls -la’ we can see the data.txt file. If we cat this file we get a long list of passwords. We need to find the one that only occurs once. Looking at the referred commands we probably need uniq. Lets see the manpage of it.
man uniq

The option -u only prints unique lines. Lets try this one, we can see the password now.
uniq -u data.txt

This doesn’t seem to be right. lets try the -c option and see which line is only counted once, we have to scroll through the count to find the line that only occurred once.
uniq -c data.txt

They all show as one, this is because we didn’t sort the textfile before executing the unique command. Lets try the next command:
sort data.txt | uniq -u

there is the password.