You need to know how many lines of /var/log/auth.log contain the text `Failed password`. Which command reports exactly that number?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands easy
Machine-checked — no person has signed for it. This question was read against the source cited below by an automated pass, which found no contradiction. That is a weaker claim than it sounds: the same kind of process wrote the question, so it can confirm its own mistake.
Treat it as a good draft rather than as settled fact, and read the source below before you rely on it. It is not used in mock exams here — only questions a person has signed for are.
How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct grep -c 'Failed password' /var/log/auth.log
Correct. -c suppresses the matching lines and prints the count of lines that matched.
Not correct grep -n 'Failed password' /var/log/auth.log
Wrong. -n prefixes each matching line with its line number; you would still have to count the output yourself.
Not correct grep -l 'Failed password' /var/log/auth.log
Wrong. -l prints only the name of each file that contains at least one match, so the answer would be the file name.
Not correct grep -o 'Failed password' /var/log/auth.log
Wrong on its own. -o prints each matched substring on its own line, which counts occurrences rather than lines once piped into wc -l.
Why
grep -c counts matching LINES, not matches: a line holding the string twice still contributes 1. When occurrences are what you want, `grep -o pattern file | wc -l` is the idiom, because -o emits one line per match. Note also that -c combined with -v counts the non-matching lines, which is the quick way to size the remainder of a file.
Where this comes from
- Cited
- manual page grep(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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