System logs (/var/log) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this command?

You run the command tail -n 3 /var/log/syslog on a Linux system. What does this command do?

Linux CLI

tail -n 3 /var/log/syslog

A Shows the first 3 lines of the syslog file

B Shows the last 3 lines of the syslog file

C Deletes the last 3 lines of the syslog file

D Shows all lines except the last 3 lines of the syslog file

💡 Hint

Think about what the 'tail' command does with the '-n' option.

The tail command shows the end of a file. The -n 3 option tells it to show the last 3 lines.

💻 Command Output

intermediate

What does this command output?

You run grep -i error /var/log/auth.log | wc -l. What does this command do?

Linux CLI

grep -i error /var/log/auth.log | wc -l

A Shows all lines with the word 'error' in auth.log

B Deletes lines containing 'error' from auth.log

C Counts all lines in auth.log

D Counts how many lines contain the word 'error' (case insensitive) in auth.log

💡 Hint

Remember what grep and wc -l do.

grep -i error finds lines with 'error' ignoring case. wc -l counts those lines.

🔧 Debug

advanced

Why does this command fail?

You try to run cat /var/log/secure | grep 'Failed password' but get a permission denied error. Why?

Linux CLI

cat /var/log/secure | grep 'Failed password'

A The grep command syntax is wrong

B The file /var/log/secure does not exist

C You need root permissions to read /var/log/secure

D The pipe symbol '|' is not supported in this shell

💡 Hint

Check file permissions for /var/log/secure.

The /var/log/secure file is usually readable only by root. Without root, you get permission denied.

🚀 Application

advanced

Create a command to monitor new log entries

Which command will continuously show new lines added to /var/log/messages in real time?

A tail -f /var/log/messages

B head -n 10 /var/log/messages

C cat /var/log/messages

D grep 'new' /var/log/messages

💡 Hint

Think about commands that follow file changes live.

tail -f shows the end of a file and updates as new lines are added.

🧠 Conceptual

expert

What is the purpose of log rotation in /var/log?

Why do Linux systems use log rotation for files in /var/log?

A To prevent log files from growing too large and consuming disk space

B To delete all logs automatically after one day

C To merge all logs into one big file

D To encrypt log files for security

💡 Hint

Think about disk space and file management.

Log rotation moves or compresses old logs to keep file sizes manageable and save disk space.