journalctl for systemd logs in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to show all systemd logs.

Linux CLI

journalctl [1]

Drag options to blanks, or click blank then click option'

A-f

B-b

C-u

D--no-pager

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-b' shows logs only from the current boot.

Using '-u' requires a service name and filters logs for that service.

Using '-f' follows logs live but does not show all past logs.

The option '--no-pager' shows all logs without paging, displaying the full output at once.

2fill in blank

medium

Complete the command to show logs only for the sshd service.

Linux CLI

journalctl [1] sshd.service

Drag options to blanks, or click blank then click option'

A--since

B-b

C-u

D-f

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-b' shows logs from current boot but not filtered by service.

Using '--since' filters by time, not service.

Using '-f' follows logs live but does not filter by service.

The '-u' option filters logs for a specific systemd unit, here 'sshd.service'.

3fill in blank

hard

Fix the error in the command to follow logs live for the nginx service.

Linux CLI

journalctl -u nginx.service [1]

Drag options to blanks, or click blank then click option'

A-f

B--no-pager

C--since today

D-b

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--since today' shows logs only from today but does not follow live.

Using '--no-pager' disables paging but does not follow live.

Using '-b' shows logs from current boot but does not follow live.

The '-f' option makes journalctl follow logs live, showing new entries as they appear.

4fill in blank

hard

Fill both blanks to show logs from the current boot and disable paging.

Linux CLI

journalctl [1] [2]

Drag options to blanks, or click blank then click option'

A-b

B-u

C--no-pager

D-f

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-u' filters by service, not boot.

Using '-f' follows logs live, not needed here.

The '-b' option shows logs from the current boot, and '--no-pager' disables paging to show all logs at once.

5fill in blank

hard

Fill all three blanks to show logs for the cron service since yesterday and follow live.

Linux CLI

journalctl [1] cron.service [2] yesterday [3]

Drag options to blanks, or click blank then click option'

A-u

B--since

C-f

D--no-pager

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-b' instead of '--since' does not filter by time.

Using '--no-pager' disables paging but does not follow live.

Forgetting '-f' means logs won't update live.

Use '-u' to filter by cron service, '--since' to specify time from yesterday, and '-f' to follow logs live.

Practice

1. What is the primary purpose of the journalctl command in Linux?

easy

A. To edit configuration files for systemd services

B. To start and stop systemd services

C. To view system and service logs managed by systemd

D. To display disk usage statistics

Solution

1. Step 1: Understand the role of journalctl

   The journalctl command is used to access logs collected by systemd's journal service.

2. Step 2: Compare options with command purpose

   Editing configuration files, starting/stopping services, and displaying disk usage are handled by other commands, unrelated to viewing logs.

3. Final Answer:

   To view system and service logs managed by systemd -> Option C

4. Quick Check:

   journalctl = view logs [OK]

Hint: Remember: journalctl = journal + control = view logs [OK]

Common Mistakes:

• Confusing journalctl with systemctl for service control
• Thinking journalctl edits files
• Assuming journalctl shows disk info

2. Which of the following is the correct syntax to show the last 10 lines of system logs using journalctl?

easy

A. journalctl -n 10

B. journalctl --last 10

C. journalctl -l 10

D. journalctl -t 10

Solution

1. Step 1: Recall journalctl option for number of lines

   The -n option followed by a number shows that many recent log lines.

2. Step 2: Check other options for correctness

   The other options are not valid journalctl options for limiting output lines.

3. Final Answer:

   journalctl -n 10 -> Option A

4. Quick Check:

   -n = number of lines [OK]

Hint: Use -n to limit lines shown quickly [OK]

Common Mistakes:

• Using --last instead of -n
• Confusing -l (line wrap) with line count
• Using -t which filters by syslog identifier

3. What will be the output of the command journalctl -u sshd.service -n 3?

medium

A. Shows the last 3 log entries related to the sshd service

B. Shows all logs except those from sshd service

C. Shows the first 3 lines of the system log

D. Shows logs from all services except sshd

Solution

1. Step 1: Understand the -u option

   The -u sshd.service option filters logs to only those from the sshd service.

2. Step 2: Understand the -n 3 option

   The -n 3 option limits output to the last 3 log entries.

3. Final Answer:

   Shows the last 3 log entries related to the sshd service -> Option A

4. Quick Check:

   -u sshd + -n 3 = last 3 sshd logs [OK]

Hint: -u filters by service, -n limits lines [OK]

Common Mistakes:

• Thinking -u excludes the service logs
• Confusing -n with showing first lines
• Assuming it shows all logs

4. You run journalctl -u nginx.service --since "2024-01-01" --until "2024-01-02" but get no output, even though you know nginx was active. What is the likely problem?

medium

A. The date format is incorrect; journalctl requires YYYY-MM-DD HH:MM:SS

B. The service name is wrong; it should be nginx without .service

C. The journal is empty because logging is disabled

D. The system clock is set to a different timezone causing no matching logs

Solution

1. Step 1: Check date format validity

   The date format "YYYY-MM-DD" is valid for journalctl; it does not require HH:MM:SS.

2. Step 2: Consider timezone impact

   If the system clock or journal timestamps use a different timezone, the specified range may not match any logs, causing no output.

3. Step 3: Verify service name and logging

   The service name with .service is correct, and nginx is usually logged to the journal, making incorrect service name or disabled logging unlikely.

4. Final Answer:

   The system clock is set to a different timezone causing no matching logs -> Option D

5. Quick Check:

   Timezone mismatch = no logs in range [OK]

Hint: Check timezone if date filters show no logs [OK]

Common Mistakes:

• Assuming date format is wrong
• Removing .service from unit name
• Ignoring system clock timezone

5. You want to monitor live logs from the docker.service as they happen. Which command should you use?

hard

A. journalctl -u docker.service --since now

B. journalctl -u docker.service -f

C. journalctl -u docker.service -n 0

D. journalctl -u docker.service --no-pager

Solution

1. Step 1: Identify option for live log streaming

   The -f option in journalctl streams new log entries live, similar to tail -f.

2. Step 2: Evaluate other options

   journalctl -u docker.service --since now shows logs since now but does not follow live updates. journalctl -u docker.service -n 0 shows zero lines, so no output. journalctl -u docker.service --no-pager disables paging but does not stream live.

3. Final Answer:

   journalctl -u docker.service -f -> Option B

4. Quick Check:

   -f = follow live logs [OK]

Hint: Use -f to follow logs live like tail -f [OK]

Common Mistakes:

• Using --since now without -f for live updates
• Using -n 0 which shows no lines
• Confusing --no-pager with live streaming