LFCS Networking Practice Question
A system administrator is troubleshooting a DHCP issue on a Linux client. After running 'dhclient -r eth0' and then 'dhclient eth0', the interface does not get an IP address. What command can be used to ensure the DHCP client process is fully released and restarted?
⚠ Common exam trap
The trap is that candidates may think `-x` is the best approach because it is interface-specific and appears cleaner, but `killall` ensures that all dhclient processes are killed, including any zombie or orphaned daemons that might persist even after `-x`. In troubleshooting scenarios, a brute-force kill is often more reliable.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
killall dhclient && dhclient eth0
The command sequence `killall dhclient && dhclient eth0` ensures that all existing dhclient processes are terminated before starting a new one. This guarantees that any stale daemon holding the lease or maintaining state is completely removed, allowing a fresh DHCP handshake without interference. While `dhclient -x eth0` releases and stops the daemon for a specific interface, `killall` is more robust if multiple dhclient processes or orphaned instances exist, which can occur after a series of failures or manual interventions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
dhclient -s 10.0.0.1 eth0
Why it's wrong here
This option specifies a DHCP server to use via `-s`, but does not release the current lease or restart the client. It cannot ensure a fresh release and restart.
- ✗
dhclient -r eth0 && dhclient -v eth0
Why it's wrong here
This repeats the same commands the administrator already tried (`-r` then `-v`), which only releases the lease but may leave the dhclient daemon running and holding onto state, failing to guarantee a full restart.
- ✓
killall dhclient && dhclient eth0
Why this is correct
Correct. `killall dhclient` forcefully terminates all dhclient processes, ensuring no stale daemon remains. Then `dhclient eth0` starts a fresh client, completing a full release and restart cycle.
- ✗
dhclient -x eth0 && dhclient eth0
Why it's wrong here
While `-x` releases the lease and stops the dhclient daemon for that interface, it may not terminate all dhclient processes (e.g., if multiple interfaces are managed). This can leave residual state, making it less reliable than `killall` for a thorough restart.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LFCS exam.