LFCS Practice Test 25 — 15 Questions

Question 1

A system administrator manages a database server service (database.service) that experiences periodic CPU spikes, causing excessive load on the server. The administrator wants to limit the service's CPU usage to 25% of a single CPU core. The service is running on a system with cgroup v2. Which directive should be added to the [Service] section of the unit file to achieve this?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

CPUQuota=25%. In cgroup v2, the `CPUQuota=` directive in a systemd unit file directly limits the CPU time a service can use, expressed as a percentage of a single CPU core. Setting `CPUQuota=25%` restricts the service to using at most 25% of one core, which matches the administrator's requirement to cap CPU usage at 25% of a single core.

Answer

CPUAccounting=true

Answer

CPUWeight=100

Answer

CPUShares=256

Question 2

Which TWO directives are typically used in a systemd service unit file to configure dependencies?

Accepted Answer

Wants. In a systemd unit file, Wants= (option B) and Requires= (option E) are dependency directives that pull in other units: Wants= establishes a weak dependency where the listed units are started if possible but failure does not stop this unit, while Requires= establishes a strong dependency where the listed units must be activated successfully or this unit fails. Both belong to the [Unit] section and define which other units are needed, which is exactly what the question asks. By contrast, After= (option A) and Before= (option C) only control ordering — they specify start/stop sequence relative to other units but do not create a dependency that pulls those units in. Alias= (option D) merely provides an alternative name for the unit and has nothing to do with dependencies.

Answer

After

Answer

Before

Answer

Alias

Question 3

A system has a process stuck in uninterruptible sleep (D state). The administrator wants to identify which kernel function it is waiting on. Which tool should be used?

Accepted Answer

cat /proc/PID/stack. Reading /proc/PID/stack directly shows the kernel stack trace of the process, revealing the exact kernel function or wait queue the process is blocked on while in uninterruptible sleep (D state). This is the only tool listed that can inspect the kernel-side call stack without attaching a debugger or altering process state.

Answer

gdb -p PID

Answer

perf top -p PID

Answer

strace -p PID

Question 4

A process is stuck in an uninterruptible sleep (D state) and cannot be killed. What is the most likely cause?

Accepted Answer

The process is waiting for I/O from a failing disk. A process in uninterruptible sleep (D state) is typically waiting for I/O from a block device, such as a disk. When a disk is failing or unresponsive, the kernel cannot complete the I/O request, and the process cannot be killed because doing so would risk data corruption or filesystem inconsistency. This state is a kernel-level wait that ignores signals, including SIGKILL.

Answer

The process has been stopped by a signal

Answer

The process is waiting for a network response

Answer

The process is waiting for CPU

Question 5

A system administrator cannot restart a service because another unit 'stop' the request. The status message says 'Unit test.service is not running, but has pending stop job'. What is the most likely cause?

Accepted Answer

A previous stop command is still being processed. The message 'Unit test.service is not running, but has pending stop job' indicates that systemd has queued a stop operation for the service, but the stop job has not yet completed. This typically happens when a previous 'systemctl stop' command was issued but the service's stop process (e.g., ExecStop script) is still running or hanging. Until that job finishes, any attempt to restart the service will be blocked because systemd serializes jobs for the same unit.

Answer

The service unit file has RefuseManualStop=yes

Answer

The service has a dependency that is stopping

Answer

The service is masked

Question 6

A security policy requires that a user account 'temp_audit' be locked immediately without changing the password. Which command locks the account and prevents login?

Accepted Answer

usermod -L temp_audit. The `usermod -L` command locks a user account by placing an exclamation mark (!) at the beginning of the password hash in /etc/shadow, effectively disabling password-based authentication without altering the existing password. This satisfies the security policy requirement to immediately prevent login without changing the password.

Answer

userdel temp_audit

Answer

chage -E 0 temp_audit

Answer

passwd -u temp_audit

Question 7

A server runs out of inodes. The administrator needs to find which filesystem is exhausted and which directory has the most files. Which command sequence best accomplishes this?

Accepted Answer

df -i; find / -xdev -type f -printf '%h\0' | sort -z | uniq -c -z | sort -rn | head. `df -i` first checks inode usage across all mounted filesystems to identify which one is exhausted. Then the `find / -xdev -type f -printf '%h\0' | sort -z | uniq -c -z | sort -rn | head` command counts files per directory on the root filesystem only (due to `-xdev`), using null-delimited output to handle special characters in filenames, and sorts to show the directory with the most files. This directly addresses both parts of the problem: identifying the exhausted filesystem and the directory with the most files.

Answer

df -i; find / -type f | wc -l

Answer

df -i; du --inodes /

Answer

df -h; du -sh /

Question 8

A junior administrator needs to check the current runlevel and then change the system to runlevel 3 (multi-user, no GUI) on a SysVinit-based system. Which command sequence will accomplish this?

Accepted Answer

runlevel; init 3. On SysVinit systems, the 'runlevel' command displays the current and previous runlevel, and 'init 3' changes to runlevel 3 (multi-user, no GUI). The other options use systemd commands or incorrect utilities that do not fulfill both requirements.

Answer

telinit -q; telinit 3

Answer

chkconfig --list; init 3

Answer

systemctl get-default; systemctl isolate multi-user.target

Question 9

A user 'dlee' reports that they cannot run 'sudo' commands despite being in the 'wheel' group. The /etc/sudoers file contains the line '%wheel ALL=(ALL) ALL'. What is the most likely cause?

Accepted Answer

The user has not logged out and back in after being added to the 'wheel' group.. The most common reason a user cannot use sudo after being added to a group is that the group membership change has not taken effect in their current session. Linux processes inherit group memberships at login, so a new login is required. After logging out and back in, the user's session will include the 'wheel' group, and sudo will grant access according to the sudoers rule.

Answer

The user's primary group is not 'wheel'.

Answer

The 'wheel' group does not exist on the system.

Answer

The sudoers file must be edited with visudo, otherwise changes are ignored.

Question 10

A system administrator needs to identify the absolute path of the executable that would be run when typing the command 'ls'. Which command should they use?

Accepted Answer

which ls. The which command is designed to search the PATH and report the full path of the executable that would be run. whereis, locate, and find do not respect the PATH or executable resolution order, so they cannot reliably answer which binary would execute. Thus, which is the correct choice.

Answer

find / -name ls

Answer

whereis ls

Answer

locate ls

Question 11

A junior administrator has written a custom systemd service unit file named backup.service in /etc/systemd/system/. The unit is intended to run a backup script once per day. After placing the file, the administrator runs systemctl start backup.service, but systemd reports 'Unit backup.service not found.' The file exists and has correct syntax. Which command should the administrator run to make systemd aware of the new unit file?

Accepted Answer

systemctl daemon-reload. systemd maintains an in-memory cache of unit files and does not watch /etc/systemd/system/ for new files. After adding or modifying a unit, systemctl daemon-reload must be run so systemd re-reads unit definitions and rebuilds dependencies. Only then does systemctl start recognize the new backup.service unit.

Answer

systemctl reload backup.service

Answer

systemctl reset-failed backup.service

Answer

systemctl enable backup.service

Question 12

A Linux administrator needs to schedule a backup script to run every day at 2:30 AM. The script is located at /usr/local/bin/backup.sh. Which command should the administrator use to edit the crontab for the root user?

Accepted Answer

crontab -e. The command 'crontab -e' opens the crontab file for the current user (root in this case) in an editor, allowing the administrator to add the line '30 2 * * * /usr/local/bin/backup.sh'. This is the standard and safest way to schedule a recurring job. Other options either list jobs, edit a system file inappropriately, or modify the service unit, none of which achieve the goal.

Answer

systemctl edit cron.service

Answer

vi /etc/crontab

Answer

crontab -l

Question 13

A Linux server has a DNS resolver configuration in /etc/resolv.conf. You need to add a new DNS server at 8.8.8.8 and ensure it is used before the existing server. Which line should you add to the top of /etc/resolv.conf?

Accepted Answer

nameserver 8.8.8.8. The correct line is 'nameserver 8.8.8.8'. The resolver reads nameserver entries in order, so placing it at the top makes it the first server used. The other options use invalid keywords or syntax that would not be recognized by the resolver.

Answer

dns 8.8.8.8

Answer

nameserver 8.8.8.8:53

Answer

search 8.8.8.8

Question 14

A system administrator needs to ensure that the 'nginx' service starts automatically after a reboot on a system using systemd. The service unit file exists and is currently disabled. Which command should be used?

Accepted Answer

systemctl enable nginx. The systemctl enable nginx command is the correct way to configure a service to start automatically at boot. It creates the necessary symlinks without starting the service now, which matches the requirement to ensure automatic startup after a reboot.

Answer

systemctl start nginx

Answer

systemctl daemon-reload

Answer

systemctl enable --now nginx

Question 15

A Linux administrator needs to ensure that the nginx.service is restarted automatically if it crashes, but only after a 10-second delay, and that it does not restart more than 5 times within 1 minute to avoid a restart loop. Which set of directives in the [Service] section achieves this?

Accepted Answer

Restart=on-failure, RestartSec=10, StartLimitIntervalSec=60, StartLimitBurst=5. The correct directives are Restart=on-failure, RestartSec=10, StartLimitIntervalSec=60, and StartLimitBurst=5. Restart=on-failure ensures restarts only on crashes, RestartSec=10 adds the delay, and the start limit directives restrict restarts to 5 per 60 seconds. The other options either use the wrong restart policy, an outdated directive name, or an incorrect burst value.

Answer

Restart=on-failure, RestartSec=10, StartLimitIntervalSec=60, StartLimitBurst=10

Answer

Restart=always, RestartSec=10, StartLimitInterval=60, StartLimitBurst=5

Answer

Restart=on-abnormal, RestartSec=10, StartLimitIntervalSec=60, StartLimitBurst=5