LFCS Practice Test 23 — 15 Questions

Question 1

A system administrator configures a new server with multiple disks. After partitioning and formatting, they mount a partition to /data. Several days later, they notice that the /data filesystem is full, but 'du -sh /data' reports only 2 GB used, while the partition is 100 GB. 'df -h' shows /data is 98% full. What is the most likely cause and the correct action?

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

Accepted Answer

There are deleted files still held open by processes. Use 'lsof /data' to find and restart those processes.. When a file is deleted but still held open by a running process, the filesystem does not release the disk blocks until the process closes the file descriptor. This causes 'df' to report the space as used, while 'du' cannot see the deleted file's data, leading to the discrepancy. Using 'lsof /data' identifies the processes holding the deleted files, and restarting them frees the space.

Answer

The filesystem is fragmented. Run 'e4defrag' to defragment.

Answer

The filesystem has reserved blocks for root. Reduce the reserved percentage with 'tune2fs -m 0'.

Answer

The 'du' command is not counting hidden files (dot files). Use 'du -sh .*' to include them.

Question 2

A DevOps engineer is writing a continuous integration pipeline that runs a script to deploy an application. The script is stored in a Git repository and is executed on a build server. The script works locally on the engineer's workstation, but when executed on the build server, it fails with '/bin/sh: line 12: somecommand: command not found'. The 'somecommand' is a standard Linux tool that is installed on the build server. The build server uses a minimal Docker container. Which of the following is the most likely cause and solution?

Accepted Answer

The PATH environment variable is not set correctly in the non-interactive shell. Use the full path to 'somecommand' or set PATH explicitly in the script.. The error 'command not found' despite the tool being installed indicates that the shell cannot locate the executable. In a non-interactive shell (like those used in CI/CD pipelines or minimal Docker containers), the PATH environment variable is often not set or is minimal. The fix is to either use the absolute path to the command or explicitly set PATH in the script to include the directory containing the command.

Answer

The script does not have execute permissions. Add 'chmod +x' before running the script.

Answer

The script requires root privileges. Use 'sudo' to run the script.

Answer

The script is using a different shell than the build server's default. Change the shebang to '#!/bin/sh'.

Question 3

Which command displays the current status of all active services?

Accepted Answer

systemctl list-units --type=service --state=active. `systemctl list-units --type=service --state=active` filters systemd units to show only those of type 'service' that are currently in the 'active' state (i.e., running or exited but still considered active). This is the precise command to list all active services without showing inactive or failed units.

Answer

systemctl status --all

Answer

systemctl show --type=service

Answer

systemctl list-unit-files --type=service

Question 4

A user reports that they cannot log in via SSH, but other users can. The administrator checks /var/log/auth.log and sees 'Failed password for invalid user'. What is the most likely cause?

Accepted Answer

The user does not exist on the system. The log message 'Failed password for invalid user' specifically indicates that the username presented during the SSH authentication attempt does not correspond to any account in the system's user database (e.g., /etc/passwd). This is distinct from a valid user failing authentication; the SSH server (sshd) rejects the session at the authentication stage because the user does not exist. Therefore, the most likely cause is that the user account does not exist on the system.

Answer

The user's SSH key is not authorized

Answer

The user account is locked

Answer

The user's password has expired

Question 5

A process (PID 1234) is hung and cannot be killed with SIGTERM. To force termination, which signal should be sent?

Accepted Answer

kill -9 1234 (SIGKILL). SIGKILL (signal 9) is the correct choice because it cannot be caught, blocked, or ignored by the process. Unlike SIGTERM, which allows the process to perform cleanup, SIGKILL immediately terminates the process at the kernel level, making it the only reliable way to force-kill a hung process that ignores other signals.

Answer

kill -15 1234 (SIGTERM)

Answer

kill -2 1234 (SIGINT)

Answer

kill -1 1234 (SIGHUP)

Question 6

Which command shows the default target for systemd?

Accepted Answer

systemctl get-default. The correct command to display the default target (the systemd unit that the system boots into by default) is `systemctl get-default`. This command reads the symlink at `/etc/systemd/system/default.target` and outputs its target, such as `multi-user.target` or `graphical.target`. Option C is correct because it directly queries systemd for the current default boot target.

Answer

systemctl show default

Answer

systemctl list-default

Answer

systemctl default

Question 7

An admin notices a PV in a VG has failed. The VG is still accessible with redundancy. Which command sequence should be used to replace the faulty PV with a new one (/dev/sde) while the VG is active and without data loss?

Accepted Answer

pvcreate /dev/sde; vgextend VG_name /dev/sde; pvmove /dev/sdb /dev/sde; vgreduce VG_name /dev/sdb. It first creates the new PV on /dev/sde, extends the VG to include it, then uses pvmove to migrate data from the failing PV (/dev/sdb) to the new PV while the VG is active, and finally removes the faulty PV from the VG with vgreduce. This sequence ensures no data loss and maintains VG availability throughout the replacement process.

Answer

pvcreate /dev/sde; vgreduce VG_name /dev/sdb; vgextend VG_name /dev/sde; pvmove /dev/sdb

Answer

pvcreate /dev/sde; pvmove /dev/sdb /dev/sde; vgextend VG_name /dev/sde; vgreduce VG_name /dev/sdb

Answer

vgreduce --removemissing VG_name; pvcreate /dev/sde; vgextend VG_name /dev/sde; pvmove /dev/sde

Question 8

A company's database server uses LVM for storage. The system administrator notices that the logical volume /dev/vg_db/lv_data is at 95% capacity. The server is in production and cannot be taken offline. The volume group vg_db has free physical extents. Which command sequence should the administrator use to safely increase the size of the logical volume and filesystem without unmounting?

Accepted Answer

lvextend -L +10G /dev/vg_db/lv_data; resize2fs /dev/vg_db/lv_data. It first extends the logical volume using `lvextend -L +10G` to allocate additional physical extents from the volume group, then resizes the ext4 filesystem online with `resize2fs` to utilize the new space. Both operations can be performed without unmounting the filesystem, as ext4 supports online resizing and LVM allows live extension of logical volumes.

Answer

lvextend /dev/vg_db/lv_data /dev/sdb; resize2fs /dev/vg_db/lv_data

Answer

lvresize -L +10G /dev/vg_db/lv_data; mkfs.ext4 /dev/vg_db/lv_data

Answer

lvextend -L +10G /dev/vg_db/lv_data; mount -o remount /dev/vg_db/lv_data

Question 9

To check the details of a failed systemd service unit, including the last log entries, which command is most appropriate?

Accepted Answer

systemctl status service. `systemctl status service` is the most appropriate command because it displays the current state of the service unit, including whether it is active, failed, or inactive, along with the last several log entries from the journal for that unit. This provides both the failure status and the contextual log output needed to diagnose why the service failed, all in a single command.

Answer

systemctl list-units --failed

Answer

systemctl is-failed service

Answer

systemctl show service

Question 10

Which systemd unit type is used to group services and other units together for boot execution?

Accepted Answer

target. In systemd, the 'target' unit type is designed to group services, sockets, timers, and other units into a logical synchronization point for boot execution. Targets do not execute code themselves but instead define dependencies (via Wants, Requires, and After directives) that ensure all associated units are started in the correct order to reach a desired system state, such as multi-user.target or graphical.target.

Answer

socket

Answer

timer

Answer

service

Question 11

Refer to the exhibit. An administrator tries to start myapp.service with 'systemctl start myapp.service' but receives 'Failed to start myapp.service: Unit myapp.service is not loaded properly: Invalid argument'. What is the most likely issue?

Accepted Answer

The unit file has a syntax error.. The error 'Unit myapp.service is not loaded properly: Invalid argument' indicates that systemd attempted to parse the unit file but encountered a syntax error or an invalid directive. This typically happens when a key-value pair in the unit file is malformed, such as a missing equals sign, an unsupported option, or a value that does not conform to systemd's expected format. Unlike a runtime failure (e.g., a missing ExecStart binary), this error occurs during the loading phase, before any execution attempt.

Answer

The service name is misspelled.

Answer

The ExecStart path is invalid.

Answer

The service is masked.

Question 12

An administrator wants to see the disk usage of the /var directory in a human-readable format. Which command should be used?

Accepted Answer

du -sh /var. The `du -sh /var` command is correct because `du` (disk usage) estimates file and directory space usage, and the `-s` flag summarizes the total for `/var` while `-h` provides human-readable output (e.g., KiB, MiB, GiB). This directly shows the disk space consumed by the `/var` directory and its contents.

Answer

df -h /var

Answer

fdisk -l /var

Answer

ls -lh /var

Question 13

An administrator wants to run a script daily at 2 AM. They create a timer unit and a service unit. The service unit uses Type=oneshot. Which of the following timer configurations is correct?

Accepted Answer

OnCalendar=*-*-* 02:00:00. `OnCalendar=*-*-* 02:00:00` specifies an absolute calendar event that triggers the timer at 2:00 AM every day, regardless of when the system booted or when the service last ran. This matches the requirement to run a script daily at a fixed time, and it works correctly with a `Type=oneshot` service unit.

Answer

OnUnitActiveSec=24h

Answer

OnBootSec=1d

Answer

OnActiveSec=24h

Question 14

An administrator wants to limit the CPU usage of a service to at most 50% of a single CPU core. Which directive should be set in the [Service] section of the unit file?

Accepted Answer

CPUQuota=50%. `CPUQuota=` is the systemd directive that limits the CPU time a service can use, expressed as a percentage of a single CPU core. Setting `CPUQuota=50%` restricts the service to at most 50% of one core's time, effectively capping its CPU usage to half a core.

Answer

CPUAccounting=true

Answer

CPUWeight=100

Answer

CPUShares=512

Question 15

Which command can be used to display the UUID of a filesystem on /dev/sdb1?

Accepted Answer

blkid /dev/sdb1. The blkid command is specifically designed to locate and print block device attributes, including the UUID and filesystem type. When run against a device like /dev/sdb1, it queries the kernel's device mapper and reads the filesystem superblock to extract the universally unique identifier (UUID). This is the most direct and reliable method for displaying a filesystem's UUID.

Answer

tune2fs -l /dev/sdb1

Answer

df -h /dev/sdb1

Answer

lsblk /dev/sdb1