LFCS Operation of Running Systems Practice Test 4 — 15 Questions

Question 1

A system administrator needs to schedule a one-time job that will run a script at 2:30 AM on the next day. The job should not recur. Which command should the administrator use?

Accepted Answer

echo "/path/to/script" | at 02:30. The 'at' command is designed for scheduling one-time jobs at a specific time. Piping the script to 'at 02:30' schedules it for the next occurrence of 2:30 AM. Cron entries recur, systemd-run timers may recur, and 'sleep' does not schedule at a specific clock time. Thus, 'at' is the correct choice.

Answer

systemd-run --on-calendar="*-*-* 02:30:00" /path/to/script

Answer

sleep 86400 && /path/to/script &

Answer

crontab -e and add: 30 2 * * * /path/to/script

Question 2

A Linux administrator needs to schedule a one-time job that will run a backup script at 2:00 AM tomorrow. The job should not run if the system is powered off at that time, and it should not repeat. Which command should be used?

Accepted Answer

at 2:00 AM tomorrow. The at command is designed for scheduling one-time jobs at a specific time. It reads commands from standard input or a file and executes them once at the specified time. If the system is down at that time, the job will run when the system is next booted, provided the atd service is running. This matches the need for a non-repeating backup at 2:00 AM tomorrow.

Answer

batch

Answer

systemd-run --on-calendar='tomorrow 02:00'

Answer

cron -e

Question 3

A production server is experiencing intermittent failures, and the administrator suspects that a critical systemd service is being restarted by systemd due to crashes. The administrator wants to see how many times the service has been restarted and why. Which command provides this information?

Accepted Answer

systemctl show <service>. The systemctl show command exposes unit properties, including NRestarts, which tracks how many times systemd has restarted the service due to failures. It also provides exit status details. While journalctl can show restart events, it does not summarize the count. systemctl status and list-units --failed focus on current state rather than restart history.

Answer

journalctl -u <service>

Answer

systemctl status <service>

Answer

systemctl list-units --failed

Question 4

A Linux server running systemd is configured with a custom service unit `backup.service` that should run daily at 02:00. The administrator enabled the service and started the timer with `systemctl enable --now backup.timer`. The next day, the backup did not run. The output of `systemctl list-timers --all` shows the timer as `inactive (dead)`. Which command should the administrator run to diagnose why the timer is not triggering?

Accepted Answer

systemctl status backup.timer. The timer is inactive despite being enabled, so the administrator must inspect its runtime state and logs. The `systemctl status` command shows whether the timer is waiting, dead, or failed, and includes recent journal entries that often point to a missing or invalid OnCalendar setting. The other commands either focus on the service or only list static unit files, which do not reveal why the timer stopped.

Answer

systemd-analyze verify backup.timer

Answer

systemctl list-unit-files --type=timer

Answer

journalctl -u backup.service --since '1 day ago'

Question 5

A Linux administrator needs to limit the total amount of memory available to a specific user's processes to 2 GB to prevent a runaway script from affecting other services. The system uses systemd and cgroups v2. Which command should the administrator use to apply this limit persistently for the user 'deploy'?

Accepted Answer

Create a drop-in file /etc/systemd/system/user-$(id -u deploy).slice.d/50-memory.conf with MemoryMax=2G and run systemctl daemon-reload. The correct approach is to create a drop-in configuration for the user's systemd slice. Each user gets a slice named `user-<UID>.slice`. By adding a drop-in with `MemoryMax=2G`, the limit is applied persistently to all processes in that slice. The `systemctl set-property` command can also work but is not persistent unless combined with `--runtime` and saved, and it requires knowing the UID. The drop-in method is explicit and survives reboots.

Answer

systemctl set-property user-1000.slice MemoryMax=2G

Answer

Edit /etc/security/limits.conf and add 'deploy hard memlock 2097152'

Answer

systemd-run --scope -p MemoryMax=2G --uid=deploy /path/to/script

Question 6

A system administrator wants to view the last 10 lines of the system log file '/var/log/syslog' and continue to watch for new lines as they are appended. Which command should be used?

Accepted Answer

tail -n 10 -f /var/log/syslog. The `tail -n 10 -f /var/log/syslog` command first displays the last 10 lines of the file and then uses the `-f` (follow) flag to continuously monitor the file for new appended lines, outputting them in real time. This matches the requirement to both view the last 10 lines and watch for new entries.

Answer

tail -n 10 /var/log/syslog

Answer

less /var/log/syslog

Answer

head -n 10 /var/log/syslog

Question 7

An administrator is troubleshooting a server that runs a critical application. The server has 16 GB of RAM and 8 CPU cores. The administrator notices that the server becomes very slow during peak hours. Analysis of 'iostat -x 1' shows that the average wait time (await) for the main disk (sda) is consistently above 1000 ms, while the average service time (svctm) is around 5 ms. What is the most likely cause?

Accepted Answer

There is a large queue of I/O requests waiting to be serviced.. The 'await' value in iostat represents the average time (in milliseconds) for I/O requests to be serviced, including time spent waiting in the queue. With 'await' at 1000+ ms and 'svctm' at only 5 ms, the vast majority of the time is spent waiting, not being serviced. This indicates a large queue of pending I/O requests, which is the direct cause of the slowdown.

Answer

The CPU is overloaded, causing processes to wait for CPU time.

Answer

The system is using swap space heavily, causing disk I/O.

Answer

The disk is experiencing hardware errors.

Question 8

A systems administrator is troubleshooting a server that runs a database application. The server has 64 GB of RAM and 16 CPU cores. The administrator notices that the system is using a significant amount of swap space even though there is plenty of free memory. The 'free -m' command shows: total memory = 65536, used = 50000, free = 15536, buffers/cache = 10000, swap total = 8192, swap used = 6000. Which of the following is the most likely cause?

Accepted Answer

The vm.swappiness value is set too high.. A high vm.swappiness value (default 60) causes the kernel to aggressively swap out anonymous pages even when ample free memory exists. With 15 GB free and 10 GB in buffers/cache, the system should not be using 6 GB of swap unless swappiness is set too high, forcing premature swapping.

Answer

The vm.dirty_ratio and vm.dirty_background_ratio are set too high.

Answer

The database is configured to use huge pages, which are not swappable.

Answer

The vm.vfs_cache_pressure is set too low.

Question 9

Which TWO of the following are correct statements about systemd journald configuration?

Accepted Answer

The 'MaxRetentionSec' directive sets the maximum time to retain journal entries.. The 'MaxRetentionSec' directive in journald.conf specifies the maximum time (in seconds) that journal entries are retained before they are deleted. This is a time-based retention policy, distinct from size-based limits, and is used to automatically prune old log entries to manage disk usage.

Answer

The 'RuntimeMaxUse' directive applies to the journal stored in /var/log/journal.

Answer

The 'Compress' directive is set to 'no' by default.

Answer

The 'ForwardToSyslog' directive is set to 'yes' by default.

Question 10

A system administrator needs to check the current CPU load and memory usage on a Linux server. Which command should be used to display a dynamic, real-time view of running processes and system resource utilization?

Accepted Answer

top. (top) is correct because it provides a dynamic, real-time view of running processes and system resource utilization, including CPU load, memory usage, and process details. It updates continuously by default, making it ideal for monitoring live system performance.

Answer

uptime

Answer

ps aux

Answer

free -h

Question 11

Based on the journalctl output, what is the most likely cause of the service failure?

Accepted Answer

Another process is already using port 8080.. The journalctl output shows a bind error on port 8080 with 'Address already in use'. This indicates that another process is already listening on that port, preventing the service from starting. In systemd, such a failure is logged with the specific errno EADDRINUSE, which directly points to a port conflict.

Answer

The service configuration file has a syntax error.

Answer

The system is out of memory.

Answer

The service is trying to write to a read-only filesystem.

Question 12

Order the steps to set up a LVM logical volume from a new disk.

Accepted Answer

Create physical volume (pvcreate), then volume group (vgcreate), then logical volume (lvcreate), then format with filesystem (mkfs), then mount.. The correct sequence for setting up an LVM logical volume from a new disk is: first create a physical volume (PV) using pvcreate, then create a volume group (VG) with vgcreate, then create a logical volume (LV) with lvcreate, then format the LV with a filesystem using mkfs, and finally mount it to a directory. This order ensures all dependencies are satisfied: the VG requires the PV, the LV requires the VG, and the filesystem requires the LV.

Answer

Create volume group (vgcreate), then physical volume (pvcreate), then logical volume (lvcreate), then format, then mount.

Answer

Create physical volume (pvcreate), then format (mkfs), then volume group (vgcreate), then logical volume (lvcreate), then mount.

Answer

Create logical volume (lvcreate), then physical volume (pvcreate), then volume group (vgcreate), then format, then mount.

Question 13

Order the steps to recover a forgotten root password on a Linux system using single-user mode.

Accepted Answer

1. Boot into single-user mode, 2. Remount filesystem as read-write, 3. Change root password, 4. Reboot.. To recover a forgotten root password on Linux using single-user mode, you must first boot into single-user mode (e.g., by adding 'single' to the kernel command line). At the root prompt, the filesystem is mounted read-only, so you must remount it as read-write with 'mount -o remount,rw /'. Then use 'passwd root' to set a new password. Finally, reboot the system. Attempting to change the password without remounting or rebooting prematurely will cause the recovery to fail.

Answer

1. Boot into single-user mode, 2. Change root password, 3. Remount filesystem as read-write, 4. Reboot.

Answer

1. Boot into single-user mode, 2. Remount filesystem as read-write, 3. Reboot, 4. Change root password.

Answer

1. Change root password, 2. Boot into single-user mode, 3. Remount filesystem as read-write, 4. Reboot.

Question 14

Match each file system type to its typical use case.

Accepted Answer

ext4: General-purpose file system for Linux distributions, widely used on desktops and servers.. Common file systems in Linux include ext4 for general use, XFS for high-performance and large files, and Btrfs for advanced features like snapshots. Swapping definitions is a common error.

Answer

ext4: High-performance file system suitable for large files and parallel I/O, often used in enterprise storage.

Answer

XFS: Modern file system with snapshot and compression capabilities, designed for scalability and fault tolerance.

Question 15

A system administrator notices that a process is consuming 100% CPU and is unresponsive. Which command should be used to immediately stop the process if the PID is 2345?

Accepted Answer

kill -9 2345. `kill -9 2345` sends the SIGKILL signal (signal 9) to process ID 2345, which immediately terminates the process without allowing it to clean up or ignore the signal. This is the appropriate action for an unresponsive process consuming 100% CPU, as SIGKILL cannot be caught or blocked by the process.

Answer

pkill -9 processname

Answer

systemctl stop processname

Answer

kill -15 2345