LFCS Operation of Running Systems — 10 Questions

Question 1

Which TWO commands can be used to display the current runlevel or target of a systemd-based system?

Accepted Answer

runlevel. The `runlevel` command displays the previous and current runlevel, which works on systemd-based systems by reading the last runlevel change. Option A (`systemctl get-default`) is incorrect because it shows the default target that will be used at boot, not the currently active runlevel or target. Options B and C change the runlevel, and option D lists all targets but does not isolate the current one without additional filtering. Therefore, only `runlevel` correctly displays the current runlevel or target.

Answer

systemctl get-default

Answer

telinit

Answer

init 3

Answer

systemctl list-units --type=target

Question 2

Which TWO commands can be used to display the current block devices and their partitions?

Accepted Answer

lsblk. B is correct because `lsblk` lists all block devices and their partitions in a tree-like format from sysfs. C is correct because `parted -l` displays partition tables for all block devices, including MBR and GPT layouts. D is correct because `fdisk -l` also shows partition tables. All three commands can be used to display current block devices and their partitions.

Answer

df -h

Answer

blkid

Question 3

A system administrator needs to ensure that a specific service, 'myapp', starts automatically after a system crash and also restarts if it fails. Which systemd unit directive should be used to achieve this behavior?

Accepted Answer

Restart=on-failure and WantedBy=multi-user.target. The combination of `Restart=on-failure` ensures the service restarts automatically if it exits with a non-zero exit code or is terminated by a signal, and `WantedBy=multi-user.target` creates a dependency that starts the service at boot, including after a system crash. This satisfies both requirements: automatic start after crash (via systemd's dependency-based boot) and restart on failure (via the Restart directive).

Answer

RemainAfterExit=yes

Answer

Restart=always

Answer

ExecStopPost=/bin/systemctl restart myapp.service

Question 4

A Linux system reports 'Out of memory' errors frequently. The administrator checks memory usage with 'free -m' and notices that most memory is used by file cache. Which command can the administrator run to immediately free up the cache without affecting running processes?

Accepted Answer

sysctl vm.drop_caches=1. Both options A and C are correct methods to free pagecache (file cache) without terminating processes. Writing to /proc/sys/vm/drop_caches via echo or using the sysctl command achieve the same result. The administrator can use either command to immediately reclaim memory used by file cache. Option B disables swap but does not free cache, and option D kills a process unnecessarily.

Answer

swapoff -a

Answer

kill -9 $(pidof some_process)

Question 5

An administrator needs to schedule a cron job that runs a script every day at 3:00 AM, but the system is in a different time zone (UTC) than the administrator's local time (EST). The administrator wants the job to run at 3:00 AM local time regardless of system time zone changes. What is the best approach?

Accepted Answer

Use the CRON_TZ variable in the crontab file to specify EST and schedule at 3:00 AM. The CRON_TZ variable, when set in a crontab file, allows you to specify a time zone for the cron daemon to interpret the schedule entries. This ensures the job runs at 3:00 AM EST regardless of the system's default time zone (UTC), and it persists even if the system time zone changes, as cron uses the variable for scheduling.

Answer

Change the system time zone to EST and set the cron job to run at 3:00 AM

Answer

Set the TZ environment variable in the crontab file before the job definition

Answer

Calculate the UTC equivalent (8:00 AM UTC) and schedule the job at that time

Question 6

Which THREE steps are necessary to permanently disable a systemd service from starting at boot?

Accepted Answer

systemctl mask myapp.service. To permanently prevent a systemd service from starting at boot, two steps are necessary: disable it (`systemctl disable`) to remove the symbolic links that cause it to start on boot, and mask it (`systemctl mask`) to prevent manual or dependency-based activation. Stopping the service (`systemctl stop`) is optional and does not affect its boot behavior; it only stops the current running instance. Therefore, only disable and mask are required to permanently disable the service from booting.

Answer

systemctl stop myapp.service

Answer

systemctl reset-failed myapp.service

Answer

systemctl daemon-reload

Question 7

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 8

A systems administrator receives reports that a web server running Nginx is intermittently unresponsive. The server has 8 GB of RAM and 4 CPU cores. The administrator runs 'free -m' and sees that available memory is low, and 'top' shows that several nginx worker processes are using a high percentage of CPU. Which of the following is the most likely cause of the issue?

Accepted Answer

The nginx worker_connections setting is too high.. When `worker_connections` is set too high, each Nginx worker process attempts to handle more concurrent connections than the system can support, leading to CPU saturation and memory exhaustion. This matches the symptoms of high CPU usage by worker processes and low available memory, causing intermittent unresponsiveness.

Answer

The vm.swappiness value is set to 100.

Answer

The net.core.somaxconn setting is too low.

Answer

The kernel parameter kernel.pid_max is set too low.

Question 9

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 10

A Linux server experiences a kernel panic during boot. The administrator needs to capture the kernel panic message for debugging. Which of the following methods would allow capturing the panic message?

Accepted Answer

Add 'panic=0' to the kernel boot parameters.. Setting 'panic=0' in the kernel boot parameters instructs the kernel to wait indefinitely (never reboot) after a kernel panic, allowing the administrator to capture the panic message from the console output. This is essential for debugging as it prevents automatic reboot and preserves the panic screen.

Answer

Add 'quiet' to the kernel boot parameters.

Answer

Configure netconsole to send kernel messages to a remote syslog server.

Answer

Set the kernel parameter 'console=ttyS0' to redirect output to a serial console.