A Linux administrator is responsible for a critical application that runs as a systemd service on a server. The application occasionally hangs, and the administrator wants to automate the restart if the service becomes unresponsive. The administrator writes a Bash script that checks if the service is active and responsive by pinging a local health endpoint. If the health check fails three consecutive times, the script restarts the service. The script is intended to run every minute via a cron job. However, after implementing the cron job, the service is restarted even when it is functioning correctly, causing unnecessary downtime. The administrator reviews the script and finds the following logic:

#!/bin/bash
SERVICE="myapp"
COUNT_FILE="/tmp/${SERVICE}_failcount"
if curl -f http://localhost:8080/health; then
echo 0 "$COUNT_FILE"
else
FAILS=$(cat "$COUNT_FILE" 2/dev/null || echo 0)
FAILS=$((FAILS + 1))
echo "$FAILS" "$COUNT_FILE"
if [ "$FAILS" -ge 3 ]; then
systemctl restart "$SERVICE"
echo 0 "$COUNT_FILE"
fi
fi

What is the most likely cause of the false restarts?

Question

A Linux administrator is responsible for a critical application that runs as a systemd service on a server. The application occasionally hangs, and the administrator wants to automate the restart if the service becomes unresponsive. The administrator writes a Bash script that checks if the service is active and responsive by pinging a local health endpoint. If the health check fails three consecutive times, the script restarts the service. The script is intended to run every minute via a cron job. However, after implementing the cron job, the service is restarted even when it is functioning correctly, causing unnecessary downtime. The administrator reviews the script and finds the following logic:

#!/bin/bash SERVICE="myapp" COUNT_FILE="/tmp/${SERVICE}_failcount"

if curl -f http://localhost:8080/health; then

echo 0 > "$COUNT_FILE" else FAILS=$(cat "$COUNT_FILE" 2>/dev/null || echo 0) FAILS=$((FAILS + 1)) echo "$FAILS" > "$COUNT_FILE"

if [ "$FAILS" -ge 3 ]; then

systemctl restart "$SERVICE" echo 0 > "$COUNT_FILE" fi fi

What is the most likely cause of the false restarts?

#!/bin/bash
SERVICE="myapp"
COUNT_FILE="/tmp/${SERVICE}_failcount"
if curl -f http://localhost:8080/health; then
    echo 0 > "$COUNT_FILE"
else
    FAILS=$(cat "$COUNT_FILE" 2>/dev/null || echo 0)
    FAILS=$((FAILS + 1))
    echo "$FAILS" > "$COUNT_FILE"
    if [ "$FAILS" -ge 3 ]; then
        systemctl restart "$SERVICE"
        echo 0 > "$COUNT_FILE"
    fi
fi

What is the most likely cause of the false restarts?

Accepted Answer

Multiple instances of the script are running concurrently due to cron timing, causing a race condition on the count file.. The cron job runs the script every minute, but if the health check takes longer than a minute (e.g., due to network latency or a slow endpoint), multiple instances of the script can overlap. Each instance reads, increments, and writes the count file independently, causing a race condition where the fail count can be artificially inflated, leading to a false restart even when the service is healthy.

Answer

The count file is not being written because the script lacks write permissions to /tmp.

Answer

The script does not reset the count file after a successful health check.

Answer

The script does not handle the case where the count file does not exist on the first failure.

XK0-006 Practice Question: A Linux administrator is responsible for a…

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