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Ubuntu ARM port running on a RPI 5, when the connection gets spotty systemd-resolved goes nuts and network connectivity drops out. On X86 linux I don't see that behavior, but on the RPI I can hear the fan going nuts once a day. I tried every bit of piactl connect and sudo systemctl restart systemd-networkd or restart systemd-resolved to solve the issue and get the VPN to reconnect. I eventually settled on a cron job script to detect high systemd-resolved usage and reboot. sudo touch /usr/local/bin/monitor_systemd_resolved.sh sudo nano /usr/local/bin/monitor_systemd_resolved.sh

#!/bin/bash

# CPU usage threshold for systemd-resolved (90%)
THRESHOLD=90
COUNTER_FILE="/tmp/systemd_resolved_counter.txt"

# Log file
LOG_FILE="/var/log/systemd_resolved_monitor.log"

# Function to clear the log file weekly on Sunday
clear_log_weekly() {
    local day_of_week
    day_of_week=$(date +%u)  # Get the day of the week (1=Monday, 7=Sunday)
    
    if [[ "$day_of_week" -eq 7 ]]; then
        echo "$(date): Clearing log file for weekly maintenance." > "$LOG_FILE"
    fi
}

# Read or initialize the counter
if [[ -f "$COUNTER_FILE" ]]; then
    COUNTER=$(<"$COUNTER_FILE")
else
    COUNTER=0
fi

# Clear log if today is Sunday
clear_log_weekly

# Check CPU usage of systemd-resolved
USAGE=$(ps -C systemd-resolved -o %cpu= | awk '{print int($1)}')

# Increment or reset the counter based on usage
if [[ "$USAGE" -ge "$THRESHOLD" ]]; then
    ((COUNTER++))
    echo "$(date): CPU usage at $USAGE%. Counter incremented to $COUNTER." >> "$LOG_FILE"
else
    COUNTER=0
    echo "$(date): CPU usage at $USAGE%. Counter reset to 0." >> "$LOG_FILE"
fi

# Save the updated counter
echo "$COUNTER" > "$COUNTER_FILE"

# If counter reaches 3 (approx. 15 minutes of high usage), reboot
if [[ "$COUNTER" -ge 3 ]]; then
    echo "$(date): High CPU usage detected for systemd-resolved. Rebooting..." >> "$LOG_FILE"
    rm "$COUNTER_FILE"  # Reset the counter on reboot
    reboot
fi

crontab -e
*/5 * * * * /usr/local/bin/monitor_systemd_resolved.sh