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Overview

The DNS lookup phase is the most resource-intensive part of the BlackWeb update process. It validates millions of domains through actual DNS queries to exclude nonexistent or invalid domains from the final blocklist.
High Resource Consumption! This process uses parallel DNS queries that can saturate CPU and network bandwidth, especially on limited connections like satellite links.

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Why DNS Validation?

Many public blocklist sources contain:
  • Expired domains
  • Nonexistent domains (typos in original lists)
  • Domains that never existed
  • Domains that have been taken down
By validating each domain via DNS, BlackWeb ensures only active, resolvable domains are blocked, reducing false positives and improving performance.

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Two-Step Validation Process

The script performs DNS lookup in two steps with different timeout values:

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Step 1: Initial Lookup (1-second timeout)

bwupdate/bwupdate.sh
# STEP 1:
if [ ! -e "$bwupdate"/dnslookup1 ]; then
    echo "${bw08[$lang]}"
    sed 's/^\.//g' finalclean | sort -u > step1
    total=$(wc -l < step1)
    (
        while sleep 1; do
            processed=$(wc -l < dnslookup1 2>/dev/null)
            percent=$(awk -v p="$processed" -v t="$total" 'BEGIN { if (t > 0) printf "%.2f", (p/t)*100; else print 100 }')
            printf "Processed: %d / %d (%s%%)\r" "$processed" "$total" "$percent"
        done
    ) &
    progress_pid=$!
    if [ -s dnslookup1 ]; then
        awk 'FNR==NR {seen[$2]=1;next} seen[$1]!=1' dnslookup1 step1
    else
        cat step1
    fi | xargs -I {} -P "$PROCS" sh -c "if host -W 1 {} >/dev/null; then echo HIT {}; else echo FAULT {}; fi" >> dnslookup1
    kill "$progress_pid" 2>/dev/null
    echo
    sed '/^FAULT/d' dnslookup1 | awk '{print $2}' | awk '{print "." $1}' | sort -u > hit.txt
    sed '/^HIT/d' dnslookup1 | awk '{print $2}' | awk '{print "." $1}' | sort -u >> fault.txt
    sort -o fault.txt -u fault.txt
    echo "OK"
fi
Key Features:
  • Uses host -W 1 (1-second timeout)
  • Marks domains as HIT (resolved) or FAULT (failed)
  • Runs in parallel using xargs -P $PROCS
  • Real-time progress display
  • Resumes from checkpoint if interrupted

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Step 2: Retry Failed Domains (2-second timeout)

bwupdate/bwupdate.sh
sleep 10

# STEP 2:
echo "${bw09[$lang]}"
sed 's/^\.//g' fault.txt | sort -u > step2
total=$(wc -l < step2)
(
    while sleep 1; do
        processed=$(wc -l < dnslookup2 2>/dev/null)
        percent=$(awk -v p="$processed" -v t="$total" 'BEGIN { if (t > 0) printf "%.2f", (p/t)*100; else print 100 }')
        printf "Processed: %d / %d (%s%%)\r" "$processed" "$total" "$percent"
    done
) &
progress_pid=$!
if [ -s dnslookup2 ]; then
    awk 'FNR==NR {seen[$2]=1;next} seen[$1]!=1' dnslookup2 step2
else
    cat step2
fi | xargs -I {} -P "$PROCS" sh -c "if host -W 2 {} >/dev/null; then echo HIT {}; else echo FAULT {}; fi" >> dnslookup2
kill "$progress_pid" 2>/dev/null
echo
sed '/^FAULT/d' dnslookup2 | awk '{print $2}' | awk '{print "." $1}' | sort -u >> hit.txt
sed '/^HIT/d' dnslookup2 | awk '{print $2}' | awk '{print "." $1}' | sort -u > fault.txt
echo "OK"
Why Two Steps?
  1. First pass (1s timeout): Quickly filters out obviously dead domains
  2. 10-second pause: Prevents overwhelming DNS infrastructure
  3. Second pass (2s timeout): Gives slower-responding domains a second chance

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Parallel Processing Configuration

The number of parallel DNS queries is controlled by the PROCS variable:
bwupdate/bwupdate.sh
PROCS=$(($(nproc) * 4))

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Understanding PROCS

The formula is: 
PROCS = Number of Logical CPUs × Multiplier

PROCS=$(($(nproc)))        # Network-friendly
Best for:
  • Limited bandwidth connections
  • Satellite or metered internet
  • Shared DNS servers
  • Low-power systems

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Example: Core i5 CPU

For a Core i5 with 4 physical cores and 8 threads (Hyper-Threading): 
nproc             → 8
PROCS=$((8 * 4))  → 32 parallel queries

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Checking Your CPU Configuration

# Physical cores
grep '^core id' /proc/cpuinfo | sort -u | wc -l

# Logical CPUs (threads)
nproc

# Xargs parallel limit (usually 127+)
xargs --show-limits

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Real-Time Progress Display

The script shows live processing statistics: 
Processed: 2463489 / 7244989 (34.00%)
This progress indicator:
  • Updates every second
  • Shows domains processed vs. total
  • Displays percentage completion
  • Runs in a background process

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Implementation

bwupdate/bwupdate.sh
total=$(wc -l < step1)
(
    while sleep 1; do
        processed=$(wc -l < dnslookup1 2>/dev/null)
        percent=$(awk -v p="$processed" -v t="$total" 'BEGIN { if (t > 0) printf "%.2f", (p/t)*100; else print 100 }')
        printf "Processed: %d / %d (%s%%)\r" "$processed" "$total" "$percent"
    done
) &
progress_pid=$!
The progress monitor is killed after completion: 
kill "$progress_pid" 2>/dev/null

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DNS Query Results

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HIT (Domain Resolved)

HIT google.com
google.com has address 142.251.35.238
google.com has IPv6 address 2607:f8b0:4008:80b::200e
google.com mail is handled by 10 smtp.google.com.
A “HIT” means:
  • Domain exists
  • DNS resolves successfully
  • Domain will be included in final blocklist

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FAULT (Domain Failed)

FAULT testfaultdomain.com
Host testfaultdomain.com not found: 3(NXDOMAIN)
A “FAULT” means:
  • Domain doesn’t exist (NXDOMAIN)
  • DNS query timed out
  • Temporary DNS failure
  • Domain will be excluded from blocklist

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Resume Capability

The script can resume DNS lookup if interrupted:
bwupdate/bwupdate.sh
if [ -s dnslookup1 ]; then
    awk 'FNR==NR {seen[$2]=1;next} seen[$1]!=1' dnslookup1 step1
else
    cat step1
fi | xargs -I {} -P "$PROCS" sh -c "..."
This logic:
  • Checks if dnslookup1 file exists and has content
  • Excludes already-processed domains
  • Only queries remaining domains
  • Prevents duplicate work
If you interrupt the script during DNS lookup (Ctrl+C), it automatically resumes from where it left off on the next run.

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Adjusting for Your Environment

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Factors to Consider

FactorLower PROCSHigher PROCS
CPUOlder/slower CPUModern multi-core CPU
NetworkSatellite, metered, slowFiber, unlimited, fast
DNS ServerPublic DNS (8.8.8.8)Local caching DNS
System LoadProduction serverDedicated test machine
PriorityMinimize impactMaximize speed
Edit bwupdate.sh line 388: 
# Change this line based on your needs:
PROCS=$(($(nproc) * 4))  # Default: Aggressive
Replace with your preferred setting: 
PROCS=$(($(nproc)))      # Conservative
PROCS=$(($(nproc) * 2))  # Balanced  
PROCS=$(($(nproc) * 8))  # Extreme

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Performance Impact

Network Saturation: High PROCS values can saturate DNS servers, causing:
  • Rate limiting
  • Temporary bans
  • Increased FAULT results (false negatives)
  • Slower overall performance

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Monitoring Performance

While the script runs, monitor: 
# CPU usage
htop

# Network traffic
iftop

# DNS query rate
watch -n 1 'wc -l dnslookup1'

# System load
uptime

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Troubleshooting

  • Reduce PROCS value (network/DNS overload)
  • Check DNS server responsiveness
  • Verify internet connection stability
  • Consider using local caching DNS (dnsmasq, unbound)
  • Increase PROCS value (if system can handle it)
  • Use faster DNS servers (Cloudflare 1.1.1.1, Google 8.8.8.8)
  • Check for bandwidth throttling
  • Verify CPU isn’t maxed out
  • Immediately reduce PROCS value
  • Kill the script and restart with lower parallelism
  • Monitor system resources before restarting
  • Consider running on dedicated hardware
  • Use local recursive DNS resolver
  • Reduce PROCS significantly
  • Add delays between queries
  • Spread queries across multiple DNS servers

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Next Steps

Domain Debugging

Learn about domain validation, TLD checking, Punycode conversion, and ASCII cleanup

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