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Network

Network diagnostics on the server: reachability, open ports, HTTP headers, response times and routing. curl is the most important tool here.

18 one-liners: 18 harmless, 0 caution, 0 destructive

curl 6ss 4ip 4troubleshooting 3ports 3connections 3http 2seo 2firewall 2interfaces 2

All Network one-liners

Analyze the network path with mtr

$mtr -rwc 50 example.com
harmless

Capture network traffic on a port with tcpdump

#tcpdump -i any -nn -c 100 port 25
harmless

Check HTTP status codes for a list of URLs

$while read -r u; do printf '%s %s\n' "$(curl -o /dev/null -sS -w '%{http_code}' "$u")" "$u"; done < urls.txt
harmless

Check server ports from outside with nmap

$nmap -Pn -p 21,22,25,80,110,143,443,465,587,993,995,3306,8443,8880 server.example.com
harmless

Count TCP connections by state

$ss -Htan | awk '{print $1}' | sort | uniq -c | sort -rn
harmless

Count web server connections per IP address

$ss -Htn state established '( sport = :80 or sport = :443 )' | awk '{print $4}' | rev | cut -d: -f2- | rev | sort | uniq -c | sort -rn | head -20
harmless

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Find the public IP address of a server

$curl -4 -s https://icanhazip.com
harmless

Find the route and source IP for a destination

$ip route get 1.1.1.1
harmless

Follow and show the redirect chain of a URL

$curl -sSIL http://example.com/ | grep -iE '^(HTTP/|location:)'
harmless

List open ports and listening services

#ss -tulpn
harmless

Measure HTTP load times and TTFB with curl

$curl -o /dev/null -sS -w 'DNS: %{time_namelookup}s Connect: %{time_connect}s TLS: %{time_appconnect}s TTFB: %{time_starttransfer}s Gesamt: %{time_total}s\n' https://example.com/
harmless

Show all IP addresses in a compact overview

$ip -br -c addr
harmless

Show outgoing SMTP connections and their processes

#ss -Htnp state established '( dport = :25 )'
harmless

Show the HTTP response headers of a website

$curl -sSI https://example.com/
harmless

Show traffic and error counters of a network interface

$ip -s link show eth0
harmless

Test a website on a new server before the DNS change

$curl -sSI --resolve example.com:443:203.0.113.10 https://example.com/
harmless

Test if a TCP port is reachable without telnet or nc

$timeout 3 bash -c '</dev/tcp/db.example.com/3306' && echo offen || echo "geschlossen oder gefiltert"
harmless

Test the MTU with ping

$ping -M do -s 1472 -c 3 example.com
harmless

Read first, then run.

The commands on myline.de act directly on servers, files and databases. A wrong path or placeholder can delete data irreversibly or make a server unreachable.

  • All commands are provided without warranty and are not tested on every system.
  • Understand what a command does before running it, and check every placeholder.
  • Make a backup first and, if possible, try it on a test system.
  • You run commands at your own risk. Liability for damages is excluded to the extent permitted by law.