Network

HTTP

Command	Action
curl URL	GET
curl -I URL	HEAD (headers only)
curl -fsSL URL	fail-on-error, silent, show errors, follow redirects
curl -X POST -d '...' URL	POST form
curl -X POST -H 'content-type: application/json' -d '{"a":1}' URL	JSON
curl -u user:pass URL	basic auth
curl -H 'Authorization: Bearer TOKEN' URL
curl -o file URL	save to file
curl -O URL	save with remote filename
curl --resolve host:port:IP URL	override DNS for one request
curl -w '%{http_code} %{time_total}s\n' -o /dev/null -s URL	timing
curl --insecure URL	skip TLS verify (don’t in prod)
wget URL	alternative downloader
wget -mkEpnp URL	mirror site

HTTPie alternative:

$ http GET https://api.example.com/users/1
$ http POST https://api.example.com/users name=operator
$ http -A bearer -a TOKEN GET https://...

DNS

Command	Action
getent hosts NAME	use system resolver (recommended)
dig NAME	detailed lookup
dig +short NAME	just answers
dig +short NAME AAAA	IPv6
dig NAME MX	mail
dig NAME TXT	TXT records
dig @8.8.8.8 NAME	specific server
dig +trace NAME	full delegation trace
dig -x 1.2.3.4	reverse DNS
host NAME	concise lookup
nslookup NAME	classic
resolvectl status	systemd-resolved view
resolvectl flush-caches	flush

Sockets and Ports

Command	Action
ss -tulpn	listening TCP/UDP with PID
ss -ant	all TCP
ss -ant state established
ss -s	summary stats
netstat -tulpn	older equivalent
lsof -i :PORT	who has the port
lsof -nP -iTCP -sTCP:LISTEN listeners (numeric)
nc -zv host PORT	TCP probe
nc -u -zv host PORT	UDP probe
nc -l -p PORT	listen
nc host PORT	connect (chat)

Reachability

Command	Action
ping -c 4 HOST
ping6 -c 4 HOST
traceroute HOST
mtr HOST	interactive trace + ping
tracepath HOST	no root needed
hping3 -S -p 443 HOST	SYN probe (root)

SSH

Command	Action
ssh user@host
ssh -p 2222 user@host
ssh -i ~/.ssh/key user@host
ssh -L 5432:db:5432 user@host	local port forward
ssh -R 9000:localhost:9000 user@host	remote forward
ssh -D 1080 user@host	SOCKS proxy
ssh -A user@host	agent forwarding (use carefully)
ssh -o ProxyCommand="ssh bastion -W %h:%p" user@target
ssh-keygen -t ed25519 -C "comment"	new key
ssh-keygen -t ed25519-sk	hardware-backed key (FIDO2)
ssh-copy-id user@host	install pubkey
ssh-add -L	list agent keys
ssh-keyscan host	fetch host keys

Useful ~/.ssh/config:

Host bastion
  HostName bastion.example.com
  User operator

Host prod-*
  ProxyJump bastion
  User ops
  IdentityFile ~/.ssh/prod_ed25519
  ServerAliveInterval 60

File Transfer

Command	Action
scp file user@host:/path
scp -r dir user@host:/path
scp user@host:/path .	pull
rsync -aP src/ user@host:/path/	incremental, progress
rsync -aP --delete src/ host:/path/ mirror
rsync -aPe ssh src/ host:/path/	explicit ssh
sftp user@host	interactive

TLS / Certificates

Command	Action
openssl s_client -connect host:443 -servername host
openssl s_client -showcerts -connect host:443
openssl x509 -in cert.pem -noout -text	inspect cert
openssl x509 -in cert.pem -noout -dates	validity dates
openssl x509 -in cert.pem -noout -fingerprint -sha256
openssl crl2pkcs7 -nocrl -certfile cert.pem | openssl pkcs7 -print_certs	full chain
echo | openssl s_client -connect host:443 2>/dev/null | openssl x509 -noout -dates
testssl.sh host	script-based TLS audit

Packet Capture

Command	Action
sudo tcpdump -i any port 443
sudo tcpdump -i any host 1.2.3.4 -w out.pcap
sudo tshark -i any -f 'port 53'
sudo tcpdump -nn -i any 'tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn'

Networking Tools by Distro

• ip (iproute2), modern; preferred over ifconfig.

• ss, modern; preferred over netstat.

• nmcli, NetworkManager CLI.

• iw / iwctl, wireless.

• firewall-cmd, firewalld (RHEL).

• ufw, Uncomplicated Firewall (Ubuntu).

• iptables / nft, low-level firewall rules.