Networking
Get DNS record information
dig domainName
The record type can also be specified for non-A records, i.e. dig _acme-challenge.www TXT
Useful options
-x ipAddr- Reverse lookup.
Hostname
Set
sudo hostnamectl set-hostname vm7.orgDomain
View
Use one of the following commands.
hostnamectl status
cat /etc/hostname
HTTP protocol
Sending arguments
GET method
Sent as a query string after the ? in the url.
http://example.com/page?parameter=value&also=another
POST/PUT methods
Stored as key-value pairs in the body (not visible in the url).
{ "key": "value" }
IP
Add a route temporarily (until reboot)
ip route add 192.168.2.1/23 via 10.11.12.3
Add an IP address to an interface temporarily (until reboot)
sudo ip address add 192.168.1.1/24 dev eth0
Bring interfaces up and down
sudo ip link set eth0 up
sudo ip link set eth0 down
Delete a route temporarily (until reboot)
sudo ip route delete 192.168.2.1/23 via 10.11.12.3
sudo ip route delete 192.168.2.1/23 # for all routes to target
Show ARP cache (MAC addresses)
ip -c neighbor show
Show information for all interfaces
ip -c link show
Show ip addresses allocated to interfaces
ip -c address show
Show public ip address
curl ifconfig.me
Show statistics of an interface
ip -c -h -s link show eth0
Options -c and -h add color and human-readable values to output.
Ping
Used to test whether or not a packet can reach a host. Works by sending ICMP echo request (Type 8) packets to the destination host and waits for an ICMP echo reply (Type 0).
The icmp_seq field shows the sequence number of packets sent. If sequence numbers are missing, some
connectivity issue is happening and not all packets are getting through. If the sequence number is out of order,
the connection is probably very slow as packets are exceeding the one second default.
Useful options
-c X- Stop sending echo request packets after the count has been reached.-I name- Use the specified interface.-4or-6- Use only IPv4 or v6.
Route
Add route temporarily (until reboot)
sudo route add -net 192.168.0.0 netmask 255.255.255.0 gw 192.168.0.1
# Add default gateway.
sudo route add default gw 192.168.0.1
Delete route temporarily (until reboot)
sudo route del -net 192.168.0.0 netmask 255.255.255.0
# Delete default gateway.
sudo route del default
Show routing table
route
Ss
Useful options
| Option | Description |
|---|---|
| -4 | IPv4 sockets only. |
| -a | Listening and non-listening sockets (established for TCP). |
| -l | Listening sockets only. |
| -m | Socket memory usage. |
| -n | Don't resolve numeric adresses/ports. |
| -o | Options (i. e. state established). |
| -p | Process using socket. |
| -t | TCP sockets. |
| -u | UDP sockets. |
| -x | Unix domain sockets. |
| -Z | Process and security context (SELinux). |
Traceroute
See route to target host (how packets are being routed until they get to its final destination).
traceroute targetHost
To bypass firewalls that block ICMP traffic try one of these options: --udp or --tcp
The commands on this page were tested on Fedora 40 (unless otherwise specified).