| Command |
Example |
| Send request |
$ arping -I enp4s0 -c 3 192.168.1.1 |
| Find duplicate IP |
$ arping -D -I <NETWORK DEVICE> -c 3 192.168.2.1 |
| IP neighbor |
$ ip n |
| Command |
Example |
| List USB devices (verbose) |
$ lsusb -v |
| List PCI devices with kernel driver |
$ lspci -k |
| List network interfaces |
$ ls -la /sys/class/net/ -> eno1 -> ../../devices/pci0000:0
|
| List network interfaces (systemd, networkd) |
$ networkctl list |
| List wireless interfaces |
$ iw dev |
| MAC address for interface |
$ cat /sys/class/net/eno1/address |
| Command |
Example |
List processes (p) listing (l) on numerical (n) ports for TCP (t) and UDP (u) |
ss -ltunp |
For the return values in the examples, given:
| Test |
Example |
What is the current host's FQDN? |
$ hostname -f -> nd1.localdomain
|
What is the current host's IP? |
$ hostname -i -> 192.168.0.101 192.168.1.101 192.168.2.101
|
What is the corresponding hostname and IP? |
$ getent hosts 192.168.0.101 -> 192.168.0.101 nd1.localdomain server servernd1 or getent hosts nd1.localdomain -> 192.168.0.101. |
What is the corresponding IP to hostname? |
$ getent ahosts client1 -> 192.168.1.102 STREAM client1.localdomain ...
|
Is the IP reachable? |
$ ping -c 3 192.168.0.101 -> ... 3 packets transmitted, 3 received, 0% packet loss, time 2023ms
|
Is the IP reachable through the DNS? |
$ ping -c 3 server.domain -> ... 3 packets transmitted, 3 received, 0% packet loss, time 2017ms
|
| Error |
Cause |
Remedy |
Code 1 "Unspecific Reason" "We don’t know what’s wrong"
Nov 29 01:16:37 <hostname> kernel: <WIRELESS DEVICE>: authenticate with <MAC ADDRESS>
Nov 29 01:16:37 <hostname> kernel: <WIRELESS DEVICE>: send auth to <MAC ADDRESS> (try 1/3)
Nov 29 01:16:37 <hostname> kernel: <WIRELESS DEVICE>: authenticated
Nov 29 01:16:37 <hostname> kernel: <WIRELESS DEVICE>: associate with <MAC ADDRESS> (try 1/3)
Nov 29 01:16:37 <hostname> kernel: <WIRELESS DEVICE>: RX AssocResp from <MAC ADDRESS> (capab=0x431 status=0 aid=4)
Nov 29 01:16:37 <hostname> kernel: <WIRELESS DEVICE>: associated
Nov 29 01:16:38 <hostname> kernel: <WIRELESS DEVICE>: Limiting TX power to 20 (20 - 0) dBm as advertised by <MAC ADDRESS>
Nov 29 01:16:38 <hostname> kernel: <WIRELESS DEVICE>: deauthenticating from <MAC ADDRESS> by local choice (Reason: 1=UNSPECIFIED)
|
unknown |
pinging? Cannot confirm whether the connection worked or the ping caused the connection to work. The ip addr did not show an assigned IPv4 address for <WIRELESS DEVICE>. However, an attempt to test the connection with ping -c 3 8.8.8.8 resulted in success. |
RTNETLINK answers operation not possible due to RF-kill |
|
rfkill unblock all |
| Test |
Example |
Connect three times (-c3) and return failed responses (-O) while ignoring successful ones (-q). |
$ ping -Oqc3 example.org |
| Error |
Cause |
Remedy |
Destination Host Unreachable |
No Internet connection because of strict firewall rules. |
|
Destination Host Unreachable |
No Internet connection because of wrong Gateway. |
|
Name or service not known |
Unknown |
|
System Error |
An invalid syntax in /etc/nsswitch.conf
|
|
-
tcpdump -i <NETWORK INTERFACE>eth0 -nn -s<INTEGER>0 -v -A port <PORT>80
- Do not resolve hostname (
-n) and port name (-nn).
- Decode package as Ascii (
-A).
- Truncate the "snap" length of the package "snaplen" (
-s), where 0 represents the default value of 262144 bytes.
- Filter packages that are not TCP (
tcp or proto 6).
- Filter packages that are not UDP (
udp or proto 17).
- The
host parameter captures all incoming and outcoming traffic to host. The parameters src and dst captures traffic to and from the host respectively.