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Linux Commands

  • Check your linux version

    lsb_release -a

  • Check system startup time

    systemd-analyze

  • Check startup time by individual service

    systemd-analyze blame

  • Disable an individual service

    sudo systemctl disable NetworkManager-wait-online.service

  • Find process ids based on name patterns:

    pgrep firefox

  • Find process ids based on username: 

    pgrep -u <username>

WiFi Commands

The lshw command can be used to quickly identify network hardware on your device:

sudo lshw -C network

The output will include both MAC address in the 'serial' field and IP address in the 'configuration' field, along with other information such as the 'logical name' and the 'bus id'. ifconfig will also provide the MAC and IP addresses for connect wireless adapters. Use iwconfig to see the speed and link quality for your wireless adapter The nmcli command provides useful information from Network Manager. To see the saved connections for your device use:

nmcli connection show

To see a list of Access Points and stats on their signal strength and capabilities, use:

nmcli dev wifi

wavemon is an ncurses-based monitoring tool for WiFi

Network Commands

To see your current IP address instead of using ifconfig try ip:

ip address show

This will show:

  1. Interface name
  2. MAC address: link/ether
  3. IP address: inet
  4. State of the Interface: UP or DOWN

You can also use ip link show to check the state of your interfaces.

Use the route command to show the routing table on a computer:

route

The default route shows you which interface is used if no specific route matches the address specified.

You can also use ip route show to show the route to a specific network:

ip route show 10.0.0.0/8

You can get help on the ip command using man ip-address, man ip-link or man ip-route.

Use the arp command to check the ARP table (data link layer) addresses stored locally. This will show the mapping of physical addresses to ip addresses for devices on the same LAN (e.g. your gateway or router):

arp -a

To check for ports on localhost use ss:

ss -tunlp4

Whilst telnet can be used to test connectivity to TCP ports, netcat also provides the ability to check connections to UDP ports:

nc 192.168.0.3 -u 80 -v
nc 127.0.0.1 8000 -v

Netcat can also be used to quickly setup a server to listen on a specified port. 

nc -l 1234 > filename.out

All the input sent to port 1234 will be copied to filename.out:

nc -N myhost.example.com 1234 < filename.in

These two commands will allow you to transfer the contents if filename.in to filename.out on the listening server.

The -N option closes the connection on termination.

sed

sed stands for Stream Editor, and can be used to replace text from input to output:

echo 'Hello, World!' | sed 's/World/Universe/'

sed can also be used directly on a file:

sed 's/left/right/' <filename>

By default output is sent to STDOUT, but you can change the file contents using the -i switch:

sed -i 's/left/right/' <filename>

Sed allows capturing groups and backreferences. To capture IP Address from the weblog.txt use:

sed -nE 's/.* h=(\d+\.\d+\.\d+\.\d+).*$/\1/p' weblog.txt

Sed works well in pipelines: to find unique values of ip_address in above example use:

sed -nE 's/.* h=(\d+\.\d+\.\d+\.\d+).*$/\1/p' weblog.txt | sort -u

To count the occurrences for each unique IP Address use:

sed -nE 's/.* h=(\d+\.\d+\.\d+\.\d+).*$/\1/p' weblog.txt | sort | uniq -c

You can also pipe the list of IPs to lookup the hostnames:

sed -nE 's/.* h=(\d+\.\d+\.\d+\.\d+).*$/\1/p' weblog.txt | \
sort -u | awk '{ cmd = "dig +short -x " $1; system(cmd) }'