socat - connect anything to anything

for example

socat - tcp-connect:remote-server:12345

socat tcp-listen:12345 -

socat tcp-listen:12345 tcp-connect:remote-server:12345

Pandoc.

nmap *your_local_ip_address*

for example

nmap 192.168.1.43/24 will show you what devices are connected to the local network, and what ports are open there. really useful, for example, when you forgot the address of your printer or raspi yet again.

you can also use it to understand what ports on your computer are open from an attacker's perspective, or simply to figure out what services are running (ssh service).

losetup

it's useful for dealing with virtual disk images. like a real physical hard disk, but it's a file on the computer. you can mount it, format it, and write it to a real physical disk.

it's sometimes used with virtual machines, with iso images, or when preparing a bootable disk.

netstat -tunl shows all open ports on the machine to help diagnose any firewall issues.

Not powerful, but often useful, column -t aligns columns in all lines. EG

$ echo {a,bb,ccc}{5,10,9999,888} | xargs -n3
a5 a10 a9999
a888 bb5 bb10
bb9999 bb888 ccc5
ccc10 ccc9999 ccc888
$ echo {a,bb,ccc}{5,10,9999,888} | xargs -n3 | column -t
a5      a10      a9999
a888    bb5      bb10
bb9999  bb888    ccc5
ccc10   ccc9999  ccc888

Control+r == search through your bash history.

I used linux for ten years before finding out about that one.

xargs

Man

probably well known at this point but rsync is incredible and I use it all the time

batcat

It's like cat but better. Great for when you just want to look at the contents of a file, without loading a whole text editor.

Oh also, tldr

My procedure for learning how to use a cli command goes tldr page -> --help if the tldr fails to help me -> THEN the full manpage

bc

It's a simple command line calculator! I use it all the time.

jq - super powerful json parser. Useful by hand and in scripts

kde connect

yes

The most positive command you'll ever use.

Run it normally and it just spams 'y' from the keyboard. But when one of the commands above is piped to it, then it will respond with 'y'. Not every command has a true -y to automate acceptance of prompts and that's what this is for.

motion

After spending years dealing with shady freeware and junk software on windows, I was floored by how easy and nonchalantly I was able to set up a simple security camera on my PC

ip eg:

# ip a
# ip a a 192.168.1.99/24 dev enp160

The first incantation - ip address (you can abbreviate whilst it is unambiguous) gets you a quick report of interfaces, MAC, IPs and so on. The second command assigns another IP address to an interface. Handy for setting up devices which don't do DHCP out of the box or already have an IP and need a good talking to.

Oh and you can completely set up your IP stack, interfaces and routing etc with it. Throw in nft or iptables (old school these days - sigh!) for filtering and other network packet mangling shenanigans.