CLI Magic
These are the commands I reach for when things get real.
Navigation & Discovery
System Info & Process Control
File & Text Manipulation
Permissions & Users
chmodchownusermodwhoamigroupssudopasswd
Networking
Archives & Packages
tarzipunzipdpkgaptrpmdnfpacman
Dangerous but Useful
rm -rfddmkfsmountumountkillpkillrebootshutdown
Misc & Meta
aliashistory!manwhichtypetimeyes
cat
What it does: It shows what is inside the file you append.
Example: I use it all the time to read out the flag on some CTF's.
Tip: Awesomt for any automation, where you want to work with some text inside a file.
Just use cat | secondCommand.
That also makes it perfect for searching though large files, like logs, together with grep
cd
What it does: Let's you move to the directory of your choosing.
Tip: Don't forget about the special usecases:
..move up the file structure~move to home directory of the current user/move to root, but also let's you move anywhere you want, as long as you know the path
chmod
What it does:
Used to change permissions of a file.
Real use case:
Whenever you make a script so you are actually able to run it.
Example:
In the example above, making a file executable, it would like that chmod -x [file]
Tip:
Learning the numbercodes is extremly helpful. First number for the user, second for the group, and last for others. Each digit represents a combination of read (4), write (2), and execute (1).
du
What it does:
Calculates actual disk space used by files and directories.
Real use case: Good to identify how the space is used in case of low disk space.
Tip:
You can pipe it through sort -rh to sort it by biggest size first.
find
What it does:
Used to search for files in a specifed directory. You can search for all kinds of properties that you already know about it.
Real use case:
I used it to find the flag while playing OWT Bandit. For the level you got the size and some of the properties of the flag, and had to find it.
Example:
find / -user bandit7 -group bandit6 -size 33c 2>/dev/null
That is how I found the specific flag.
Tip:
I really want to remember the 2>/dev/null part for throwing out strerr.
htop
What it does:
An enhanced, interactive version of top with better visuals and controls.
Real use case:
Quickly kill, renice, or inspect processes without needing multiple commands
Tip:
It is really important do learn the short cuts and ways to use it to be effectiv.
ls
What it does:
Shows the inside of the current directory.
Tip:
Best used with a -al flag to list all files in long format.
nc
What it does:
Used for everything concering connections via TCP or UDP.
You can do soo much with it that it would probably be to much for this little section, and I need to make a whole page for netcat in the futur.
Real use case:
Mainly to set up listeners to get a reverse shell.
That would look something like this:
nc -l 1234
Also netcat can be used to connect to some port and set it something manuel or in a script.
ping
What it does:
Sends an ICMP echo request to a target host.
Real use case:
Perfect to test if there is a connection. Eighter to the target on the way in, or from the mashine on the way out (by pinging something that is alway reachable)
Example:
ping 8.8.8.8 to try to ping the google DNS server, which should always work if you have connection to the internet.
Tip: Is often used to monitor server uptime from afar, by regularly sending a ping.
ps
What it does:
Prints out the current processes.
Real use case:
Audit running processes precisely, grep specific patterns, or script behavior.
Tip:
ps faux shows process hierachy, kind of like tree for files.
This really helps with finding out where everything is comming from.
ssh
What it does:
Creates a secure connetion with access to the local terminal.
Real use case:
Maintaining remote servers where it is not reasonable to have direkt access, and which might not have a GUI.
Example:
Accessing the Bandit Wargame from OvertheWire:
ssh -p 2220 bandit0@bandit.labs.overthewire.org
top
What it does:
Real-time view of system processes and resource usage.
Real use case:
Monitor CPU and detect runaway processes.
Tip:
You can press M to sort instantly by memory usage.
tree
What it does:
It prints out a skeleton of file system you give it.
Awesome to get an overview of where everything lives and to better understand what you are working with.
uniq
What it does:
Filter adjacent matching lines. It is mostly used when you have to omit or report repeating lines. Really helpful to dens down loads of data.
Real use case:
For me it was alo really helpful in one of the OTW Bandit levels. It was mainly designed to teach the uniq command, so I am really excited to find some more real world use cases.