Linux Basics

Useful Find command reference

When capturing flags use the following for searching of specific files:

find / -type f -iname "file.txt" 2>/dev/null 

Base64 Encode & Decode

# Encode File
cat <file> |base64 -w 0;echo

# Decode File
echo -n <file> |base64 -d 

wget

wget <url> -O file.sh

curl

curl <url> -o file.sh

Fileless Downloads

curl <url> -o file.sh |bash 

SSH

scp <user>@<ip>:/<file> . 

Option	Description
-type f	Hereby, we define the type of the searched object. In this case, 'f' stands for 'file'.
-name *.conf	With '-name', we indicate the name of the file we are looking for. The asterisk (*) stands for 'all' files with the '.conf' extension.
-user root	This option filters all files whose owner is the root user.
-size +20k	We can then filter all the located files and specify that we only want to see the files that are larger than 20 KiB.
-newermt 2020-03-03	With this option, we set the date. Only files newer than the specified date will be presented.
-exec ls -al {} \;	This option executes the specified command, using the curly brackets as placeholders for each result. The backslash escapes the next character from being interpreted by the shell because otherwise, the semicolon would terminate the command and not reach the redirection.
2>/dev/null	This is a STDERR redirection to the 'null device', which we will come back to in the next section. This redirection ensures that no errors are displayed in the terminal. This redirection must not be an option of the 'find' command.

Practical example using multiple options to filter the search:

find / -type f -name *.conf -user root -size +20k -newermt 2020-03-03 -exec ls -al {} \; 2>/dev/null

Path	Description
/	The top-level directory is the root filesystem and contains all of the files required to boot the operating system before other filesystems are mounted as well as the files required to boot the other filesystems. After boot, all of the other filesystems are mounted at standard mount points as subdirectories of the root.
/bin	Contains essential command binaries.
/boot	Consists of the static bootloader, kernel executable, and files required to boot the Linux OS.
/dev	Contains device files to facilitate access to every hardware device attached to the system.
/etc	Local system configuration files. Configuration files for installed applications may be saved here as well.
/home	Each user on the system has a subdirectory here for storage.
/lib	Shared library files that are required for system boot.
/media	External removable media devices such as USB drives are mounted here.
/mnt	Temporary mount point for regular filesystems.
/opt	Optional files such as third-party tools can be saved here.
/root	The home directory for the root user.
/sbin	This directory contains executables used for system administration (binary system files).
/tmp	The operating system and many programs use this directory to store temporary files. This directory is generally cleared upon system boot and may be deleted at other times without any warning.
/usr	Contains executables, libraries, man files, etc.
/var	This directory contains variable data files such as log files, email in-boxes, web application related files, cron files, and more.

Command	Description
Command	Description
man <tool>	Opens man pages for the specified tool.
<tool> -h	Prints the help page of the tool.
apropos <keyword>	Searches through man pages' descriptions for instances of a given keyword.
cat	Concatenate and print files.
whoami	Displays current username.
id	Returns users identity.
hostname	Sets or prints the name of the current host system.
uname	Prints operating system name.
pwd	Returns working directory name.
ifconfig	The ifconfig utility is used to assign or view an address to a network interface and/or configure network interface parameters.
ip	Ip is a utility to show or manipulate routing, network devices, interfaces, and tunnels.
netstat	Shows network status.
ss	Another utility to investigate sockets.
ps	Shows process status.
who	Displays who is logged in.
env	Prints environment or sets and executes a command.
lsblk	Lists block devices.
lsusb	Lists USB devices.
lsof	Lists opened files.
lspci	Lists PCI devices.
sudo	Execute command as a different user.
su	The su utility requests appropriate user credentials via PAM and switches to that user ID (the default user is the superuser). A shell is then executed.
useradd	Creates a new user or update default new user information.
userdel	Deletes a user account and related files.
usermod	Modifies a user account.
addgroup	Adds a group to the system.
delgroup	Removes a group from the system.
passwd	Changes user password.
dpkg	Install, remove and configure Debian-based packages.
apt	High-level package management command-line utility.
aptitude	Alternative to apt.
snap	Install, remove and configure snap packages.
gem	Standard package manager for Ruby.
pip	Standard package manager for Python.
git	Revision control system command-line utility.
systemctl	Command-line based service and systemd control manager.
ps	Prints a snapshot of the current processes.
journalctl	Query the systemd journal.
kill	Sends a signal to a process.
bg	Puts a process into background.
jobs	Lists all processes that are running in the background.
fg	Puts a process into the foreground.
curl	Command-line utility to transfer data from or to a server.
wget	An alternative to curl that downloads files from FTP or HTTP(s) server.
python3 -m http.server	Starts a Python3 web server on TCP port 8000.
ls	Lists directory contents.
cd	Changes the directory.
clear	Clears the terminal.
touch	Creates an empty file.
mkdir	Creates a directory.
tree	Lists the contents of a directory recursively.
mv	Move or rename files or directories.
cp	Copy files or directories.
nano	Terminal based text editor.
which	Returns the path to a file or link.
find	Searches for files in a directory hierarchy.
updatedb	Updates the locale database for existing contents on the system.
locate	Uses the locale database to find contents on the system.
more	Pager that is used to read STDOUT or files.
less	An alternative to more with more features.
head	Prints the first ten lines of STDOUT or a file.
tail	Prints the last ten lines of STDOUT or a file.
sort	Sorts the contents of STDOUT or a file.
grep	Searches for specific results that contain given patterns.
cut	Removes sections from each line of files.
tr	Replaces certain characters.
column	Command-line based utility that formats its input into multiple columns.
awk	Pattern scanning and processing language.
sed	A stream editor for filtering and transforming text.
wc	Prints newline, word, and byte counts for a given input.
chmod	Changes permission of a file or directory.
chown	Changes the owner and group of a file or directory.