Cheatsheet

Command	Usage	Description
`whoami`	`whoami`	Print effective username.
`id`	`id` / `id <user>`	Print user and group IDs.
`hostname`	`hostname`	Show or set system hostname.
`uname`	`uname -a`	Print system and kernel information.
`pwd`	`pwd`	Print current working directory.
`ifconfig`	`ifconfig` / `ifconfig <iface>`	Display or configure network interfaces.
`ip`	`ip a`	Show or manage network devices and IP addresses.
`netstat`	`netstat -tunlp`	Display active connections and listening ports.
`ss`	`ss -tunlp`	Dump socket statistics (modern `netstat` replacement).
`ps`	`ps aux`	Display snapshot of active processes.
`who`	`who`	Show logged-in users.
`env`	`env`	Print environment variables or run a command in a modified environment.
`lsblk`	`lsblk`	List block devices and partitions.
`lsusb`	`lsusb`	List connected USB devices.
`lsof`	`lsof -i`	List open files and network sockets.
`lspci`	`lspci`	List PCI devices.
`cd`	`cd <dir>`	Change working directory.
`touch`	`touch <file>`	Create empty file or update timestamps.
`mkdir`	`mkdir <dir>`	Create new directory.
`mv`	`mv <src> <dst>`	Move or rename files and directories.
`cp`	`cp <src> <dst>`	Copy files and directories.
`which`	`which <cmd>`	Print full path of executable binary.
`find`	`find / -name <file> 2>/dev/null`	Search filesystem for files (suppress permission errors).
`locate`	`locate <file>`	Find files by name using indexed database.
`du`	`du -h -d 1 <dir>`	Identify file and directory space consumption (-a: all files, -c: total, --time: timestamp).
`stat`	`stat <file>`	Display detailed status and metadata of a file or directory.
`more`	`more <file>`	View file page-by-page (forward navigation only).
`less`	`less <file>`	View file page-by-page (bidirectional scroll).
`head`	`head <file>`	Output first 10 lines of file.
`tail`	`tail <file>`	Output last 10 lines of file.
`sort`	`sort <file>`	Sort lines of text files.
`grep`	`grep "pattern" <file>`	Filter lines matching pattern (use -v to invert match).
`tr`	`tr ":" " "`	Translate, squeeze, and/or delete characters from standard input.
`column`	`column -t`	Format input into aligned columns.
`awk`	`awk '{print $1}' <file>`	Extract and process specific column fields.
`ping`	`ping <ip>`	Test network reachability using ICMP ECHO.
`traceroute`	`traceroute <ip>`	Trace packet route path to target host.
`apt`	`apt update && apt install <pkg>`	Package manager to update indices and install software.
`dpkg`	`dpkg -i <file.deb>`	Install Debian software package directly.
`systemctl`	`systemctl status <service>`	Manage and check state of systemd services/daemons.
`crontab`	`crontab -e` / `crontab -l`	Edit or list scheduled background tasks (cron jobs).

File Descriptors & Redirectors#

Linux manages standard input and output through three kernel file descriptors:

0 (STDIN): Standard Input (keyboard / data input)
1 (STDOUT): Standard Output (valid execution results)
2 (STDERR): Standard Error (error messages)

Redirection Operators & Pipes#

2>/dev/null - Suppresses error messages by sending STDERR to the null device:

bash

  find /etc/ -name shadow 2>/dev/null

> - Redirects STDOUT to a file (overwrites existing file):

bash

find /etc/ -name shadow > results.txt

2> - Redirects STDERR to a file:

bash

find /etc/ -name shadow 2> stderr.txt

1> stdout.txt 2> stderr.txt - Separates STDOUT and STDERR into distinct files:

bash

find /etc/ -name shadow 1> stdout.txt 2> stderr.txt

< - Passes file content as STDIN to a command:

bash

cat < stdout.txt

>> - Appends STDOUT to a file without overwriting:

bash

find /etc/ -name passwd >> stdout.txt

<< EOF - Sends a multi-line input stream to a command until the EOF delimiter is reached:

bash

cat << EOF > file.txt
EOF

| - Passes STDOUT of the first command directly as STDIN to the second command:

bash

find /etc/ -name *.conf | grep systemd