linux cheat sheet

1. System Information

uname -a	Display full system information
uname -r	Show kernel release version
cat /etc/os-release or cat /etc/redhat-release	Show distribution name and version
uptime	Show how long the system has been running + load average
hostname	Display hostname
hostname -I	Show all local IP addresses
last reboot	Show reboot history
date	Current date and time
cal	Display current month's calendar
w	Show who is logged in and what they are doing
whoami	Current logged-in username

2. Hardware Information

dmesg | tail -50	Show recent kernel messages
lscpu or cat /proc/cpuinfo	CPU information
free -h	Memory and swap usage (human readable)
lsblk	List block devices and partitions
lspci -v	List PCI devices with details
lsusb -v	List USB devices with details
dmidecode --type system	BIOS / hardware information
hdparm -I /dev/sda	Detailed disk information

3. Performance Monitoring

top / htop	Real-time process viewer
vmstat 1	Virtual memory statistics (every 1 second)
iostat -x 1	Disk I/O statistics (extended)
mpstat -P ALL 1	CPU usage per core
sar -u 1 5	CPU usage history (requires sysstat)
watch -n 1 df -h	Refresh disk usage every second

4. User & Group Management

id	Show current user and group IDs
who / w	Show logged-in users
last	Login history
useradd -m -s /bin/bash username	Create new user with home directory
passwd username	Change user password
usermod -aG sudo username	Add user to sudo group
userdel -r username	Delete user and home directory
groupadd groupname	Create new group

5. File & Directory Commands

ls -la	List all files with details
pwd	Print working directory
mkdir -p dir/subdir	Create directory including parents
rm -rf folder	Force remove directory and contents
cp -r source dest	Copy directory recursively
mv old new	Rename or move file/folder
ln -s /path/to/target linkname	Create symbolic link
touch file.txt	Create empty file or update timestamp
tail -f /var/log/syslog	Follow log file in real time

6. File Permissions (chmod)

Numeric (Octal)

Mode	Permission	Typical Use
777	rwx rwx rwx	Full access for everyone (avoid!)
775	rwx rwx r-x	Shared group folders
755	rwx r-x r-x	Scripts & public directories (most common)
644	rw- r-- r--	Regular files (most common)
600	rw- --- ---	Private files (only owner)

Symbolic Notation

Command Example	Meaning
chmod u+x script.sh	Add execute for owner
chmod go-w file.txt	Remove write from group & others
chmod a+rx public/	Add read+execute for all
chmod u=rw,go=r secret.txt	Owner rw, others read-only
chmod +t /tmp/share	Add sticky bit
chmod u+s /usr/bin/passwd	Setuid bit (run as owner)
chmod g+s /projects/team	Setgid bit on directory

u = user/owner, g = group, o = others, a = all
+ = add, - = remove, = = set exactly
r = read, w = write, x = execute, t = sticky bit, s = setuid/setgid

7. Networking

ip addr show or ifconfig	Show network interfaces and IPs
ping -c 4 google.com	Test connectivity (4 packets)
curl ifconfig.me	Get public IP address
dig google.com	DNS lookup
ss -tuln or netstat -tuln	List listening TCP/UDP ports
wget -c https://example.com/file	Download file (resumable)

8. Archives (Tar & Compression)

tar czf archive.tar.gz folder/	Create gzip compressed tar
tar xzf archive.tar.gz	Extract .tar.gz
tar cjf archive.tar.bz2 folder/	Create bzip2 compressed tar
zip -r archive.zip folder/	Create zip archive
unzip archive.zip	Extract zip file

9. Package Management

Debian/Ubuntu (apt)	RHEL/Fedora (dnf/yum)	Purpose
sudo apt update	sudo dnf check-update	Refresh package list
sudo apt install pkg	sudo dnf install pkg	Install package
sudo apt search keyword	dnf search keyword	Search for package
sudo apt remove pkg	sudo dnf remove pkg	Uninstall package

10. Search & Find

grep -r "text" /path/	Search recursively inside files
find / -name "file.txt"	Find file by name
find . -type f -size +100M	Find files larger than 100 MB
locate filename	Fast search (run updatedb first if needed)

11. Process Management

ps aux | grep name	Find running process
kill -9 PID	Force kill process
pkill processname	Kill all processes by name
nohup command &	Run in background (survives logout)

12. SSH & Remote Access

ssh user@host	Connect via SSH
ssh -p 2222 user@host	SSH to custom port
ssh-keygen -t ed25519	Generate new SSH key pair
ssh-copy-id user@host	Copy public key to remote server

13. File Transfer

scp file.txt user@host:/tmp/	Secure copy file to remote
scp -r folder/ user@host:/dest/	Copy directory recursively
rsync -avz --progress src/ user@host:/dest/	Efficient sync with progress

14. Disk Usage

df -h	Human-readable disk usage
du -sh /path	Total size of directory
du -ah | sort -rh | head -20	Top 20 largest files/folders

15. Directory Navigation & Shortcuts

cd ..	Go up one directory level
cd -	Return to previous directory
cd ~ or cd	Go to home directory
pushd /path & popd	Save and return to directory stack

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