Red Hat Enterprise Linux Cheatsheet

System Information & Monitoring

System Version: cat /etc/redhat-release

Display the RHEL version and release information.

# Show RHEL version
cat /etc/redhat-release
# Alternative method
cat /etc/os-release
# Show kernel version
uname -r
# Show system architecture
uname -m

System Performance: top / htop

Display running processes and system resource usage.

# Real-time process monitor
top
# Enhanced process viewer (if installed)
htop
# Show process tree
pstree
# Show all processes
ps aux

Memory Information: free / cat /proc/meminfo

Display memory usage and availability.

# Show memory usage in human-readable format
free -h
# Show detailed memory information
cat /proc/meminfo
# Show swap usage
swapon --show

Disk Usage: df / du

Monitor filesystem and directory usage.

# Show filesystem usage
df -h
# Show directory sizes
du -sh /var/log/*
# Show largest directories
du -h --max-depth=1 / | sort -hr

System Uptime: uptime / who

Check system uptime and logged-in users.

# Show system uptime and load
uptime
# Show logged-in users
who
# Show current user
whoami
# Show last logins
last

Hardware Information: lscpu / lsblk

Display hardware components and configuration.

# Show CPU information
lscpu
# Show block devices
lsblk
# Show PCI devices
lspci
# Show USB devices
lsusb

Package Management

Package Installation: dnf install / yum install

Install software packages and dependencies.

# Install a package (RHEL 8+)
sudo dnf install package-name
# Install a package (RHEL 7)
sudo yum install package-name
# Install local RPM file
sudo rpm -i package.rpm
# Install from specific repository
sudo dnf install --enablerepo=repo-
name package

Package Updates: dnf update / yum update

Update packages to the latest versions.

# Update all packages
sudo dnf update
# Update specific package
sudo dnf update package-name
# Check for available updates
dnf check-update
# Update security patches only
sudo dnf update --security

Package Information: dnf info / rpm -q

Query package information and dependencies.

# Show package information
dnf info package-name
# List installed packages
rpm -qa
# Search for packages
dnf search keyword
# Show package dependencies
dnf deplist package-name

File & Directory Operations

Navigation: cd / pwd / ls

Navigate filesystem and list contents.

# Change directory
cd /path/to/directory
# Show current directory
pwd
# List files and directories
ls -la
# List with file sizes
ls -lh
# Show hidden files
ls -a

File Operations: cp / mv / rm

Copy, move, and delete files and directories.

# Copy file
cp source.txt destination.txt
# Copy directory recursively
cp -r /source/dir/ /dest/dir/
# Move/rename file
mv oldname.txt newname.txt
# Remove file
rm filename.txt
# Remove directory recursively
rm -rf directory/

File Content: cat / less / head / tail

View and examine file contents.

# Display file content
cat filename.txt
# View file page by page
less filename.txt
# Show first 10 lines
head filename.txt
# Show last 10 lines
tail filename.txt
# Follow log file in real-time
tail -f /var/log/messages

File Permissions: chmod / chown / chgrp

Manage file permissions and ownership.

# Change file permissions
chmod 755 script.sh
# Change file ownership
sudo chown user:group filename.txt
# Change group ownership
sudo chgrp newgroup filename.txt
# Recursive permission change
sudo chmod -R 644 /path/to/directory/

File Search: find / locate / grep

Search for files and content within files.

# Find files by name
find /path -name "*.txt"
# Find files by size
find /path -size +100M
# Search text in files
grep "pattern" filename.txt
# Recursive text search
grep -r "pattern" /path/to/directory/

Archive & Compression: tar / gzip

Create and extract compressed archives.

# Create tar archive
tar -czf archive.tar.gz /path/to/directory/
# Extract tar archive
tar -xzf archive.tar.gz
# Create zip archive
zip -r archive.zip /path/to/directory/
# Extract zip archive
unzip archive.zip

Service Management

Service Control: systemctl

Manage system services using systemd.

# Start a service
sudo systemctl start service-name
# Stop a service
sudo systemctl stop service-name
# Restart a service
sudo systemctl restart service-name
# Check service status
systemctl status service-name
# Enable service at boot
sudo systemctl enable service-name
# Disable service at boot
sudo systemctl disable service-name

Service Information: systemctl list-units

List and query system services.

# List all active services
systemctl list-units --type=service
# List all enabled services
systemctl list-unit-files --type=service --state=enabled
# Show service dependencies
systemctl list-dependencies service-name

System Logs: journalctl

View and analyze system logs using journald.

# View all logs
journalctl
# View logs for specific service
journalctl -u service-name
# Follow logs in real-time
journalctl -f
# View logs from last boot
journalctl -b
# View logs by time range
journalctl --since "2024-01-01" --until "2024-01-31"

Process Management: ps / kill / killall

Monitor and control running processes.

# Show running processes
ps aux
# Kill process by PID
kill 1234
# Kill process by name
killall process-name
# Force kill process
kill -9 1234
# Show process hierarchy
pstree

User & Group Management

User Management: useradd / usermod / userdel

Create, modify, and delete user accounts.

# Add new user
sudo useradd -m username
# Set user password
sudo passwd username
# Modify user account
sudo usermod -aG groupname
username
# Delete user account
sudo userdel -r username
# Lock user account
sudo usermod -L username

Group Management: groupadd / groupmod / groupdel

Create, modify, and delete groups.

# Add new group
sudo groupadd groupname
# Add user to group
sudo usermod -aG groupname
username
# Remove user from group
sudo gpasswd -d username
groupname
# Delete group
sudo groupdel groupname
# List user groups
groups username

Access Control: su / sudo

Switch users and execute commands with elevated privileges.

# Switch to root user
su -
# Switch to specific user
su - username
# Execute command as root
sudo command
# Edit sudoers file
sudo visudo
# Check sudo permissions
sudo -l

Network Configuration

Network Information: ip / nmcli

Display network interface and configuration details.

# Show network interfaces
ip addr show
# Show routing table
ip route show
# Show network manager connections
nmcli connection show
# Show interface status
nmcli device status

Network Configuration: nmtui / nmcli

Configure network settings using NetworkManager.

# Text-based network configuration
sudo nmtui
# Add new connection
sudo nmcli connection add type ethernet con-name
"eth0" ifname eth0
# Modify connection
sudo nmcli connection modify "eth0" ipv4.addresses
192.168.1.100/24
# Activate connection
sudo nmcli connection up "eth0"

Network Testing: ping / curl / wget

Test network connectivity and download files.

# Test connectivity
ping google.com
# Test specific port
telnet hostname 80
# Download file
wget http://example.com/file.txt
# Test HTTP requests
curl -I http://example.com

Firewall Management: firewall-cmd

Configure firewall rules using firewalld.

# Show firewall status
sudo firewall-cmd --state
# List active zones
sudo firewall-cmd --get-active-zones
# Add service to firewall
sudo firewall-cmd --permanent --add-service=http
# Reload firewall rules
sudo firewall-cmd --reload

Storage Management

Disk Management: fdisk / parted

Create and manage disk partitions.

# List disk partitions
sudo fdisk -l
# Interactive partition editor
sudo fdisk /dev/sda
# Create partition table
sudo parted /dev/sda mklabel gpt
# Create new partition
sudo parted /dev/sda mkpart primary ext4 1MiB 100GiB

Filesystem Management: mkfs / mount

Create filesystems and mount storage devices.

# Create ext4 filesystem
sudo mkfs.ext4 /dev/sda1
# Mount filesystem
sudo mount /dev/sda1 /mnt/data
# Unmount filesystem
sudo umount /mnt/data
# Check filesystem
sudo fsck /dev/sda1

LVM Management: pvcreate / vgcreate / lvcreate

Manage Logical Volume Manager (LVM) storage.

# Create physical volume
sudo pvcreate /dev/sdb
# Create volume group
sudo vgcreate vg_data /dev/sdb
# Create logical volume
sudo lvcreate -L 10G -n lv_data vg_data
# Extend logical volume
sudo lvextend -L +5G /dev/vg_data/lv_data

Mount Configuration: /etc/fstab

Configure permanent mount points.

# Edit fstab file
sudo vi /etc/fstab
# Test fstab entries
sudo mount -a
# Show mounted filesystems
mount | column -t

Security & SELinux

SELinux Management: getenforce / setenforce

Control SELinux enforcement and policies.

# Check SELinux status
getenforce
# Set SELinux to permissive
sudo setenforce 0
# Set SELinux to enforcing
sudo setenforce 1
# Check SELinux context
ls -Z filename
# Change SELinux context
sudo chcon -t httpd_exec_t /path/to/file

SELinux Tools: sealert / ausearch

Analyze SELinux denials and audit logs.

# Check SELinux alerts
sudo sealert -a /var/log/audit/audit.log
# Search audit logs
sudo ausearch -m avc -ts recent
# Generate SELinux policy
sudo audit2allow -M mypolicy < /var/log/audit/audit.log

SSH Configuration: /etc/ssh/sshd_config

Configure SSH daemon for secure remote access.

# Edit SSH configuration
sudo vi /etc/ssh/sshd_config
# Restart SSH service
sudo systemctl restart sshd
# Test SSH connection
ssh user@hostname
# Copy SSH key
ssh-copy-id user@hostname

System Updates: dnf update

Keep system secure with regular updates.

# Update all packages
sudo dnf update
# Update security patches only
sudo dnf update --security
# Check for available updates
dnf check-update --security
# Enable automatic updates
sudo systemctl enable dnf-automatic.timer

Performance Monitoring

System Monitoring: iostat / vmstat

Monitor system performance and resource usage.

# Show I/O statistics
iostat -x 1
# Show virtual memory statistics
vmstat 1
# Show network statistics
ss -tuln
# Show disk I/O
iotop

Resource Usage: sar / top

Analyze historical and real-time system metrics.

# System activity report
sar -u 1 3
# Memory usage report
sar -r
# Network activity report
sar -n DEV
# Load average monitoring
uptime

Process Analysis: strace / lsof

Debug processes and file access.

# Trace system calls
strace -p 1234
# List open files
lsof
# Show files opened by process
lsof -p 1234
# Show network connections
lsof -i

Performance Tuning: tuned

Optimize system performance for specific workloads.

# List available profiles
tuned-adm list
# Show active profile
tuned-adm active
# Set performance profile
sudo tuned-adm profile throughput-performance
# Create custom profile
sudo tuned-adm profile_mode

RHEL Installation & Setup

System Registration: subscription-manager

Register system with Red Hat Customer Portal.

# Register system
sudo subscription-manager
register --username
your_username
# Auto-attach subscriptions
sudo subscription-manager
attach --auto
# List available subscriptions
subscription-manager list --
available
# Show system status
subscription-manager status

Repository Management: dnf config-manager

Manage software repositories.

# List enabled repositories
dnf repolist
# Enable repository
sudo dnf config-manager --
enable repository-name
# Disable repository
sudo dnf config-manager --
disable repository-name
# Add new repository
sudo dnf config-manager --add-
repo https://example.com/repo

System Configuration: hostnamectl / timedatectl

Configure basic system settings.

# Set hostname
sudo hostnamectl set-hostname
new-hostname
# Show system information
hostnamectl
# Set timezone
sudo timedatectl set-timezone
America/New_York
# Show time settings
timedatectl

Troubleshooting & Diagnostics

System Logs: /var/log/

Examine system log files for issues.

# View system messages
sudo tail -f /var/log/messages
# View authentication logs
sudo tail -f /var/log/secure
# View boot logs
sudo journalctl -b
# View kernel messages
dmesg | tail

Hardware Diagnostics: dmidecode / lshw

Examine hardware information and health.

# Show hardware information
sudo dmidecode -t system
# List hardware components
sudo lshw -short
# Check memory information
sudo dmidecode -t memory
# Show CPU information
lscpu

Network Troubleshooting: netstat / ss

Network diagnostic tools and utilities.

# Show network connections
ss -tuln
# Show routing table
ip route show
# Test DNS resolution
nslookup google.com
# Trace network path
traceroute google.com

Recovery & Rescue: systemctl rescue

System recovery and emergency procedures.

# Enter rescue mode
sudo systemctl rescue
# Enter emergency mode
sudo systemctl emergency
# Reset failed services
sudo systemctl reset-failed
# Reconfigure boot loader
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Automation & Scripting

Cron Jobs: crontab

Schedule automated tasks and maintenance.

# Edit user crontab
crontab -e
# List user crontab
crontab -l
# Remove user crontab
crontab -r
# Example: Run script daily at 2 AM
0 2 * * * /path/to/script.sh

Shell Scripting: bash

Create and execute shell scripts for automation.

#!/bin/bash
# Simple backup script
DATE=$(date +%Y%m%d)
tar -czf backup_$DATE.tar.gz /home/user/documents
echo "Backup completed: backup_$DATE.tar.gz"

Environment Variables: export / env

Manage environment variables and shell settings.

# Set environment variable
export MY_VAR="value"
# Show all environment variables
env
# Show specific variable
echo $PATH
# Add to PATH
export PATH=$PATH:/new/directory

System Automation: systemd timers

Create systemd-based scheduled tasks.

# Create timer unit file
sudo vi /etc/systemd/system/backup.timer
# Enable and start timer
sudo systemctl enable backup.timer
sudo systemctl start backup.timer
# List active timers
systemctl list-timers

Relevant Links

• Linux Cheatsheet
• Shell Cheatsheet
• Git Cheatsheet
• Docker Cheatsheet
• Kubernetes Cheatsheet
• Ansible Cheatsheet
• DevOps Cheatsheet
• Cybersecurity Cheatsheet