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Cheatsheet for Sysadmins

Table of Contents

General Information about the System

Use lshw to list the hardware on the system 

lshw  # List the hardware on the system
lscpu # List the CPU information
uname -a  # Get information about the system (kernel, version, hostname, etc)
who  # Shows who is logged into the system
w    # More detailed version of 'who'
last # Show the last users to log into the system (prints in reverse)
cat /etc/*release  # Get information about the operating system
cat /proc/cmdline  # Get the kernel command line arguments (boot parameters, boot image)
ethtool  # Show info on the network interfaces
ip a     # Show info on the network interfaces
ip r     # Show the routing table (shows network gateway)

File and Directory Management

ls -la     # List files and directories in long format, including hidden files
mkdir dir  # Create a new directory
rmdir dir  # Remove an empty directory
rm -rf /dir  # Recursively remove directory and contents (use with caution)
cp src dest  # Copy files and directories
mv src dest  # Move or rename files and directories
touch file  # Create an empty file or update the timestamp
cat file    # Display contents of a file
less file   # View file contents one page at a time
head -n 10 file  # Show first 10 lines of a file
tail -n 10 file  # Show last 10 lines of a file
find /dir -name "filename"  # Search for files and directories
locate filename  # Quickly find location of files (using a pre-built database)
ln -s target linkname  # Create a symbolic (soft) link

User and Group Management

useradd username  # Add a new user
usermod -aG groupname username  # Add user to a supplementary group
userdel username  # Delete a user account
passwd username  # Set or change password for a user
groupadd groupname  # Add a new group
groupdel groupname  # Delete a group
id username  # Display user and group IDs
whoami  # Display your current username
su - username  # Switch to another user account
sudo command  # Run command as superuser (or another user)

Permissions and Ownership

ls -l filename  # View file permissions
chmod 644 file  # Change permissions (owner=read/write, group=read, others=read)
chown user:group file  # Change owner and group of a file
chgrp groupname file  # Change the group ownership of a file
umask 022  # Set default file permissions for new files

Package Management

Also see Package Management.

For Debian-based systems (Debian, Ubuntu):

apt update  # Update package lists
apt upgrade  # Upgrade all packages
apt install package  # Install a package
apt search package  # Search for a package
apt show package  # Show details about a package
apt remove package  # Remove a package
dpkg -i package.deb  # Install a .deb package manually

For Red Hat-based systems (RHEL, Rocky, CentOS):

dnf update  # Update packages
dnf install package  # Install a package
dnf remove package  # Remove a package
dnf whatprovides command  # Show what package provides a command  
rpm -ivh package.rpm  # Install an .rpm package manually
rpm -qa  # List all packages

Process Management

ps aux      # View all processes
top         # Interactive process viewer
htop        # Enhanced interactive process viewer (often pre-installed)
kill PID    # Kill a process by PID
killall processname  # Kill all instances of a process by name
pkill -u username  # Kill all processes from a specific user
nice -n 10 command  # Start a command with a priority (lower values = higher priority)
renice -n 10 -p PID  # Change the priority of an existing process
pwdx PID    # Show the current working directory of a process
prtstat PID # Show the stats of a process (CPU, mem, etc)

System Monitoring and Logging

dmesg | less  # View boot and kernel-related messages
journalctl    # Query the systemd journal logs
tail -f /var/log/syslog  # Follow system logs in real-time
uptime        # Show how long the system has been running
vmstat 5      # Display memory, CPU, and I/O statistics every 5 seconds
iostat 5      # Display disk I/O statistics every 5 seconds

Network Management

ping hostname_or_IP  # Test connectivity to another host
nslookup hostname  # Query DNS for a host
traceroute hostname  # Trace the route packets take to reach a host
ss -tuln       # Show open ports and sockets  
netstat -tuln  # Older version of ss. Shows open ports and connections
iptables -L    # View firewall rules
firewalld-cmd --list-all  # View firewalld rules (CentOS/RedHat)
curl url       # Transfer data from or to a server
wget url       # Download files from the internet
scp file user@remote:/path  # Securely copy files to a remote system

Disk and Filesystem Management

fdisk -l       # List partition tables
mkfs.ext4 /dev/sdX1   # Create an ext4 filesystem on a partition
mount /dev/sdX1 /mnt  # Mount a filesystem
umount /mnt     # Unmount a filesystem
lsblk           # List all available block devices
df -h           # Display disk usage (human-readable)
du -sh /dir     # Show disk usage of a directory
fsck /dev/sdX1  # Check and repair a filesystem

Archive and Compression

tar -cvf archive.tar /dir  # Create a .tar archive
tar -xvf archive.tar       # Extract a .tar archive
gzip file                  # Compress a file with gzip
gunzip file.gz             # Decompress a .gz file
zip -r archive.zip /dir    # Create a .zip archive
unzip archive.zip          # Extract a .zip archive

Task Automation and Scheduling

crontab -e  # Edit the crontab file for scheduled tasks
crontab -l  # List all crontab jobs for current user
systemctl enable service  # Enable a service to start on boot
systemctl disable service # Disable a service from starting on boot