# Display messages in kernel ring buffer.dmesg# Display logs stored in the systemd journal.journalctl# Display logs for a specific unit (service).journalctl -u servicename

# Change the current user's password.passwd# Switch to the root account with root's environment. (Login shell.)sudo -i# Execute your current shell as root. (Non-login shell.)sudo -s# List sudo privileges for the current user.sudo -l# Edit the sudoers configuration file.visudo# Display the current SE

# To go up one level of the directory tree.  (Change into the parent directory.)cd ..# Go to the $HOME directorycd# Change to the /etc directorycd /etc

# Show free and used space on mounted filesystemsdf -h# Show free and used inodes on mounted filesystemsdf -i# Display disks partitions sizes and typesfdisk -l# Display disk usage for all files and directories in human readable formatdu -ah# Display total disk usage off the current directorydu -sh&n

# Secure copy file.txt to the /tmp folder on serverscp file.txt server:/tmp# Copy *.html files from server to the local /tmp folder.scp server:/var/www/*.html /tmp# Copy all files and directories recursively from server to the current system's /tmp folder.scp -r server:/var/www /tmp# Synchronize /ho

# Connect to host as your local username.ssh host# Connect to host as userssh user@host# Connect to host using portssh -p port user@host

# Search for pattern in filegrep pattern file# Search recursively for pattern in directorygrep -r pattern directory# Find files and directories by namelocate name# Find files in /home/john that start with "prefix".find /home/john -name 'prefix*'# Find files larger than 100MB in /homefind /home -size

# Search for a package by keyword.yum search keyword# Install package.yum install package# Display description and summary information about package.yum info package# Install package from local file named package.rpmrpm -i package.rpm# Remove/uninstall package.yum remove package# Install software fr