1 – SYSTEM INFORMATION
# Display Linux system information uname -a # Display kernel release information uname -r # Show which version of redhat installed cat /etc/redhat-release # Show how long the system has been running + load uptime # Show system host name hostname # Display the IP addresses of the host hostname -I # Show system reboot history last reboot # Show the current date and time date # Show this month's calendar cal # Display who is online w # Who you are logged in as whoami
2 – HARDWARE INFORMATION
# Display messages in kernel ring buffer dmesg # Display CPU information cat /proc/cpuinfo # Display memory information cat /proc/meminfo # Display free and used memory ( -h for human readable, -m for MB, -g for GB.) free -h # Display PCI devices lspci -tv # Display USB devices lsusb -tv # Display DMI/SMBIOS (hardware info) from the BIOS dmidecode # Show info about disk sda hdparm -i /dev/sda # Perform a read speed test on disk sda hdparm -tT /dev/sda # Test for unreadable blocks on disk sda badblocks -s /dev/sda
3 – PERFORMANCE MONITORING AND STATISTICS
# Display and manage the top processes top # Interactive process viewer (top alternative) htop # Display processor related statistics mpstat 1 # Display virtual memory statistics vmstat 1 # Display I/O statistics iostat 1 # Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.) tail 100 /var/log/messages # Capture and display all packets on interface eth0 tcpdump -i eth0 # Monitor all traffic on port 80 ( HTTP ) tcpdump -i eth0 'port 80' # List all open files on the system lsof # List files opened by user lsof -u user # Display free and used memory ( -h for human readable, -m for MB, -g for GB.) free -h # Execute "df -h", showing periodic updates watch df -h
4 – USER INFORMATION AND MANAGEMENT
# Display the user and group ids of your current user. id # Display the last users who have logged onto the system. last # Show who is logged into the system. who # Show who is logged in and what they are doing. w # Create a group named "test". groupadd test # Create an account named john, with a comment of "John Smith" and create the user's home directory. useradd -c "John Smith" -m john # Delete the john account. userdel john # Add the john account to the sales group usermod -aG sales john
5 – FILE AND DIRECTORY COMMANDS
# List all files in a long listing (detailed) format ls -al # Display the present working directory pwd # Create a directory mkdir directory # Remove (delete) file rm file # Remove the directory and its contents recursively rm -r directory # Force removal of file without prompting for confirmation rm -f file # Forcefully remove directory recursively rm -rf directory # Copy file1 to file2 cp file1 file2 # Copy source_directory recursively to destination. If destination exists, copy source_directory into destination, otherwise create destination with the contents of source_directory. cp -r source_directory destination # Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2 mv file1 file2 # Create symbolic link to linkname ln -s /path/to/file linkname # Create an empty file or update the access and modification times of file. touch file # View the contents of file cat file # Browse through a text file less file # Display the first 10 lines of file head file # Display the last 10 lines of file tail file # Display the last 10 lines of file and "follow" the file as it grows. tail -f file
6 – PROCESS MANAGEMENT
# Display your currently running processes ps # Display all the currently running processes on the system. ps -ef # Display process information for processname ps -ef | grep processname # Display and manage the top processes top # Interactive process viewer (top alternative) htop # Kill process with process ID of pid kill pid # Kill all processes named processname killall processname # Start program in the background program & # Display stopped or background jobs bg # Brings the most recent background job to foreground fg # Brings job n to the foreground fg n
7 – FILE PERMISSIONS
PERMISSION EXAMPLE U G W rwx rwx rwx chmod 777 filename rwx rwx r-x chmod 775 filename rwx r-x r-x chmod 755 filename rw- rw- r-- chmod 664 filename rw- r-- r-- chmod 644 filename # NOTE: Use 777 sparingly! LEGEND U = User G = Group W = World r = Read w = write x = execute - = no access
8 – NETWORKING
# Display all network interfaces and ip address ifconfig -a # Display eth0 address and details ifconfig eth0 # Query or control network driver and hardware settings ethtool eth0 # Send ICMP echo request to host ping host # Display whois information for domain whois domain # Display DNS information for domain dig domain # Reverse lookup of IP_ADDRESS dig -x IP_ADDRESS # Display DNS ip address for domain host domain # Display the network address of the host name. hostname -i # Display all local ip addresses hostname -I # Download http://domain.com/file wget http://domain.com/file # Display listening tcp and udp ports and corresponding programs netstat -nutlp
9 – ARCHIVES (TAR FILES)
# Create tar named archive.tar containing directory. tar cf archive.tar directory # Extract the contents from archive.tar. tar xf archive.tar # Create a gzip compressed tar file name archive.tar.gz. tar czf archive.tar.gz directory # Extract a gzip compressed tar file. tar xzf archive.tar.gz # Create a tar file with bzip2 compression tar cjf archive.tar.bz2 directory # Extract a bzip2 compressed tar file. tar xjf archive.tar.bz2
10 – INSTALLING PACKAGES
# 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.rpm rpm -i package.rpm # Remove/uninstall package. yum remove package # Install software from source code. tar zxvf sourcecode.tar.gz cd sourcecode ./configure make make install
11 – SEARCH
# Search for pattern in file grep pattern file # Search recursively for pattern in directory grep -r pattern directory # Find files and directories by name locate name # Find files in /home/john that start with "prefix". find /home/john -name 'prefix*' # Find files larger than 100MB in /home find /home -size +100M
12 – SSH LOGINS
# Connect to host as your local username. ssh host # Connect to host as user ssh user@host # Connect to host using port ssh -p port user@host
13 – FILE TRANSFERS
# Secure copy file.txt to the /tmp folder on server scp 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 /home to /backups/home rsync -a /home /backups/ # Synchronize files/directories between the local and remote system with compression enabled rsync -avz /home server:/backups/
14 – DISK USAGE
# Show free and used space on mounted filesystems df -h # Show free and used inodes on mounted filesystems df -i # Display disks partitions sizes and types fdisk -l # Display disk usage for all files and directories in human readable format du -ah # Display total disk usage off the current directory du -sh
15 – DIRECTORY NAVIGATION
# To go up one level of the directory tree. (Change into the parent directory.) cd .. # Go to the $HOME directory cd # Change to the /etc directory cd /etc
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