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
