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