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CheatSheet.md

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CheatSheet

Display Linux system information

uname -a

Display kernel release information

uname -r

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

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

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

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

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

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

Linux chmod example

    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

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