Basic Commands

Getting Help Commands

Command

Description

man [command]

manual pages explaining a given command

man -k [search_term]

option -k will look through all man pages to find your term and display to the screen

info [command]

similar to man command, but more detailed, will print info about a given command

vim --help or vim -h

--help command provides guidance for application use, in this example we use vim a single dash (-) is used before single-letter options, for example -h a double dash (--) on the other hand before word options, such as --help

Navigating Files and Directories

Command

Description

pwd

present working directory - shows you a current location within the directory structure

ls

list command - list the content of the directory

ls -a

Show visible and hidden files and directories, option -a is --all

ls -l

-l option stands for long - give you more information about the files and directories - permissions, owner, size, and when they were last modified

ls -lh

this option shows you human-readable sizes, for example, 5M or 1.9K

ls -lhS

-S flag will sort the results by file size, default is the name

ls -lt

sort by last modified time -t

ls -lr

reverse sort, using the -r flag

ls -R

recursive listing

cd [path]

change directory, if used alone will go to the home directory ~

cd ..

move one level up in the file structure

cd ../..

move two levels up in the file structure and so on

cd /

move to the root level of the file system

cd -

go back to the last location

cd ~

go to the user's home directory; you can also use cd $HOME

Creating and Managing Files/Directories/Links

Command

Description

touch [file_name]

create an empty file

mkdir [directory]

create a directory

mkdir -p [directory/subdirectory]

create nested directories

rm [file_name]

remove a file

rmdir [directory]

remove the empty directory

rmdir -p [direcotory/subdirectory]

delete the set of nested directories, as long as they don't hold non-directory files (so only containing folders)

rm -rf [directory]

remove a file or directory (can have files within)

cp [source_file] [target_file]

copy a file

cp [source_file1] [source_file2] [target_fdir]

this command allows to copy several files, the last argument has to be the target directory

cp -R [source_directory] [target_directory]

used to copy directories and their contents

cp -i [file_name1] [file_name2]

confirm overwriting of a file, so when file_name2 exist we will see a prompt to confirm the action

mv [file_name1] [file_name2]

move or rename files

ln [source_file] [linked_file]

create a hard link between files

ln -s [source_file] [linked_file]

create a symbolic link (it's like a shortcut)

Searching, Extracting and Displaying Data

Command

Description

echo "text"

print "text " string to the screen

locate [file_name]

search for a [file_name], will print the absolute path of all files and directories that matches the search pattern and for which the user has read permission

grep

used for search files containing specifying string, pattern, based on pattern

grep -E [regular_expression]

search to match pattern using regex

grep "example" [files]

search for "example" string in files, which you can replace it with your pattern

grep -n [searching_phrase] RREADME.md

searching with -n flag will display numbers as a part of the output

grep -R "example" [directory]

search recursively through the directory, and it all subdirectories

grep -v "example"

search for everything apart from "example"

ls | grep [file1]

|- piping allows combining two or more commands, in this case, we use grep to look for file1 in ls output

ls > file1

send the output to file1 (save the output in this file)

ls >> file1

append output to a file1

grep test < file1

read input from a file1

find [path_to_search] [flag] [pattern_to+search_for]

search for a file

find / -name test.txt

search in home directory for a file named test.txt

find . $ -name \*.png -or -name \*.jpg $ -type f

search the current directory for files whose name either end in .png or .jpg format

cat [file_name]

display content of a file in the terminal

more [file_name]

output the contents of a file, good when you need to look into big files, you can scroll the page

less [file_name]

similar to more command, it used to read the contents of a file, one page at the time

head [file_name]

it outputs the first 10 lines of a file to the screen

tail [file_name]

it outputs the last 10 lines of a file to the screen

tail -n 5 [path/file_name]

output the last 5 lines of a file

sed s/mysql/MYSQL/g /etc/filename.conf > snort2.conf

sed command is used to find and replace keywords or phrases - in the example, we are looking for mysql (s used to search) and replacing it with MySQL (g means replace globally - all occurrences of it in a file)

sed s/mysql/MYSQL/ /etc/filename.conf > snort2.conf

in the example, only the first occurrence of mysql will be replaced with MySQL

sed s/mysql/MYSQL/2 /etc/filename.conf > snort2.conf

this command affects only the second occurence of mysql

Networking Commands

Command

Description

ping [ip_address]

ping host and output results

ping -c 5 [ip_address]

do 5 pings

whois [domain_name]

get whois info for a given domain

dig [domain_name]

DNS lookup utility, get DNS info for a given domain

dig -x [addr]

DNS reverse lookup

host [domain_name]

DNS lookup utility, get DNS info for a given domain

cat /etc/reslov.conf

shows which configuration file is used to determine which hosts to use for DNS queries

/etc/hosts

used for statically mapping IP addresses to hostnames

ip route show

shows the current routing table

ip addr show

show the current IP addresses

ifconfig

view and change the interface configuration; for wireless interface use iwconfig

traceroute google.com

shows you all the hops/routes with IP addresses your packets travel

wget [url]

it allows you to download the zipped module

wget -c [file]

continue a stopped download

netstat

view listing services and active connections

ss

similar to netstat - list out all the network (socket) connections on a system

curl [url]

make an HTTP request to a given server and print its response in the terminal console

curl -i [url]

gives you more information about the response

SSH Access Commands

Command

Description

sudo apt install openssh-server

install ssh service

sudo systemctl enable ssh

enable ssh service

sudo systemctl start ssh

start ssh service on the device

sudo systemctl status ssh

show the status of the ssh service (you can also restart, stop or disable the service)

ssh user@host

connect to the host as user

ssh -p [port] user@host

connect to the host as user on port

sudo ufw allow ssh

you might need to configure the firewall to open port 22 on Ubuntu

sudo ufw enable

enable ufw

sudo ufw status

check status of ufw

ssh-copy-id vivek@power9

copy and install the public key so you can use passwordless login

Process Management Commands

Command

Description

ps

list the processes started by logged in user

ps aux

display all processes running on the system

top

display top running processes, based on CPU and memory usage

kill [pid]

kill a process by providing its PID

nice -n -10 /bin/slowprocess

this command gives higher priority (scale from -20 to 19, where -20 is the most priority) to the slowprocess

renice 20 6996

this command set the priority to a given process; in the example, we set priority 20 (you can set also a negative number which will give higher priority) for a process 6996

System Info Commands

Command

Description

whoami

show which user you're logged in as

last

show a listing of last logged in users

who

display who is currently logged in

w

used to show who is logged in and what they are doing (login name, the tty name, the remote host, login time, idle time, JCPU (time used by all processes), PCPU (time used by the current process), WHAT - the command line of their current process

date

print the system date

cal

show calendar

df

show system disk space usage

du

show estimate directory space usage

free

show memory and swap usage

cat /proc/cpuinfo

show the cpu information

cat /proc/meminfo

show the memory info

whereis [app_name]

show location of a given application

which [app_name]

return the path of a file which will be executed for a given application

uname -a

show kernel information

dmesg

print all messages from the kernel ring buffer

hostnamectl

display info about the hostname, OS, kernel, architecture, etc.

lsb_release -a

show basic info about OS and its distribution

fdisk -l

using fdisk utility with -l switch will list all the partitions pf all drives with their capacity; requires root privileges

lsblk

useful command that stands for list block and lists some basic information about each block device listed in /dev. Similar to fdisk -l with the difference that will also display devices with multiple partitions in a tree, showing each device with its partitons as branches; doesn't require root privileges to run

mount /dev/sdb1 /mnt

this is used to mount the new hard drive sdb1 at /mnt directory

mount /dev/sdc1 /media

this command will mount your USB drive

umount /dev/sdb1

unmount your drive (command spelt umount without n)

fsck

check and repair Linux filesystem errors

umount /dev/sdb1 \ fsck -p /dev/sdb1

to use fsck command you need first unmount your device and then runfsck command. -p switch will automatically repair any problems with the device

id [user_name]

show info about user and his groups

File/User Permissions Commands

Command

Description

chmod 774 [file_name]

set the permission subsequently for the owner, group, all users (others) to a given file Available permissions: -r (read - octal value: 4) -w (write - octal value: 2) -x (execute - octal value: 1) in the example, the owner and group get all permissions (4+2+1), and all users only read access (4). When you create or download a file - Linux automatically assigns base permissions - 666 for files and 777 for directories

chmod u-w [file_name]

removes (-) the write (w) permission from hashcat.hcsta for the user/owner (u)

chmod u+x,o+x [file_name]

you can add (+) the executable (x) permission for a user (u) and other users (o). UGO syntax use: - user/owner (u) - groups (g) - others (o) You can use three operators to set permissions: - Remove permission with - - Add a premission wiht + - Set permission with = Permissions are comma-separeted (,) and there is no space

chown [user] [file_name]

change a file's user ownership

chown :group_name [file_name]

change a file's group ownership

chown user:group file1

changes a file's user and group ownership

chgrp [groupname] [filename]

change group of a given file

useradd -m [user_name]

create a user and its directory

sudo passwd [user_name]

change user password

sudo -l passwd [user_name]

lock a user account

userdel [user_name]

delete a user

sudo usermod -a -G developers,employes [user_name]

add a user to groups: developers and employees (done with usermod - as the user already exist so we need to modify his permissions

Installation Commands

Command

Description

apt-get install [package_name]

install a given package on Ubuntu

apt-cache search keyword

check if a package is available in your repository

apt-get remove [package_name]

removes a package from your repo, but keeps the configuration files

apt-get purge [package_name]

removes package and configuration files from your repo

apt-get update

update your system packages

apt-get upgrade

upgrade existing packages on your system

yum install [package_name]

install a package using yum - used in the different distro, like CentOS

Archiving Commands

Options/Flags: -c create archive -x extract archive -r append to an archive -t list the contents of an archive -f read from or write to a file -v show which files are being added to the archive

Command

Description

tar cf archive.tar [target_file1] [target_file2]

create the .tar (tape archive)

tar xf archive.tar

extract the archive

gzip archive.tar.gz

Another method that is used for archiving files, size of the archive is much lower -> results in a file with extension: .gz

gunizp archive.tar.gz

extract archive using GNU unzip command; alternatively, you can use gz -d file.gz

bzip2 archive.*

Another method to zip files - similar to gzip, slower but better compression ratios, which means generated file is smaller and results in: .bz2 format - for example TestArchive.bz2 , if a file has an extension let's say .sh file will be in the following format filname.sh.bz2

bunizp2 archive.bz

unzip the compressed file

xz -z [target_file]

zip file in the .xz format, -z or --compress usually used; this utility offers the best compression

unxz [archive_name]

decompress a file, you can also use xz -d [archive_name]

zip archive_name.zip [file1] [file2]

another command to archive files

unzip

used to unzip files while using zip command

Other Commands

Command

Description

history

it shows you a list of commands that you've entered since the session started

export

view all exported variables, use export VARIABLENAMEto export VARIABLENAME

printenv

print all environment variables to the screen, they are upper case

type [command_name]

it will describe how its argument would be translated if used as commands; also used to find out whether it is a built-in or external binary file

clear

clear the terminal screen

sort [fil_name]

sort the contents of the file and display it on the screen

cut -b 1-3,5-7 test.txt

the command that will extract a text from a field within a file, pull information from a file and write the result to standard output; this particular example is using -b flag (byte) to extract specific bytes, a list with ranges 1-3,5-7

wc -l

word count command, used to find a number of newline count, word count, byte and character count; options:

-l - print new lines count
-c - print bytes count
-m - print chars count

Keyboard Shortcuts

Command

Description

ctrl + alt + t

open terminal

More commands can be found in this repo: https://github.com/devluke88/linux-repo

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Last updated 3 years ago

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