Linux

# Ubuntu

//How to see Linux version
lsb_release -a
cat /etc/centos-release

//Add user
adduser tomcat

//Add user with home directory
useradd -m -d $path $user

w // See who is connected
ps -ft pts/0 //Get PID

//How to see my Linux version
cat /etc/centos-release
cat /etc/redhat-release

//Install package from rpm
 sudo rpm -ivh nginx-release-rhel-7-0.el7.ngx.noarch.rpm

##SSH login without password
//Generate a pair of authentication keys from clien A. Do not enter a passphrase:

ssh-keygen -t rsa

//append a's new public key to b@B:.ssh/authorized_keys and enter b's password one last time:

cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'

//Change the permissions of .ssh to 700
//Change the permissions of .ssh/authorized_keys to 640

// Change from .java to .groovy in files
rename "s/java/groovy/" *.java 

##Install zsh
sudo yum install zsh

##Install Oh My Zsh
sh -c "$(curl -fsSL https://raw.github.com/robbyrussell/oh-my-zsh/master/tools/install.sh)"

##Remove OpenJDK in Centos

// See what pagkage is installed
rpm -qa | grep jdk 

//Uninstall
 sudo yum remove ${PackageName}
 
//Search for a text in all files under each directory, recursively
$ grep -r "redeem reward" /home/tom

//Find a file with keyword including sub-directories
find . -name "*lying*"

//Changing java to groovy extensions
rename "s/java/groovy/" *.java 

//Count directories in a path
ls | wc -l

//Counting files in a directory
find . -type f | wc -l

1. -type f to include only files.
2. wc world count

//Set date
sudo date --set="16 DEC 2015 13:07:00"

//Active connections 80 http listing whos is connecting (ip)
netstat -an | grep 80

//Number conections 80
netstat | grep http | wc -l

//Monitoring request
sudo tcpflow -p -c -i eth0 port 80 | grep -oE '(GET|POST|HEAD) .* HTTP/1.[01]|Host: .*'

//Ubuntu distribution
lsb_release -a

//Force install in Ubuntu
sudo apt-get install -f

//The size of all the directories,files etc in current directory in human readable format
du -sh *

//How to escape spaces in path during scp copy in linux
sudo scp -r josdem@192.168.2.4:Ubuntu\\\ One/Music/Ambient .

//Verifying Which Ports Are Listening
netstat -tanp | grep LISTEN

//Displays the last part of a file
tail -f -n 100 /var/log/syslog

# Centos
//Version
cat /etc/centos-release

//Memory Information
cat /proc/meminfo

//CPU Information
lscpu

//HD Information
df -H

//List all rpm packages by keyword
yum search all java

# Both
//Change hostname
hostnamectl set-hostname new-hostname

//See graphic card
lspci -vnn | grep VGA

//See process running
ps -o pid,user,%mem,command ax | sort -b -k3 -r