Centos : Create User with Root privilledges

This command can be execute to user who has root priviledge

• Create user :

$ sudo /etc/sbin/useradd namefouser

• Setting user password "

$ sudo /etc/bin/passwd nameofuser

• Allow user to ssh

$ sudo vim /etc/ssh/sshd_config

There's some way to allow user to execute command :

• Add user to sudoers  

$ sudo /etc/sbin/visudo

• Add user to wheel group which is wheel is a group that sudoers allowed group.

$ sudo /etc/sbin/usermod -a -G wheel namefouser

Flush DNS on Linux

On Windows Operating system to delete all DNS query result we use to be use command IPCONFIG /FLUSHDNS, in Linux there's serveral command to flush DNS :

1. Flush dns by restarting NSCD service : 

• $ sudo /etc/init.d/nscd restart
• # service nscd restart
• # service nscd reload

2. Flush dnsmasq DNS cache :

• $ sudo /etc/init.d/dnsmasq restart
• # service dnsmasq restart

3. Flush Caching BIND server DNS Cache :

• # /etc/init.d/named restart
• # rndc restart
• # rndc exec