In this article we are going to check how to disable SELinux in Centos Box.SELinux brings lot of security measures to your Linux box.It will provide an additional level of access control mechanism to files and folders on top of normal Linux security tools.

NAT-Network Address Translation is used to communicate from one network to other network with different sub-net.So your Linux box will act as a gateway and will allow to communicate between two different networks.

password expiry for users is configuring in /etc/login.defs file.These are the password aging parameters PASS_MAX_DAYS                Maximum number of days a password may be used. PASS_MIN_DAYS                 Minimum number of days allowed between password changes. PASS_WARN_AGE               Number of days warning given before a password expires. By default PASS_MAX_DAYS will be 99999 days that means no password expiry.So [...]

selinux is created by National Security Agency. NSA created a project to enforce Mandatory Access Control (MAC) inside the Linux Kernel which is known as Security Enhanced Linux or SELinux

Rsync: rsync is an application used in unix systems which synchronize files and directories between two machines.rsync behaves like rcp(remote file copy),but it much faster than rcp.because rsync sends the differences in the files instead of sending entire files. Servers are SERVER_SOURCE & SERVER_DESTINATION Configure SSH key authentication In SERVER_DESTINATION open sshd_config file vi /etc/ssh/sshd_config [...]

Login as root user Enter grub mode: # grub Use md5crypt to encrypt password: grub> md5crypt Password: ****** Encrypted: $1$jxcdN0$hVHViq1aiPf8FziuGJGZp0 Copy encrypted password Exit grub mode: grub> quit Modify file /boot/grub/grub.conf: vi /boot/grub/grub.conf Insert this line after splashimage  “password –md5 $1$jxcdN0$hVHViq1aiPf8FziuGJGZp0″ splashimage=(hd0,0)/boot/grub/splash.xpm.gz password –md5 $1$jxcdN0$hVHViq1aiPf8FziuGJGZp0 then save& exit /boot/grub/grub.conf Incoming search terms:grub md5crypt online (1)

login as root and execute the following command #watch lsof -i To list all open Internet files, use: #lsof -i -U You can also get very specific about ports. Do this as root for low ports. #lsof -i TCP:3306 Or, look at UDP ports as follows: #lsof -i UDP:1812 Also try fuser. Suppose you have [...]

To monitor all Network Traffic Except Your Current ssh Connection, #tcpdump -i eth0 -nN -vvv -xX -s 1500 port not 22 To filter out port 123 as well getting the full length of the packet (-s 0), use the following: #tcpdump -i eth0 -nN -vvv -xX -s 0 port not 22 and port not 123 [...]

When a user starts a command, it runs with the permissions of that user. What if you want to allow them to run some commands with root permissions? You can, and that’s called suid.So  SUID permission makes a script to run as the user who is the owner of the script, rather than the user [...]

Open /etc/ssh/sshd_config using vi editor vi /etc/ssh/sshd_config Then uncomment the line #Banner /etc/motd save & exit Now create some banner text in /etc/motd like This computer system is for authorized users only. All activity is logged and regulary checked by systems personal. Individuals using this system without authority or in excess of their authority are [...]

By using lsof command,we can view active ssh connections on your server.So let’s find out how.
lsof command is used to list open files like disk files, pipes, network sockets and devices opened by all processes.