important uses of LSOF Command – lsof is a Linux utility which lists the information about files opened by processes.LSOF is one of the powerful tool available for troubleshooting problems.

Autoconf is a set of tools which makes your project configurable and portable for running in Linux distributions. Simply, autoconf will help you to create configure script and Makefile for your code. Before going to generate configure script using autoconf, we need to define set of rules and dependencies. We are defining that rules and [...]

The basic network discovery always start with ping utility.So blocking the ping requests will make the system discovery difficult.To disable ping requests ,we just need to add/modify some kernel parameters. What we are doing here is the permanent change. So open /etc/sysctl.conf  and add the following line to /etc/sysctl.conf net.ipv4.icmp_echo_ignore_all = 1 And reload kernel [...]

Building a centralized log host in your network will ease the process of troubleshooting your servers from a single window.Centralized log host will accepts all the log messages from client and store in that server.

Environment variables in Unix are a set of dynamic named values that can affect the way running processes will be have on a computer

What is run level in Unix??? Run level defines the predefined set of operational state for Unix system.The operational state is defined in file  inittab which is located in /etc. init command used to switch between different run levels.init command followed by runlevel will switch system to corresponding runlevel Eg:  init 3 This will switch [...]

First runlevel for Linux system which only one user is allowed to access that root user.Single user mode is useful for fixing some system problem like filesystem errors,recovering root password etc.So these are the steps for entering to single user mode in Linux.This is based on redhat enterprise linux 5( RHEL 5) Steps: Press any [...]

First we need to find out which disks and partitions are being used. So we could use the following commands #df -h [This  will display which partitions  are being used] #fdisk -l [This will show which disks are being used and disks that are not mounted.] Now we can start the lvm implementation,we have two [...]

How to mark volume groups as active or inactive in Linux using lvchange command in Linux

Fencing is the disconnection of a node from the cluster’s shared storage. Fencing cuts off I/O from shared storage, thus ensuring data integrity. There are two fencing programs fenced Configured with CMAN/DLM GULM Configured with GULM servers When the cluster manager determines that a node has failed, it communicates to other cluster-infrastructure components that the [...]

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 [...]

RAID is an acronym for Redundant Array of Independent Disks. With RAID enabled on a storage system you can connect two or more drives in the system so that they act like one big fast drive or set them up so that one drive in the system is used to automatically and instantaneously duplicate (or mirror) your data for real-time backup.

Get linux kernel version with this command # uname -a Now perform this steps # cd /usr/src/linux # make mrproper # make oldconfig # make bzImage # make modules # make modules_install # make install # reboot In new Redhat systems, the headers are included in the kernel-devel package and the compile process is a [...]

RT-Linux is an operating system in which a small real-time kernel coexists with the Linux kernel which was originally developed by Victor Yodaiken at the New Mexico Institute of Mining and Technology.RTLinux supports hard real-time operation through interrupt control between the hardware and the operating system. Interrupts needed for deterministic processing are processed by the [...]

The IPTables program that comes with Linux distributions allows administrators to configure the operating system so that it allows applications and clients to connect through the network and stop unwanted applications and clients from communicating and corrupting the operating system.It is really a front end tool to manage netfilters which is integrated with the linux [...]

/etc/passwd file stores  user account information, which is required during login. /etc/passwd is a text file, that contains a list of the system’s accounts, giving for each account some useful information like user ID, group ID, home directory, shell, etc. It should have general read permission as many utilities, like ls use it to map [...]

Linux Commands for managing users: 1. adduser – Command used to add user accounts. 2. chage – Used to change the time the user’s password will expire. 3. chfn – Change a user’s finger information 4. chsh – Change a user’s shell. 5. chgrp – Changes the group ownership of files. 6. chown – Change [...]

There are three types of access: 1. read 2. write 3. execute Each file belongs to a specific user and group. Access to the files is controlled by user, group, and what is called other. The term, other, is used to refer to someone who is not the user (owner) of the file, nor is [...]

cat Sends file contents to standard output.This is a way to list the contents of short files to the screen.It works well with piping. Eg:cat .bashrc (Sends content of “.bashrc” file to screen). cd Change directory eg:cd /home Change the current working directory to /home. The ‘/’ indicates relative to root, and no matter what [...]

Linux booting process includes the following events 1. BIOS: The system’s BIOS(Basic Input Output System) initializes and perform internal checks on the hardware components of the system,including CPU,memory,harddrives video system etc 2. MBR: The system checks the MBR(Master Boot Record) of the boot harddrive ,which loads into memory the boot loader for the system.For linux [...]