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Apache and the web :         Developed since 1995     Core Technology responsible for initial web growth     Currently serves over 54% of all websites.         Handles large amount of traffic.         Serves many kinds of content with Minimal configuration.         Scales Easily.         Free to use.         Apache Versions :     Included Functionality changes.     Configuration differences.     1.3 - 1998 to 2010     2.0 - 2000 to 2013     2.2 - 2005 to present     2.3 - 2009 to present         Apache Structure :         Parent service with multiple child processes.         Each child can serve different pages at the same time.         Control is lika a manager with a team.         Interactions through the Parent.         Parent manages children.         Fault tolerant and high performance.     Interacting with Apache :         apachectl - script to control service.         Some distributions provide another layer on top of apachectl.         Ap

How to set up and use iSCSI target on Linux What is iSCSI? iSCSI is an Internet Protocol based storage networking standard for linking data storage facilities. By carrying SCSI commands over IP networks, iSCSI can facilitate data transfers over local area networks (LANs), wide area networks (WANs), or the Internet. Through iSCSI, the space on storage server will be regarded as local disks by client's operation system. But in reality, all data transferred to the disk are actually transferred over network to the storage server. What is iSCSI Target and LUN? In SCSI terminology, A LUN (logical unit number) represents an individually addressable (logical) SCSI device that is part of a physical SCSI device (called "Target"). An iSCSI environment emulates the connection to a SCSI hard disk. An iSCSI Target is like a connection interface, and LUNs are essentially numbered disk drives. When an iSCSI Target is connected by an iSCSI initiator (a client), all the LUNs mappe

what is load average ? Number of jobs in run queue are waiting for disk IO averaged over 1, 5 and 15 mins. mpstat -P ALL 1 (produces all CPU's utilization for every 1 second) while true; do true; done debug cpu performance issue  ---------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------------------------------------- How to get a UUID of san devices from file?  ll /dev/disk/by-uuid/    how to block particular lun using multipath.conf file  Edit /etc/multipath/multipath.conf file and add your device in blacklist section  blacklist {       wwid 26353900f02796769       devnode "^(ram|raw|loop|fd|md|dm-|sr|scd|st)[0-9]*"       devnode "^hd[a-z]" }  How to scan scsi and fc devices for new disks? FC :   # echo "1" > /sys/class/fc_host/host0/issue_lip # echo "1" > /sys/class/fc_host/host1/issue_lip SCSI # echo "- -

Ansible : We can use it for configuration management, orchestration and provisioning. Configuration Management : Whatever changes we do to our users, files, services, application related files.. etc.... is called configuration management.                            Any setup we are doing is install the software, configure it as per our environment and start to use it.                            We can use Ansible to do the configuration                           Provisioning : Building new servers.                We can use Ansible for provisioning as well.               Orchestration : Executing the steps in structured way. Latest Version of Ansible is 2.4 It is a open source tool. It also has a enterprise product called ansible tower. Agent less tool. (No agent need to be installed on the remote systems). It communicates to client based on SSH. Ansible Server : On system where we install the Ansible is called controller.                  On windows we can not i