Connect KVM over GRE

Hi Folks, As you may know, Libvirt virtual network switches operates in NAT mode in default (IP Masquerading rather than SNAT or DNAT). In this mode Virtual guests can communicate outside world. But, Computers external to the host can’t initiate communications to the guests inside, when the virtual network switch is operating in NAT mode. […]

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DRBD(without clustering)

Do you need transparent, real-time replication of block devices without the need for specialty hardware without paying anything ? If your answer is YES. DRBD is your solution. DRBD is a distributed replicated storage system for the Linux platform. It is implemented as a kernel driver, several userspace management applications, and some shell scripts. DRBD […]

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Checking Connection without Telnet

Some of the minimal Linux distributions have no telnet client utility or similar utilities such as nc,ncat unless you install it. Most of time we need to do troubleshooting to check connection if  server/service is accessible. Do not worry–You still have mechanism inside the Linux kernel without installing above utilities. Take a look at below examples […]

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How to Change I/O Scheduler in Linux

Linux kernel is one of the most complicated software which is being used variety of systems such as laptops, embedded devices, hand-held devices, Database servers, supercomputers etc., All these kind of devices  demand different type of requirements. Some of the applications require fast response to user input. As you know, disk is the slowest physical […]

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Sharing Internet in Linux

Hi Folks! Today, I installed Ubuntu 18.04 LTS on my personal laptop. But I could not connect to the Internet as Ubuntu does not recognize my wireless driver. After couple of googling I have found my wireless driver .[model:Broadcom Limited BCM43142 802.11b/g/n]. But the problem is how I am going to hook-up to the Internet  […]

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Cheksum On Linux and Windows

Hello Folks, When you transfer files from Windows to Linux or vice versa, checksum of these files will be changed unless you transfer it in binary mode(in FTP terminology). It is normal because representation of  new line in Linux differ from the Windows system. In Unix systems new line represented by \n [line feed] whereas, […]

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Diskless Machine(PxE boot)

PxE is a way of booting OS kernel over the network rather than from disk. It consist of one or more PxE servers which holds all kernel and initial ramdisk image. And PxE clients which are actual host where user application and services start. It is depicted in the Figure-1. PxE server running tftp and […]

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Fake Kernel Panic for Testing(Magic SysRq)

Sometimes we need to crash the system for testing of cluster  fencing functionality  and fail-over functionality.  Actually in Linux we can create a fake kernel panic by issuing below commands.  

  c Will perform a system crash by a NULL pointer dereference. A crash dump will be taken if configured. Reference: https://www.kernel.org/doc/html/v4.11/admin-guide/sysrq.html

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System Restore with Rsync

Rsync is one of the  super-duper *nix utility for synchronizing or transferring files among the computers. It has so much functionality that I could not explain it to you in one post. In this post, I will use rsync utility to backup and restore my system. In this activity, I am using CentOS7(virtual guest) on […]

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Configuring PAM for crontab

Because of some strict rules such as PCI DSS compliances, we could not set password for root user to “never expire”. But, when password expires for any account in the Linux systems crontab jobs will not work. Unless, you configure the PAM to run it, or extending root password. Or you need to buy some […]

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