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Virtualization Restrictions in RedHat Linux with KVM

This article covers Virtualization Restrictions in RedHat Linux which are additional support and product restrictions of the virtualization packages.


The following notes apply to all versions of Red Hat Virtualization:

1. Supported limits reflect the current state of system testing by Red Hat and its partners. Systems exceeding these supported limits may be included in the Hardware Catalog after joint testing between Red Hat and its partners. If they exceed the supported limits posted here, entries in the Hardware Catalog are fully supported. In addition to supported limits reflecting hardware capability, there may be additional limits under the Red Hat Enterprise Linux subscription terms. Supported limits are subject to change based on ongoing testing activities.


2. These limits do not apply to Red Hat Enterprise Linux (RHEL) with KVM virtualization, which offers virtualization for low-density environments.


3. Guest operating systems have different minimum memory requirements. Virtual machine memory can be allocated as small as required.

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dhclient to persistently look for an IP address lease - Configure it Now

This article covers how to use dhclient command. Basically, Linux dhclient command can provide an IP lease until DHCP Server/Router grants one.

With this guide, you can easily configure Linux dhclient command to continuously requests an IP lease until one is granted by DHCP Server / Router.

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Create CentOS Fedora RHEL VM Template on KVM - How to do it

This article covers how to create CentOS/Fedora/RHEL VM Templates on KVM. VM Templates are more useful when deploying high numbers of similar VMs that require consistency across deployments. If something goes wrong in an instance created from the Template, you can clone a fresh VM from the template with minimal effort.


To install KVM in your Linux system:

The KVM service (libvirtd) should be running and enabled to start at boot.

$ sudo systemctl start libvirtd

$ sudo systemctl enable libvirtd

Enable vhost-net kernel module on Ubuntu/Debian.

$ sudo modprobe vhost_net

# echo vhost_net | sudo tee -a /etc/modules


How to Prepare CentOS / Fedora / RHEL VM template ?

1. Update system

After you finish VM installation, login to the instance and update all system packages to the latest versions.

$ sudo yum -y update

2. Install standard basic packages missing:

$ sudo yum install -y epel-release vim bash-completion wget curl telnet net-tools unzip lvm2 

3. Install acpid and cloud-init packages.

$ sudo yum -y install acpid cloud-init cloud-utils-growpart

$ sudo sudo systemctl enable --now acpid

4. Disable the zeroconf route

$ echo "NOZEROCONF=yes" | sudo tee -a /etc/sysconfig/network

5. Configure GRUB_CMDLINE_LINUX – For Openstack usage.

If you plan on exporting template to Openstack Glance image service, edit the /etc/default/grub file and configure the GRUB_CMDLINE_LINUX option. Your line should look like below – remove rhgb quiet and add console=tty0 console=ttyS0,115200n8.

GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap console=tty0 console=ttyS0,115200n8"

Generate grub configuration.

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg

6. Install other packages you need on your baseline template.

7. When done, power off the virtual machine.


How to Clean VM template ?

You need virt-sysprep tool for cleaning the instance.

$ sudo virt-sysprep -d centos7

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Install Linux Software Via Command line

This article will guide you on methods to install #Linux #Software via command line. #Debian, Ubuntu, Mint, and other Debian-based distributions all use . deb files and the dpkg package management system. There are two ways to install apps via this system. You can use the apt application to install from a repository, or you can use the dpkg app to install apps from .


To compile a program from a source in Linux:

i. Open a console.

ii. Use the #command cd to navigate to the correct folder. If there is a README file with installation instructions, use that instead.

iii. Extract the files with one of the commands.

iv. ./configure.

v. make.

vi. sudo make install (or with checkinstall ).


To Check os version in Linux:

1. Open the #terminal application (bash shell)

2. For remote server login using the ssh: ssh user@server-name.

3. Type any one of the following command to find os name and version in Linux: cat /etc/os-release. lsb_release -a. hostnamectl.

4. Type the following command to find Linux kernel version: uname -r.

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Install Graylog on CentOS 7 How to do it

This article will guide you on steps to #Graylog on #CentOS 7 and an effective method to make the logs more structured and searchable.

Graylog is a leading centralized log management solution built to open standards for capturing, storing, and enabling real-time analysis of terabytes of #machine data. 

Graylog is an open source log management platform which enables you to aggregate up to terabytes of log data, from multiple log sources, DCs, and geographies with the capability to scale horizontally in your data center, #cloud, or both.

To #Install Graylog 3 with Elasticsearch on CentOS 7:

1. Configure #SELinux. 

2. Add required #repositories 

3. Install #Java, #Elasticsearch, and #MongoDB. 

4. Configure Elasticsearch for Graylog. 

5. Install Graylog 3 on CentOS 7. 

6. Start Graylog service on CentOS 7.

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NFS Server on RHEL CentOS 8 Steps to install and configure

This article will guide you on the steps to Install and Configure #NFS Server on #RHEL or #CentOS.

The terms client and server are used to describe the roles that a computer plays when sharing file systems. The NFS service enables any given computer to access any other computer's file systems and, at the same time, to provide access to its own file systems.

To install NFS server:

1. Install NFS #Kernel Server. 

2. Create the #Export #Directory. 

3. Assign server access to client(s) through NFS export file. 

4. Export the shared directory. 

5. Open #firewall for the client (s).

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Detecting Memory Overcommit in the Guest OS

This article will guide you on how to go about detecting Memory Overcommit in the Guest #OS.

#Memory overcommit is a #hypervisor feature that allows us to allocate to virtual #machines more memory than is available on a physical #host.

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NFS server not responding timed out error How to fix

This article will guide you on how to fix #NFS server not responding timed out #error which occurs when there is a heavy #server or #network load.

Why NFS is not working?

i. Check the file /proc/fs/nfs/exports and make sure the volume and client are listed correctly.

ii. Finally, try to ping the client from the server, and try to ping the server from the client. 

iii. If this doesn't work, or if there is packet loss, you may have lower-level network problems.

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Install Nagios XI in an offline environment

This article will guide you on how to install Nagios XI in an offline environment using powershell.

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Steps to install SQL Tools on RedHat Linux

This article will guide you on how to install SQL tools on Redhat.

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