Install and Configure DHCP Server on CentOS 7 / RHEL 7

DHCP (Dynamic Host Configuration Protocol) is a network protocol used for dynamically assigning IP addresses for computers attached to the network. Standard port used for DHCP service: 67(UDP).

In this tutorial we will launch dhcp server on CentOS 7 / RHEL 7 and define example subnets.
Continue reading “Install and Configure DHCP Server on CentOS 7 / RHEL 7”

How to Manually Extend Cinder Volumes Group in OpenStack

openstack
Cinder Volumes group is a block storage based on LVM (Logical Volume Manager) volume group, usually situated in Controller node in OpenStack cloud. It provides persistent block storage for runtime instances.

During typical packstack installation Cinder Volumes group size is determined in answer file (insert file) by following parameter:

CONFIG_CINDER_VOLUMES_SIZE=20G

If the Cinder Volumes group size we chose upon packstack installation turns out to be insufficient to create new volumes, we can attach additional physical volume on Controller node to the existing Cinder Volumes group and extend it with the new physical volume to gain more space.
Continue reading “How to Manually Extend Cinder Volumes Group in OpenStack”

How To Reset Forgotten Root Password on RedHat 7 / CentOS 7

RedHat 7 / CentOS 7 unlike previous version 6, doesn’t provide the ability to reset / recover root password in signle-user mode any more. This situation takes place, because RedHat 7 / CentOS 7 uses systemd manager instead of sysVinit / upstart and both systemd targets: rescue.target and emergency.target require root password. That’s why in RedHat 7 / CentOS 7 we need installation disk to boot from.
Continue reading “How To Reset Forgotten Root Password on RedHat 7 / CentOS 7”

How To Reset Forgotten Root Password on RedHat 6 / CentOS 6

RedHat 6 / CentOS 6 system gives us the opportunity to reset root password in case we forget it, on condition that we have a direct access to the machine on which we want to reset root password. Password can be reset after booting the system into single-user mode.

Steps:

1. Reboot the system

2. At the screen: “Booting Red Hat Enterprise Linux…” or “Booting CentOS…” press any key to display GRUB menu.
Continue reading “How To Reset Forgotten Root Password on RedHat 6 / CentOS 6”