Find out short living UDP requests (e.g. DNS requests) with auditd

Think about the following situation. You need to modify the address of your internal DNS server and therefore you need to change /etc/resolv.conf on all your Linux boxes. It might be that this change will not be recognized by every service running on your Linux box. Oracle for instance is a good example where you have to restart your database after such change because Oracle loads the DNS information once the database is started. So Oracle would querry your old DNS server IP unless you restart the database.

There are several ways to find out which process requests your old DNS server. Here I will explain how to utilize auditd on Red Hat derivatives to find out short living DNS requests via UDP. Continue reading Find out short living UDP requests (e.g. DNS requests) with auditd

RHEL 7 supports online disk resize with active partition tables on disk

One of the interesting features in RHEL 7 is the fact that it supports online disk re-sizing even if there is an active partitioning table on the disk. This feature is interesting in case you want to re-size your virtual disk. You can do this online for example in VMWare. If you have a LVM partition on the disk you want to resize then you need to perform the steps described in this article from Red Hat.

In order to resize online a partition which is in use please observe the following steps:

Continue reading RHEL 7 supports online disk resize with active partition tables on disk

Policy based routing on RHEL

If you configure multiple network cards in your RHEL machine with more than one gateway then you can use “policy based routing” to configure the network traffic in a way where the traffic will leave the same interface where the traffic came from.

This procedure is described in this Red Hat KCS article.

I also created a Puppet module to configure policy based routing on RHEL 6 / 7. Currently this module does not handle Bond or VLAN tagged interfaces. You can find my module here.

Satellite 6 => Configure multiple network cards with static IP’s during host provisioning on VMWare

Satellite 6 offers the possibility to provision a host with multiple network cards, however an issue is faced when using VMWare in conjuction with Satellite 6 and you want to provision multiple network interfaces with static IP addresses.

What happens is that after the provisioning of a virtual machine is complete, multiple network cards are added, but only the primary interface (which is used for PXE / DHCP during installation) is configured correctly.

I created a workaround to get this working. I described this solution in an official Red Hat KCS article which is now verified by Red Hat Engineering and published to the public. You can find this article here.