Posts filed under ‘Linux’

Using RHEL Subscription in Virtual Data Center.

Hi All

Recently I got an opportunity to work in a project that involved with RHEL 7.4 Deployment. This projects required several VM’s as it was intended to use Kubernetes on RHEL. In this post I am focusing on how to register the RHEL VM’s using the  RHEL Virtual DataCenter Subscription licenses. In my case VMware was being used as the Hypervisor.

Once you procure the required license and RH Customer portal access is ready. You need to configure virt-who on one of the VM’s(This VM does not need to be the production VM , as I prefered in my case). Below steps will outline the process.

  •  On the newly created VM , you need to install the virt-who (using the RHEL Media as the REPO. This VM will be the virt-who host).
  • Run the command subscription-managaer register
  • Run the command subscription-manager idenetity.(Note down the value for Org ID as you will use it in the below steps)
  •  Browse to /etc/virt-who.d .
  • In order to create the configuration file you could use the URL as it provide a step-by-step wizard to create the required entries.
  • Copy the the contents to a file in the folder mentioned in step-4
  • name of the file should match with the configuration name in the file created by the wizard.(File extension should be .conf)
  • Edit the virt-who file /etc/sysconfig/virt-who and add the below
  • Run the command virt-who  –one-shot(This will verify the configuration parameter’s are correct)
  • Then start the virt-who services(systemctl start virt-who)
  • Run the command on the virt-who VM
    subscription-manager attach –auto
  • On the remaining VM’s run
    subscription-manager register
    subscription-manager  attach –auto. (You don’t need to configure virt-who services on the other VM’s)

    That’s it login to RHEL portal and verify that you could see the Hypervisor and the VM’s

NOTE1: When creating the virt-who.conf you need to provide a username & password who have access to your VCenter server .This user needs only a Read-Only Permission

NOTE2: For best practices you could configure 2 VM’s with virt-who services.

NOTE3: You should be able to see the ESXi host and the VM’s in the URL - You need to ensure that the proper subscription has been entitled to both.



April 8, 2018 at 3:03 pm Leave a comment

How to use the RHEL / CentOS Media as the Repository.

When you don’t have an active subscription with RHN , you will not be ale to install any packages via yum command. In that case the only way to overcome this situation is to use your installation CD or the binary CD you have downloaded from the RHEL website.

#mount /dev/sr0 /mnt

2.Copy the media.repo file from the root of the mounted directory to /etc/yum.repos.d/ and set the permissions to something sane,

#cp /mnt/media.repo /etc/yum.repos.d/rhel7dvd.repo
#chmod 644 /etc/yum.repos.d/rhel7dvd.repo

3.Edit the new repo file, changing the gpgcheck=0 setting to 1 and adding the following 3 lines

baseurl=file:///mnt/  –> Here provide the mount point you used in Step1—>


# yum clean all
# subscription-manager clean

5. Once the above steps are completed you could begin with your familiar yum installation.

NOTE: I have not tried these steps in CentOS , but I believe it is portable and applicable.


March 6, 2018 at 10:39 am Leave a comment

How to check the Physical Status of Network Card in Linux

On Linux servers the status of NIC cards cannot be determined via the ipconfig command alone , in that case you could use one of the below commands to get the required infromation

# mii-tool eth0

# cat /sys/class/net/eth0/operatestate

# ethtool eth0

# ip link ls dev eth0



Good Luck .





March 14, 2017 at 12:53 pm Leave a comment

Cannot retreive metalink for repository epel


If some body receive the above error first you should check the connectivity and firewall issues and still if the problem persist.

Sample Error

metalink_error_1You should edit the  /etc/yum/repos.d/CentOS-base.repo or epel.repo

and change all the URL’s that pointing to https  to  http  save the file

Restart the yum process.

Hint –  Always start the yum process with debug switch ,which helps us in troubleshooting –  ( yum -d6 update)




December 17, 2013 at 9:02 am Leave a comment

CentOS yum error 14: PCYURL ERROR 7 – “Failed to connect to 2a02:2498:1:3d:5054:ff:fed3:e9

Dear Folks

When you are trying to update the system with yum , you may come with the above error , In which the yum tool is trying to resolve the mirrorlist url’s via IPv6 Address.

update_error_1What happens here is that when the yum is unable to resolve and reach the IPv4 address it end up trying the IPv6.

Hence if you face the similar issue , I would advice you to go through the below steps and identify the real cause.

Step 1 –  Check whether you could resolve the URL  ( via nslookup or dig and get an IPV6 address.

If  you fail at the above step check for the DNS configurations in /etc/resolv.conf

Step 2 –   Check with the firewall team that they have allowed the ports 80 , 443 ,21   from the linux server.

In my case it was the firewall blockage.

I have been googling  regarding the same issue and found out that several articles pointing to IPV6   saying that to disable it. Hence you could try that as a  last resort , if the above steps did not succeed.

– edit  the  /etc/sysconfig/network and the /etc/sysconfig/network-scripts/ifcfg-eth* files  to  disable any entries pointing to IPv6

– edit /etc/sysctl.conf and put the below entries and reboot the server

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 =

– disable the ip6tables.

Good Luck

December 17, 2013 at 8:50 am Leave a comment

How to install only Security Updates on CentOS

Hi Folks

These commands are useful when you want to install  only the sceurity updates  in order to meet any compliance such as PCI

First you need to install the  security plugin for the Yum

#yum install yum-security

Once it installed

#yum  list-security —–> To check the security updates avaialable

#yum update –security  ——> To install  only the Securuty Updates.

Good Luck..

February 3, 2013 at 8:16 am Leave a comment

How to idenitfy a process ID using the TCP Port

Recently i had an issue  in one of my linux machines, where I was unable to start the acronis_agent service which listens on TCP Port ;

Later I realised  that already so many processes are listening on the TCP port.

To check the open connection for a TCP  port

# netstat -an | grep 9876   ( In my case acronis_agent uses TCP 9876)

It was showing multiple connections………….

To check the PID(Process ID ) for all the sessions  which are using the port 9876

#lsof -i TCP:9876

finally you could use  the  almighty command “kill -9 PID”  …. boom everything became normal.

October 23, 2011 at 1:57 pm 1 comment

Linux Guide

Anyy body looking for a brief documentation on  RHEL can make use of the below files , which I made for my linux class

Introduction to Linux


October 23, 2011 at 11:09 am Leave a comment

Sendmail STARTTLS: read error=generic SSL error

I was having an issue with my sendmail server where I receives this error which will cause the sendmails logs grow drastically and fill the /var partition.

further it will stop the mail flow ( when /var partition is full)

So i wrote this bash script which does the following;

– look for this error in the maillog

– when it finds it will kill the sendmail process which is causing the  sendmail to log multiple     entries in the logfile and will restart the sendmail and syslog daemons.

anybody is welcome to give their comment on improvements or any drawbacks on this script good luck…….

LAST=’last message’
SSL=”STARTTLS: read error=generic SSL error (0)”

cp /var/log/maillog /home/muralee/log_check/maillog
grep “STARTTLS: read error=generic SSL error (0)”   /home/muralee/log_check/maillog |awk ‘/sendmail/ {print $5}’ | tr -d [digit:]”sendmail[]” > records.txt
#grep “STARTTLS: read error=generic SSL error (0)”   /home/muralee/maillog.1 |awk ‘/sendmail/ {print $5}’ | tr -d [digit:]”sendmail[]” > records.txt
results=$(wc -l records.txt | awk ‘/records/ {print $1}’)
if [[ $results -eq 0 ]];then
echo “Sendmail is Fine”
if [[ $results -ne 0 ]]; then
pkill sendmail
/etc/init.d/sendmail restart
/etc/init.d/syslog restart
echo “Problem resolved”
cat /dev/null > records.txt

September 20, 2011 at 12:14 pm Leave a comment

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