How to clear UDID mismatch in VCS Cluster(online thinrclm udid_mismatch)?

In this post, we are going to see How to clear UDID mismatch in VCS Cluster(online thinrclm udid_mismatch)?

We are doing this activity in VCS 3 node cluster with Linux environment.

In VCS Cluster udid_mismtach might lead to disk failures.

Error:
#vxdisk -l alldgs list | grep udid
emc4_184a auto:cdsdisk   -   (vxfendg)   online thinrclm udid_mismatch
emc4_184b auto:cdsdisk   -   (vxfendg)   online thinrclm udid_mismatch
emc4_184c auto:cdsdisk   -   (vxfendg)   online thinrclm udid_mismatch
Resolution:

Verify the fencing disks using “vxdisk -l alldgs list | grep udid” command to know whether it’s having udid_mismatch or not. Using that command we came to know all the three fencing disks has udid_mismatch.

#vxdisk -l alldgs list | grep udid
emc4_184a auto:cdsdisk   -   (vxfendg)   online thinrclm udid_mismatch
emc4_184b auto:cdsdisk   -   (vxfendg)   online thinrclm udid_mismatch
emc4_184c auto:cdsdisk   -   (vxfendg)   online thinrclm udid_mismatch

Verify the all 3 disks udid and udid_asl values are different or not.

Using below command we found that, udid & udid_mismatch values are different.

#vxdisk -v list emc4_184a | grep -i udid 
flags:   online  ready  private autoconfig udid_mismatch coordinator thinrclm 
udid:   EMC%5FSYMMETRIX%5FF000197500111%5F110184A008 
tag:     udid_asl=EMC%5FSYNNETRIX%5F000195702690%5F9002F64000

How to clear UDID mismatch in VCS Cluster(online thinrclm udid_mismatch)?

 

Like the above use the same command to check udid & udid_mismatch values for another two disks(emc4_184b, emc4_184c)

Then check whether the fencing keys on the coordinator disks are fine using below command

#vxfenadm -s /dev/vx/rdmp/emc4_184a

All the fencing keys are looking good on the coordinator disks.

How to clear UDID mismatch in VCS Cluster(online thinrclm udid_mismatch)?

Finally, command to clear the udid_mismatch flag from all 3 fencing disks.

#vxdisk updateudid emc4_184a

#vxdisk updateudid emc4_184b

#vxdisk updateudid emc4_184c

Confirm udid_mismatch has been cleared or not using the below command.

#vxdisk -o alldgs list | grep -i udid

How to install Docker EE in RHEL7

How to install Docker EE in RHEL7

Will see How to install Docker EE in RHEL7 in this post. We have other steps as well on our blog to install the Docker in Linux.

It’s a container virtualization technology and more efficient in the deploy an application.

We have two option to install the Docker EE in RedHat Linux.

  1. Yum Repository: Create/ Enable YUM Repository and install using that. this is the recommended one to install/ upgrade a package in Linux.
  2. RPM: We have to download and install manually. This will be useful to install when the system doesn’t have internet access.

Requirement:

RHEL 7.1 or Higher Operating System.

overlay2 or device-mapper storage driver(direct-lvm mode for production environment)

Yum repository.

Disable SELinux in IBM Power Systems before install/ Upgrade

Enabling YUM Repository for Docker EE Installation:

Browse “https://store.docker.com/my-content” and login. You should at least registered for the trail.

Once logged in, Click “Setup” to get the URL to enable the repository.

Copy the URL from “Copy and paste this URL to download your Edition:” and save it for later use.

You will use this URL to create the variable called “DOCKERURL“.

Use the below command to remove existing docker repo.

[root@localhost ~]# rm /etc/yum.repos.d/docker*.repo

Save the copied URL in the environmental variable(DOCKERURL). Replace with URL where “<DOCKER-URL>” is mentioned in below command.

#export DOCKERURL="<DOCKER-EE-URL>"

Than now store the variable(DOCKERURL) in yum variable /etc/yum/vars

[root@localhost ~]# sudo -E sh -c 'echo "$DOCKERURL/rhel" > /etc/yum/vars/dockerurl'

Now store the OS version in /etc/yum/vars/dockerosversion:

[root@localhost ~]# sh -c 'echo "7.3" > /etc/yum/vars/dockerosversion'

Then install the required packages yum-utils, device-mapper-persistent-data and lvm2

[root@localhost ~]# yum -y install yum-utils device-mapper-persistent-data lvm2

Now will enable extras RHEL repository and This will ensure the access to container-selinux which is package required by “Docker-EE” and the below command will be used in all Architecture except IBM Power Systems.

[root@localhost ~]# yum-config-manager --enable rhel-7-server-extras-rpms
Loaded plugins: product-id

For IBM Power System use the below command:

#yum-config-manager --enable extras
#subscription-manager repos --enable=rhel-7-for-power-le-extras-rpms
#yum makecache fast
#yum -y install container-selinux

Add the Docker EE repository using below command.

[root@localhost ~]# yum-config-manager --add-repo "$DOCKERURL/rhel/docker-ee.repo"

Installing Docker EE in RedHat Linux:

Now using the docker repository will install the Docker-EE by executing below command.

[root@localhost ~]# yum install docker-ee

Note: If the above command failed for “container-selinux” dependency. Then we should install the container-selinux and below two are dependency packages for container-selinux

policycoreutils.2.5-11.el7 Click here to download

policycoreutils-python (This will be available in your OS packages list)

Now again try to install the docker-ee using yum.

Start the docker using systemctl.

[root@localhost ~]# systemctl start docker

Now we completed docker-ee installation.

To verify Docker-EE installed correctly, use the hello-world image. This will download a test image and run it in a container. Will give you the information.

[root@localhost ~]# docker run hello-world
Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
9bb5a5d4561a: Pull complete
Digest: sha256:f5233545e43561214ca4891fd1157e1c3c563316ed8e237750d59bde73361e77
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
(amd64)
3. The Docker daemon created a new container from that image which runs the
executable that produces the output you are currently reading.
4. The Docker daemon streamed that output to the Docker client, which sent it
to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
$ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:
https://hub.docker.com/

For more examples and ideas, visit:
https://docs.docker.com/engine/userguide/

 

So, Finally we completed the Docker installation.

Refernce: docs.docker.com

List of tools in Kali Linux

List of tools in Kali Linux

We have more than 500 List of tools in Kali Linux and below are the categories of available tools with numbers.

List of tools in Kali Linux:
  1. Exploitation tools (21)
  2. Forensics (23)
  3. Hardware hacking (6)
  4. Information Gathering (69)
  5. Maintaining Access (18)
  6. Password Attacks (41)
  7. Reporting Tools (10)
  8. Reverse Engineering (11)
  9. Sniffing/ Spoofing (32)
  10. Stress testing (14)
  11. Uncategorized (10)
  12. Vulnerability Analysis (29)
  13. Web Applications (44)
  14. Wireless Attacks (53)

Will see briefly in future posts about these categorized tools.

Thanks for your support. Comments are always welcome to provide you the better experience on learning technologies.

Reference: Kali Docs

What is Kali Linux

What is Kali Linux

What is Kali Linux?

Will see what is Kali Linux in this post. Nowadays Linux is everywhere in use in the form of Smartphones, Cars, Supercomputers, Robots and Home appliances, etc…

This belongs to Debian distribution and its developed towards Penetration testing, Security auditing, Forensics and reverse engineering.

It’s funded, developed and maintained by Offensive Security(leading information security company).

Features of Kali:
  1. Free Operating system
  2. Open source Git tree
  3. More than 600 penetration tools
  4. FHS Compliant
  5. Wide range wireless support
  6. Developed in a secure environment
  7. Custom kernel, patched for injection
  8. Customizable
  9. GPG Signed packages and repositories
  10. ARMEL and ARMHF Support
  11. Multi-language support

 

Reference:  Kali Docs

VNC installation in rhel7

VNC installation in rhel7

Will see how to install VNC installation in rhel7 in this post.

VNC will help us to share the desktop with GUI and for that in both server VNC Server/client should be installed.

Before installing VNC, we should install GNOME in RHEL7.

Installing VNC Server:

Use yum to install the VNC Server. Before that yum should be configured on your server.

[root@localhost ~]# yum -y install vnc*

Configuring VNC Server in RHEL7:

To configure the port and user, need to copy vncserver@.service from /lib/systemd/system/ to /etc/systemd/system/.

5900 is default listening port.

[root@localhost ~]# cp /lib/systemd/system/vncserver@.service /etc/systemd/system/

Now open the /etc/systemd/system/vncserver@.service file using vi editor and locate <USER> replace with your respective username which you are going to use for remote access.

[root@localhost ~]# vi /etc/systemd/system/vncserver\@.service

[Unit]
Description=Remote desktop service (VNC)
After=syslog.target network.target

[Service]
Type=forking
# Clean any existing files in /tmp/.X11-unix environment
ExecStartPre=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'
ExecStart=/usr/sbin/runuser -l <USER> -c "/usr/bin/vncserver %i"
PIDFile=/home/<USER>/.vnc/%H%i.pid
ExecStop=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'

[Install]
WantedBy=multi-user.target

Updated:

[Unit]
Description=Remote desktop service (VNC)
After=syslog.target network.target

[Service]
Type=forking
# Clean any existing files in /tmp/.X11-unix environment
ExecStartPre=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'
ExecStart=/usr/sbin/runuser -l root -c "/usr/bin/vncserver %i"
PIDFile=/home/root/.vnc/%H%i.pid
ExecStop=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'

[Install]
WantedBy=multi-user.target

Now enable the port over the firewall to allow VNC access using firewalld.

[root@localhost ~]# firewall-cmd --permanent --add-port=5900/tcp
success
[root@localhost ~]# firewall-cmd --reload
success

Than start VNC server

[root@localhost ~]# vncserver

Now it will prompt to set the password to access the desktop.

You will require a password to access your desktops.
Password:
Verify:
xauth: file /root/.Xauthority does not exist

New 'localhost.localdomain:1 (root)' desktop is localhost.localdomain:1

Creating default startup script /root/.vnc/xstartup
Starting applications specified in /root/.vnc/xstartup
Log file is /root/.vnc/localhost.localdomain:1.log

Now reload the systemctl daemon

[root@localhost ~]# systemctl daemon-reload

 

And start and enable the service in this run level permanently using below command.

[root@localhost ~]# systemctl start vncserver@.service

[root@localhost ~]# systemctl enable vncserver@.service

Finally, we completed all the configuration on Linux Machine and to check this open VNC on a windows machine and try to access using our Linux machine IP Address and port number

192.168.1.104:5900

and it will prompt for the password, provide de password to access the Linux machine.

Reference: itzgeek

About Ubuntu 18.04

About Ubuntu 18.04

We are going to see about Ubuntu 18.04 Operating system, which is going to release on 26th April 2018.

Features of Ubuntu 18.04:

GNOME 3.28 Desktop

Ubuntu 18.04 going to give us a new experience.

Kernel 4.15

Ubuntu has scheduled to come up with new kernel version for every 6 months. Now Kernel 14.5 going to give more power to Ubuntu.

Xorg

Xorg is the default one for Ubuntu and from next release, TLS will come with both traditional Xorg graphics and Way-land based stack. It will give better performance to software like Skype, hangout and it will recover better from the shell crashes.

Minimal installation method

From ubuntu 18.04 we have an option to install with minimal packages and it will give us a desktop environment.Note: This is not a replacement for existing Ubuntu minimal ISO.

Ubuntu will collect data

As per Ubuntu announcement, canonical will collect some user data like system configuration and installed packages and this option will be available in the installer.

New installer

Subiquity will be the default one in an upcoming release and this will give new look to server installation.

Color emojis

Its important in messaging and communication. It will display colorful emojis in all the apps.

Faster boot time

Using systemd it will speed up the booting time.

zstd compression algorithm

Using facebook’s zstd compression algorithm it speeds up the Ubuntu installation process.

refrence: Ubuntu wiki

Logrotate in Linux

Will see how to configure/ use logrotate in Linux

to compress, move, delete or mail log files at the periodic time. By doing this will keep away the filesystem from the filesystem full issue.

Setting up and Manage logrotate in Linux:

In Linux/ Unix, environment /var/log is most important directory and it keeps all the activities as a log.

System administrators will use the logs to analyze any issue’s.

/var/log keeps lots of log files and here is the list.

[root@localhost ~]# ls /var/log
anaconda boot.log cron dmesg.old lastlog messages rhsm spooler tuned wtmp
audit btmp dmesg firewalld maillog ppp secure tallylog vmware-vmsvc.log

Installing logrotate:

Here I am going to use the yum package manager to install the logrotate.

[root@localhost ~]# yum install logrotate
Loaded plugins: product-id, search-disabled-repos, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Package logrotate-3.8.6-12.el7.x86_64 already installed and latest version
Nothing to do

look likes the package is already installed on my machine.

/etc/logrotate.conf is an important configuration file which contains all the configuration of log rotation and “include /etc/logrotate.d ” this line should be uncommented.

We have plenty of option in logrotate and below is that.

Will create /etc/logrotate.d/apache2.conf file and insert below content.

/var/log/apache/* {
weekly
rotate 5
size 25M
compress
delaycompress
}

Daily, Weekly, Monthly:  Based on this input the tool will rotate the logs.

rotate 5: This will keep the only 5 files and the old files will be removed.

size 25: log file minimum size for log rotation.

Compress & Delaycompress:  These are used to say that all are already rotated logs.

Now will do s test using the below command

[root@localhost ~]# logrotate -d /etc/logrotate.d/apache2.conf

 

 

Reference: Tecmint

About Veritas Cluster Server

About Veritas Cluster Server

We will start to learn About Veritas Cluster Server and how to manage it, in this post.

VCS is Symantec product and it connects single, multiple nodes under a framework to provide increased availability.

All the nodes will run using their own operating system.

VCS will connect the hardware’s using intelligent software to provide failover, load balancing, and control. when the monitored node or application failed, it will invoke another node or application which is hosted on a node within the cluster.

 

Reference: Symantec

RedHat Enterprise Linux 7 Installation

Will start learning RedHat Enterprise Linux 7 Installation in this post.

We have many new features in RHEL7 and simple differences in installation as well comparing to old version’s that we were given input like hostname, timezone, package selection, network configuration, kdump configuration, etc… in next next screen’s. But, in RHEL7 we can provide those details on a single screen. However all the remaining will be the same.

Using RHEL7 media boot the machine and you will receive a screen like below.

RedHat Enterprise Linux 7 Installation

Now select “Install Red Hat Enterprise Linux 7.3” to begin the installation.

As first part, you will get a screen that is asking you to select the System language and keyboard layout like below.

Then next you will get a screen which is the place to provide all information to install the operating system.

In this screen, you can provide all the information like Software selection, Partitioning in Installation destination tab, time zone, etc…

Now, will edit some of the configuration based on our requirement.

As first, here editing time zone part and selecting Asia/ Kolkata like below.

you can select the time zone in two ways one is by clicking on India over the map and another one is selecting Asia and Kolkata in the drop-down list.

And, click on the done button which is showing the left corner of upper on the screen to complete this part.

Likewise, we should click on done for each and every part.

Now, Click on “Software selection” tab to select packages

Will continue with default one which is “minimal installation”.

Based on the selected packages group, it will install the required packages.

Next, Click on “Installation destination” to create partitions.

We have two option at this stage. One is “Automatically configure partitions” and another one is “I will configure partitioning”

If you select the first option, it will create the partition automatically with LVM and if you select the second option, we need to provide the partition details manually.

Here let us see how to create manual partitions.

Once you selected the second option, you will get a screen asking for partition type Standard, LVM, etc…

select on Standard one to create a normal partition.

and click done to go next screen of partition creation.

It will ask for the mount point with size like below. Below filesystem, creation is compulsory while doing manual partitioning.

  1. boot – Contains bootloader and partition information
  2. / (root)
  3. swap – Virtual memory

Like above will create the three mandate partition to continue the installation.

and click done to go back to the main screen.

and it will ask our confirmation to write the partition changes on the disk. Click “Accept Changes”.

And now, click “Begin Installation” to start the package installation.

In package installation screen, we can see that password has not been set still. So, click on “Root Password” to set the root password. and click done.

See the screen after root password has been assigned.

Once installation completed, will ask for the reboot. Click on “Reboot” button to complete the installation.

We compeleted RHEL7 installation successfully.

 

 

 

 

 

How to boot with an old kernel version in RHEL7

In this post, will see how to boot with an old kernel version in RHEL7. When the updated kernel not suitable for your application or OS not booting.

There might be a requirement to upgrade the operating system or kernel version alone in Linux/Unix machines.

In such case, we might face issue with the upgraded kernel version. To, fix that, follow the below steps.

By default, /etc/default/grub file has entry called GRUB_DEFAULT=saved.

[root@localhost ~]# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=auto rhgb quiet"
GRUB_DISABLE_RECOVERY="true"

This entry instructs the system which kernel will be used to load the operating system by checking the saved_entry in the grubenv file, which is in /boot/grub2/grubenv.

[root@localhost ~]# cat /boot/grub2/grubenv
# GRUB Environment Block
saved_entry=0
#########################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################[root@localhost ~]#

So we can set the default kernel by editing /boot/grub2/grubenv file or using grub2-set-default command.

To do this, select the old kernel to boot the operating system from grub splash screen.

How to boot with old kernel in RHEL7

And use the grub2-set-default command to change the kernel.

Before changing we should remember that, the always updated kernel will be on top and will use numeric value “0” to mention this kernel in command

The old one will be available by next. So, to mention the old kernel will use numeric value “1”. Like this numeric will start from 0.

/boot/grub2/grub.cfg file contains Kernel and initramfs image details.

below command will show us the list of the kernel installed on this machine.

[root@localhost ~]# awk -F\' '$1=="menuentry " {print $2}' /etc/grub2.cfg
Red Hat Enterprise Linux Server (3.10.0-693.17.1.el7.x86_64) 7.3 (Maipo)
Red Hat Enterprise Linux Server (3.10.0-514.el7.x86_64) 7.3 (Maipo)
Red Hat Enterprise Linux Server (0-rescue-ffc8e857b7b84166b88e7b0522c168a4) 7.3 (Maipo)

By default, saved_entry will be the latest one, which you updated.

Using below command will change the default kernel as the old one to boot the operating system without any issue.

[root@localhost ~]# grub2-set-default 1

and now check again in /boot/grub2/grunenv file to verify the default kernel.

[root@localhost ~]# cat /boot/grub2/grubenv | grep saved
saved_entry=1

Now you can see in above screen that the old kernel is set as default one.

Now rebuild the /boot/grub2/grub.cfg file using grub2-mkconfig -o command.

Use the below command in BIOS based machines:

[root@localhost ~]# grub2-mkconfig -o /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-693.17.1.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-693.17.1.el7.x86_64.img
Found linux image: /boot/vmlinuz-3.10.0-514.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-514.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-ffc8e857b7b84166b88e7b0522c168a4
Found initrd image: /boot/initramfs-0-rescue-ffc8e857b7b84166b88e7b0522c168a4.img
done

Use below command for UEFI based machines:

[root@localhost ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

finally, restart the machine and check whether the machine booting using old kernel.

reference: Red Hat Document