RedHat Enterprise Linux Server Backup and Restore for Disaster Recovery Purpose

http://unixadminschool.com/blog/2015/07/redhat-enterprise-linux-server-backup-and-restore-for-disaster-recovery-purpose

This article is to explain the procedure to backup and restore a RHEL server for the purpose of Disaster recovery situation. For the purpose of simplification we will  be backing of the entire server data into an additional disk of the same server. But in real time scenarios, the backup should be taken to a remote server / tape/ backup device. 

Assumptions that we made for this procedure:

1. We are going to backup and restore the data to same server with same disk configuration.

2. We are not making any change to partition table or MBR ( Master Boot Record) , and so we are not taking backup of the MBR.

3. If you want to restore data to a complete new disk, you must recreate the partition table as per the original server, otherwise the server wont’ boot.

4. We are assuming that our Linux server having only non-LVM root partition. If your server is having LVM root file system, then the procedure will change a little bit before you start the restore.

Backup Procedure

Step 1:  Take note of below below configuration information and files,

# cat /etc/fstab
LABEL=/ / ext3 defaults 1 1
LABEL=/boot1 /boot ext3 defaults 1 2
LABEL=/data /data ext3 defaults 0 0
tmpfs /dev/shm tmpfs defaults 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
LABEL=SWAP-sda5 swap swap defaults 0 0
/dev/sda6 /backup-files ext3 defaults 0 0

# fdisk -l
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 1925 15358140 83 Linux
/dev/sda3 1926 3200 10241437+ 83 Linux
/dev/sda4 3201 4864 13366080 5 Extended
/dev/sda5 3201 3391 1534176 82 Linux swap / Solaris
/dev/sda6 3392 4864 11831841 83 Linux

Step  2: Backup all the partitions of RHEL server

Note: In this example, we will use the /dev/sda6 partition to save backup files, and we assume that /dev/sda6 is mounted on /backup-files.

Step 2a: Bootup your system into Single User Mode

Single user mode can be accessed by appending an “S“, “s“, or “single” to the kernel command line in GRUB. Likewise, a “3” can be used to boot to runlevel 3. To do this, restart the system and when the GRUB splash screen presents itself:

1. Select/highlight the desired kernel using the up/down arrow keys.
2. Press the letter a to modify the kernel line.
3. On the new screen, press the spacebar to add a space, then type the letter s and press Enter.

This will boot the system into single user mode, i.e. the boot process will stop immediately after execution of rc.sysinit and present a root BASH shell.

Step 2b; Use “dump” command to backup the contents of the partitions

If the system has been running for a long time, it is advisable to run e2fsck on the partitions before backup.  Please note that “dump command ”  should) not be used at heavily loaded and mounted filesystem as it could backup corrupted version of files.

If you want to take the Backups into Local Disk i.e . /dev/sda6

# dump -0uf /backup-files/sda1.dump /dev/sda1
# dump -0uf /backup-files/sda2.dump /dev/sda2
# dump -0uf /backup-files/sda3.dump /dev/sda3

If you want to the backups into remote server

Start the network services in single user mode using the below command

#/sbin/service network restart

Dump the local disk date to remote server i.e. bkpserver.igurkul.com

# dump -0u -f – /dev/sda1 | ssh root@bkpserver.igurkul.com dd of=/tmp/sda1.dump

Simulate the Disk Failure Scenario 

             We can simulate a disk failure by using fdisk to delete the partitions that have been backed up.

Restore the Backup data and test the Server

Step 1:  Bootup your system into Rescue Mode using below procedure

• Get the first disc of installation media for the major version of the installed Red Hat Enterprise Linux (or the binary DVD). 
• Note: boot.iso can be used for booting instead of the installation media, but the installation tree (including rescue programs) is still needed in HTTP server or anywhere.

Follow the instructions given by the rescue boot process:

• Boot the system from boot disc
• once the system has successfully booted from the ISO image and Red Hat Enterprise Linux boot screen will appear.     

      Type: linux rescue without the quotes, and hit enter at the prompt.

    [F1-Main] [F2-Options] [F3-General] [F4-Kernel] [F5-Rescue]

    boot: linux rescue

• When prompted for language, keyboard, and network, provide the pertinent information for the system
• Select: Continue when prompted to allow the rescue environment to mount Red Hat Enterprise Linux installation under /mnt/sysimage directory.
• Run the command chroot /mnt/sysimage and then chroot to your system image.

Step 2: Rebuild sda1/sda2/sda3/sda4/sda5 by using the fdisk command

Notice: When rebuild all the partitions, please use the same “Start” and “End” number as before.  

Step 3: Create file systems

Create New filesystem on top of sda1, sda2, sda3 and sda5 by using the mkfs command, as shown below.

Note: DO NOT format /dev/sda6 because it saves backup files.

# mkfs.ext3 /dev/sda1
# mkfs.ext3 /dev/sda2
# mkfs.ext3 /dev/sda3

Step 4: Re-label all the partitions

So they match how they were before. This step is important for the restore to work.

# e2label /dev/sda1 /boot1
# e2label /dev/sda2 /
# e2label /dev/sda3 /data
# mkswap -L SWAP-sda5 /dev/sda5

Step 5: Prepare the working directories and mount the target filesystems

# mkdir /mnt/sda1
# mount -t ext3 /dev/sda1 /mnt/sda1
# mkdir /mnt/sda2
# mount -t ext3 /dev/sda2 /mnt/sda2
# mkdir /mnt/sda3
# mount -t ext3 /dev/sda3 /mnt/sda3
# mkdir /backup-files
# mount -t ext3 /dev/sda6 /backup-files

Step 6: Restore the data

To Restore data from local disks:

# cd /mnt/sda1
# restore -rf /backup-files/sda1.dump
# cd /mnt/sda2
# restore -rf /backup-files/sda2.dump
# cd /mnt/sda3
# restore -rf /backup-files/sda3.dump

To restore data from Remote Server  i.e. bkpserver.igurkul.com

login into bkpserver.igurkul.com, and restore sda1 from sda1.dump file:

# cd /mnt/sda1

# /usr/bin/ssh restore -r -f bkpserver.igurkul.com:/tmp/sda1.dump

Step 7: Reboot the server to verify that it is booting properly

Procedure to backup and Restore the Linux Partition Table:

Procedure A:    Using  the “sfdisk” command:

Run the command below to backup the partition table on device /dev/sda to /root/partition-sda.img:

# sfdisk -d /dev/sda > /root/partition-sda.img

You should then copy /root/partition-sda.img to some other storage, for example a portable USB disk.

If the partition is damaged and needs to be restored from backup, please connect your USB disk to the server and boot the server with installation media and enter rescue mode.
Do not mount the root partition at this time – select “Skip” when the system asks if you want to mount the root partition on /mnt/sysimage.

Create a temporary directory, for example /mnt/temp and mount the filesystem of your USB device which contains your backup. For example:

# mkdir /mnt/temp
# mount /dev/sdb1 /mnt/temp/
# cd /mnt/temp/
where /dev/sdb1 is the file system of the USB disk. After that, run:

# sfdisk /dev/sda < /mnt/temp/partition-sda.img

To verify that the partition table has been restored, run:

fdisk -l /dev/sda

Procedure B: Using  the “dd” command:

The MBR (Master Boot Record) occupies the first 446 bytes of the disk while the partition table occupies the next 64 bytes. We can use “dd” to dump the range from 447 – 510 bytes in the first sector.

 For example, if the harddisk is /dev/sda, then run the command below:

# dd if=/dev/sda of=/root/partition-sda.img bs=1 count=64 skip=446

You should then copy /root/partition-sda.img to some other storage, for example a portable USB disk.  If the partition is damaged and needs to be restored from backup, please connect your USB disk to the server and boot the server with installation media and enter rescue mode. 
Do not mount the root partition at this time – select “Skip” when the system asks if you want to mount the root partition on /mnt/sysimage.

Create a temporary directory, for example /mnt/temp and mount the filesystem of your USB device which contains your backup. For example:

# mkdir /mnt/temp
# mount /dev/sdb1 /mnt/temp/
# cd /mnt/temp/
where /dev/sdb1 is the file system of the USB disk. After that, run:

# dd if=/mnt/temp/partition-sda.img of=/dev/sda bs=1 count=64 seek=446

To verify that the partition table has been restored, run:

# fdisk -l /dev/sda

SubNetCalc 2.4.2 (Command-Line Subnet Address Calculator)

http://linuxg.net/install-subnetcalc-on-ubuntu/

As you may know, SubNetCalc is a useful command-line app for calculating IPv4 or IPv6 subnet address calculator. For given ip addresses, masks or prefix lentgs, the app calculates network addresses, broadcast addresses, the max number of hosts and host address ranges, the output being displayed in colors.

The latest version available is SubNetCalc 2.4.2, which has been recently released, bringing fixes.

Installation instructions:

Up to date packages are available via some third party PPA, so installing the software on Ubuntu 15.04 Vivid Vervet, Ubuntu 14.10 Utopic Unicorn, Ubuntu 14.04 Trusty Tahr, Ubuntu 12.04 Precise Pangolin and derivative systems like Linux Mint 17.2 Rafaela, Linux Mint 17.1 Rebecca, Linux Mint 17 Qiana, Linux Mint 13 Maya, Pinguy OS 14.04, Elementary OS 0.3 Freya, Elementary OS 0.2 Luna, Deepin 2014, Peppermint 6, Peppermint 5, LXLE 14.04 and Linux Lite 2 is easy. You need to add the PPA to your system, update the local repository index and install the subnetcalc package:

$ sudo add-apt-repository ppa:dreibh/ppa
$ sudo apt-get update
$ sudo apt-get install subnetcalc

Optional, to remove subnetcalc, do:

$ sudo apt-get remove subnetcalc

Setting Up ‘XR’ (Crossroads) Load Balancer for Web Servers on RHEL/CentOS

http://www.tecmint.com/setting-up-xr-crossroads-load-balancer-for-web-servers-on-rhel-centos/

Crossroads is a service independent, open source load balance and fail-over utility for Linux and TCP based services. It can be used for HTTP, HTTPS, SSH, SMTP and DNS etc. It is also a multi-threaded utility which consumes only one memory space which leads to increase the performance when balancing load.

Let’s have a look at how XR works. We can locate XR between network clients and a nest of servers which dispatches client requests to the servers balancing the load.

If a server is down, XR forwards next client request to the next server in line, so client feels no down time. Have a look at the below diagram to understand what kind of a situation we are going to handle with XR.

Install XR Crossroads Load Balancer

There are two web-servers, one gateway server which we install and setup XR to receive client requests and distribute them among the servers.

XR Crossroads Gateway Server : 172.16.1.204
Web Server 01 : 172.16.1.222
Web Server 02 : 192.168.1.161

In above scenario, my gateway server (i.e XR Crossroads) bears the IP address 172.16.1.222, webserver01 is172.16.1.222 and it listens through port 8888 and webserver02 is 192.168.1.161 and it listens through port5555.

Now all I need is to balance the load of all the requests that receives by the XR gateway from internet and distribute them among two web-servers balancing the load.

Step1: Install XR Crossroads Load Balancer on Gateway Server

1. Unfortunately, there isn’t any binary RPM packages available for crosscroads, the only way to install XR crossroads from source tarball.

To compile XR, you must have C++ compiler and Gnu make utilities installed on the system in order to continue installation error free.

# yum install gcc gcc-c++ make

Next, download the source tarball by going to their official site (https://crossroads.e-tunity.com), and grab the archived package (i.e. crossroads-stable.tar.gz).

Alternatively, you may use following wget utility to download the package and extract it in any location (eg:/usr/src/), go to unpacked directory and issue “make install” command.

# wget https://crossroads.e-tunity.com/downloads/crossroads-stable.tar.gz
# tar -xvf crossroads-stable.tar.gz
# cd crossroads-2.74/
# make install

Install XR Crossroads Load Balancer

After installation finishes, the binary files are created under /usr/sbin/ and XR configuration within /etc namely “xrctl.xml”.

2. As the last prerequisite, you need two web-servers. For ease of use, I have created two pythonSimpleHTTPServer instances in one server.

To see how to setup a python SimpleHTTPServer, read our article at Create Two Web Servers Easily Using SimpleHTTPServer.

As I said, we’re using two web-servers, and they are webserver01 running on 172.16.1.222 through port 8888and webserver02 running on 192.168.1.161 through port 5555.

XR WebServer 01

XR WebServer 02

Step 2: Configure XR Crossroads Load Balancer

3. All requisites are in place. Now what we have to do is configure the xrctl.xml file to distribute the load among the web-servers which receives by the XR server from the internet.

Now open xrctl.xml file with vi/vim editor.

# vim /etc/xrctl.xml

and make the changes as suggested below.

1.0<94> encoding=<94>UTF-8<94>?>


true
/tmp


Tecmint


172.16.1.204:8080
tcp
0:8010
yes
0
0

0 0

172.16.1.222:8888

192.168.1.161:5555

Configure XR Crossroads Load Balancer

Here, you can see a very basic XR configuration done within xrctl.xml. I have defined what the XR server is, what are the back end servers and their ports and web interface port for the XR.

4. Now you need to start the XR daemon by issuing below commands.

# xrctl start
# xrctl status

Start XR Crossroads

5. Okay great. Now it’s time to check whether the configs are working fine. Open two web browsers and enter the IP address of the XR server with port and see the output.

Verify Web Server Load Balancing

Fantastic. It works fine. now it’s time to play with XR.

6. Now it’s time to login into XR Crossroads dashboard and see the port we’ve configured for web-interface. Enter your XR server’s IP address with the port number for web-interface you have configured in xrctl.xml.

http://172.16.1.204:8010

XR Crossroads Dashboard

This is what it looks like. It’s easy to understand, user-friendly and easy to use. It shows how many connections each back end server received in the top right corner along with the additional details regarding the requests receiving. Even you can set the load weight each server you need to bear, maximum number of connections and load average etc..

The best part is, you actually can do this even without configuring xrctl.xml. Only thing you have to do is issue the command with following syntax and it will do the job done.

# xr --verbose --server tcp:172.16.1.204:8080 --backend 172.16.1.222:8888 --backend 192.168.1.161:5555

Explanation of above syntax in detail:

1. –verbose will show what happens when the command has executed.
2. –server defines the XR server you have installed the package in.
3. –backend defines the webservers you need to balance the traffic to.
4. Tcp defines it uses tcp services.

For more details, about documentations and configuration of CROSSROADS, please visit their official site at:https://crossroads.e-tunity.com/.

XR Corssroads enables many ways to enhance your server performance, protect downtime’s and make your admin tasks easier and handier.