Booting into Rescue Mode
Rescue mode provides the ability to boot a small Red Hat Enterprise
Linux environment entirely from CD-ROM, or some other boot method,
instead of the system's hard drive.
As the name implies, rescue mode is provided to rescue you from
something. During normal operation, your Red Hat Enterprise Linux system
uses files located on your system's hard drive to do everything — run
programs, store your files, and more.
However, there may be times when you are unable to get Red Hat
Enterprise Linux running completely enough to access files on your
system's hard drive. Using rescue mode, you can access the files stored
on your system's hard drive, even if you cannot actually run Red Hat
Enterprise Linux from that hard drive.
To boot into rescue mode, you must be able to boot the system using one of the following methods[1]:
- By booting the system from an installation boot CD-ROM.
- By booting the system from other installation boot media, such as USB flash devices.
- By booting the system from the Red Hat Enterprise Linux CD-ROM #1.
Once you have booted using one of the described methods, add the keyword
rescue as a kernel parameter. For example, for an x86 system, type the following command at the installation boot prompt:
linux rescue
You are prompted to answer a few basic questions, including which
language to use. It also prompts you to select where a valid rescue
image is located. Select from Local CD-ROM, Hard Drive, NFS image, FTP, or HTTP.
The location selected must contain a valid installation tree, and the
installation tree must be for the same version of Red Hat Enterprise
Linux as the Red Hat Enterprise Linux disk from which you booted. If you
used a boot CD-ROM or other media to start rescue mode, the
installation tree must be from the same tree from which the media was
created. For more information about how to setup an installation tree on
a hard drive, NFS server, FTP server, or HTTP server, refer to the
earlier section of this guide.
If you select a rescue image that does not require a network
connection, you are asked whether or not you want to establish a network
connection. A network connection is useful if you need to backup files
to a different computer or install some RPM packages from a shared
network location, for example.
The following message is displayed:
The rescue environment will now attempt to find your Linux installation and mount it under the directory /mnt/sysimage. You can then make any changes required to your system. If you want to proceed with this step choose 'Continue'. You can also choose to mount your file systems read-only instead of read-write by choosing 'Read-only'. If for some reason this process fails you can choose 'Skip' and this step will be skipped and you will go directly to a command shell.
If you select , it attempts to mount your file system under the directory
/mnt/sysimage/. If it fails to mount a partition, it notifies you. If you select , it attempts to mount your file system under the directory /mnt/sysimage/, but in read-only mode. If you select , your file system is not mounted. Choose if you think your file system is corrupted.
Once you have your system in rescue mode, a prompt appears on VC (virtual console) 1 and VC 2 (use the Ctrl-Alt-F1 key combination to access VC 1 and Ctrl-Alt-F2 to access VC 2):
sh-3.00b#
If you selected to mount your partitions automatically and they were mounted successfully, you are in single-user mode.
Even if your file system is mounted, the default root partition while
in rescue mode is a temporary root partition, not the root partition of
the file system used during normal user mode (runlevel 3 or 5). If you
selected to mount your file system and it mounted successfully, you can
change the root partition of the rescue mode environment to the root
partition of your file system by executing the following command:
chroot /mnt/sysimage
This is useful if you need to run commands such as
rpm that require your root partition to be mounted as /. To exit the chroot environment, type exit to return to the prompt.
If you selected , you can still try to mount a partition or LVM2 logical volume manually inside rescue mode by creating a directory such as
/foomount -t ext3 /dev/mapper/VolGroup00-LogVol02 /foo
In the above command,
/foo/dev/mapper/VolGroup00-LogVol02ext2, replace ext3 with ext2.
If you do not know the names of all physical partitions, use the following command to list them:
fdisk -l
If you do not know the names of all LVM2 physical volumes, volume
groups, or logical volumes, use the following commands to list them:
pvdisplayvgdisplaylvdisplay
From the prompt, you can run many useful commands, such as:
ssh,scp, andpingif the network is starteddumpandrestorefor users with tape drivespartedandfdiskfor managing partitionsrpmfor installing or upgrading softwarejoefor editing configuration filesNoteIf you try to start other popular editors such asemacs,pico, orvi, thejoeeditor is started.
5.2.1. Reinstalling the Boot Loader
In many cases, the GRUB boot loader can mistakenly be deleted, corrupted, or replaced by other operating systems.
The following steps detail the process on how GRUB is reinstalled on the master boot record:
- Boot the system from an installation boot medium.
- Type
linux rescueat the installation boot prompt to enter the rescue environment. - Type
chroot /mnt/sysimageto mount the root partition. - Type
/sbin/grub-install /dev/hdato reinstall the GRUB boot loader, where/dev/hdais the boot partition. - Review the
/boot/grub/grub.conffile, as additional entries may be needed for GRUB to control additional operating systems. - Reboot the system.
Linux – LVM Free Training / Tutorial
Link - https://www.unixarena.com/2013/08/linux-lvm-free-training-tutorial.html/
In UnixArena Tutorial series, Here we are going to see about Linux’s Logical volume manager which is default volume manage on all of the Linux flavors which are available now a days in market.In this tutorial, you will learn how to integrate, operate, LVM on Redhat Linux. This training provides instruction on operational management procedures for LVM and you will learn how to install and configure LVM and how to manage disks,volume groups, and volumes by using the command line.The advantage of using LVM is that space can be added to or removed from logical volumes as needed on demand basis.For your kind information , I am not going to explain LVM theory in depth on this tutorial.Prerequisites:1.Skills:Knowledge of LINUX/UNIX system administration.2.Lab: VM RHEL 6 or physical machine with RHEL 6.0Logical Volume Manager objects:There are several Logical Volume Manager objects that must be understood before you can use the LVM to perform disk management tasks:Physical objects:Physical disks – Its a physical disk or LUN from storage.Disk groups:A disk group is a collection of physical disks that share a common configuration.Volumes:A volume is a virtual disk device that appears to applications, databases, and file systems like a physical disk partition, but does not have the physical limitations of a physical disk partition.
Overall LVM configuration Layout: 
- In this tutorial,we
are going to cover the below topics.In the end of these tutorials you
will very familiar with Logical volume manager and its operation.Your
suggestions are always welcome to improve this tutorial.
Topics Description Installation of LVM using YUM Step by Step Guide of LVM installation Disk operations on LVM LVM disk operations & Replacing Failed Disk Volume Group operations on LVM Step by Step Guide for volume group operation Volume creation and supported volume Layouts Step by Step Guide for Volume Creation Resizing a Logical volume How to resize the volume? Step by Step Guide Various LVM volume Attributes Discuss about various LVM attributes LVM Relayout – Volume conversion How to convert Existing volume layouts LVM snapshots Step by Step Guide for Volume snapshots
I am very sure you may gone through each and every topic and learned about LVM.
If you have any doubts,Please leave a comment.I will get back to you .
Visit World’s bests volume manage aka Veritas volume manager training/tutorial page from here. - Solaris Troubleshooting Skills
- https://www.thegeekdiary.com/a-beginners-guide-to-solaris-performance-monitoring-and-troubleshooting/ Solaris Boot Issue
Veritas Volume Manager (VxVM)
Private region data corruption recovery in VXVM
Plex Issue troubleshooting
Disk Issues in VxVM
Link - https://www.veritas.com/support/en_US/article.000080622
https://www.thegeekdiary.com/vxvm-tutorials-replacing-a-failed-disk-under-vxvm/
VXVM Guide from installation to configuration
Link - https://www.unixarena.com/2013/03/vxvm-veritas-volume-manager-training.html/
VCS (Veritas Cluster Server)
Architecture of VCS
Link - https://sort.veritas.com/public/documents/sf/5.0MP3/solaris/html/sfrac_admin/ch01s03s07s01.htm
https://www.veritas.com/content/support/en_US/doc/133049644-133049647-0/br74_v8608563-133049647
Troubleshooting in VCS
Link - https://www.unixarena.com/2014/07/troubleshoot-vcs-cluster-starting.html/
http://unixadminschool.com/blog/2011/11/vcs-starting-llt-gab-and-vcs-manually/
https://www.thegeekdiary.com/troubleshooting-solaris-ipmp/
https://vox.veritas.com/t5/Cluster-Server/VCS-Cluster-not-starting/td-p/617224
Performing activities on servers which are in VCS
Troubleshooting in issues for split brain
Link - https://www.thegeekdiary.com/vcs-cluster-101-communication-faults-jeopardy-split-brain-io-fencing/
https://www.veritas.com/support/en_US/doc/122863985-122863998-0/uxrt-72_v6528242-122863998
http://www.unixbabuforum.in/2013/10/WhatIsSplitBraininVCS.html
VCS Cluster - can perform activities for cluster build
Link - https://sort-static.veritas.com/public/documents/sfha/6.0/solaris/productguides/pdf/vcs_admin_60_sol.pdf
https://www.veritas.com/content/support/en_US/doc/ka6j0000000BNlfAAG
