Linux: Installing a different kernel - Revision history

Michael: /* Downgrading a Kernel */

2013-07-19T10:41:27Z

Downgrading a Kernel

Michael: /* Downgrading a Kernel */

2013-07-19T10:41:17Z

Downgrading a Kernel

Michael: /* Downgrading a Kernel */

2013-07-19T10:38:19Z

Downgrading a Kernel

Michael: /* grub.conf */

2013-07-19T10:36:18Z

grub.conf

Michael: Created page with "== Kernels == The best version of the kernel to have for general use is the newest one. It is important to keep your system up todate. This will make sure that all packages..."

2013-07-19T10:34:54Z

Created page with "== Kernels == The best version of the kernel to have for general use is the newest one. It is important to keep your system up todate. This will make sure that all packages..."

New page

== Kernels ==

The best version of the kernel to have for general use is the newest one. It is important to keep your system up todate. This will make sure that all packages will work together and have the latest security updates.

However in certain cases it is required to change the kernel version. Usually this will be the the previous kernel as the newest one isn't yet supported.

Installing a different kernel version does not remove the current one. They will both remain installed. The Grub boot loader controls which kernel is booted.

== Installing a new Kernel ==

To install a new kernel using yum:

<syntaxhighlight>
yum update kernel
</syntaxhighlight>

The new kernel will be installed and grub updated to boot by default the new kernel.

== Downgrading a Kernel ==

Note: Downgrading a kernel can result in problems, due to software and package dependencies. Do this only if needed.

<syntaxhighlight>
yum downgrade kernel
</syntaxhighlight>

This will not resolve any dependencies. All packages must be manually downgraded.

Grub.conf will be updated, but the defalt kernel will still be the newest version. This must be changed manually to force it to be booted by default.

== grub.conf ==

Grub is the Grand Unified BootLoader. Grub configures how the system is booted.

To change the settings for a one off boot, the settings can be manually changed at the splash screen. Hit any key and GRUB will give you a list of options one for each kernel.

To permanently change the default boot kernel,the grub.conf fille must be edited.

grub.conf is located in the /etc folder and will look something like this:

<syntaxhighlight>
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You have a /boot partition. This means that
# all kernel and initrd paths are relative to /boot/, eg.
# root (hd0,0)
# kernel /vmlinuz-version ro root=/dev/mapper/VolGroup-lv_root
# initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.32-358.14.1.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-358.14.1.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=VolGroup/lv_root KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
initrd /initramfs-2.6.32-358.14.1.el6.x86_64.img
title CentOS (2.6.32-358.el6.x86_64)
root (hd0,0)
kernel /vmlinuz-2.6.32-358.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_LVM_LV=VolGroup/lv_root KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet
initrd /initramfs-2.6.32-358.el6.x86_64.img

</syntaxhighlight>

Each kernel will be listed on a separate line. To change the default kernel you can change the default variable.

In the example above this has been set to one. This will boot the SECOND kernel (it starts at 0) - so in this case it boots 2.6.32-358.el6.x86_64.

← Older revision		Revision as of 10:41, 19 July 2013
Line 21:		Line 21:

	Note: I'm confirming the exact command to install an old package as yum may require an additional flag.		Note: I'm confirming the exact command to install an old package as yum may require an additional flag.
		+
	Note: Downgrading a kernel can result in problems, due to software and package dependencies. Do this only if needed.		Note: Downgrading a kernel can result in problems, due to software and package dependencies. Do this only if needed.

← Older revision		Revision as of 10:41, 19 July 2013
Line 20:		Line 20:
	== Downgrading a Kernel ==		== Downgrading a Kernel ==

		+	Note: I'm confirming the exact command to install an old package as yum may require an additional flag.
	Note: Downgrading a kernel can result in problems, due to software and package dependencies. Do this only if needed.		Note: Downgrading a kernel can result in problems, due to software and package dependencies. Do this only if needed.

@@ Line 21: / Line 21: @@
 Note:  Downgrading a kernel can result in problems, due to software and package dependencies.  Do this only if needed.
 <syntaxhighlight>
-yum downgrade kernel
+yum install <kernel-version>
 </syntaxhighlight>
@@ Line 29: / Line 37: @@
 Grub.conf will be updated, but the defalt kernel will still be the newest version.  This must be changed manually to force it to be booted by default.
 == grub.conf ==

@@ Line 37: / Line 37: @@
 To change the settings for a one off boot, the settings can be manually changed at the splash screen.  Hit any key and GRUB will give you a list of options one for each kernel.
-To permanently change the default boot kernel,the grub.conf fille must be edited.
+To permanently change the default boot kernel,the grub.conf file must be edited.  grub.conf is located in the /etc folder and will look something like this:
 <syntaxhighlight>
@@ Line 69: / Line 67: @@
 In the example above this has been set to one.  This will boot the  SECOND kernel (it starts at 0) - so in this case it boots 2.6.32-358.el6.x86_64.