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选题[tech]: 20230816 How to Change the default kernel in RHEL 8 and 9
sources/tech/20230816 How to Change the default kernel in RHEL 8 and 9.md
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[#]: subject: "How to Change the default kernel in RHEL 8 and 9"
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[#]: via: "https://www.2daygeek.com/changing-default-kernel-rhel-8-rhel-9/"
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[#]: author: "Rasool Cool https://www.2daygeek.com/author/rasool/"
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[#]: collector: "lujun9972"
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[#]: translator: " "
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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How to Change the default kernel in RHEL 8 and 9
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======
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Usually a Linux system boots with the latest installed kernel, which is set by default. It keeps maximum 3 recent versions of Linux Kernel boot entries.
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Let’s say you’ve done the yum update, and a new kernel is installed as part of this update. This prevents the application from starting as this kernel is incompatible with the application.
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To temporarily fix this problem, you should continue to boot the system into an older kernel.
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In this article, we’ll show you how to set old kernel version as default on RHEL 8 and RHEL 9 systems using grubby utility.
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* [**How to Upgrade from RHEL 7 to RHEL 8**][1]
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### What is grubby
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grubby is a command line tool used for updating and displaying information about the boot loaders configuration files across multiple architectures.
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### Checking currently booted kernel
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You can check booted/loaded kernel using **uname command** as shown below.
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```
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uname -r
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4.18.0-477.13.1.el8_8.x86_64
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```
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### Listing the Default Kernel
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To verify the default kernel version using grubby, run:
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```
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grubby --default-kernel
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/boot/vmlinuz-4.18.0-477.13.1.el8_8.x86_64
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```
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To obtain the index number of the current default kernel, run:
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```
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grubby --default-index
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0
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```
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### Checking installed kernels
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To check list of installed kernels, run:
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Let’s explain the below output. The latest kernel installed will have the **entry-index** of **`0`** , the next **older kernel** version will get **`1`** , second older kernel version will get **`2`** , and the **rescue kernel** will get an entry-index of **`3`**.
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```
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grubby --info=ALL | egrep -i 'index|title'
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index=0
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title="Red Hat Enterprise Linux (4.18.0-477.13.1.el8_8.x86_64) 8.8 (Ootpa)"
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index=1
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title="Red Hat Enterprise Linux (4.18.0-425.19.2.el8_7.x86_64) 8.7 (Ootpa)"
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index=2
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title="Red Hat Enterprise Linux (4.18.0-425.13.1.el8_7.x86_64) 8.7 (Ootpa)"
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index=3
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title="Red Hat Enterprise Linux (0-rescue-13iu76884ec5490puc67j8789s249b0c) 8.2 (Ootpa)"
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```
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### Changing default kernel Boot entry
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This can be done in two ways either using **`'kernel filename'`** or **`'kernel entry-index'`**. We will be going to set ‘ **index=1 (4.18.0-425.19.2.el8_7.x86_64)** ‘ as default kernel due to application dependency.
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```
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Syntax:
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grubby --set-default [kernel-filename]
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```
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```
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grubby --set-default /boot/vmlinuz-4.18.0-425.19.2.el8_7.x86_64
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OR
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grubby --set-default vmlinuz-4.18.0-425.19.2.el8_7.x86_64
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```
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To change the default kernel boot entry using kernel entry-index:
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```
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Syntax:
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grubby --set-default-index=[kernel-entry-index]
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```
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```
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grubby --set-default-index=1
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```
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### Rebooting the system
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Reboot the system to check whether the old kernel is persistent or not.
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```
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reboot
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or
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init 6
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```
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### Verifying the Changes
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Let’s check if the kernel added in the previous step has taken effect or not. Yes, it booted with older kernel **`'N-1'`** as expected.
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```
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uname -r
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4.18.0-425.19.2.el8_7.x86_64
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grubby --default-kernel
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/boot/vmlinuz-4.18.0-425.19.2.el8_7.x86_64
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```
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To check detailed information of all kernel, run:
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```
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grubby --info=ALL
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```
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![][2]
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##### Wrapping Up
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In this tutorial, we’ve shown you how to set old kernel version as default on RHEL 8 and RHEL 9 systems using grubby utility.
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If you have any questions or feedback, feel free to comment below.
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--------------------------------------------------------------------------------
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via: https://www.2daygeek.com/changing-default-kernel-rhel-8-rhel-9/
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作者：[Rasool Cool][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.2daygeek.com/author/rasool/
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[b]: https://github.com/lujun9972
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[1]: https://www.2daygeek.com/upgrading-from-rhel-7-to-rhel-8/
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[2]: https://www.2daygeek.com/wp-content/uploads/2023/06/changing-default-kernel-rhel-8-rhel-9-1024x494.jpg
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