linux_wiki:modify_the_system_bootloader [Owlbear Consulting

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====== Modify The System Bootloader ======

**General Information**

Managing Grub2; the system boot loader. 

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===== Grub2 Structure =====

**Grub2 files:**
  * /boot/grub2/grub.cfg => grub2 generated menu (**do not edit directly**)
  * /etc/default/grub => grub2 variables (**can be edited**, then menus re-generated)
  * /etc/grub.d/ => individual files used internally by grub2

**Grub2 symlinks**
  * /etc/grub2.cfg => symlink to /boot/grub2/grub.cfg
  * /etc/sysconfig/grub => symlink to /etc/default/grub

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===== Grub2 Commands =====

**View the active kernel that is default for system boot**
<code bash>
grub2-editenv list

saved_entry=CentOS Linux (3.10.0-327.3.1.el7.x86_64) 7 (Core)
</code>

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**View list of kernels displayed on grub menu**
<code bash>
grep ^menuentry /boot/grub2/grub.cfg 

menuentry 'CentOS Linux (3.10.0-327.3.1.el7.x86_64) 7 (Core)' ...
menuentry 'CentOS Linux (3.10.0-327.el7.x86_64) 7 (Core)' ...
menuentry 'CentOS Linux (0-rescue-15bdd5425c924660bb6c9979dc071d56) 7 (Core)' ...
</code>

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**Set default kernel for grub system boot (permanent)**
<code bash>
grub2-set-default 'CentOS Linux (3.10.0-327.3.1.el7.x86_64) 7 (Core)'
</code>
  * Note: Copy/paste including the single quotes from the "grep ^menuentry" output

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**Changing Grub2 settings**
  - Edit grub2 variables<code bash>vim /etc/default/grub</code>
  - After making changes, re-generate the grub2 menu<code bash>grub2-mkconfig -o /boot/grub2/grub.cfg</code>

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