linux_wiki:grub2 [Owlbear Consulting

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====== Grub2 ======

**General Information**

Grub2 is used by RHEL/CentOS 7. It is quite different from Grub1. 

**Checklist**
  * Distro(s): Any
  * Other: Grub2

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====== Grub2 Files ======

Grub2 files:
  * /etc/default/grub => grub2 variables (can be edited, then menus re-generated)
    * **Typically, this is the only file you should be hand editing.**

  * grub2 generated menu (**do not edit directly; changes will be over-written**)
    * EL7: /boot/grub2/grub.cfg
    * Ubuntu: /boot/grub/grub.cfg 

  * /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 the default the system will boot to**
<code bash>
grub2-editenv list

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

\\
**View list of available 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>

\\
**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

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

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