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How to edit the grub on RHEL 7 ?

The default boot loader in Redhat enterprise Linux 7 is grub2(GRand Unified Bootloader2).  The  “grub2” supports almost all the operating systems. The main configuration file for grub2 is /boot/grub2/grub.cfg.  If you want to make any configuration change on the grub menu , you need to use the utility called “grub2-mkconfig” . If you manually edit the grub.cfg using vi or vim, grub will be corrupted. grub2-mkconfig read the /etc/default/grub file and it displays on the terminal. Here we will see that how we can update/edit the grub.cfg using grub2-mkconfig utility.

1. Login to the RHEL 7 system .

2. Check the current grub2 settings . (Look at only for timed-out )

[root@UnixArena-RHEL7 ~]# cat /boot/grub2/grub.cfg  |grep timeout
if [ x$feature_timeout_style = xy ] ; then
  set timeout_style=menu
  set timeout=5
# Fallback normal timeout code in case the timeout_style feature is
  set timeout=5
[root@UnixArena-RHEL7 ~]#

Here is the default “grub”

[root@UnixArena-RHEL7 ~]# cat /etc/default/grub
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/root crashkernel=auto  rd.lvm.lv=rhel/swap vconsole.font=latarcyrheb-sun16 vconsole.keymap=us rhgb quiet"
GRUB_DISABLE_RECOVERY="true"
[root@UnixArena-RHEL7 ~]#

3. Edit the /etc/default/grub and set the “GRUB_TIMEOUT=15” .

[root@UnixArena-RHEL7 ~]# grep TIMEOUT  /etc/default/grub
GRUB_TIMEOUT=15
[root@UnixArena-RHEL7 ~]#

4. Run the grub2-mkconfig to view the current settings. It will not going to over-write the  existing configuration.It just like a dry run before committing the changes.

[root@UnixArena-RHEL7 ~]# grub2-mkconfig
Generating grub configuration file ...

5. Commit the changes to grub.cfg.

[root@UnixArena-RHEL7 ~]# grub2-mkconfig > /boot/grub2/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-3.10.0-123.el7.x86_64
Found initrd image: /boot/initramfs-3.10.0-123.el7.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-48314559db574327888736c3905146eb
Found initrd image: /boot/initramfs-0-rescue-48314559db574327888736c3905146eb.img
done
[root@UnixArena-RHEL7 ~]#

6. Let me verify the grub.cfg file. We can  see that timeout has been changed from 5 to 15 seconds.

[root@UnixArena-RHEL7 ~]# cat /boot/grub2/grub.cfg |grep timeout
if [ x$feature_timeout_style = xy ] ; then
  set timeout_style=menu
  set timeout=15
# Fallback normal timeout code in case the timeout_style feature is
  set timeout=15
[root@UnixArena-RHEL7 ~]#

7. Let me reboot my system and verify it .

Timeout
Timeout

We have successfully edited the grub.cfg using grub2-mkconfig utility. The same way you can edit the other settings too if required.

Hope this article is informative to you .

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