Fedora 34 : The grubby command line tool.

The grubby command line tool used to configure bootloader menu entries across multiple architectures.

All information can be find with the manual linux commands:

[root@desk mythcat]# man grubby

Let's see some simple examples.

This command can list all the installed kernel:

[root@desk mythcat]# grubby --info=ALL | grep ^kernel
kernel="/boot/vmlinuz-5.12.10-300.fc34.x86_64"
kernel="/boot/vmlinuz-5.12.8-300.fc34.x86_64"
kernel="/boot/vmlinuz-0-rescue-fc76db87af524282b0c7e05a9c5d18f4

To get more details on the installed kernel:

[root@desk mythcat]# grubby --info="/boot/vmlinuz-$(uname -r)"
index=0
kernel="/boot/vmlinuz-5.12.10-300.fc34.x86_64"
args="ro resume=/dev/mapper/fedora-swap rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet splash 
acpi_osi=Linux"
root="/dev/mapper/fedora-root"
initrd="/boot/initramfs-5.12.10-300.fc34.x86_64.img"
title="Fedora (5.12.10-300.fc34.x86_64) 34 (MATE-Compiz)"
id="fc76db87af524282b0c7e05a9c5d18f4-5.12.10-300.fc34.x86_64"

Add selinux=0 to the kernel with this tool:

[root@desk mythcat]# grubby --update-kernel ALL --args selinux=0

Let's see if is added:

[root@desk mythcat]# grubby --info="/boot/vmlinuz-$(uname -r)"
index=0
kernel="/boot/vmlinuz-5.12.10-300.fc34.x86_64"
args="ro resume=/dev/mapper/fedora-swap rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet splash 
acpi_osi=Linux selinux=0"
root="/dev/mapper/fedora-root"
initrd="/boot/initramfs-5.12.10-300.fc34.x86_64.img"
title="Fedora (5.12.10-300.fc34.x86_64) 34 (MATE-Compiz)"
id="fc76db87af524282b0c7e05a9c5d18f4-5.12.10-300.fc34.x86_64"

Remove the selinux=0 option from the bootloader with this tool:

[root@desk mythcat]# grubby --update-kernel ALL --remove-args selinux

Let's see if is removed:

[root@desk mythcat]# grubby --info="/boot/vmlinuz-$(uname -r)"
index=0
kernel="/boot/vmlinuz-5.12.10-300.fc34.x86_64"
args="ro resume=/dev/mapper/fedora-swap rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap rhgb quiet splash 
acpi_osi=Linux"
root="/dev/mapper/fedora-root"
initrd="/boot/initramfs-5.12.10-300.fc34.x86_64.img"
title="Fedora (5.12.10-300.fc34.x86_64) 34 (MATE-Compiz)"
id="fc76db87af524282b0c7e05a9c5d18f4-5.12.10-300.fc34.x86_64"

You can see is removed.

Get the index number of all the installed kernels:

[root@desk mythcat]# grubby --info=ALL | grep -E "^kernel|^index"
index=0
kernel="/boot/vmlinuz-5.12.10-300.fc34.x86_64"
index=1
kernel="/boot/vmlinuz-5.12.8-300.fc34.x86_64"
index=2
kernel="/boot/vmlinuz-0-rescue-fc76db87af524282b0c7e05a9c5d18f4"

I can set the default kernel by index with this tool:

[root@desk mythcat]# grubby --set-default-index=1

These are not all features of this command.