Modify Linux kernel startup sequence

Linux changes the kernel startup sequence

1. Modify the kernel startup sequence of RHEL6/CentOS6

Check the /etc/grub.conf file to determine the system kernel status. According to the document, there are two kernel versions in the system, namely 2.6.32-573.18.1.el6.x86_64 and 2.6.32-431.23.3.el6.x86_64. Kernel versions are listed from top to bottom.

In the grub.conf file, you can decide which kernel version to use when the system starts by adjusting the default parameters. The default value is 0, which means the system will boot the latest kernel version. A value of 0 corresponds to the first kernel version listed in the grub.conf file, and so on. By changing the default value, you can easily switch the kernel version used when the system starts, ensuring that the system can start and run normally. This setting is very useful for system maintenance and troubleshooting, allowing the flexibility to adjust the kernel version as needed to meet the needs of the system. It should be noted that when modifying the grub.conf file

2. Modify the kernel startup sequence of RHEL7/CentOS7

1. Execute the following command to check how many cores there are in the system.

/boot/grub2/grub.cfg #(non-UEFI configurations) Note: Non-UEFI mode execution

/boot/efi/EFI/redhat/grub.cfg #(UEFI configurations)Note: UEFI mode execution

cat /boot/grub2/grub.cfg |grep menuentry

cat /boot/efi/EFI/redhat/grub.cfg |grep menuentry

2. Refer to the following command to configure booting from the default kernel. The kernel name is replaced based on the actual name found within the system. grub2-set-default 0

grub2-set-default “CentOS Linux (3.10.0-123.9.3.el7.x86_64) 7 (Core)”

grub2-set-default ‘Red Hat Enterprise Linux Server (3.10.0-1160.el7.x86_64) 7.9 (Maipo)’

3. Execute the following command to confirm that the configuration is successful.

grub2-editenv list

3. Modify the kernel startup sequence of centos8

1. View the default kernel

grubby –default-kernel

2. View all cores

grubby –info=ALL

3. Modify the default startup kernel

grubby –set-default /boot/vmlinuz-4.18.0-80.11.2.el8_0.x86_64

4. Ubuntu changes the kernel startup sequence

1. Check the startup sequence of the current kernel

cat /boot/grub/grub.cfg |grep menuentry

2. Modify grub file

Assuming that you want to modify the kernel startup to 3.13.0-166, modify the file /etc/default/grub

$
sudo vim /etc/default/grub

GRUB_DEFAULT=0 ##Modify to

GRUB_DEFAULT=”Advanced options for Ubuntu>Ubuntu, with Linux 4.4.0-31-generic”

3. Update the modified grub

update-grub

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