CentOS 7 switching boot kernel and switching boot mode explanation

centos7 switch boot kernel

Note: If necessary, it is recommended to execute yum update -y first to upgrade all packages

Note:

1. The CentOS I used for testing is version 7.2, with the default minimal installation and the system kernel is 3.10.0-327.

2. After upgrading to 4.4.x, if you use the yum update -y command to upgrade the software at will, the 3.10.0-693 kernel package in CentOS7.4 will continue to be installed and will be the first startup item.

3. After each yum update -y , you need to use the grub2-set-default 0 command to modify the default kernel startup item. 0 is the first item, 1 is the second item, and so on. Check GRU

1. View the current system kernel

uname -r

3.18.6-2.el7.centos.x86_64

View the list of available kernels

awk -F\' '$1=="menuentry " {print i++ " : " $2}' /etc/grub2.cfg

The results are as follows:

0 : CentOS Linux (3.18.6-2.el7.centos.x86_64) 7 (Core)

1 : CentOS Linux (3.10.0-514.el7.x86_64) 7 (Core)

2 : CentOS Linux (0-rescue-05653d304ed443db9b60529d6cf7d242) 7 (Core)

2. View the current default kernel startup item

grub2-editenv list

The results are as follows:

saved_entry=0

That is, the default kernel loaded when the system is currently started is CentOS Linux (3.18.6-2.el7.centos.x86_64) 7 (Core)

3. Change the default startup kernel item

grub2-set-default 1

Check the default kernel boot entry again and find that the saved_entry field changes to 1

4. Restart the system

reboot

View the current system kernel

uname -r

3.10.0-514.el7.x86_64

You can see that the kernel of the current system has been changed

centos7 switch boot mode

1. CentOS has only two startup modes:

multi-user.target: analogous to runlevel 3 # Command line mode graphical.target: analogous to runlevel 5 # Graphics mode

Check the vim /etc/inittab file, there is a command to change the mode

2. View the current mode:

systemctl get-default 

3. Change the startup mode

Start with command:

systemctl set-default multi-user.target

Start in graphical mode:

systemctl set-default graphical.target

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