网上的说法：
yum -y update
升级所有包同时也升级软件、系统版本和系统内核
yum -y upgrade
只升级所有包和系统版本，不升级软件和系统内核

实际测试结果：
使用了Centos 7.9测试
分别执行命令yum update -y 和yum upgrade -y后
内核从 

[root@ansible ~]# uname -r
3.10.0-1160.45.1.el7.x86_64

变成​ 

[root@ansible ~]# uname -r
3.10.0-1160.49.1.el7.x86_64

说明内核都升级了，而且是升级到相同版本。

3.官网说法：

If run without any packages, update will update every currently installed package.  If one or more packages or package globs are specified, Yum will only update the  listed
packages.  While updating packages, yum will ensure that all dependencies are satisfied. (See Specifying package names for more information) If the packages or globs speci-
fied match to packages which are not currently installed then update will not install them. update operates on groups, files, provides and filelists just like the "install"
command.

If  the  main  obsoletes configure option is true (default) or the --obsoletes flag is present yum will include package obsoletes in its calculations - this makes it better
for distro-version changes, for example: upgrading from somelinux 8.0 to somelinux 9.

Note that "update" works on installed packages first, and only if there are no matches does it look for available packages. The difference is most noticeable  when  you  do
"update foo-1-2" which will act exactly as "update foo" if foo-1-2 is installed. You can use the "update-to" if you’d prefer that nothing happen in the above case.
yum upgrade：
Is the same as the update command with the --obsoletes flag set. See update for more details.

版权声明：本文为博主原创文章，未经博主允许不得转载。

LINUX