Linux升級命令有兩個分別是yum upgrade和yum update, 這個兩個命令是有區別的:
yum -y update
升級所有包同時也升級軟件、系統版本和系統內核
yum -y upgrade
只升級所有包和系統版本，不升級軟件和系統內核
這個說法是錯誤的！！！兩個命令是一樣的！
yum update：
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.