Testing yum -y upgrade and yum -y update Separately
Before Upgrade
OS Version: centos5.5
Kernel Version: 2.6.18-194.el5
Simple configuration file modifications were made before the upgrade.
After yum -y upgrade
OS Version: centos5.7
Kernel Version: 2.6.18-194.el5
System and software configurations remain unchanged.
After yum -y update
OS Version: centos5.7
Kernel Version: 2.6.18-238.el5
System and software configuration files are updated.
Conclusion:
yum -y update
Upgrades all packages, changes software settings and system settings. Both the system version and kernel are upgraded.
yum -y upgrade
Upgrades all packages without changing software settings and system settings. The system version is upgraded, but the kernel remains unchanged.