How to fix Yum or rhn_check when it hangs at “Setting up Package Sacks”

Issue

• Executing yum or rhn_check hangs at Setting up Package Sacks

# rhn_check -vvvv
[.. SNIP..]
Setting up Package Sacks

# yum repolist -v
[.. SNIP..]
# yum update -v -v
Loading "rhnplugin" plugin
Loading "fastestmirror" plugin
Config time: 0.098
Setting up Package Sacks

• Issue can also occur when yum repolist hangs on the message:

Updating Subscription Management repositories.