Red Hat Enterprise Linux extends the FHS structure slightly to accommodate special files.
Most files pertaining to RPM are kept in the /var/lib/rpm/ directory. For more information on RPM, refer to the chapter titled Package Management with RPM in the Red Hat Enterprise Linux System Administration Guide.
The /var/spool/up2date/ directory contains files used by Red Hat Update Agent, including RPM header information for the system. This location may also be used to temporarily store RPMs downloaded while updating the system. For more information about Red Hat Network, refer to the documentation online at https://rhn.redhat.com/.
Another location specific to Red Hat Enterprise Linux is the /etc/sysconfig/ directory. This directory stores a variety of configuration information. Many scripts that run at boot time use the files in this directory. Refer to Chapter 4 The sysconfig Directory for more information about what is within this directory and the role these files play in the boot process.
Finally, one more directory worth noting is the /initrd/ directory. It is empty, but is used as a critical mount point during the boot process.
Do not remove the /initrd/ directory for any reason. Removing this directory causes the system to fail to boot with a kernel panic error message.