The Fedora "mkinitrd" can read certain defaults from "/etc/sysconfig/mkinitrd", but this file is not really documented in the basic setup. If your normal mkinitrd is missing certain modules, you can use the following syntax to cause them to be created as part of the initrd.

MODULES: This environment variable can be set to a space-separated list of modules to load into the initrd. For example: MODULES="aes sha256 cbc". This is like specifying "--with", so see the man page for mkinitrd for more information.

PROBE: If set to "yes", mkinitrd will try to auto-detect certain settings including: rootfs, rootopts, rootdev, devname, majmin, dev, swsuspdev, and additionally will detect root on NFS, swap on LVM, and modular root file-systems.

PREMODS: Modules to be loaded as if the command-line --preload had been specified. See the "--preload" section of the mkinitrd manual page.

DMDEVS: This is listed in the same section as being able to be configured, but even by looking at the code and searching the web I wasn't able to figure out what this was supposed to be used for.
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