If you need to automatically rebuild all initrds for all installed kernels:
rpm -qa | grep kernel | grep -v headers | grep -v tools | sed 's/^kernel\-//g' | xargs -i dracut -v -f /boot/initramfs-{}.img {}
Oh, and while we're at it, the same for Ubuntu
update-initramfs -u -k all
It's this now:
dracut –regenerate-all -v -f