This page describes what problems can you have with sysfs
Sysfs can exist in two layouts. They are selected by the
config option. There are two main differences between them
- block devices are stored in the
/sys/blockor in the
- some devices live in the
/sys/devicesor in the
Although sysfs puts symlinks between old and new entries where possible, not all userspace can work with it.
Old nash on new layout
Nash is a small shell used on initrd/initramdisk-s to boot the system.
With the new sysfs layout (i.e. the option is question is not set) the old
tool (such as the one used in CentOS-5) cannot recognise the block devices. This results in
inability to mount the root filesystem.
To workaround the issue you should turn the deprecated layout on in .config and rebuild the kernel. All OpenVZ kernel prior to 2.6.27 (and including one) are build with this layout.
New udev on old layout
With the old sysfs layout (i.e. with the option set to
y) the udev used in newer
distros (such as FC12) prints a warning about the old layout used.
Currently this doesn't bring any problems to user, but in future situation may change.
To workaround the issue you should turn the deprecated layout off in .config and rebuild the kernel.
In 2.6.32 OpenVZ kernel there's a boot option called
old_sysfs which turns the
deprecated layout on at boot. This one is off by default, so if you're using the 2.6.32 kernel
on old distro, you should probably boot it with the option in question set.