[blfs-support] Filesystem recovery messages at every boot

Pierre M.R. prousselet at sfr.fr
Sat May 11 23:08:30 PDT 2013


Bruce Dubbs wrote:
> I do think there is a bug in umount.
Some changes in mount/umount introduced in utils-linux-2.21.1 are 
documented in the code. There are useful comments in 
libmount/src/context_umount.c,context_mount.c, tab.c
>
> I edited my mountfs script to add some debugging output below the line:
>
> umount -a -d -r -t notmpfs,nosysfs,nodevtmpfs,noproc
>
Starting from utils-linux>=2.21.1 the root fs is ignored by umount -a 
(and by mount -a)
> In other words mount -r does not work for the root file system any more.
the umount of root fs doesn't fail, it is IGNORED.
>   
>    It seems a little strange to me that the kernel uses /dev/root because
> that entry is not in the /dev devtmpfs.  Also, I don't understand the
> rootfs in /proc/mounts.  It does not get changed when remounting / read
> only.  This condition is normally only present for the fraction of a
> second between stopping mountfs and the halt/reboot scripts.
from /usr/src/linux/Documentation/filesystems/ramfs-rootfs-initramfs.txt
...
What is rootfs?
---------------

Rootfs is a special instance of ramfs (or tmpfs, if that's enabled), 
which is
always present in 2.6 systems.  You can't unmount rootfs for 
approximately the
same reason you can't kill the init process; rather than having special code
to check for and handle an empty list, it's smaller and simpler for the 
kernel
to just make sure certain lists can't become empty.

Most systems just mount another filesystem over rootfs and ignore it.  The
amount of space an empty instance of ramfs takes up is tiny.
...

Pierre




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