two root entries in /proc/mounts, neither in fstab?

Message

drwook · Post by **drwook** » Sun Apr 20, 2008 2:33 pm

hey guys,

Well this has confused me, at the top of /proc/mounts (and /etc/mtab) I've got this;

rootfs / rootfs rw 0 0
/dev/root / reiserfs rw,noatime 0 0

I don't recall making one, but /dev/root appears to be a symlink to /dev/hdc3 (the actual root partition for the system). Not sure if this may be udev upgrade weirdness? (or outside chance openrc/baselayout-2, but I can't see it if it is...)

my /etc/fstab starts ;

/dev/hdc6 /boot ext2 noauto,noatime 1 1
/dev/hdc3 / reiserfs noatime 0 0
/dev/hdc5 none swap sw 0 0

but /proc/mounts has no mention of hdc3 at all....?

Maybe I'm being stupid and having a bad day, but if so can someone point out what's going on here?

Cazzantonio · Post by **Cazzantonio** » Sun Apr 20, 2008 6:34 pm

I have the same problem, but it is an opernc/baselayout-2 issue since it happened after that upgrade.
It isn't an udev issue since a similar installation with same udev and stable baselayout doesn't have two root mounted.

enito · Post by **enito** » Sun Apr 20, 2008 6:39 pm

Hi, any way for fix this? i tryed manualy edit mtab and delete dupped / and setup correctly, but when you reboot , all back again, duped entry...thx

Dairinin · Post by **Dairinin** » Sun Apr 20, 2008 9:00 pm

Looks like a new "feature" to me. Had to change "/dev/sdb6" to "/dev/root" in cacti data source.

uzz75 · Post by **uzz75** » Sun Apr 20, 2008 9:27 pm

I don't think it's from udev

# cd /etc/udev/
# grep rootfs * -R

Dairinin · Post by **Dairinin** » Sun Apr 20, 2008 9:58 pm

It's here:
/lib64/udev/write_root_link_rule

called from /lib/rcscripts/addons/udev-start.sh

enito · Post by **enito** » Sun Apr 20, 2008 11:58 pm

and how we can disable this new feature?

greets

ABCDwp · Post by **ABCDwp** » Mon Apr 21, 2008 12:38 am

The actual change is that baselayout-2/openrc copies /proc/mounts onto /etc/mtab during boot - it does so, so that the mount table in /etc/mtab is correct (/proc/mounts is what the kernel actually mounted - not what you thought you mounted). The /dev/root symlink is so that things make a little more sense to the average end-user, but is unneeded - the kernel will call the initramfs "rootfs" and the root=/dev/XYZ parameter "/dev/root" no matter what you do (IIRC).

drwook · Post by **drwook** » Mon Apr 21, 2008 5:37 am

ABCDwp wrote:The actual change is that baselayout-2/openrc copies /proc/mounts onto /etc/mtab during boot - it does so, so that the mount table in /etc/mtab is correct (/proc/mounts is what the kernel actually mounted - not what you thought you mounted). The /dev/root symlink is so that things make a little more sense to the average end-user, but is unneeded - the kernel will call the initramfs "rootfs" and the root=/dev/XYZ parameter "/dev/root" no matter what you do (IIRC).

hmm. No initramfs here so can't quite see why there's a 'double mount' on /. I won't have much of a chance to dig until the weekend but I'll check it out then....

The Unknown · Post by **The Unknown** » Mon Apr 21, 2008 7:11 am

This is not new, I have stable systems with the old baselayout and its the exact same.
Your not really double mounting root either. This quote is from some kernel documentation

70 What is rootfs?
71 ---------------
72
73 Rootfs is a special instance of ramfs (or tmpfs, if that's enabled), which is
74 always present in 2.6 systems. You can't unmount rootfs for approximately the
75 same reason you can't kill the init process; rather than having special code
76 to check for and handle an empty list, it's smaller and simpler for the kernel
77 to just make sure certain lists can't become empty.
78
79 Most systems just mount another filesystem over rootfs and ignore it. The
80 amount of space an empty instance of ramfs takes up is tiny.

And the /dev/root symlink is the same as well, my guess is its the same reason as why they provide /dev/cdrom symlinks etc.

Quaoar · Post by **Quaoar** » Mon Apr 21, 2008 8:36 am

but this "feature" definitely hit me with baselayou2/openrc - never had this before and I still don't have it on the baselayout1-machines.

mv · Post by mv » Mon Apr 21, 2008 11:48 am

I had googled about this quite a while ago. From my memory, these were the results:
baselayout-1 was once artificially modified to remove rootfs.
openrc wants to be more conformal to the standard (e.g. it should not run only under gentoo) and since some scripts out there rely on /dev/root, openrc makes no attempt to "hide" this filesystem.

Cazzantonio · Post by **Cazzantonio** » Mon Apr 21, 2008 1:56 pm

I understand that this rootfs, mounted "below" the standard /dev/root, is something that the kernel does independently of openrc.
/proc/mounts lists correctly this rootfs with or without openrc. What openrc does is exactly copying all entries from /proc/mounts in /etc/mtab, so that's why this rootfs appears with baselayout-2.

What I don't really understand is what this rootfs really is. During the boot process root get mounted readonly and then remounted rw. This rootfs isn't the first mount of the root filesystem, since it is mounted rw. Also the rw remount should be made with "mount -o remount", which won't mount /dev/root above the old mount.

rootfs is present in ubuntu too so it isn't something gentoo-specific.

Can anyone explain me what rootfs is and what is there for?

Desintegr · Post by **Desintegr** » Mon Apr 21, 2008 10:43 pm

Another problem : options in /etc/fstab are not respected :

/etc/fstab :

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[...]
/dev/sda2		/			xfs		noatime,nodiratime,logbufs=8		0 0
/dev/sda6		/home		xfs		noatime,nodiratime,logbufs=8		0 0
[...]

mount :

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rootfs on / type rootfs (rw)
/dev/root on / type xfs (rw,noatime,nodiratime,noquota)
[...]
/dev/sda6 on /home type xfs (rw,noatime,nodiratime,logbufs=8)
[...]

The logbufs=8 option is ignored for /.

ABCDwp · Post by **ABCDwp** » Tue Apr 22, 2008 2:29 am

Desintegr wrote:The logbufs=8 option is ignored for /.

What happens if you try to mount -oremount,logbufs=8 /? (If there is an error, then you will have to change the mount options on the kernel command line - this has not changed from baselayout-1, it may only have appeared to work, while not actually doing anything).

Desintegr · Post by **Desintegr** » Tue Apr 22, 2008 2:29 pm

Just after boot :

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/dev/root on / type xfs (rw,noatime,nodiratime,noquota)

After mount -o remount / :

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/dev/root on / type xfs (rw,noatime,nodiratime,logbufs=8)

It's ok because the option is already in the fstab.

After mount -oremount,logbufs=8 / :

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/dev/root on / type xfs (rw,noatime,nodiratime,logbufs=8,logbufs=8)

The option appears twice because it is both in the fstab and in the command line.

BitJam · Post by **BitJam** » Thu May 26, 2011 12:58 am

I've run into this too after upgrading to baselayout-2. I don't mind the two / entries so much, what seems broken to me is that the device that is actually mounted at / no longer shows up in the output of df:

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$ df -h
Filesystem            Size  Used Avail Use% Mounted on
rootfs                 31G   15G   15G  50% /
/dev/root              31G   15G   15G  50% /

I don't understand the purpose of hiding/obscuring this rather important information. It seems like just a horrible idea. I suppose I could process the output of df and run readlink on the first parameter but why make people go through all this effort? IMO this is a big bug.

krinn · Post by **krinn** » Thu May 26, 2011 11:42 pm

it's an old thing : http://forums.gentoo.org/viewtopic-p-62 ... ml#6204542
and the new openrc (it wasn't doing it by this time) now auto mount itself shm (you can check it with mount)

So if anyone wish to disable the rootfs he should hack sysfs to remove shm mount and this should remove rootfs (as this user was doing by this time, when openrc wasn't mounting shm, we were ask to add that in fstab)
shm /dev/shm tmpfs nodev,nosuid,noexec 0 0

dunno if this work to just disable shm fs mount, AND, more dunno how your system will play if you do that.
as it's the new "standard" i can just tell you that you shouldn't disable it, as some new tools might use and expect its presence (and specially as it was add by kernel at first)

theBlackDragon · Post by **theBlackDragon** » Fri May 27, 2011 2:21 pm

I've run into this as well now, so should I replace the direct link to my root partition with /dev/root ?

Right now I get this:

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% df -h
rootfs                293G  121G  158G  44% /
/dev/sda3             293G  121G  158G  44% /

This seems to confuse phpsysinfo and Munin, both think I have 293G more space than I actually have which is a tad annoying.

They also seem to be mounted with different options:

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% mount
rootfs on / type rootfs (rw)
/dev/sda3 on / type ext3 (rw,noatime,errors=continue,barrier=0,data=ordered)

Is there some proper documentation about this? I'm obviously confused and while my install still works properly the change causes annoying issues (as mentioned above)