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Linux - Embedded & Single-board computer This forum is for the discussion of Linux on both embedded devices and single-board computers (such as the Raspberry Pi, BeagleBoard and PandaBoard). Discussions involving Arduino, plug computers and other micro-controller like devices are also welcome.

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Old 03-03-2014, 12:06 PM   #1
elsutjr
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Registered: Feb 2014
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What would cause an NFS-mounted rootfs to come up read-only?


I'm working on an embedded linux board, and had been running with an NFS mounted ROOTFS. All was good. Then for a while I had switched over to a ramdisk based rootfs, that was fine too. I've since switched back to an NFS-based rootfs and now it always comes up read-only. Something has obviously changed (yea I know, I probably changed it!); but I don't know what. My host machine (from which the NFS mount is achieved) still has an /etc/exports entry similar to :
/full_path_to_my_rootfs *(rw,no_root_squash)
and on my kernel command line:
console=ttymxc0,115200 ip=dhcp root=/dev/nfs nfsroot=${srvrip}:/full_path_to_my_rootfs,v3,tcp

At boot time I see the message:
VFS: Mounted root (nfs filesystem) readonly on device 0:11.

and then other stuff fails because of inability to write.

Any idea what might cause this?

EDIT>>>
Some more detail (that just makes me more confused)...
The rootfs is created by buildroot, and it is configured to remount rootfs to RW as shown by the line in /inittab:
null::sysinit:/bin/mount -o remount,rw / # REMOUNT_ROOTFS_RW

Last edited by elsutjr; 03-03-2014 at 04:57 PM.
 
Old 03-04-2014, 01:41 AM   #2
sebastian.heyn
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Hi,

maybe you are now using a different kernel version?
Add "rw" to your command line and you're done.
I guess the kernel usually mounts the rootfs readonly, as usually the fs is checked whether its clean before writing to it.
 
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Old 03-04-2014, 07:53 AM   #3
elsutjr
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That did it!
Didn't need this in the past, but apparently now I do!
Yep, I did change my kernel.
Thanks much,
Ed
 
Old 03-04-2014, 08:40 AM   #4
sebastian.heyn
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I had the same with a diskless nfs client. after kernel update a while ago it would not boot properly.
the rw flag is not a goot idea for hdd machines, but for nfs who cares :-)
 
  


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