Re: kernel panic when accessing local filesystems on NFS server

[Guillaume Rousse <Guillaume.Rousse@inria.fr>]

Jim Carter wrote:
> On Thu, 13 Apr 2006, Guillaume Rousse wrote:
>> However, it seems automount is still taking priority on direct access if
>> a mount point is activated.
>>
>> If my /etc/fstab says:
>> /dev/hda1 /home
>>
>> and /etc/init.d/autofs status says:
>> /usr/sbin/automount /home/graves ldap
>> ou=auto.home.graves,ou=autofs,dc=village,dc=inria,dc=fr
>>
>> Any attempt to access /home/graves on graves host will mount it through
>> autofs, and access it through NFS, masking local filesystem and probably
>> wasting resources.
> 
> I'm not 100% sure of your configuration; however, my experience is that if 
> I use autofs to access a filesystem on the same host, it will do a bind 
> mount rather than a NFS mount, and the bind mount has (I think) totally 
> zero cost once made.
Right, it was a bind mount, not a NFS mount.

> As an example, here's what we do:
> 
> On host1, the homedir of userA is /h3/userA (not really capitalized).
> On host2, the homedir of userB is /h4/userB.
> 
> On both hosts we do: automount /net file /etc/auto.net
> /etc/auto.net says:
> * -other,options,fstype=autofs,-DSERVER=&  file:/etc/auto.net.generic
> /etc/auto.net.generic says:
> * ${SERVER}:/&
> 
> In other words, if you refer to /net/$anyhost/$anything, the leader process 
> will spawn a submount process specific to $anyhost which will attempt to 
> mount /$anything off of $anyhost.  ($anyhost only delivers directories 
> (filesystems) in /etc/exports, and off-site traffic is blocked at the 
> firewall, but the mount will be attempted even so.)
> 
> The password map says that the homedir of userA is /net/host1/h3/userA,
> and ~userB is /net/host2/h4/userB.  
> 
> Executing on host1, you use /net/host2/h4/userB and the automount process
> does "mount -t nfs host2:/h4 /net/host2/h4".  On the other hand, if you
> refer to /net/host1/h3/userA it is smart enough to do "mount --bind /h3 
> /net/host1/h3", and /proc/mounts says:
> /dev/sdb4 /h3 ext3 rw 0 0
> /dev/sdb4 /net/sunset/h3 ext3 rw 0 0
> 
> We have the actual filesystems (here, /h3) separated from the automounted 
> path names (here, /net/host1/h3).  If we tried to have both "real" 
> directories and automount points in the same containing directory, I doubt
> it would work; at best it would be a can of worms.
Yes, that's my point :)