Autofs ampersand mount in hostfield

deadeyes · 01-28-2016, 10:49 AM

Hi all,

I've read the following:

Code:

*         mysever:/export/home/&

I understand that the key would be used as the path on the remote server so: /export/home/keyvalue

However I don't get how this works:

Code:

*         &:/export/home/&

Quote:

You can use the ampersand character to represent both the remote server and the remote subdirectory, in the same line of the indirect map. For example, if the user’s home directories are physically located on many different servers, but the directory under which the home directories are located is called /export/home/servername on all the servers, the following line in the /etc/auto_home map mounts all the users home directories from any server:

So how does autofs know what all those NFS servers are? There is no definition of what NFS servers to use.

I'm probably missing something obvious here.

MadeInGermany · 01-29-2016, 01:10 AM

It will substitute all & by the key.
Say the map is rooted in /home according to auto.master then going to /home/user1 will do

Code:

user1      user1:/export/home/user1

deadeyes · 01-29-2016, 07:36 AM

Quote:

Originally Posted by MadeInGermany

It will substitute all & by the key.
Say the map is rooted in /home according to auto.master then going to /home/user1 will do

Code:

user1      user1:/export/home/user1

Thanks for your reply.
I really wonder why you would ever use that. It's not like you have a server for each user.
And the quote

Quote:

if the user’s home directories are physically located on many different servers ...

looks misleading to me and not clear.

GazL · 01-29-2016, 08:39 AM

I think where your thinking is going wrong is in assuming that the key will always represent a user. For a user home directory export it certainly doesn't make much sense, but if you had a bunch of servers, each exporting a /export/$hostname then an indirect "* &:/export/&" map attached at /servers may actually be useful.

deadeyes · 01-29-2016, 04:14 PM

Quote:

Originally Posted by GazL

I think where your thinking is going wrong is in assuming that the key will always represent a user. For a user home directory export it certainly doesn't make much sense, but if you had a bunch of servers, each exporting a /export/$hostname then an indirect "* &:/export/&" map attached at /servers may actually be useful.

Ow yes yes yes

Thanks! That makes it clear.
It just looks a bit weird to do an export on the server that has the same directory name as the server itself. It could be as well /nfsexport(on each server), ...
And then this on the autofs client side would work too

Quote:

* &:/nfsexport/

.

Thanks for clarifying!

GazL · 01-29-2016, 05:12 PM

Quote:

Originally Posted by deadeyes

It just looks a bit weird to do an export on the server that has the same directory name

Yes, I know what you mean, and I don't think anyone would use that naming scheme on a standalone server as there's no point, but if you had a 2 node cluster where the nodes provide mutual application fail-over for each other, in the event of failure you could potentially end up with both /export/hostname-1 and /export/hostname-2 on the same node at the same time, so you couldn't use the same name for the directory. Of course, this was the way things were done in the pre-virtualisation/containerisation days. I expect you'd just move the whole virtual machine image across nowadays, but this was how it was done before virtual-machines came along. I installed and supported a couple of warehouse management systems on clusters that worked just like this back in the good old days.