[mythtv-users] Diskless Front End (again)

[Rich West]

Neil Sedger wrote:
> Rich West wrote:
>   
>> My understanding is that the idea is supposed to be that you have one
>> _generic_ image for your hosts, and the configuration files are the ones
>> that are symbolically linked off to the individual snapshots for each of
>> the hosts.  This way, you just have one image to deal with, and, when
>> you do updates, you do them via the server and chroot to the diskless
>> environment (as you said).  The configuration files will get updated,
>> but only in the image.  The snapshot files will get mounted over top of
>> the image's configuration files upon boot up.  This way, you can update
>> all of your diskless clients at one time.
>>     
>
> ...but what if rpm needs to update some of the files which are included 
> in the snapshot? It won't know and will update the files in nfsroot, 
> which are not used as the snapshot files are mapped over them when the 
> real system boots.
>   

That is where some see the administration of diskless booting systems as
a pain.  Those individual files would have to be manually managed.  In
other words, you would have to make the necessary updates to the
corresponding snapshot tree.

>> Now, that's the way it is supposed to work.  I haven't gotten to the
>> point where the snapshot is getting mounted on top of the existing files
>> (that's via pivot_root or something, if I remember correctly).
>>     
>
> Its not really explained well... 'pivot_root' just swaps root - / - with 
> another directory. disklessrc starts off with / being the ramdisk, 
> mounts the nfsroot at /mnt, then the pivot_root command moves the 
> ramdisk to /.oldroot and the nfsroot to /.
> The 'mount snapshot files on top of existing files' is done by 'mount 
> --bind'. The whole snapshot dir is mounted in /.snapshot then each entry 
> in the files and files.custom lists is 'mount --bind'ed from the 
> .snapshot dir over the 'real' location under /.

OK.  Like you, mine sits at /sbin/init for a while, then finally comes
up, but never does the mounting of the snapshot files over top of the
existing files in the netboot root area.  I didn't have a chance to
tinker with this last night (and probably won't have time over the next
few evenings, either).. I'm hoping that it is just something I missed.

Either that, or I am just going to try maintaining three separate trees,
one for each of my frontend systems (~2.6GB each), and avoid the whole
"snapshot" thing all together..

-Rich