Subject: Re: [vserver] glibc on guest system
From: Nirmal Guhan <vavatutu@gmail.com>
Date: Fri, 28 May 2010 14:32:10 -0700
Fri, 28 May 2010 14:32:10 -0700
On Fri, May 28, 2010 at 1:01 PM, Herbert Poetzl <herbert@13thfloor.at>wrote:

> On Fri, May 28, 2010 at 11:04:24AM -0700, Nirmal Guhan wrote:
> > Hi,
>
> > I see that guest system uses its own glibc.
> > Guest (centos5) :
> > libglib-2.0.so.0
> > libglib-2.0.so.0.1200.3
>
> > Host(Fedora12)
> > libglib-2.0.so.0
> > libglib-2.0.so.0.2200.2
>
> > Since there is always some depedency between glibc
> > and kernel, I wonder if vserver requires guest system
>
> newer kernels are always ABI compatible to older
> ones (Linus takes great care not to break anything
> there :) so older glibc will work fine with newer
> kernels, although they might not be able to utilize
> newer kernel features ...
>

I am considering a case where the glibc is newer and kernel is older (in
other words, guest has an updated or latest version of glibc). This new
glibc might be using newer kernel features that are not supported by the
host (older) kernel. I understand the recommendation to use the recent
kernel for vserver but am thinking of a case where guest system moves faster
than the host though they start off at the same version. In this case, any
upgrade to guest might involve upgrading the host as well and hence there is
a dependency/compatibility requirement. Please correct me if am wrong.


>
> it is always suggested to use a recent kernel for
> Linux-VServer, that said, there are no known issues
> between kernel and guest glibc (regardless of the
> libc version)
>
> > glibc to be compatible (in other words, guest system
> > glibc version < host system glibc version) the kernel?
>
> why should the guest glibc have any dependancy
> with the host glibc?
>

> > If so, how this is guaranteed?
>
> nothing is guaranteed, but it works for the reasons
> mentioned above, of course, if you decide to run
> an ubuntu guest on an ancient debian host kernel
> you might get into troubles ....
>
> > Please clarify.
>
> HTC,
> Herbert
>
> > Thanks,
> > Nirmal
>


On Fri, May 28, 2010 at 1:01 PM, Herbert Poetzl <herbert@13thfloor.at> wrote:
On Fri, May 28, 2010 at 11:04:24AM -0700, Nirmal Guhan wrote:
> Hi,

> I see that guest system uses its own glibc.
> Guest (centos5) :
> libglib-2.0.so.0
> libglib-2.0.so.0.1200.3

> Host(Fedora12)
> libglib-2.0.so.0
> libglib-2.0.so.0.2200.2

> Since there is always some depedency between glibc
> and kernel, I wonder if vserver requires guest system

newer kernels are always ABI compatible to older
ones (Linus takes great care not to break anything
there :) so older glibc will work fine with newer
kernels, although they might not be able to utilize
newer kernel features ...

I am considering a case where the glibc is newer and kernel is older (in other words, guest has an updated or latest version of glibc). This new glibc might be using newer kernel features that are not supported by the host (older) kernel. I understand the recommendation to use the recent kernel for vserver but am thinking of a case where guest system moves faster than the host though they start off at the same version. In this case, any upgrade to guest might involve upgrading the host as well and hence there is a dependency/compatibility requirement. Please correct me if am wrong.
 

it is always suggested to use a recent kernel for
Linux-VServer, that said, there are no known issues
between kernel and guest glibc (regardless of the
libc version)

> glibc to be compatible (in other words, guest system
> glibc version < host system glibc version) the kernel?

why should the guest glibc have any dependancy
with the host glibc?

> If so, how this is guaranteed?

nothing is guaranteed, but it works for the reasons
mentioned above, of course, if you decide to run
an ubuntu guest on an ancient debian host kernel
you might get into troubles ....

> Please clarify.

HTC,
Herbert

> Thanks,
> Nirmal