[NCLUG] 32 bit app, 64 bit OS

[Stephen Warren]

On 05/25/2012 08:44 AM, grant at amadensor.com wrote:
> I am wondering the pitfalls of running 32 bit applications on 64 bit Linux.
> 
> We are looking at upgrading a large enterprise system.   It would be  
> very helpful if we could upgrade the operating system first, because  
> then we can upgrade the application in place and carry over all of our  
> settings and data more easily.   The old version is a 32 bit  
> application, the new one is a 64 bit application.   If we upgrade the  
> hardware and operating system first, this is better, since it is due a  
> hardware upgrade anyway, and we are looking at maybe moving it to a  
> new data center.   We would like to run this way for a while, then do  
> the upgrade, since it is a large project to upgrade this mess.  Where  
> is this going to bite us?

In general, 32-bit applications run fine on 64-bit hosts, at least as
far as e.g. interaction with the Linux kernel.

The issue is that your 32-bit application will need 32-bit libraries.
64-bit OSs provide 64-bit libraries by default. In many cases, 32-bit
libraries are available as additional packages you can install. However,
depending on the OS and version, the set of available 32-bit libraries
will vary.

To determine whether this will work, install the 64-bit OS and on a test
machine, and see if you can find the appropriate packages to get it
running. Packages are often named ia32-libs, *-compat32, etc.

If you can find the right dependencies, you probably won't have any
ongoing issues in this area; once it works, it /should/ just keep on
working, unless distro updates do something really broken.

Another issue is if this is binary-only software, it may do things like
hard-code certain paths, whereas a 64-bit OS may lay out especially its
/lib directory differently. The only real way to tell if this will be a
problem is to try installing it, and perform a thorough evaluation of
whether the SW still works OK.

Finally, there may of course be bugs. It's supposed to work, but this is
obviously a less common setup, so you're slightly more exposed to this.