Re: MD5SUMs differ across cluster nodes: Any ideas?

Hi Junhao,

On Friday 09,April,2010 09:53 AM, Junhao wrote:
> A couple of us dug further. It seems that dynamically linked binaries 
> have different md5sums, while static binaries have the same. Still not 
> quite sure why though...
>
> Regards,
> Junhao

If the systems had prelinking (popular in fedora a few years ago), all 
of the the shared objects get rewritten with non-conflicting link 
addresses (to avoid runtime relocation overhead). It is usually set up 
in /etc/cron (check cron.daily, cron.weekly, etc)

I'm not sure if more recent linux systems use prelinking or not - it may 
conflict with link address randomisation (a security mechanism, so that 
exploits can't run code that targets known address offsets). e.g. look 
at the link addresses of /bin/ls over two runs (on Debian Sid/2.6.32):

mclark@monty:~$ ldd /bin/ls
     libselinux.so.1 => /lib/libselinux.so.1 (0xb777f000)
     librt.so.1 => /lib/i686/cmov/librt.so.1 (0xb7776000)
     libacl.so.1 => /lib/libacl.so.1 (0xb776e000)
     libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb7627000)
     libdl.so.2 => /lib/i686/cmov/libdl.so.2 (0xb7623000)
     /lib/ld-linux.so.2 (0xb77b6000)
     libpthread.so.0 => /lib/i686/cmov/libpthread.so.0 (0xb760a000)
     libattr.so.1 => /lib/libattr.so.1 (0xb7605000)
mclark@monty:~$ ldd /bin/ls
     libselinux.so.1 => /lib/libselinux.so.1 (0xb788a000)
     librt.so.1 => /lib/i686/cmov/librt.so.1 (0xb7881000)
     libacl.so.1 => /lib/libacl.so.1 (0xb7879000)
     libc.so.6 => /lib/i686/cmov/libc.so.6 (0xb7732000)
     libdl.so.2 => /lib/i686/cmov/libdl.so.2 (0xb772e000)
     /lib/ld-linux.so.2 (0xb78c1000)
     libpthread.so.0 => /lib/i686/cmov/libpthread.so.0 (0xb7715000)
     libattr.so.1 => /lib/libattr.so.1 (0xb7710000)


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