Can I change 'rpath' in an already compiled binary?

Question

I have an old executable that's scheduled for the scrap heap, but it's not there yet. It relies on some libs that have been removed from my environment, but I have some stub libs someplace where it works fine. Id like to point this executable to these stub libs. Yes, i could set LD_LIBRARY_PATH, but this executable is called from many scripts, and many users and I'd love to fix it in one spot.

I don't have source for this, and would be hard to get it. I was thinking - can I edit this file, using an ELF aware editor, and add a simple PATH to rpath to have it hit the new libs? Is this possible, or once you create an ELF binary, you fix things to locations and they can't be moved?

Answer 1

There is a tool called chrpath which can do this - it's probably available in your distribution's packages.

Answer 2

There is a more universal tool than chrpath called patchelf. It was originally created for use in making packages for Nix and NixOS (packaging system and a GNU/Linux distribution).

In case there is no rpath in a binary (here called rdsamp), chrpath fails:

chrpath -r '$ORIGIN/../lib64' rdsamp 
rdsamp: no rpath or runpath tag found.

On the other hand,

patchelf --set-rpath '$ORIGIN/../lib64' rdsamp

succeeds just fine.

Answer 3

Just like @user7610 said, the right way to go is the patchelf tool.

But, I feel that I can give a more comprehensive answer, covering all the commands one needs to do exactly that.

If you want to read a comprehensive explanation on the subject, you can find more information here.

First of all, many developers talk about RPATH, but they actually mean RUNPATH. These are two different optional dynamic sections, and the loader handles them very differently. You can read more about the difference between them in the link I mentioned before.

For now, just remember:

• If RUNPATH is set, RPATH is ignored
• RPATH is deprecated and should be avoided
• RUNPATH is preferred because it can be overridden by LD_LIBRARY_PATH

See the current R[UN]PATH

readelf -d <path-to-elf> | egrep "RPATH|RUNPATH"

Clear the R[UN]PATH

patchelf --remove-rpath <path-to-elf>

Notes:

• Removes both RPATH and RUNPATH

Add values to R[UN]PATH

patchelf [--force-rpath] --set-rpath "<desired-rpath>" <path-to-elf>

Notes:

• <desired-path> is a comma separated directories list, e.g: /my/libs:/my/other/libs
• If you specify --force-rpath, sets RPATH, otherwise sets RUNPATH

Answer 4

This worked for me, replacing XORIGIN with $ORIGIN.

chrpath -r '\$\ORIGIN/../lib64' httpd