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Date: Mon, 6 Jun 2016 21:15:39 -0400
From: Rich Felker <>
Subject: Re: realpath() depends on a mounted /proc to work

On Tue, Jun 07, 2016 at 08:27:18AM +0800, Lei Zhang wrote:
> Hi,
> I observed that realpath() doesn't work correctly without a mounted
> /proc while experimenting in a chroot system, where musl is the
> default libc. OTOH, the same program statically linked against glibc
> worked just as expected.
> Is the dependence on a mounted /proc intentional? Then what's the
> rationale behind it?

As a whole, musl depends on having /proc; the rationale is simply that
Linux does not expose all the functionality needed to implement POSIX
without /proc.

As for realpath, it could be done without /proc, but being that musl
already requires /proc for full functionality, and that non-/proc
versions of realpath are significantly heavier, more complex, and less
reliable, simply using /proc for realpath was the natural choice.

If someone wants to do a survey of what functionality actually depends
on /proc, we could document that and also evaluate whether realpath is
sufficiently more "basic" than other things which need /proc that we
might want to consider having a fallback implementation for when /proc
is missign.


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