Hi,

I tried building guix from source, as described in the manual, from
within a `guix environment guix` shell.  I've seen this same problem on
three separate computers, all installed with the binary distribution on
top of Arch Linux.

Steps to reproduce:
1. $ git clone git://git.savannah.gnu.org/guix.git && cd guix
2. $ guix environment guix
3. $ ./bootstrap && ./configure && make check

Expected output: no test failures

Actual output:
tests/guix-pack.sh and tests/guix-pack-relocatable.sh both fail.
Looking at the log, the same error is to blame: "unshare failed:
Operation not permitted".  The full log is attached.