Hi,

look:

$ TMPDIR=/var/tmp/live mmdebstrap sid /dev/null
I: automatically chosen mode: unshare
I: chroot architecture amd64 is equal to the host's architecture
I: finding correct signed-by value...
done
I: automatically chosen format: null
I: using /tmp/mmdebstrap.3sNDppTmUk as tempdir
I: running apt-get update...

I would expect "I: using /var/tmp/live as tempdir" at this point. That
works if /var/tmp/live is writeable by the local user. I guess that
mmdebstrap silently falls back to /tmp in that case It should issue a
warning or even error out.

Grüße
Marc