Identifying architecture dependent location of nsswitch libraries - linux

Question

I have a DEB package which dynamically creates a chroot filesystem in package postinst helper script. The package works fine for x86, amd64, and arm64 on Debian Stretch/Buster/Bullseye and Ubuntu Bionic/Focal/Jammy. However, I recently tried to install it on Raspbian arm32 and it failed.
The problem is that the pathname of the nsswitch libraries is constructed differently than on the other platforms. In other words, the piece meal assembly of the library path using uname -m is not matching what's present in the file-system.
#!/bin/bash -eu
U=chroot_user
UHOME=/home/$U
ARCH=$(uname -m)
function add_executable () {
FROM="$1"; shift
TO="$(basename $FROM)"
if [ $# -ge 1 ]; then
TO=$1; shift
fi
cp "$FROM" "$UHOME/bin/$TO"
ldd "$FROM" | grep "=> /" | awk '{print $3}' | xargs -I '{}' cp '{}' $UHOME/lib/
LIBNAME="ld-linux-$(echo $ARCH | tr '_' '-').so*"
if compgen -G "/lib64/${LIBNAME}" > /dev/null; then
cp /lib64/${LIBNAME} $UHOME/lib64/
elif compgen -G "/lib/${LIBNAME}" > /dev/null; then
cp /lib/${LIBNAME} $UHOME/lib/
fi
}
if [ "$1" = "configure" ]; then
# Create a system user that has restricted bash as its login shell.
IS_USER=$(grep $U /etc/passwd || true)
if [ ! -z "$IS_USER" ]; then
killall -u $U || true
userdel -f $U > /dev/null 2>&1 || true
fi
adduser --system --home ${UHOME} --no-create-home --group --shell /bin/rbash ${U}
# Create a clean usable chroot
rm -rf $UHOME
mkdir -p $UHOME
mkdir -p $UHOME/dev/
mknod -m 666 $UHOME/dev/null c 1 3
mknod -m 666 $UHOME/dev/tty c 5 0
mknod -m 666 $UHOME/dev/zero c 1 5
mknod -m 666 $UHOME/dev/random c 1 8
mknod -m 644 $UHOME/dev/urandom c 1 9
chown root:root $UHOME
chmod 0755 $UHOME
mkdir -p $UHOME/bin
mkdir -p $UHOME/etc
mkdir -p $UHOME/lib
mkdir -p $UHOME/usr
cd $UHOME/usr
ln -s ../bin bin
cd - > /dev/null
cd $UHOME
ln -s lib lib64
cd - > /dev/null
mkdir $UHOME/lib/${ARCH}-linux-gnu
cp /lib/${ARCH}-linux-gnu/libnss* $UHOME/lib/${ARCH}-linux-gnu
cat <<EOT>$UHOME/etc/nsswitch.conf
passwd: files
group: files
EOT
chmod 0444 $UHOME/etc/nsswitch.conf
echo "127.0.0.1 localhost" > $UHOME/etc/hosts
chmod 0444 $UHOME/etc/hosts
if [ -d /etc/terminfo/ ]; then
cp -R /etc/terminfo $UHOME/etc
fi
if [ -d /lib/terminfo/ ]; then
cp -R /lib/terminfo $UHOME/lib
fi
# Add restricted bash and ssh/scp executables into the chroot. There is no
# need for any other executable.
add_executable /bin/bash rbash
add_executable /usr/bin/ssh
add_executable /usr/bin/scp
add_executable /bin/date
add_executable /bin/ls
add_executable /bin/rm
add_executable /bin/mv
add_executable /bin/cp
grep $U /etc/passwd > $UHOME/etc/passwd
grep $U /etc/group > $UHOME/etc/group
mkdir -p $UHOME/.ssh
chmod 700 $UHOME/.ssh
chown -R $U:$U $UHOME/.ssh
# When using SSH to get out of the jail onto localhost machine, we don't want
# to be constantly told about fingerprints and permanently added hosts
mkdir -p $UHOME/home/$U/.ssh
chmod 0700 $UHOME/home/$U/.ssh
chown -R $U:$U $UHOME/home/$U
fi
#DEBHELPER#
exit 0
# vim: set ts=2 sw=2 tw=0 et :

Answer 1

Not in the expected location ... well, more like: the architecture type in uname's output doesn't match the directory name you want to construct ...
But you could find the directory in a different way, since you're on apt based distros.
dpkg -L libnss3 | awk '/libnss3.so/{gsub(/\/libnss3.so/,"",$0);print}'
This worked for me on both Ubuntu 20.04 and Raspbian GNU/Linux 10 (buster)
Raspbian:
$ dpkg -L libnss3 | awk '/libnss3.so/{gsub(/\/libnss3.so/,"",$0);print}'
/usr/lib/arm-linux-gnueabihf
Ubuntu:
$ dpkg -L libnss3 | awk '/libnss3.so/{gsub(/\/libnss3.so/,"",$0);print}'
/usr/lib/x86_64-linux-gnu