Enter a shell with ~/nix privately mounted in /nix, using mount namespaces. sudo required

nix-enter

#!/bin/bash

set -e -x

TMP=$(mktemp)
trap 'rm -f $TMP' EXIT
chmod u+x "$TMP"

cat > "$TMP"  <<END
sudo mkdir /nix
sudo mount -n -o bind $HOME/nix /nix
if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
  . "$HOME/.nix-profile/etc/profile.d/nix.sh"
fi
END

if [ "$#" = 0 ]; then
    echo "$@" >> "$TMP"
else
    echo "$SHELL -i" >> "$TMP"
fi

sudo unshare -m -- sudo -u "$USER" "$TMP"