diff --git a/alpine-uncloud-image.sh b/alpine-uncloud-image.sh
index 4789a81..332fd2b 100755
--- a/alpine-uncloud-image.sh
+++ b/alpine-uncloud-image.sh
@@ -40,7 +40,7 @@ if [ "$(whoami)" != 'root' ]; then
 	exit 1
 fi
 
-if [ $(lsb_release --short --id) != "Alpine" ]; then
+if [ "$(lsb_release --short --id)" != "Alpine" ]; then
 	echo "WARNING: this script has been designed to run on an Alpine system." >&2
 	echo "WARNING: Not running Alpine. Giving you 5 seconds to abort." >&2
 	sleep 5
diff --git a/debian-uncloud-image.sh b/debian-uncloud-image.sh
index d696a72..a691920 100755
--- a/debian-uncloud-image.sh
+++ b/debian-uncloud-image.sh
@@ -40,7 +40,7 @@ if [ "$(whoami)" != 'root' ]; then
 	exit 1
 fi
 
-if [ $(lsb_release --short --id) != "Debian" ]; then
+if [ "$(lsb_release --short --id)" != "Debian" ]; then
 	echo "WARNING: this script has been designed to run on a Debian system." >&2
 	echo "WARNING: Not running Debian. Giving you 5 seconds to abort." >&2
 	sleep 5
@@ -109,7 +109,7 @@ EOF
 run_root apt-get update
 
 # Install RDNSSD for DNS discovery from router advertisement. The service is enabled by default.
-run_root apt-get install rdnssd
+run_root apt-get install -y rdnssd
 
 # Initialize base services.
 run_root systemd-machine-id-setup
diff --git a/fedora-uncloud-image.sh b/fedora-uncloud-image.sh
index cecd23d..35527b2 100755
--- a/fedora-uncloud-image.sh
+++ b/fedora-uncloud-image.sh
@@ -16,7 +16,7 @@ RELEASE=31
 ARCH=x86_64
 IMAGE_PATH=fedora-uncloud-$RELEASE-$(date +%+F).img.qcow2
 IMAGE_SIZE=10G
-NBD_DEVICE=/dev/nbd5
+NBD_DEVICE=/dev/nbd0
 
 cleanup() {
 	# The order here is important.
@@ -146,8 +146,8 @@ run_root dnf -y install kernel grub2
 cat > /mnt/etc/dracut.conf.d/virtio-blk.conf <<EOF
 add_drivers="virtio-blk"
 EOF
-kernel_version=$(ls /mnt/boot | grep "vmlinuz.*.$ARCH" | cut -d- -f2-)
-run_root dracut --force --kver $kernel_version
+kernel_version=$(find /mnt/boot -name "vmlinuz-*.$ARCH" | cut -d- -f2-)
+run_root dracut --force --kver "$kernel_version"
 
 # Configure grub2.
 run_root grub2-install --target=i386-pc "${NBD_DEVICE}"
diff --git a/ubuntu-unclound-image.sh b/ubuntu-unclound-image.sh
index c9ffeb7..07ba50e 100755
--- a/ubuntu-unclound-image.sh
+++ b/ubuntu-unclound-image.sh
@@ -40,7 +40,7 @@ if [ "$(whoami)" != 'root' ]; then
 	exit 1
 fi
 
-if [ $(lsb_release --short --id) != "Ubuntu" ]; then
+if [ "$(lsb_release --short --id)" != "Ubuntu" ]; then
 	echo "WARNING: this script has been designed to run on an Ubuntu system." >&2
 	echo "WARNING: Not running Ubuntu. Giving you 5 seconds to abort." >&2
 	sleep 5