update create-image.sh to fail early

README.md

@@ -2,6 +2,24 @@
 
 ## Rocky Linux 9 generic ARM64/Aarch64 images
 
+### Extracting the image
+
+You probably downloaded the `Rocky-9-aarch64-minimal-YYYY.MM.DD-HHMMSS.raw.zst` file and are wondering how to extract. Run the following command:
+
+```bash
+zst --decompress Rocky-9-aarch64-minimal-YYYY.MM.DD-HHMMSS.raw.zst
+```
+
+### Flashing the image
+
+```bash
+# flash the extracted image
+dd if=Rocky-9-aarch64-minimal-YYYY.MM.DD-HHMMSS.raw of=<device> bs=4M conv=sync status=progress
+
+# flash without extracting the '.zst' file
+zstdcat Rocky-9-aarch64-minimal-YYYY.MM.DD-HHMMSS.raw.zst | dd bs=4M conv=sync status=progress of=<device>
+```
+
 ### SSH
 
 SSH is enabled on port `22`. Logging-in as **`root` is disabled**, but you can login as user `rocky`.
@@ -26,6 +44,15 @@ password: <disabled>
 
 There are two repositories that are maintained by Rocky Linux. One repository provides packages that are specific to SIG/AltArch for SBC enablement. Another repository is basically ELRepo + some Rocky stuff. Depending on your needs, this may or may not be a good thing. Please act accordingly.
 
+## Notes for executing the script
+
+Firstly, the prerequisite for running all the commands in the `create-image.sh` script can be installed with the following command:
+
+```bash
+# enable EPEL first, because `appliance-tools` is from EPEL
+dnf install appliance-tools perl-Digest-SHA zstd
+```
+
 ## OTHER
 
 **Kickstart syntax reference**: https://docs.fedoraproject.org/en-US/fedora/f36/install-guide/appendixes/Kickstart_Syntax_Reference/

create-image.sh

@@ -8,7 +8,17 @@ IMAGE_NAME="${APPLIANCE_NAME}-$(TZ='UTC' date +%Y.%m.%d-%H%M%S).raw"
 COMPRESSED_IMAGE_NAME="${IMAGE_NAME}.zst"
 
 if [[ ${EUID} -ne 0 ]]; then
-    >&2 echo "ERROR: Please run this script as root"
+    >&2 echo "$0: error: Please run this script as root"
+    exit 1
+fi
+
+if ! command -v appliance-creator > /dev/null; then
+    >&2 echo "$0: error: unable to find command 'appliance-creator'"
+    exit 1
+fi
+
+if ! command -v shasum > /dev/null; then
+    >&2 echo "$0: error: unable to find command 'shasum'"
     exit 1
 fi