fix: say nothing was run when the fingerprint differs

install.ps1

@@ -38,7 +38,7 @@ try {
         }
         $actual = (Get-FileHash -LiteralPath $temporary -Algorithm SHA256).Hash.ToLowerInvariant()
         if ($actual -ne $expected.ToLowerInvariant()) {
-            throw "install.py SHA-256 mismatch."
+            throw "The downloaded installer does not match its expected fingerprint. Nothing was run and nothing was written. The download was most likely cut short; try again, on another network if possible."
         }
         $installer = $temporary
     }

install.sh

@@ -56,7 +56,8 @@ if [ -z "$INSTALLER" ] || [ ! -f "$INSTALLER" ]; then
   elif command -v wget >/dev/null 2>&1; then
     wget --https-only --output-document="$TEMP_INSTALLER" "$install_url"
   else
-    echo "Error: curl or wget is required." >&2
+    echo "Error: curl or wget is required to download the installer." >&2
+    echo "  On Debian or Ubuntu: sudo apt install curl" >&2
     exit 1
   fi
   actual_size=$(wc -c < "$TEMP_INSTALLER" | tr -d ' ')
@@ -74,7 +75,9 @@ if [ -z "$INSTALLER" ] || [ ! -f "$INSTALLER" ]; then
   fi
   expected=$(printf '%s' "$expected" | tr '[:upper:]' '[:lower:]')
   if [ "$actual" != "$expected" ]; then
-    echo "Error: install.py SHA-256 mismatch." >&2
+    echo "Error: the downloaded installer does not match its expected fingerprint." >&2
+    echo "  Nothing was run and nothing was written." >&2
+    echo "  The download was most likely cut short. Try again, on another network if possible." >&2
     exit 1
   fi
   INSTALLER="$TEMP_INSTALLER"
@@ -89,7 +92,8 @@ for command_name in python3 python; do
   fi
 done
 if [ -z "$PYTHON" ]; then
-  echo "Error: Python 3 is required." >&2
+  echo "Error: Python 3.8 or newer is required." >&2
+  echo "  Install it, then run this command again. On Debian or Ubuntu: sudo apt install python3" >&2
   exit 1
 fi
 

wiki/first-install.md

@@ -148,16 +148,16 @@ its BIOS folder, see [Getting started](getting-started.md).
 
 ### Error: Python 3.8 or newer is required.
 
-Python is missing from the machine. On Debian and Ubuntu, `sudo apt install
-python3`; on a handheld running Batocera or Recalbox it is already there, so
+Python is missing from the machine. The message names the command that installs
+it, `sudo apt install python3` on Debian and Ubuntu; on a handheld running Batocera or Recalbox it is already there, so
 this message usually means the command ran on the computer rather than on the
 console.
 
-### Error: install.py SHA-256 mismatch.
+### Error: the downloaded installer does not match its expected fingerprint.
 
-Nothing was run. The download did not match the fingerprint the script expects,
-which is almost always a truncated or intercepted transfer. Running the command
-again, on another network if possible, is the answer.
+Nothing was run and nothing was written. The download did not match the
+fingerprint the script carries, which is almost always a transfer cut short.
+Running the command again, on another network if possible, is the answer.
 
 ### Cannot create ...