Use MemTotal if MemAvailable does not exist

unbound.sh

@@ -3,10 +3,12 @@
 KEYS_DIR="/opt/dnscrypt-wrapper/etc/keys"
 
 reserved=12582912
-availableMemory=$((1024 * $(fgrep MemAvailable /proc/meminfo | sed 's/[^0-9]//g') - $reserved))
-if [ $availableMemory -le 0 ]; then
+availableMemory=$((1024 * $((fgrep MemAvailable /proc/meminfo || fgrep MemTotal /proc/meminfo) | sed 's/[^0-9]//g')))
+if [ $availableMemory -le $(($reserved * 2)) ]; then
+    echo "Not enough memory" >&2
     exit 1
 fi
+availableMemory=$(($availableMemory - $reserved))
 msg_cache_size=$(($availableMemory / 3))
 rr_cache_size=$(($availableMemory / 3))
 nproc=$(nproc)