Force lowmem (fixes #45) (#66)

* Add --force-lowmem

* Fix

README.md

@@ -147,6 +147,7 @@ Otherwise, you can run this command to revert all changes made by the script:
  * `--firmware` Load additional [non-free firmwares](https://wiki.debian.org/Firmware#Firmware_during_the_installation)
  * `--no-force-efi-extra-removable` [See](https://wiki.debian.org/UEFI#Force_grub-efi_installation_to_the_removable_media_path)
  * `--grub-timeout 5` How many seconds the GRUB menu shows before entering the installer
+ * `--force-lowmem <integer>` Valid values: 0, 1, 2. Force [low memory level](https://salsa.debian.org/installer-team/lowmem). Useful if your machine has memory less than 500M where level 2 is set (see issue #45). `--force-lowmem 1` may solve it. 
  * `--dry-run` Print generated preseed and GRUB entry without downloading the installer and actually saving them
 
 ### Presets

debi.sh

@@ -228,6 +228,7 @@ install_recommends=true
 install='ca-certificates libpam-systemd'
 upgrade=
 kernel_params=
+force_lowmem=
 bbr=false
 ssh_port=
 hold=false
@@ -348,6 +349,11 @@ while [ $# -gt 0 ]; do
         --no-part|--no-disk-partitioning)
             disk_partitioning=false
             ;;
+        --force-lowmem)
+            [ "$2" != 0 ] && [ "$2" != 1 ] && [ "$2" != 2 ] && err 'Low memory level can only be 0, 1 or 2'
+            force_lowmem=$2
+            shift
+            ;;
         --disk)
             disk=$2
             shift
@@ -822,6 +828,8 @@ installer_directory=$(grub2-mkrelpath "$mkrelpath" 2> /dev/null) || {
 
 kernel_params="$kernel_params lowmem/low=1"
 
+[ -n "$force_lowmem" ] && kernel_params="$kernel_params lowmem=+$force_lowmem"
+
 initrd="$installer_directory/initrd.gz"
 [ "$firmware" = true ] && initrd="$initrd $installer_directory/firmware.cpio.gz"