I would like to replace Synology's DSM with Debian on a DS718+ for various reasons. Not much can be found in the internet concerning this topic for this special model (Intel apollolake, x86_64) so I am trying to find a way my myself.
First thing we need is a UART connection to the serial console of the device. When turning down the box so that power button and leds are on the lower sider, on the right side near the opening (near the RAM module) there is a 6 pin header:
The pins on the front side must be connected this way:
Pins 4, 5 and 6 are not needed.
When the serial connection is established (e.g. screen /dev/ttyUSB0 115200), power on the device, press ESC immediately and continue up to one minute until the EFI bootmanager opens. There is the possibility to enter BIOS but I did not change anything there. BIOS seems configured fine but highly and hard customized by Synology.
The bootmanager lets you select a different boot device but only USB devices are accepted. The device boots by default from a USB DOM but a USB stick plugged into the front usb port is recognized as well and is selectable. Elsewhere in the internet I found informations that these custom USB sticks must have the very same vendor and product id as the default USB DOM (both f400) but I cannot confirm that. I am using an ADATA C802 without modification of vendorid/productid.
So now we have a serial connection and a recognized USB stick. Next thing to mention is that the usual Debian installer iso images installed on this USB stick are not accepted by the bootloader. There must be an EFI partition containing grub, kernel image and initrd. So next problem is to install grub on the stick. Create an EFI partition and install grub there from a compatible x86_64 computer. I found a script with the important steps here.
Now it is important to rename on this EFI boot partition
Otherwise grub is not found. The boot entries are as usual in /EFI/BOOT/grub.cfg
A sample entry in grub.cfg could be (templates can be found on Synology's USB DOM device):
So now I want to start the debian installer from USB stick. Debian offers a kernel and initrd for the installer as download thought for running the installer from hard disk. This initrd can be used as a base but kernel modules which must be selfcompiled later must be added. The kernel cannot be used at all (at least this was my experience).
So the next big problem is to compile a customized kernel and modules. Synology has toolchains and source code ready for download but the kernel config ("4.4.59+") must be modified. The original version configures a lot of Synology proprietary steps mainly for signing kernel modules and initrd. These parameters must be removed and a kernel recompiled (attached my working kernel config). I found also that the Synology toolchain is really necessary. I've got a running kernel only when compiled with their toolchain. The gcc from a usual debian installation did not produce a runnable kernel.
At this point I have an initrd from the debian installer (enriched by kernel modules from the previous build) and a selfcompiled modified kernel and can configure grub to start the debian installer. When selecting my USB stick as boot device, the grub menu starts and I can select the debian installer. The installer starts fine, I can pass all dialogs and then the base system should get installed. But during this step at a certain point the installation fails with an error. From the installation log files I can see that the problem is that the installer cannot mount the target file system (-> attached syslog file from installer).
I have tried other solutions but until now without success:
No way out. Always the step when mounting the target filesystem from initrd fails with one or another error concerning missing mount permissions. Especially bind, slave and move mounts fail ("Are you root?", "Permission denied", ...). Instead mounting the target filesystem onto the initrd file system works as expected. Below the errors when booting debian installed manually with debootstrap and an initrd created there with mkinitrd:
Currently out of ideas how to resolve this problem.
Any hint what could be the problem? Could it be the kernel where something is still misconfigured? The kernel is in fact the same for all these attempts.
First thing we need is a UART connection to the serial console of the device. When turning down the box so that power button and leds are on the lower sider, on the right side near the opening (near the RAM module) there is a 6 pin header:
back: 4 5 6 front: 1 2 3
The pins on the front side must be connected this way:
1: Rx -> connect to Tx of TTL Adapter 2: Tx -> connect to Rx of TTL Adapter 3: GND: GND of TTL Adapter can be attached to screw of the bottom cover instead of this pin
Pins 4, 5 and 6 are not needed.
When the serial connection is established (e.g. screen /dev/ttyUSB0 115200), power on the device, press ESC immediately and continue up to one minute until the EFI bootmanager opens. There is the possibility to enter BIOS but I did not change anything there. BIOS seems configured fine but highly and hard customized by Synology.
The bootmanager lets you select a different boot device but only USB devices are accepted. The device boots by default from a USB DOM but a USB stick plugged into the front usb port is recognized as well and is selectable. Elsewhere in the internet I found informations that these custom USB sticks must have the very same vendor and product id as the default USB DOM (both f400) but I cannot confirm that. I am using an ADATA C802 without modification of vendorid/productid.
So now we have a serial connection and a recognized USB stick. Next thing to mention is that the usual Debian installer iso images installed on this USB stick are not accepted by the bootloader. There must be an EFI partition containing grub, kernel image and initrd. So next problem is to install grub on the stick. Create an EFI partition and install grub there from a compatible x86_64 computer. I found a script with the important steps here.
Now it is important to rename on this EFI boot partition
mv /EFI/BOOT/grubx64.efi /EFI/BOOT/SynoBootLoader.efi
Otherwise grub is not found. The boot entries are as usual in /EFI/BOOT/grub.cfg
A sample entry in grub.cfg could be (templates can be found on Synology's USB DOM device):
#if set "serial --pci=[bus],[device],[function]", use mmio to implement console uart.
serial --pci=0,24,2 --speed=115200
terminal_input serial
terminal_output serial
set default='1'
set timeout='3'
set fallback='0'
menuentry 'My Debian installer' {
insmod part_gpt
insmod ext2
linux /bzImage root=/dev/md0 earlyprintk=apl console=ttyS2,115200n8 ihd_num=2 netif_num=2 HddHotplug=1 SataPortMap=21 syno_hw_version=DS718+ vender_format_version=2 syno_hdd_detect=18,179,176,175 syno_hdd_enable=21,20,19,9 syno_usb_vbus_gpio="13@0000:00:15.0@3"
initrd /initrd.gz
}
So now I want to start the debian installer from USB stick. Debian offers a kernel and initrd for the installer as download thought for running the installer from hard disk. This initrd can be used as a base but kernel modules which must be selfcompiled later must be added. The kernel cannot be used at all (at least this was my experience).
So the next big problem is to compile a customized kernel and modules. Synology has toolchains and source code ready for download but the kernel config ("4.4.59+") must be modified. The original version configures a lot of Synology proprietary steps mainly for signing kernel modules and initrd. These parameters must be removed and a kernel recompiled (attached my working kernel config). I found also that the Synology toolchain is really necessary. I've got a running kernel only when compiled with their toolchain. The gcc from a usual debian installation did not produce a runnable kernel.
At this point I have an initrd from the debian installer (enriched by kernel modules from the previous build) and a selfcompiled modified kernel and can configure grub to start the debian installer. When selecting my USB stick as boot device, the grub menu starts and I can select the debian installer. The installer starts fine, I can pass all dialogs and then the base system should get installed. But during this step at a certain point the installation fails with an error. From the installation log files I can see that the problem is that the installer cannot mount the target file system (-> attached syslog file from installer).
I have tried other solutions but until now without success:
- installation of debian with debootstrap (exit from debian installer into terminal and continue with this method)
- recompile util-linux (containing mount, libmount ..) with Synology's toolchain
- finally created my own toolchain using crosstool-ng (Synology used this for creating their toolchain as well)
No way out. Always the step when mounting the target filesystem from initrd fails with one or another error concerning missing mount permissions. Especially bind, slave and move mounts fail ("Are you root?", "Permission denied", ...). Instead mounting the target filesystem onto the initrd file system works as expected. Below the errors when booting debian installed manually with debootstrap and an initrd created there with mkinitrd:
Begin: Loading essential drivers ... done. Begin: Running /scripts/init-premount ... done. Begin: M[ 9.346825] usb 1-3: new high-speed USB device number 2 using xhci_hcd ounting root file system ... Begin: Running /scripts/local-top ... done. Begin: Running /scripts/local-premount ... done. Begin: Will now check root file system ... fsck from util-linux 2.33.1 [/sbin/fsck.ext4 (1) -- /dev/sda2] fsck.ext4 -a -C0 /dev/sda2 /dev/sda2: clean, 31847/4890624 files, 628870/19531264 blocks [ 9.447121] random: nonblocking pool is initialized done. [ 9.483270] EXT4-fs (sda2): barriers disabled [ 9.492247] usb-storage 1-3:1.0: USB Mass Storage device detected done. [ 9.493852] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null) [ 9.508513] scsi host3: usb-storage 1-3:1.0 [ 9.513333] usbcore: registered new interface driver usb-storagele [ 9.612832] usb 1-4: new high-speed USB device number 3 using xhci_hcd Begin: Running /scripts/local-bottom ... done. Begin: Running /scripts/init-bottom ... mount: Operation not permitted mount: invalid option -- done. mount: Operation not permitted mount: Operation not permitted [ 9.744014] EXT4-fs (sda2): ext4_find_entry:1465: inode #3407873: comm run-init: checksumming directory block 0 [ 9.744014] [ 9.757334] usb-storage 1-4:1.0: USB Mass Storage device detected [ 9.764291] scsi host4: usb-storage 1-4:1.0 [ 9.814884] EXT4-fs (sda2): ext4_find_entry:1465: inode #4456451: comm run-init: checksumming directory block 0 [ 9.814884] mount: Operation not permitted mount: Operation not permitted run-init: overmounting root: Operation not permitted [ 9.997939] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100
Currently out of ideas how to resolve this problem.
Any hint what could be the problem? Could it be the kernel where something is still misconfigured? The kernel is in fact the same for all these attempts.