Setting mem=768M on QNAP TS-41x/TS-42x

Debian doesn't work on QNAP devices with 1 GB of RAM (i.e. TS-420U, TS-421 and TS-421U). Even though we reported this to the Linux kernel developers, they found it difficult to investigate this issue and it never got fixed. The best workaround is to add mem=768M to the kernel command line to limit the RAM.

QNAP firmware

If you have the QNAP firmware, you can make the change with the following commands. These commands will:

  • Write the current u-boot configuration to /tmp/debian.uboot and add mem=768M to bootargs.
  • Output bootargs from the file so you can verify it looks good.
  • Write the new u-boot configuration to flash.
ubootcfg -b 0 -f /dev/mtdblock4 -o - | sed "s/^\(bootargs=.*\)/\1 mem=768M/" > /tmp/debian.uboot
grep "^bootargs" /tmp/debian.uboot # Check it looks sane
ubootcfg -b 0 -f /dev/mtdblock4 -i /tmp/debian.uboot


If you're running Debian (1 GB was working fine with Debian jessie), you can change the kernel arguments as follows.

sudo cp /usr/share/doc/u-boot-tools/examples/qnap_ts119-219.config /etc/fw_env.config
sudo fw_printenv bootargs

Note: I'm not sure if this configuration will work on the TS-41x/TS-42x. I believe it should. If the command gives the right output, it's working. If so, please email me at to confirm.

The output should be something like this:

bootargs=console=ttyS0,115200 root=/dev/ram initrd=0xa00000,0x900000 ramdisk=34816

You have to append mem=768M to these boot arguments in order to restrict the memory to 768 MB.

sudo fw_setenv bootargs "console=ttyS0,115200 root=/dev/ram initrd=0xa00000,0x900000 ramdisk=34816 mem=768M"

Finally, you can run sudo fw_printenv bootargs again to verify that mem=768M has been adding to the boot arguments.

Now you can either perform an upgrade or put the installer in flash and perform a new installation.