Restic is a modern backup program for most of the Operating systems and more information about it is available on

Restic provides backends or repository options where the backups can be stored, one of that is Rest Server.

The wrapper for rest-server is available at that-awesome-organization/gokrazy-restic-rest-server.

Disk Setup

Before running the rest-server we need to setup the disk so that it can be used directly.


We need a directory inside the external disk which can be used. for example we can use a directory named restic/ which will have all the named directories by username and other configurations.

cd /run/media/username/diskname
mkdir restic/


If rest-server is used in authentication mode the directory should have .htpasswd file with bcrypt hashed password. This can be carried out by running following command

touch restic/.htpasswd
htpasswd -B restic/.htpasswd username

For all the users needed for authentication we can repeat the last command.

gokrazy Setup

gokrazy does not support mounting a disk directly, so this project wraps the original arm64 binary of restic’s rest-server into /usr/local/bin with mount options.

Before we begin, we setup the directory where we can keep package files for gokrazy.

go mod init rpi4-gorilla                # this is an arbitrary name

# Install rest-server as a normal go program/binary
go get

# Following is the wrapper for rest-server that mounts as specified
go get

# Following is an empty package with extrafiles that currently contain blkid binary
# Used in case if the source is UUID instead of a path like /dev/sda1
go get

The gokr-packer will need to add these two packages in the list.

gokr-packer -hostname rpi4-gorilla.local \
  -update=yes -serial_console=disabled \ \ \ \ \

We don’t want rest-server to start directly, so we disable it using dontstart.txt.

mkdir -p dontstart/
touch dontstart/

Mount Specifications

This program uses three environment variables for this specification

  • MNT_SOURCE: source device for mounting.
  • MNT_TARGET: target directory where the device should be mounted.
  • MNT_FSTYPE: filesystem type of the device, e.g. exfat, ext4, vfat, etc…

Note: The default kernel package ( has support for only vfat/fat/ext4 file systems, so using disks formatted with exfat, btrfs, etc. won’t work out of the box.

To use these variables there needs to be the following file in the directory where the gokr-packer command is being run.

# in the same directory as go.mod

mkdir -p env/
cat << EOF > env/


This program transparently passes all arguments to rest-server command and also the stdout/stderr from it, so the flags or arguments which we want to pass will be actually going in to rest-server

To add flags we can just create flags.txt same as the env.txt

mkdir -p flags/
cat << EOF > flags/

Here we are defining where the root of the rest-server should be available. Also in case if there’s need to add more arguments/flags just add it in this file separated by new lines.

Enabling Private Access to repositories

Other flags can be --private-repos which enables authentication and prevents anyone accessing the repository without basic auth.

Enabling Prometheus Metrics

Passing --prometheus enables the Prometheus /metrics endpoint, but if that is used with --private-repos a new user should be created with name metrics to access the endpoint.

Other options

In some cases the command/program will run before the /perm/ directory is mounted and that will make it fail and retry after a second. To avoid that, we can have a delay in startup using waitforclock feature.

mkdir -p waitforclock/
touch waitforclock/

These commands will actually instruct gokrazy to start the rest-server only after the NTP has synced the clock, which from my observations is also after mounting the /perm/ directory.


The MNT_SOURCE environment variable also accepts UUID strings of disks, it is something that I use in my backup storage, but it has not been tested properly with other devices.

The Problem

This is more like a problem specific to my use-case, but there’s no harm in adding some details about it here.

I had two external hard drives lying around of 500 GB storage each, using them individually will create multiple directories and may not help taking my laptop’s full backup as a whole.

So I decided to find a way to use those two as a single storage with btrfs.

The problem doesn’t end there…

btrfs Support

The gokrazy’s default kernel distribution doesn’t have btrfs support, and as this usecase was very specific, I didn’t add the feature there, instead created my own kernel distribution with btrfs support and other features that may help in future.


Devices and Mount Data

As gokrazy is all go code, I had issues mounting the btrfs devices using the syscall.Mount. It needs a data string that has something like device=/dev/sda,device=/dev/sdb.

That sounds easy, to mitigate that I added an extra environment variable MNT_DATA that passes the given string to syscall.Mount call and it worked, but failed intermittently.

The issue was that the device path changed after reboot or crash, like /dev/sda would become /dev/sdc and the order was random as I also have been booting it off of an USB Drive.

UUID Support

The above issue led me to use UUIDs for fetching devices with actual UUID and enable that from code. This was actually simple in testing and assumptions but not that much when I wrote the whole thing in code.

I couldn’t find the best way to find UUID of a device or list devices attached and their UUIDs, so I tried to go in util-linux space and tried blkid.

As gokrazy has busybox it doesn’t have blkid binary (or I didn’t find a way to access it from Go code), which means I needed to add that binary in the PATH that can be then used in Go code via exec.Command, then parse the output to get UUID vs Device Path.

And then it worked.

Note: The binary that is included in the distribution is static build of blkid from util-linux with config options as --disable-all-programs --enable-blkid --enable-libblkid --enable-static-programs=blkid.

The util-linux package is available at that-awesome-organization/gokrazy-util-linux.