Updating Syncthing on a Synology DM1812+ (Part 2)

In a previous post I described a way to keep your Syncthing installation on a Synology DM1812+ up-to-date as the package from the Cytec repository lags significantly behind the current version.

This method is no longer feasible. The main reason is that the current builds of Syncthing have become dynamically linked, i.e. Syncthing uses certain libraries located on the host machine. If these are incompatible (like the ones on the Diskstation) strange things happen.

Until recently these libraries were part of the Syncthing binary. This so called statically linked binary had no external references and incompatible libraries on the host machine weren't a problem.

If you use the upgrade mechanism built-into Syncthing you get the dynamically linked version. This works with most machines, but not with the DM1812+.

You have to build a statically linked version yourself and replace the binary on Diskstation manually. Fortunately this isn't so hard.

If you haven't done so already, install Syncthing from the Cytek repository. This will copy all the other necessary scripts for the Syncthing integration onto the Diskstation, e.g. scripts to start and stop Syncthing via the Synology web GUI.

The following paragraphs describe how to compile Syncthing amd64 on a fresh Ubuntu LTS 14.04 amd64 machine. It mostly repeats the steps found here on the Syncthing site, but with additional information on how to get a statically linked binary.

The CPU running in the Diskstation is amd64 compatible, but it can also run 32 bit binaries. By tweaking the environment variable GOARCH, it should be possible to cross-compile it for other architectures. I haven't tried this.


Syncthing is written in Go. In order to compile Syncthing you first have to compile Go (also as statically linked version).

Prerequisites

You only need (apart from the source code) the Ubuntu packages for git and mercurial.

I suggest to install an additional packages: libc-bin. It contains the utility ldd which can be used to check if a binary is indeed not a dynamic executable.

$ sudo apt-get install git mercurial libc-bin

Compiling Go

First get the source code for the go language. Currently Syncthing requires Go 1.3, which can be found on the golang website. There you also find the source code for other versions and architectures, if needed.

Download it:

$ wget https://storage.googleapis.com/golang/go1.3.linux-amd64.tar.gz

The Go source code wants to live in /usr/local/go and Syncthing expects it there. You need root privileges to create this folder; then change permissions so that you have access to it as a normal user (in this example “mike” - change as required).

$ sudo mkdir -p /usr/local/go
$ sudo chown mike:mike /usr/local/go

Unpack the source into /usr/local/go

$ tar -C /usr/local -xzf go1.3.linux-amd64.tar.gz

Set the following environment variables

$ export PATH=$PATH:/usr/local/go/bin
$ export GOOS=linux
$ export GOARCH=amd64
$ export CGO_ENABLED=0

CGO_ENABLED=0 is responsible to get statically linked binaries.

Start compiling

$ cd /usr/local/go/src
$ ./all.bash



This can take a while.

Check if the resulting binary is indeed statically linked

$ ldd /usr/local/go/bin/go
    not a dynamic executable

(German message:  Das Programm ist nicht dynamisch gelinkt )

If you get something that looks like the following, the binary is dynamically linked

$ ldd /usr/local/go/bin/go
    linux-vdso.so.1 =>  (0x00007fff0ed31000)
    libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f4cf9726000)
    libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f4cf9360000)
    /lib64/ld-linux-x86-64.so.2 (0x00007f4cf9966000)

Do only continue if you have the statically linked version.

Check Go

$ go version
go version go1.3 linux/amd64

Compiling Syncthing

Create a directory for the syncthing source (the example shows its preferred location) and get the source:

$ mkdir -p ~/src/github.com/syncthing
$ cd ~/src/github.com/syncthing
$ git clone https://github.com/syncthing/syncthing

Compile it

$ cd syncthing
$ go run build.go




This doesn't take long.

Check it

$ cd bin
$ ldd syncthing
    not a dynamic executable

This is the statically linked binary we need.

This file has to be copied to the Diskstation. If you have installed it in its default location (volume1), the Syncthing binary is located at:

/volume1/@appstore/syncthing/bin/syncthing

Stop the Syncthing process via the Synology web GUI, rename the old one (just in case), and copy the new one to that location. Restart the process in the GUI.

You're good to sync.

Updating Syncthing on a Synology DM1812+

Syncthing is a secure directory syncing tool still in its early development stages which runs on various platforms like Linux, Windows, Mac, BSD and Solaris. There are already ports for Android and the Synology NAS.

  

How to install Syncthing on a Synology Diskstation

Disclaimer: These instructions were only tested on a DM1812+ with DSM 4.0. Your mileage may vary.

Open the Package Center and add under Settings the following Package Source

http://cytec.us/spk/

Click Refresh

You'll find the Syncthing package under "Other Sources" from which it can install it as usual.



You can control Syncthing via its web interface on

http://your_diskstation_ip:7070

That's it... You find instructions on how to operate Syncthing here.

Updating Synthing

[Update Oct. 10, 2014]: This part has been superseded by this post.

Usually you would update the Syncthing package via the Package Center.

Currently (mid 2014) there are frequent updates to Syncthing which the cytek repository does not track.

Fortunately, the Synthing binary (the part that actually implements the syncthing server/client) can update itself by starting it with the -upgrade option from the command line.

However, this fails on the Diskstation with the error message

FATAL: Get https://api.github.com/repos/calmh/syncthing/releases?per_page=1: x509: failed to load system roots and no roots provided

The reason for this is that there are no ssl certificates present on the Diskstation.
On a Linux system these can be found in /etc/ssl/certs and usually end with .pem

On the Diskstation this directory is missing.

To fix this, copy the content from the Linux directory /etc/ssl/certs to a directory on the Diskstation and create a link with the name certs to this directory in /etc/ssl.

The following examples assumes:

• your Syncthing app is installed on volume1 (determined during install)
• you have created a shared folder on volume1 named mydata which is accessible by you
• you've copied the certificates into a folder named linuxcerts in the just mentioned shared folder

I.e. change the path names according to your setup.

log into your Diskstation via ssh as root

mkdir -p /etc/ssl
cd /etc/ssl
ln -s /volume1/mydata/linuxcerts certs

Please note:
These certificates will not be updated automatically and they will eventually expire. So you have to refresh them from time to time manually.

And the place I choose is perhaps not the most secure one; but I'm the only one using my Diskstation. Move them somewhere else, if you want.

To upgrade the binary

• First stop the service via the package center.
• ssh into your box.
• Upgrade Syncthing manually on the command line using

cd /volume1/@appstore/syncthing/bin
./syncthing -upgrade

• Now start the service again from the package center.