Searching unison

Iam using the sync-tool unison.

Its open source. Is it possible to build unison for openWRT? Or is there an other sync-tool for linux?

rsync perhaps ?

(there's also nsync, but it only works for music ...)


I built unison several times on my desktop, and even there it's not easy to build as it is written in Objective CAML. There were some attempts back in 2015:

My desktops still sync with Unison, but every now and then it stops working after an upgrade when the Unison versions don't match. For all serious file syncing tasks, I've switched to rsync, especially on small systems.

As mentioned above, rsync is the go-to for no-frills synchronisation.

Personally, I use SyncThing on a few desktops and laptops -- but not on OpenWrt yet, that's very high on my list once I get my NASboxen unpacked from their intercontinental move.

nsync is unmaintained and hasn't had a major release since 2001.

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I know syncthing ... but its to heavy for my fritzbox 7362SL.

rsync is only for one direction.

Do you use it as a NAS with USB-attached storage? I'm asking because I'm curious about the use-case for two-way sync on this relatively small box.

Its running as wlan router with an external HDD on the USB port. With sshfs, I have file access to the HDD.

OK, then you could also mount the sshfs on your destination system and run unison there?

This is the way, I do now ... but with sshfs its very slow, to sync changes in 16GB data. When unison is installed on the NAS, too it will be speed up.

Is it though? The package says some 8.5 MB installed size with few dependencies, the 7362SL comes with 128 MB of flash.

you are right ... I have a lots of free space to install packages. Thats the reason, that I want to install unison on the fritzbox 7362SL.

Yes, the first sync will be very slow, but all subsequent syncs should be much faster as unison then only checks the file metadata and not its contents (as far as I remember). But for 16GB of data this might still be slow.

If I were you, though, I would reconsider the usage of this old box as a NAS ...

I did a test with this box as a NFS Server ... this works very very fast with unison and 16GB data. On sshfs or samba its very very slow. I want to use sshfs only, coz thats enough for me. When there is a unison packages for openWRT, it will works finde, too.
Unison works fast when on the server and on the client, unison is installed.

SSHFS does the encryption in software, NFS does not encrypt at all. You could also NFS-mount on the target over Wireguard, that should give you more performance than SSHFS.

It does, until you run into a version mismatch between client and server. Been there, done that.

For Unison on OpenWrt, you will need to:

  • Port the OCaml compiler to OpenWrt
  • Port Unison to OpenWrt

According to the link I sent before, this was possible with OpenWrt 18.06, so your best bet it is to forward-port the patches to the current build system and current versions.

I use it intern ... in my own lan not over the internet.