# How does syncing among 3 or more devices work?
**URL:** https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181
**Category:** Support
**Created:** [March 22, 2015, 10:29pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181 "2015-03-22T22:29:00Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 22, 2015, 10:29pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/1 "2015-03-22T22:29:00Z")
Possible new user here investigating the service. As I understand it, 2 devices can be synced only if they have each other’s device IDs. How does this work when one wants to sync a folder among 3 or more devices _such that syncing continues even if the original device is offline_? For example, consider 3 devices: A, B, and C among which a folder _\Test_ is to be synced. Device ID exchanges would proceed as:
- A&B
- A&C
However, the problem with the above is B & C are unaware of each other and so if A goes offline B & C cannot sync. This means the Syncthing network graph in this configuration is hub-and-spoke instead of each member being connected to every other one. An obvious solution is to do the Device ID exchange:
- B&C
_However_ even if that is possible it now presents a scaling problem: as the number of peers grows, so does the number of ID exchanges. Syncing a folder across 5 devices would require a whopping 15 ID exchanges.
Do I have the above right? Is there an easier way or something I’m missing, e.g. _on a per folder basis_ does a peer automatically tell a new peer of pre-existing peers? Or is Syncthing unable to support more than 2 devices per folder?
---
### Author:  [@Arneko](https://forum.syncthing.net/u/Arneko)
#### Post date: [March 22, 2015, 11:53pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/2 "2015-03-22T23:53:05Z")
Hello and welcome to syncthing, 😄it is fairly simple to get any number of devices to sync a folder with each other. If you set up your devices, look for an option about “introducer nodes”. Any device you select as introducer node will share its known device IDs to the other device as needed. It’s kinda like “a peer [will] automatically tell a new peer of pre-existing peers”
Have fun!
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 23, 2015, 12:48am UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/3 "2015-03-23T00:48:40Z")
Thanks for the reply! I’ve been playing around with it, but the mainline executable lacks a native Windows installer and the GTK wrapper - which fixes that problem - somehow results in the announce address being unreachable. Besides that, the UX of connecting devices is extremely complicated. Given that BTS 2.0 already works on my end (most of the Android & Windows launch bugs have been ironed out in the past week), I’ll have to give this a rest for now. I’ll check back later if BTS starts acting up again.
---
### Author:  [@bigbear2nd](https://forum.syncthing.net/u/bigbear2nd)
#### Post date: [March 23, 2015, 6:32am UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/4 "2015-03-23T06:32:33Z")
Hi!
You can use [Synctrazor](https://forum.syncthing.net/t/synctrayzor-windows-host-for-syncthing-installer-auto-start-built-in-browser-tray-icon-folder-watcher-and-more/2011) to have an windows installer. You can download it over [there](https://github.com/canton7/SyncTrayzor).
Enjoy!
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 23, 2015, 2:31pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/5 "2015-03-23T14:31:15Z")
Thanks man! That worked perfectly on the Windows side. Now I’m just trying to figure out how to get folders I share with my Android device to actually show up in the Android client.
---
### Author:  [@wweich](https://forum.syncthing.net/u/wweich)
#### Post date: [March 23, 2015, 2:45pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/6 "2015-03-23T14:45:02Z")
AFAIK the Android client does not show the dialog to add a folder which was shared with you. For that I always use the web interface, where you will get a prompt for every shared folder.
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 23, 2015, 3:05pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/7 "2015-03-23T15:05:27Z")
> [@wweich](#):
>
> the web interface
Thanks, I tried that and got it to work, but the UX is awful to say the least, what with having to manually type out folder paths instead using a selector and all. Progress is progress, I guess.
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 23, 2015, 3:08pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/8 "2015-03-23T15:08:25Z")
> [@Arneko](#):
>
> Any device you select as introducer node will share its known device IDs to the other device as needed. It’s kinda like “a peer [will] automatically tell a new peer of pre-existing peers”
Does the web GUI show all the peers for a given folder, or just the one(s) that was(were) explicitly connected via ID exchange? Curious because if it does that’s great for troubleshooting and seeing what’s going on. OTOH if it doesn’t it’s difficult for the user to determine sync status.
---
### Author:  [@bigbear2nd](https://forum.syncthing.net/u/bigbear2nd)
#### Post date: [March 23, 2015, 3:15pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/9 "2015-03-23T15:15:19Z")
> [@jdrch](#):
>
> Does the web GUI show all the peers for a given folder, or just the one(s) that was(were) explicitly connected via ID exchange?
Only the ones that were connected.
eg: (no Introducers definded) A \<\> B, C, D \<\> F A is connected to B, C and D. All these 3 are connected to F. A is not connected to F All share the same folder. A cannot see (or know about) F
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 23, 2015, 4:12pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/10 "2015-03-23T16:12:08Z")
> [@bigbear2nd](#):
>
> eg: (no Introducers definded)A \<\> B, C, D \<\> FA is connected to B, C and D. All these 3 are connected to F. A is not connected to F All share the same folder. A cannot see (or know about) F
That makes sense. However, I was referring to the case in which all peers have been defined as introducers.
Do all introducer peers for a given folder show up in the client GUI, regardless of whether a manual Device ID exchange was done? e.g. If A, B, & C are introducers BUT Device ID exchanges were done between A \<\> B and A\<\>C only, will B show up as a peer in C’s UI?
Thanks all for your patience. I’m genuinely trying to learn the ropes.
---
### Author:  [@Alex](https://forum.syncthing.net/u/Alex)
#### Post date: [March 23, 2015, 5:08pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/11 "2015-03-23T17:08:30Z")
They will all show up in your device list no matter how they were added (manual or by the introducer)
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 23, 2015, 5:11pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/12 "2015-03-23T17:11:23Z")
@Alex Fantastic! Thanks man. I’ll add some other devices today and see how it goes.
---
### Author:  [@jdrch](https://forum.syncthing.net/u/jdrch)
#### Post date: [March 24, 2015, 1:14am UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/13 "2015-03-24T01:14:42Z")
So far so good. I migrated 3 Windows PCs and my Android phone to Syncthing today.
@bigbear2nd (or anyone else) what’s the best way to get Syncthing up and running on Linux Mint such that it runs at login like Synctrazor does?
---
### Author:  [@bigbear2nd](https://forum.syncthing.net/u/bigbear2nd)
#### Post date: [March 24, 2015, 8:28am UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/14 "2015-03-24T08:28:29Z")
For more detailed information about the introducers, you can have a look here: (shameless selflink:)
> [@\[v0.9.18\] Introducer Nodes](https://forum.syncthing.net/t/v0-9-18-introducer-nodes/974/9):
>
> I want to use the example of @calmh and illustrate it. @calmh please feel free to use any pictures and correct me if i am wrong. Lets assume that Alice already has connections to Charlie (trusted as introducer and trustes Alice as introducer) and Eve (not trusted as an introducer, doesnt trust Alice as an introducer). They are all sharing only one folder. [image] This means that Charlie will add Eve, but is not added back: [image] – Now Bob, an otherwise blank node, is added to Alice. Bob add…
---
### Author:  [@Arneko](https://forum.syncthing.net/u/Arneko)
#### Post date: [March 24, 2015, 9:31am UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/15 "2015-03-24T09:31:51Z")
> [@jdrch](#):
>
> what’s the best way to get Syncthing up and running on Linux Mint such that it runs at login like Synctrazor does?
For Linux I definitely recommend syncthing-gtk. While you seem to have had some bad experience with it on Windows, I run it on several Linux-machines (Mint, Arch, Ubuntu) without a problem.
---
### Author:  [@rumpelsepp](https://forum.syncthing.net/u/rumpelsepp)
#### Post date: [March 24, 2015, 9:49am UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/16 "2015-03-24T09:49:56Z")
If you are using a distro using systemd, just enable it:
> **[syncthing/syncthing](https://github.com/syncthing/syncthing/wiki)**
>
> syncthing - Open Source Continuous File Synchronization
---
### Author:  [@redhead](https://forum.syncthing.net/u/redhead)
#### Post date: [March 28, 2015, 9:38pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/17 "2015-03-28T21:38:50Z")
I have a question regarding the orriginal topic with introducer.
Say I have a configuration where A is connected to B and they are both marked as introducers, then C and D gets connected to A, at the same time E and F gets connected to B.
C, D, E and F are not marked as introducers, in the event that A should be down, automatically C and D should sync with B untill A gets online again and starts to sync with B.
In the event that A and B both are down, will C figure out to sync with say F?
---
### Author:  [@AudriusButkevicius](https://forum.syncthing.net/u/AudriusButkevicius)
#### Post date: [March 28, 2015, 10:10pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/18 "2015-03-28T22:10:21Z")
To make it less typing let’s scrap D and F.
So for you to add C, you will have to restart A, once A restarts and connects to B, B will add C. C will not add B, because from C’s perspective A is not an introducer, hence C and B will not sync.
Hence no.
---
### Author:  [@redhead](https://forum.syncthing.net/u/redhead)
#### Post date: [March 29, 2015, 12:17pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/19 "2015-03-29T12:17:00Z")
But as soon as B adds C, B will figure in C needed to be accepted, and from there on C and B should both know of each other.
Or not?
Because this is the behaviour I see on all my nodes when I make a reinstall creating new identity on one of the devices.
---
### Author:  [@AudriusButkevicius](https://forum.syncthing.net/u/AudriusButkevicius)
#### Post date: [March 29, 2015, 12:50pm UTC](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181/20 "2015-03-29T12:50:36Z")
No, C will not add B, as C does not mark A as an introducer, hence it will have to be added manually/via the prompt.
[Next page](https://forum.syncthing.net/t/how-does-syncing-among-3-or-more-devices-work/2181.md?page=2)