Conflict handling

What happens when you change too many files?

When you modify a file on one device, you expect your modification to be sent to the others, but what happens if you change the same file on more than one device between syncing? How do these programs cope, seeing as none of them include mind reading code? Rsync and Unison only sync between two devices. Rsync is a strictly one-way affair, it updates the destination to match the source. Unison, which uses Rsync protocols, compares files on both sides and copies any that have been modified since the last sync. It keeps a log of what it has done in order to know what has changed. When run interactively, it lists conflicts and files that have changed on both sides, so you can pick which one to use. In batch mode it can either skip them or you can tell it which device to give preference to.

OwnCloud is also one-to-one in that each client syncs with the server, although you can have multiple clients doing so. It handles conflicts by renaming a file with -conflict and a timestamp. Syncthing normally has no concept of destination and source, although you can set it up this way for specific directories if you need to. Files between all devices are synced, if a particular device is offline (eg, you may tell your phone to only sync via Wi-Fi), and will catch up with the others when it connects. As with OwnCloud, conflicting files are renamed. BitTorrent Sync also renames conflicting files, but without the timestamp.