This post addresses how to keep two directories in sync on a single Linux machine using Syncthing (avoiding things like rsync, unison, etc.). This is particularly useful if you have two logseq graphs on your system and you want to share a directory underneath your pages directory between both.

Setting up the mount

• Requirements:
  • util-linux v2.39
• Preparation:
  • sudo useradd -m USERNAME_helper
  • Make note of the user id and group id (usually they are the same number)
• Testing the mount one-time:
  • sudo mount --bind -oX-mount.idmap=b:1000:1001:1 /home/USERNAME/shared_logseq /home/USERNAME_helper/shared_logseq
  • This assumes your main user has uid/gid 1000 and the helper account has uid/gid 1001
  • If the target directory does not yet exist, create it first
  • If this works correctly, you can unmount it and start setting up the permanent mount as follows
• Setting the mount permanently in /etc/fstab:
  • /home/USERNAME/shared_logseq /home/USERNAME_helper/shared_logseq none defaults,user,bind,X-mount.idmap=b:1000:1001:1 0 0
  • The b flag creates both user and group mapping
  • Mount the directory: sudo mount /home/USERNAME_helper/shared_logseq

Setting up Syncthing

• Let systemd launch an extra syncthing permanently:
  • sudo systemctl enable --now syncthing@USERNAME_helper
• Check the logs and find the port number used by syncthing:
  • sudo systemctl status syncthing@USERNAME_helper
• Open the syncthing with a browser and configure it to disable NAT, global discovery and relays
• Connect your Syncthing instances together as usual, and share the folders between the syncthing instances