Nextcloud Sync Not Working: Complete Fix Guide

Quick Checks

Before diving in, verify these basics:

Can you access the Nextcloud web UI? If not, the server is down or unreachable.
Is the server healthy? Check Settings → Administration → Overview for warnings.
What version are you running? Check Settings → Administration. Update if outdated.

Common Causes and Fixes

1. Trusted Domains Not Configured

Symptom: “Access through untrusted domain” error.

Fix: Add your domain/IP to trusted domains in config.php:

'trusted_domains' => [
    0 => 'localhost',
    1 => 'cloud.yourdomain.com',
    2 => '192.168.1.100',
],

Or set via environment variable:

environment:
  - NEXTCLOUD_TRUSTED_DOMAINS=localhost cloud.yourdomain.com 192.168.1.100

2. Reverse Proxy Misconfiguration

Symptom: Redirects loop, mixed content errors, or mobile app can’t connect.

Fix: Add these to config.php:

'overwriteprotocol' => 'https',
'overwritecliurl' => 'https://cloud.yourdomain.com',
'trusted_proxies' => ['172.16.0.0/12'],  // Docker network range

3. PHP Memory Limit Too Low

Symptom: Large file uploads fail, sync drops out mid-transfer.

Fix: Increase PHP memory in your Docker environment:

environment:
  - PHP_MEMORY_LIMIT=1024M
  - PHP_UPLOAD_LIMIT=16G

4. Database Lock Issues

Symptom: Sync freezes, “file is locked” errors.

Fix:

# Clear file locks
docker exec -u www-data nextcloud php occ maintenance:mode --on
docker exec -u www-data nextcloud php occ files:scan --all
docker exec -u www-data nextcloud php occ maintenance:mode --off

5. Desktop Client “Checking for Changes” Forever

Symptom: Client shows “Checking for changes” indefinitely.

Fix:

Delete the sync journal: remove .sync_*.db files in the sync folder
Restart the desktop client
Let it rescan (may take a while for large libraries)

6. Background Jobs Not Running

Symptom: Slow syncing, notifications delayed, previews not generating.

Fix: Verify the cron container is running:

docker compose ps cron
# Should show "Up"

# Or check last cron execution:
docker exec -u www-data nextcloud php occ background:cron

In Settings → Administration → Basic settings, ensure “Cron” is selected (not AJAX or Webcron).

Still Not Working?

Check Nextcloud logs: docker exec nextcloud cat /var/www/html/data/nextcloud.log | tail -50
Check container logs: docker compose logs nextcloud
Run a server health check: docker exec -u www-data nextcloud php occ status