Error auth_rejected

The server rejected the app's credentials

The server won't accept plain AUTH_SYS (uid/gid) authentication. Either the export requires Kerberos, or the security list for the share doesn't include `sys`.

What this means

NFS has no passwords. Ordinary NFS (what NFS Files speaks) identifies you with a numeric user and group ID — the sys security flavour, also called AUTH_UNIX. The server refused that flavour outright at the RPC layer. That happens when the share is configured for Kerberos only.

Fix it on the server

Add sys to the share’s security options. Kerberos can stay enabled alongside it.

• Synology: Control Panel → Shared Folder → select the folder → Edit → NFS Permissions → edit the rule → Security: tick sys (you can leave krb5 ticked too).

• TrueNAS: Sharing → Unix (NFS) Shares → edit → Advanced Options → Security: make sure SYS is in the list (it must be first if you want it used by default). Also System → Services → NFS → Require Kerberos for NFSv4 must be off.

• Linux / Raspberry Pi: in /etc/exports, an option like sec=krb5 restricts the export. Change it to sec=sys:krb5 (or remove sec= — sys is the default), then sudo exportfs -ra.

• QNAP, Unraid, UGREEN: don’t offer Kerberos-only NFS from their UIs; if you see this error there, the server is probably restricting by client address instead — see access denied.

NFS Files does not support Kerberos

That’s deliberate: Kerberos needs a KDC, keytabs, and a domain, none of which exist on a home network. If your workplace NAS is Kerberos-only, ask the administrator for a sys-secured export for your subnet, or use their VPN and a different client.