Synology NFSv4 user mapping.

know-how/hardware/_posts/2018-01-05-synology-nfsv4-with-id-mapping.md

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+---
+title: Synology NFSv4 with id mapping
+layout: default
+language: en
+created: 2018-01-05 12:50:43 +0100
+updated: 2018-01-05 12:50:43 +0100
+toc: false
+tags:
+  - know-how
+  - hardware
+  - synology
+  - diskstation
+  - dsm
+  - nfs
+  - nfsv4
+  - nfs4
+  - idmapd
+  - idmapping
+  - export
+  - mount
+---
+**Disclaimer:** ID mapping without a Kerberos server only works halfway with NFSv4, it seems. I
+managed to get the correct usernames to show up on my client when listing files, but creating new
+files always creates them as user *nobody* because the Synology doesn't map anything in that case.
+[This bug report][1] and the [linked thread][2] suggest this is normal behaviour of `idmapd` when
+not using Kerberos for some reason. (EDIT: [More detailed explanation.][3])
+
+However, what I did:
+
+First, you have to enable idmapping after loading the NFS service. For that, you have to edit the
+file `/usr/syno/etc/rc.sysv/S83nfsd.sh` on the Synology. Find the line
+
+    SYNOLoadModules $KERNELMODULE
+
+and add the following line after that:
+
+    echo "N" > /sys/module/nfsd/parameters/nfs4_disable_idmapping
+
+Then, still on the Synology, edit the `/etc/idmap.conf` and set the `Domain` to your `ITET-PHO` if
+not already set. Disable NFS, apply and re-enable (+apply) it afterwards in the Synology's control
+centre to reload `nfds`.
+
+On your client machine, create a file `/etc/modprobe.d/nfs-idmap.conf` with the following contents:
+
+    options nfs nfs4_disable_idmapping=0
+    options nfsd nfs4_disable_idmapping=0
+
+Reload the `nfs` kernel module afterwards to apply the options.
+
+Also make sure, `idmapd` is running on your client. (On Ubuntu artful, I had to run
+`sudo systemctl start nfs-idmapd` manually, I think.) And, of course, use `nfsvers=4` as a mount
+option.
+
+(On the Synology, you can `killall idmapd` and run it in foreground using `idmapd -f -vvv` to see
+if it's doing anything.)
+
+
+  [1]: https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/966734
+  [2]: http://thread.gmane.org/gmane.linux.nfsv4/7103/focus=7105
+  [3]: https://lists.debian.org/debian-kernel/2013/03/msg00136.html