[Nix-dev] [PATCH] Root filesystem on NFS

[Rickard Nilsson]

Hi,

The only way I have managed to get root fs on NFS to work in NixOS is by  
using the "nfsmount" program from klibc. The following patch works fine  
for me, but since I'm new to NixOS I'm open for any changes:


Index: modules/system/boot/stage-1.nix
===================================================================
--- modules/system/boot/stage-1.nix	(revision 28845)
+++ modules/system/boot/stage-1.nix	(working copy)
@@ -169,6 +169,10 @@
          cp  
${kernelPackages.splashutils}/${kernelPackages.splashutils.helperName}  
$out/bin/splash_helper
        ''}

+      # Copy nfsmount
+      # TODO: Maybe only do this if there is a nfs mount point defined?
+      cp -v ${pkgs.klibc}/lib/klibc/bin.static/nfsmount $out/bin
+
        ${config.boot.initrd.extraUtilsCommands}

        # Run patchelf to make the programs refer to the copied libraries.


Index: modules/system/boot/stage-1-init.sh
===================================================================
--- modules/system/boot/stage-1-init.sh	(revision 28845)
+++ modules/system/boot/stage-1-init.sh	(working copy)
@@ -218,16 +218,20 @@

      mkdir -p "/mnt-root$mountPoint" || true

-    # For CIFS mounts, retry a few times before giving up.
-    local n=0
-    while true; do
-        if mount -t "$fsType" -o "$options" "$device"  
/mnt-root$mountPoint; then
-            break
-        fi
-        if [ "$fsType" != cifs -o "$n" -ge 10 ]; then fail; break; fi
-        echo "retrying..."
-        n=$((n + 1))
-    done
+    if [ "$fsType" = nfs ]; then
+      nfsmount "$device" /mnt-root$mountPoint
+    else
+      # For CIFS mounts, retry a few times before giving up.
+      local n=0
+      while true; do
+          if mount -t "$fsType" -o "$options" "$device"  
/mnt-root$mountPoint; then
+              break
+          fi
+          if [ "$fsType" != cifs -o "$n" -ge 10 ]; then fail; break; fi
+          echo "retrying..."
+          n=$((n + 1))
+      done
+    fi
  }


By applying this patch, the following root device specification in  
configuration.nix works perfectly for me:

   fileSystems = [
     { mountPoint = "/";
       fsType = "nfs";
       device = "192.168.42.1:/export/nixos_root";
     }
   ];


However, you of course also need to get the network up before mounting the  
root fs. I have solved this in the following way directly in  
configuration.nix, but I would really appreciate any suggestions on how to  
solve it more generally in the NixOS repository, so I could write a proper  
patch for it:

   boot.initrd.extraUtilsCommands =
     ''
       cp ${pkgs.iproute}/sbin/ip $out/bin
       cp ${pkgs.glibc}/lib/libresolv.so.* $out/lib
     '';

   boot.initrd.postDeviceCommands =
     ''
       ip link set eth0 up
       ip addr add 192.168.42.200/24 dev eth0
     '';

   # This is necessary, otherwise upstart will tear
   # down the network connection and the root fs will stop working.
   networking.useDHCP = false;


Best regards,
   Rickard Nilsson