Using Yocto SDKs to Deploy Applications Directly into NFS RootFS

When your embedded target boots its root filesystem over NFS, you can use a Yocto SDK to cross-compile and deploy applications directly into the live filesystem. This workflow allows instant updates without reflashing or image rebuilds.

#Why This Workflow Rocks

#1. Prerequisites

• Yocto build environment ready (build/ directory)

• Exported NFS root filesystem, e.g.:

   1/nfs/rootfs/ → 192.168.0.0/24(rw,no_root_squash,sync)
  

• Target board boots with:

   1root=/dev/nfs rw nfsroot=192.168.0.1:/nfs/rootfs,tcp ip=dhcp
  

• Developer workstation or build server with the generated Yocto SDK installed.

#2. Generate and Install SDK

From the Yocto build directory:

 1bitbake core-image-minimal -c populate_sdk

This produces something like:

 1tmp/deploy/sdk/poky-glibc-x86_64-core-image-minimal-cortexa9t2hf-neon-toolchain-4.0.sh

Install on your workstation:

 1chmod +x poky-*.sh
 2./poky-*.sh -d ~/yocto-sdk
 3source ~/yocto-sdk/environment-setup-cortexa9t2hf-neon-poky-linux-gnueabi

You now have a matching cross-toolchain and sysroot.

#3. Mount or Sync the NFS RootFS

#Option A — Direct Mount (recommended for lab setups)

 1sudo mkdir -p /mnt/nfs-rootfs
 2sudo mount -o rw 192.168.0.1:/nfs/rootfs /mnt/nfs-rootfs

Deploy directly into it:

 1make install DESTDIR=/mnt/nfs-rootfs

#Option B — Rsync after Build

 1rsync -a ./install/ root@192.168.0.1:/nfs/rootfs/

#4. Deploying a Custom Application

Project layout:

 1apps/
 2 ├── src/main.c
 3 └── Makefile

Example Makefile using Yocto SDK environment variables:

 1CC ?= $(CROSS_COMPILE)gcc
 2CFLAGS += --sysroot=$(SDKTARGETSYSROOT)
 3
 4all::
 5    $(CC) $(CFLAGS) src/main.c -o myapp
 6
 7install::
 8    mkdir -p $(DESTDIR)/usr/bin
 9    cp myapp $(DESTDIR)/usr/bin/

Deploy to NFS rootfs:

 1make install DESTDIR=/mnt/nfs-rootfs

Your target now instantly sees /usr/bin/myapp after reboot or remount.

#5. Running on Target

Once booted from NFS:

 1root@target:~# myapp

Verify library dependencies:

 1ldd /usr/bin/myapp

#6. Using devtool (Extensible SDK)

Generate eSDK:

 1bitbake core-image-minimal -c populate_sdk_ext

Then on your dev host:

 1source poky-glibc-x86_64-core-image-minimal-cortexa9t2hf-neon-toolchain-4.0.sh
 2devtool create-workspace ~/workspace
 3devtool modify myapp
 4devtool build myapp
 5devtool deploy-target myapp root@192.168.0.100:/usr/bin/

No full rebuilds — just rebuild and deploy changed components.

#7. CI/CD Integration Example

Automate app build and deployment:

 1#!/bin/bash
 2source ~/yocto-sdk/environment-setup-cortexa9t2hf-neon-poky-linux-gnueabi
 3make all
 4make install DESTDIR=/mnt/nfs-rootfs
 5sudo umount /mnt/nfs-rootfs || true

#8. Pro Tips

• Use overlayfs: keep /usr on NFS, /var locally writable.
• Sync SDK and image versions to avoid ABI mismatches.
• Later, integrate your app as a Yocto recipe for production images.

#Summary Workflow

 1┌────────────────────────────┐
 2│ Developer Workstation      │
 3│  • Yocto SDK               │
 4│  • source environment      │
 5│  • Build app → make install│
 6└────────────┬───────────────┘
 7             │ NFS
 8             ▼
 9┌────────────────────────────┐
10│ NFS RootFS Server          │
11│  /nfs/rootfs/usr/bin/myapp │
12└────────────┬───────────────┘
13             │ Ethernet (PXE+NFS)
14             ▼
15┌────────────────────────────┐
16│ Target Board               │
17│  Boots kernel + NFS rootfs │
18│  Runs updated app instantly│
19└────────────────────────────┘