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Complete Guide to OpenWrt in VirtualBox: Setup and Disk Expansion

#virtualbox #openwrt #ssh #linux

Default OpenWrt images have limited storage space. For development and testing, use pre-expanded images from openwrt-virtualbox-build.

Recommended: openwrt-24.10.4-x86-64-generic-ext4-combined.img.vdi

The ext4 filesystem allows post-installation expansion if you need more space later.

Pre-Configuration: Network Setup

Critical: Configure networking before the first boot, or OpenWrt won't have internet access.

Configure VirtualBox Host-Only Network

  1. Open VirtualBox → File → Host Network Manager
  2. Note the adapter IP (default: 192.168.56.1)
  3. In the DHCP Server tab, uncheck "Enable Server"

This prevents IP conflicts between VirtualBox's DHCP and OpenWrt's network configuration.

Creating the Virtual Machine

Basic Settings

  • OS Type: Linux 2.6
  • OS Version: Linux 2.6 (64-bit)
  • Memory: 4096 MB
  • CPU Cores: 4

Attach the Disk

When prompted for a hard disk, select "Use an existing virtual hard disk file" and choose the downloaded .vdi file.

Network Configuration

Configure two network adapters:

  • Adapter 1: Host-Only Adapter (for management access from host)
  • Adapter 2: Bridged Adapter (for internet access)

First Boot Configuration

Set Root Password

After booting, immediately set the administrator password:

passwd
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Configure Static IP

Set OpenWrt's IP to match your host-only network range (192.168.56.2-255). Choose a higher number to avoid conflicts:

uci set network.lan.ipaddr=192.168.56.66
uci commit
reboot
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The system will reboot with the new IP address.

Setting Up SSH Key Authentication

Generate SSH Key on Host

If you don't already have an SSH key:

ssh-keygen -t rsa
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Save it with a descriptive name like ~/.ssh/openwrt.

Add Public Key to OpenWrt

Option 1: Web UI

  1. Navigate to http://192.168.56.66
  2. Go to System → Administration → SSH-Keys
  3. Paste the contents of your ~/.ssh/openwrt.pub file
  4. Click Add Key

Option 2: Command Line

OpenWrt uses Dropbear SSH server, which stores keys in a different location:

cat ~/.ssh/openwrt.pub | ssh root@192.168.56.66 "cat > /etc/dropbear/authorized_keys"
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Note: The standard ~/.ssh/authorized_keys path won't work with Dropbear.

Connect via SSH 

ssh root@192.168.56.66 -i ~/.ssh/openwrt
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You can simplify this by adding an entry to ~/.ssh/config:

Host openwrt
    HostName 192.168.56.66
    User root
    IdentityFile ~/.ssh/openwrt
    Port 22
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Then connect with just:

ssh openwrt
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Verifying Storage

Check the current filesystem usage:

df -h
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Initial output shows limited space:

Filesystem                Size      Used Available Use% Mounted on
/dev/root                98.3M     25.5M     70.7M  27% /
tmpfs                     1.9G    204.0K      1.9G   0% /tmp
/dev/sda1                15.7M      5.7M      9.7M  37% /boot
tmpfs                   512.0K         0    512.0K   0% /dev
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Only ~70MB is available on the root filesystem, even though the VDI image is 4GB.

Expanding the Root Filesystem

To utilize the full 4GB capacity, follow the official expansion guide.

# Install packages
opkg update
opkg install parted losetup resize2fs blkid

# Download expand-root.sh
wget -U "" -O expand-root.sh "https://openwrt.org/_export/code/docs/guide-user/advanced/expand_root?codeblock=0"

# Source the script (creates /etc/uci-defaults/70-rootpt-resize and /etc/uci-defaults/80-rootpt-resize, and adds them to /etc/sysupgrade.conf so they will be re-run after a sysupgrade)
. ./expand-root.sh

# Resize root partition and filesystem (will resize partiton, reboot resize filesystem, and reboot again)
sh /etc/uci-defaults/70-rootpt-resize
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Verify Expansion

After the reboots complete, check storage again:

df -h
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Expected output:

Filesystem                Size      Used Available Use% Mounted on
/dev/root                 4.0G     27.3M      4.0G   1% /
tmpfs                     1.9G    188.0K      1.9G   0% /tmp
/dev/sda1                15.7M      5.7M      9.7M  37% /boot
tmpfs                   512.0K         0    512.0K   0% /dev
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The root filesystem now has ~4GB available, perfect for development work.

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