Safe Expansion of ImmortalWrt TF Card System

Below is the most concise, complete, and pitfall-free expansion tutorial, including all commands from partitioning, formatting, mounting to verification. This can be saved for future reuse (universal for post-flashing and TF card replacement).

🧱 ImmortalWrt TF Card Expansion Complete Tutorial (Stable Universal Version)

Applicable to: ImmortalWrt / OpenWrt / FriendlyWrt / NanoPi / R2S / R4S / X86 and other devices Goal: Expand TF card remaining space (e.g., 10G) as /overlay software installation area

🧩 Phase 1: Preparation

1️⃣ Insert TF card and view existing partitions

fdisk -l /dev/mmcblk0

Or use a more intuitive approach:

cfdisk /dev/mmcblk0

2️⃣ Typical original partition layout:

Device          Boot        Start        End    Sectors    Size   Id Type
/dev/mmcblk0p1  *            8192     139263     131072     64M    c W95 FAT32 (LBA)
/dev/mmcblk0p2             147456     761855     614400    300M   83 Linux
Free space               761856   62333951   61572096   29.4G

🧰 Phase 2: Partitioning (Using cfdisk)

1️⃣ Open partitioning tool:

cfdisk /dev/mmcblk0

2️⃣ Create a new partition in the Free space area:

Select [ New ]
Enter size, e.g., 10G
Select type ext4

3️⃣ Write changes:

Select [ Write ]
Type yes
Then select [ Quit ]

Result should be similar to:

/dev/mmcblk0p3    761856   21733375   20971520   10G   83 Linux

⚙️ Phase 3: Format New Partition

umount /dev/mmcblk0p3 2>/dev/null
mkfs.ext4 -L overlay /dev/mmcblk0p3
fsck.ext4 -f /dev/mmcblk0p3

Output should show:

Creating filesystem with ...
Writing superblocks and filesystem accounting information: done

✅ Indicates successful formatting.

🗂 Phase 4: Mount Test

mkdir -p /mnt/overlay
mount -t ext4 /dev/mmcblk0p3 /mnt/overlay
df -h | grep mmcblk0p3

You should see:

/dev/mmcblk0p3   9.7G   2.0M   9.2G   0% /mnt/overlay

This indicates successful mounting.

🧩 Phase 5: Set as System Overlay (Expansion Takes Effect)

1️⃣ Install required components:

opkg update
opkg install block-mount kmod-fs-ext4

2️⃣ Write mount configuration:

mkdir -p /overlay
uci set fstab.overlay=mount
uci set fstab.overlay.target='/overlay'
uci set fstab.overlay.device='/dev/mmcblk0p3'
uci set fstab.overlay.fstype='ext4'
uci set fstab.overlay.enabled='1'
uci commit fstab

3️⃣ Enable and reboot:

/etc/init.d/fstab enable
/etc/init.d/fstab start
reboot

🚀 Phase 6: Verify Expansion Success

After reboot, run:

mount | grep -E 'overlay|mmcblk0p3'
df -h

Output should be similar to:

/dev/mmcblk0p3 on /overlay type ext4 (rw,relatime)
overlayfs:/overlay on / type overlay (rw,noatime,lowerdir=/,upperdir=/overlay/upper,workdir=/overlay/work)

Space display:

Filesystem         Size  Used Avail Use% Mounted on
/dev/mmcblk0p3      9.7G  9.1M  9.2G   0% /overlay
overlayfs:/overlay  9.7G  9.1M  9.2G   0% /

✅ This indicates the system successfully uses /dev/mmcblk0p3 as overlay. Installed software, configurations, and cache are all written to the 10G partition.

⚙️ Phase 7: Optional Optimization

(1) Disable journaling to reduce TF card writes:

tune2fs -O ^has_journal /dev/mmcblk0p3
e2fsck -f /dev/mmcblk0p3

(2) Future expansion for more space:

If the TF card still has remaining free space, you can create /dev/mmcblk0p4 again in cfdisk and mount it to /mnt/data or /opt.

🧱 Phase 8: Verify Software Installation Location

opkg update
opkg install htop
df -h

You will see the usage of / (overlay) increase, indicating that software is indeed installed into /dev/mmcblk0p3.

✅ Summary

Create 10G partition via cfdisk → Format with mkfs.ext4 → Set /overlay in fstab → Reboot. System root directory automatically switches to 10G overlayfs. ImmortalWrt expansion successful, space persistently writable, install software freely 🚀.