How to Expand the Filesystem on a Milk-V Duo

The Milk-V Duo is a great board, but once you install your OS, you may find you need more space!

[root@milkv-duo]/bin# fdisk -l
Disk /dev/mmcblk0: 119 GB, 128177930240 bytes, 250347520 sectors
3911680 cylinders, 4 heads, 16 sectors/track
Units: sectors of 1 * 512 = 512 bytes

Device       Boot StartCHS    EndCHS        StartLBA     EndLBA    Sectors  Size Id Type
/dev/mmcblk0p1 *  0,0,2       16,81,2              1     262144     262144  128M  c Win95 FAT32 (LBA)
/dev/mmcblk0p2    16,81,3     114,57,8        262145    1835008    1572864  768M 83 Linux
/dev/mmcblk0p3    114,57,9    146,219,10     1835009    2359296     524288  256M  0 Empty
[root@milkv-duo]/bin# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/root               745.4M    154.0M    549.0M  22% /
devtmpfs                 14.2M         0     14.2M   0% /dev
tmpfs                    14.3M         0     14.3M   0% /dev/shm
tmpfs                    14.3M     52.0K     14.2M   0% /tmp
tmpfs                    14.3M     28.0K     14.2M   0% /run
[root@milkv-duo]/bin# 

That's unfortunate - I bought a fancy 128 GiB microSD just for this board! That's an affiliate link, by the way.

Luckily, we can remedy this! Start by sticking your microSD card back into your computer. Ensure you have the fdisk command alongside e2fsck and resize2fs. In general, you'll need a Linux machine (or a complex WSL/Docker setup) for these packages.

You can install these on Fedora with sudo dnf install fdisk e2fsprogs -y, or on Debian/Ubuntu/Pop_OS! with sudo apt update && sudo apt install fdisk e2fsprogs.

Also, make a backup of any important data!

With these on the computer and our data all safe, let's start by looking at our disk as-is:

barrett@farts ~> lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda      8:0    0 931.5G  0 disk 
(snip! a lot of extra junk was here)
sdf      8:80   1     0B  0 disk 
sdg      8:96   1 119.4G  0 disk <---- MY SD CARD
├─sdg1   8:97   1   128M  0 part 
├─sdg2   8:98   1   768M  0 part 
└─sdg3   8:99   1   256M  0 part 

barrett@farts ~> sudo fdisk -l /dev/sdg
[sudo] password for barrett: 
Disk /dev/sdg: 119.38 GiB, 128177930240 bytes, 250347520 sectors
Disk model: STORAGE DEVICE  
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot   Start     End Sectors  Size Id Type
/dev/sdg1  *          1  262144  262144  128M  c W95 FAT32 (LBA)
/dev/sdg2        262145 1835008 1572864  768M 83 Linux
/dev/sdg3       1835009 2359296  524288  256M  0 Empty
barrett@farts ~>

As you can see, the board wastes a lot of space here! There's also the "empty" partition that folks usually use for swap. We'll remove it, but feel free to re-add it afterward!

Remember that our card is /dev/sdg here. Your card will probably be called something different, likely some /dev/sdX, so please keep that in mind.

Expanding the Filesystem

Let's get to work! We'll unmount the microSD card, then open up fdisk. We'll ask it to tell us more about the card first, write those values down, and then make some changes!

barrett@farts ~> sudo fdisk /dev/sdg

Welcome to fdisk (util-linux 2.38.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sdg: 119.38 GiB, 128177930240 bytes, 250347520 sectors
Disk model: STORAGE DEVICE  
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot   Start     End Sectors  Size Id Type
/dev/sdg1  *          1  262144  262144  128M  c W95 FAT32 (LBA)
/dev/sdg2        262145 1835008 1572864  768M 83 Linux
/dev/sdg3       1835009 2359296  524288  256M  0 Empty

Okay, make sure to write down those values! You can also snap a photo of them or open them in Text Editor (my beloved)! 🤤️

Alright, now we have to do the hard part! We'll (temporarily) delete the Linux partition and make it much longer.

Command (m for help): d
Partition number (1-3, default 3): 2

Partition 2 has been deleted.

Command (m for help): d
Partition number (1,3, default 3): 3

Partition 3 has been deleted.

Command (m for help):

If you didn't delete sdX3, when you try to resize, you'll find that you're limited to around 1835008 sectors on the Linux partition - which you started with!

Now, we'll make a new partition that is 'pretending' to be the old one. When you do this, fdisk will ask for a few options. You want a p (for "primary") Partition Type, 2 for the Partition Number, and the default (first available) sector for the First Sector.

That said, I won't be using swap, so I'll make the Linux partition take up the whole space.

Command (m for help): n
Partition type
   p   primary (1 primary, 0 extended, 3 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2): 2
First sector (262145-250347519, default 264192): 262145
Last sector, +/-sectors or +/-size{K,M,G,T,P} (262145-250347519, default 250347519): 

Created a new partition 2 of type 'Linux' and of size 119.2 GiB.
Partition #2 contains a ext4 signature.

Do you want to remove the signature? [Y]es/[N]o:

You can see it asked us if we want to remove the signature. No, we don't!

Do you want to remove the signature? [Y]es/[N]o: n

Command (m for help):

To be safe, let's also change the partition type to 83 (Linux). The card should have kept it, though!

Command (m for help): t
Partition number (1,2, default 2): 2
Hex code or alias (type L to list all): 83

Changed type of partition 'Linux' to 'Linux'.

Good, nothing changed!

Now, you can save your changes to disk with w (for "write")!

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

You should be back at your command line! Now, we can dust off the other tools! Let's start with e2fsck. This tool runs a check on a given filesystem. It should be a good start to see if everything went well!

barrett@farts ~> sudo e2fsck -f /dev/sdg2
e2fsck 1.46.5 (30-Dec-2021)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
rootfs: 4730/49152 files (0.6% non-contiguous), 180791/786432 blocks
barrett@farts ~>

If you got an error, you likely made a mistake in fdisk. Please reflash the card and try again!

Also, let's double-check with fdisk to make sure everything looks good:

barrett@farts ~> sudo fdisk -l /dev/sdg
Disk /dev/sdg: 119.38 GiB, 128177930240 bytes, 250347520 sectors
Disk model: STORAGE DEVICE  
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x00000000

Device     Boot  Start       End   Sectors   Size Id Type
/dev/sdg1  *         1    262144    262144   128M  c W95 FAT32 (LBA)
/dev/sdg2       262145 250347519 250085375 119.2G 83 Linux
barrett@farts ~>

Looks good to me! Now, let's do the full resize:

barrett@farts ~> sudo resize2fs /dev/sdg2
resize2fs 1.46.5 (30-Dec-2021)
Resizing the filesystem on /dev/sdg2 to 125042684 (1k) blocks.
The filesystem on /dev/sdg2 is now 125042684 (1k) blocks long.

barrett@farts ~>

This action should take a moment. In fact, for my USB 2.0 SD card reader with a microSD to SD converter, it took FOREVER..!

After it's done, though, we've completed the project!

Taking a Peek

You can now mount the disk and check your work:

sudo mkdir /mnt/duo
sudo mount -t /dev/sdg2 /mnt/duo

Of course, you can also just open it in Nautilius (or some other file manager)!