Auto expand last partition to use all unallocated space, using parted in batch mode

Question

Long story short, I need to perform this all automatically on boot (embedded system).

Our engineers will flash images to production devices. These images will contain a small partition table. On boot, I need to automatically expand the last partition (#3) to use all the available space on the disk.

Here is what I get when I look at the free space on my disk.

> parted /dev/sda print free
Model: Lexar JumpDrive (scsi)
Disk /dev/sda: 32.0GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name     Flags
        17.4kB  1049kB  1031kB  Free Space
 1      1049kB  25.3MB  24.2MB  fat16        primary  legacy_boot
        25.3MB  26.2MB  922kB   Free Space
 2      26.2MB  475MB   449MB   ext4         primary
 3      475MB   1549MB  1074MB  ext4         primary
        1549MB  32.0GB  30.5GB  Free Space

I need to expand partition 3 by N (30.5GB) number of bytes

How do I perform this step automatically, with no prompt? This needs to work with a dynamic size of space available after the 3rd partition.

Answer 1

Being unable to properly script parted (it asked for confirmation because the partition was mounted and contrary to other answers I found did not understand -1s or 100%), I just found the growpart tool which does exactly this.

Usage is simple: growpart /dev/sda 3 (and then resize2fs /dev/sda3, or another appropriate command for the used filesystem type).

In Debian and Ubuntu it is packaged as cloud-guest-utils.

Answer 2

In current versions of parted, resizepart should work for the partition (parted understands 100% or things like -1s, the latter also needs -- to stop parsing options on the cmdline). To determine the exact value you can use unit s, print free. resize2fs comes afterwards for the filesystem.

---

Old versions of parted had a resize command that would resize both partition and filesystem in one go, it even worked for vfat.

In a Kobo ereader modification I used this to resize the 3rd partition of internal memory to the maximum: (it blindly assumes there to be no 4th partition and msdos table and things)

start=$(cat /sys/block/mmcblk0/mmcblk0p3/start)
end=$(($start+$(cat /sys/block/mmcblk0/mmcblk0p3/size)))
newend=$(($(cat /sys/block/mmcblk0/size)-8))

if [ "$newend" -gt "$end" ]
then
    parted -s /dev/mmcblk0 unit s resize 3 $start $newend
fi

So you can also obtain the values from /sys/block/.../ if the kernel supports it. But parted removed the resize command so you have to do two steps now, resizepart to grow the partition, and whatever tool your filesystem provides to grow that, like resize2fs for ext*.

Answer 3

The right way to do this is use the fact that parted has the notion of percentages. So

parted /dev/sda resize 3 100%

Answer 4

In Ubuntu 18.04, I am able to resize to fill unallocated space in a script with the following:

sudo parted -s /dev/sdb "resizepart 2 -1" quit
sudo mount -av
sudo umount /dev/sdb2
sudo mount /dev/sdb2 /mnt
sudo resize2fs /dev/sdb2

It may not be necessary to mount before resizing. I did it to suppress a query from resize2fs for user input.

Answer 5

Alternatively, you can do a one liner with sfdisk:

echo ", +" | sfdisk -N 3 /dev/sda

See Karel Zak's blog post for more details.

Answer 6

i know the question mentioned using parted, but here is a bash script using fdisk and resize2fs.

I use it on Raspberry Pi, but you can use it anywhere those 2 tools are available, just change the target disk (sda, sdb, ...).

Always be careful while manipulating partitions: you might end up breaking your system !

#!/bin/bash

#
#   This bash script extends the last partition of the specified disk
#   To the maximum size available.
#

# target disk
disk='mmcblk0'

# get last partition
part=$(grep  "${disk}" /proc/partitions | tail -1 | awk '{print $4}' | xargs)
partN=$(echo $part | tail -c 2)    

# fdisk: delete and recreate the last partition with the largest size possible.
(
echo d # Delete partition
echo $partN # Last partition
echo n # Add a new partition
echo p # Primary partition
echo $partN # Last partition
echo   # First sector (Accept default: 1)
echo   # Last sector (Accept default: varies)
echo w # Write changes
) | fdisk /dev/$disk 

# update filesystem to match new partition size
resize2fs /dev/$part

Answer 7

Just to summarize a few of the comments into a method: (for in my case sda2)

parted /dev/sda resizepart 2 100%

resize2fs /dev/sda2

Answer 8

In the short video step-by-step tutorial "How to Resize a Live Filesystem on Linux" is shown, how to achieve this a very simple way. I've just extended the /dev/sda2 on a VirtualBox VM after resizing the VDI (virtual hard drive). It works pretty well:

0. Back up the data.
1. Start fdisk: sudo fdisk /dev/sda.
2. Print the partitions: p.
3. Delete the partition, you want to resize (it's a kind of unlinking, the data is not removed): d. If you have multiple partitions, you'll be asked, which one should be deleted.
4. Create a new partition: n. Follow the dialog for setting the partition type, the partition number, the first sector, and the last sector. The last two parameters define the size of the new partition. By default the space between the first and the last sector will cover the complete available free space. The last option: Choose whether the signature should be removed.
5. See the changes (and compare the result with the state before): p.
6. Save the changes and quit fdisk: w (use q to exit without saving).