fdisk scripts

Low level partitioning tools such as gpart, disklabel and alike do support automation thru scripts, that is a set of commands to execute.
But what about Linux’s fdisk implementation?
Well, it turned out that it does support scripts too.
I happened to renew my set of USB sticks, and I wanted them all to be identical not only on an hardware basis, but also on a partitioning setup. Having to repeat all the low level fdisk operations by hand made me think about scripts, and so I read the man page to find out it can be done.
Not having any experience with partx, I decided to solve the problem creating a first partition scheme, and then cloning it on all other devices.

Creating a script, the quick way

Once you are inside fdisk, having created a partition scheme, you can use the O command to output the commands on a text file. The program will ask you for the file to produce, and the result will be something like the following: 

% cat keys.txt
label: dos
label-id: 0x0a186eaf
device: /dev/sdc
unit: sectors

/dev/sdc1 : start=        2048, size=    19494912, type=b
/dev/sdc2 : start=    19496960, size=    41943040, type=b


It clearly reminds a disklabel file.

Using a script

In order to re-use a script, you need to enter fdisk for the device, and then use the command I to make fidks read the script. 

% sudo fdisk /dev/sdc

Welcome to fdisk (util-linux 2.33.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): I

Enter script file name: keys.txt

Created a new DOS disklabel with disk identifier 0x0a186eaf.
Created a new partition 1 of type 'W95 FAT32' and of size 9,3 GiB.
Created a new partition 2 of type 'W95 FAT32' and of size 20 GiB.
Script successfully applied.

Command (m for help): p
Disk /dev/sdc: 29,3 GiB, 31457280000 bytes, 61440000 sectors
Disk model: PHILIPS
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: 0x0a186eaf

Device     Boot    Start      End  Sectors  Size Id Type
/dev/sdc1           2048 19496959 19494912  9,3G  b W95 FAT32
/dev/sdc2       19496960 61439999 41943040   20G  b W95 FAT32

Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Re-reading the partition table failed.: Device or resource busy

The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).


The p command has been issued only to prove that the partitions have been created.

partx, parted and fdisk friends

As far as I understand, Linux’s fdisk is based on partx, and there are a few commands to amnipulate partitions from a kernel point ogf view, like addpart and delpart.
The tool that seems to me more likely disklabel or gpart is parted.

The article fdisk scripts has been posted by Luca Ferrari on January 13, 2022

Tags: linux