Using parted’s resizepart non-interactively on a busy partition

I had a situation where I needed to spin up a virtual machine from a template, and if the new virtual machine’s disk was larger, I needed to resize the partition and then ‘grow’ the filesystem. Well, as with any thing, that you need to do for more than once, I tried to script it using Ansible and incorporate it into our existing VM provisioning scripts. First step was to figure out command we need to run. Ansible’s parted module is really bare-bones and anemic, and it didn’t have the resizepart command which I wanted, so I had to resort to using the shell module. Ensuring idempotency is difficult with bare shell commands, but we’ll use what we can get.

This is the interactive parted command which will resize partition 2 on /dev/sda.

root@test-vm-18:~# parted /dev/sda
GNU Parted 3.2
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) resizepart 2
Warning: Partition /dev/sda2 is being used. Are you sure you want to continue?
Yes/No? Yes
End? [10.7GB]? 100%
(parted) quit
Information: You may need to update /etc/fstab.

Next step is to condense the command into a single line. After looking at the manual and a bit of trial and error, this is the one which works –

parted /dev/sda resizepart 2 yes 100%

The yes is in there in order to automatically choose to continue despite the warnings. This doesn’t work on Ansible, because it still requires user interaction for the warnings. Note that parted also has a scripted mode (with the -s switch) which doesn’t expect any interaction from the user, but that turned out to be buggy in our specific combination of command and options.

The eventual solution was to use an undocumented switch ---pretend-input-tty. Since Ansible uses a TTYless SSH session, and Parted’s non-interactive mode doesn’t work, this was the only way out.

parted ---pretend-input-tty /dev/sda resizepart 2 yes 100%

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