bug#71790: parted -s emits a warning when shrinking a partition

[Sean Warner]

Hello Brian,

Thank you for your helpful reply.

There are many threads on various sites where people, like me, have incorrectly assumed that parted -s will let you do whatever you want and are left confused. It makes sense to apply the philosophy of do-no-harm with the parted --script option but perhaps the man page needs to clarify the intended behavior.

Currently it simply says: "-s --script never prompts for user intervention" instead maybe something like: "Will default safe answers to user prompts such as 'No' when parted checks if it is OK to shrink a partition." OK that sounds wordy but I think better to have verbose man pages that don't leave any doubt as to what the intended functionality is.

This bug report https://debbugs.gnu.org/cgi/bugreport.cgi?bug=27204 (Norman Shulman) proposes a patch to really make parted -s "never prompt for user intervention" even if shrinking a partition. I tried it out and it works, at least I have the option now!

--- a/parted/parted.c	2014-06-15 15:16:33.000000000 -0400
+++ b/parted/parted.c	2017-05-24 17:27:02.093371079 -0400
@@ -1551,7 +1551,7 @@ do_resizepart (PedDevice** dev, PedDisk*
                                           start, end))
                 goto error_destroy_constraint;
         /* warn when shrinking partition - might lose data */
-        if (part->geom.end < oldend)
+        if (part->geom.end < oldend && !opt_script_mode)
                 if (ped_exception_throw (
                             PED_EXCEPTION_WARNING,
                             PED_EXCEPTION_YES_NO,

Cheers,

Sean 

-----Original Message-----

From: Brian C. Lane <bcl@redhat.com>

To: Sean Warner <plica2006@gmail.com>

Cc: 71790@debbugs.gnu.org

Subject: Re: bug#71790: parted -s emits a warning when shrinking a partition

Date: 27/06/24 16:28:55

On Wed, Jun 26, 2024 at 11:51:38PM +0100, Sean Warner wrote:

I am also having this bug reported in 2017:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=879555

$ parted -v

parted (GNU parted) 3.6

Copyright (C) 2023 Free Software Foundation, Inc.

License GPLv3+

Written by

<http://git.debian.org/?p=parted/parted.git;a=blob_plain;f=AUTHORS>.

$ cat /etc/lsb-release 

DISTRIB_ID="ManjaroLinux"

DISTRIB_RELEASE="24.0.2"

DISTRIB_CODENAME="Wynsdey"

-- If increasing the size of a partition the following command works

but if shrinking a partition it gives a warning "Warning: Shrinking a

partition can cause data loss, are you sure you want to continue?" and

the command just exits back to the command prompt and no changes are

made to the partition.

sudo parted -s /dev/loop0 resizepart 1 46280703s

I assumed that parted -s would automatically supply a default value of

'Yes' in this instance?

No, in script mode parted defaults to the safe option. Automatically

saying yes will lead to data loss so it defaults to know. I admit the

message is misleading, this is because of how parted handles warnings

like this and it could use some improvement.

I don't really have any suggestion for working around this other than

doing it in interactive mode.

input-tty <-- But is this safe to keep using if not documented? Any

plans to make ---pretend-input-tty an official "thing" in Parted?

No, it's there for the tests. But there's no plan to remove it since the

tests depend on it. But I really don't recommend automating things that

could lose data.

Brian