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jernst

Member

From: Silicon Valley

Registered: 2014-03-04

Posts: 290

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Solved: Disk or partition?

Had this question: given a block device, how would I reliably determine whether it refers to a disk or a partition?

Found the answer before I could complete my question, and thought I post it here:

$ udevadm info /dev/sda | grep DEVTYPE
E: DEVTYPE=disk
$ udevadm info /dev/sda1 | grep DEVTYPE
E: DEVTYPE=partition

karol

Archivist

Registered: 2009-05-06

Posts: 25,440

Re: Solved: Disk or partition?

I'm not sure I understand, but isn't /dev/foo always a disk and /dev/foon always a partition?

jasonwryan

Anarchist

From: .nz

Registered: 2009-05-09

Posts: 30,424

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Re: Solved: Disk or partition?

Not a GNU/Linux discussion, moving to NC...

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jernst

Member

From: Silicon Valley

Registered: 2014-03-04

Posts: 290

Website

Re: Solved: Disk or partition?

Turns out that this reports DEVTYPE=disk for partitions inside of an image file, accessed as mapped devices via kpartx:

> kpartx -a imagefile
> udevadm info /dev/loop0 | grep DEVTYPE
E: DEVTYPE=disk
> udevadm info /dev/mapper/loop0p1 | grep DEVTYPE
E: DEVTYPE=disk

lsblk gets it right. I guess I'll do this instead:

> lsblk -o TYPE -n /dev/mapper/loop0p1
part

Stebalien

Member

Registered: 2010-04-27

Posts: 1,237

Website

Re: Solved: Disk or partition?

I'm not sure I understand, but isn't /dev/foo always a disk and /dev/foon always a partition?

That depends on how much udev magic is in play. OP said "reliably".

Not a GNU/Linux discussion, moving to NC...

This is not really a newbie question... (udevadm is not a newbie tool...).

Regardless, are you really sure you only want partitions? IIRC, it's possible to format a device directly without partitioning.

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nstgc

Member

Registered: 2014-03-17

Posts: 393

Re: Solved: Disk or partition?

In 14 years of using Linux, I've never known /dev/sdX do be anything other than a disk and /dev/sdXY anything other than a partition of the disk sdX. I personally would consider this "reliable" but then again your use case may be different from mine.