Arch Linux

azzka

Member

Registered: 2012-09-17

Posts: 5

[SOLVED] Issue with partition labels

Well, this is quite hard (and awkward) to explain...I'm trying to do it as better as I can.

So, this was my hd configuration

/dev/sda1 /
/dev/sda2 /home
/dev/sda3 windows
/dev/sda4 swap

It happened I messed up with the MBR and partitions' table, end it ended in losing the whole / (but I managed somehow to recover sda2 and sda4)

So I had to reinstall Arch again, and now my configuration is

/dev/sda1 (extended)
/dev/sda2: /home
/dev/sda3: windows
/dev/sda4: swap
/dev/sda5: /boot 
/dev/sda6: /var
/dev/sda7: /

Everything works well and I haven't any real problem with it (just grub complain about something during grub-install but I don't care since it worked).

The only thing that is really weird and I really can't understand is that

# ls -l /dev/disk/by-label 
lrwxrwxrwx 1 root root 10 May 21 22:36 ARCH_201305 -> ../../sda1
. . .

Basically it means that sda1 is labeled ARCH_201305. That I can't understand: sda1 is extended and containes sda5,6,7 and it is not supposed to contain any filesystem, so
it shouldn't have any label, but the kernel thinks so. That's not a big problem unless when I use an arch livecd (the release of May 2013, not with the others of course) because
I have to manually mount /run/archiso/bootmnt because it tries to mount /dev/sda1 and not the right partition (suppose /dev/sdb1 or /dev/cdrom or what else).

How can I fix it (/dev/sda1 being labeled?)
Thank you for the help in advance, the Arch community is great

EDIT: It may be useful knowing that I messed up the mbr by writing the arch iso to sda instead of sdb (using dd) for mistake, so that might be (well, that is) the cause. I know the cause, I'm just wondering how to fix it

Last edited by azzka (2013-05-22 09:32:24)

srs5694

Member

From: Woonsocket, RI

Registered: 2012-11-06

Posts: 719

Website

Re: [SOLVED] Issue with partition labels

This is pure speculation, but: My guess is that this is a kernel bug. An extended partition is likely to contain a partition record (similar to an MBR) in its first sector followed by a number of empty sectors; however, if you create an extended partition in a location that used to contain a filesystem, it's likely that some of that old filesystem's data would remain behind. Thus, if the kernel tries to probe the extended partition for a filesystem label, it might just find one amidst that leftover data.

If I'm right, you should be able to get rid of the leftover data by a suitable use of the "dd" command, but the details will depend on your disk's layout, and this action could be risky, since a mistake could end up overwriting critical filesystem data in the first (or even subsequent) logical partitions.

azzka

Member

Registered: 2012-09-17

Posts: 5

Re: [SOLVED] Issue with partition labels

Yeah I thought of something like that
I even searched in Wikipedia for a detailed description of mbr and ebr layout (didn't find anything useful)
I'll try an hexdump of sda1 trying to find something like ARCH_201305 and will try (in case) to replace an a with x to see what happens. Likely that would be even the solution (I don't really mind of what sda1 is labeled,  not used)

Anyway I have more than a reason to suspect that it won't be as easy so if someone else's got a better idea...

EDIT:
Solved: using hexedit I searched for the string ARCH_201305 and replaced the 'A' with 0x00 which is the end character of a c string.
Now everything work well.

Last edited by azzka (2013-05-22 09:31:59)