Partition Table – Is it Possible to Unmount?

partitionpartition-table

Is it possible to unmount a partition table so I only see sda and not sda1 and sda2 in /dev?

Background:

I know a partition table is not mounted.
But I did not find a better name for this.

I often use dd to overwrite a hard disk or an usb pen.
But they often have some partitions on it. And after overwriting I can still see the old (no longer existing) partition table using lsblk.

I know it's possible to reread the partition table using partprobe.

But I wonder if it is possible to unmount the partition table before overwriting the usb pen. Because I don't want a programm to access a corrupt partition while overwriting with dd.

Best Answer

You can use partx's -d option to tell the kernel to forget about partitions. For example, partx -d /dev/sda will make /dev/sda1, /dev/sda2, ... go away (temporarily). They'll show up again next time the kernel is made to re-scan the partition table.

Another option is delpart: delpart /dev/sda 1; delpart /dev/sda 2 should do it (but the partx syntax is nicer).

A third option is to wipe the partition table first then let the kernel reread it; any partition table editor tool (e.g., sfdisk, gdisk, etc.) could be used, or wipefs (which will do partition tables, not just filesystems).

Related Solutions

How to Change Partition Number from sda1 to sda2

FYI, it is a bad idea and you can lose everything. If you still want to do it, here are the steps:

Don't do it. If this doesn't help, then:

Use the sfdisk tool: First, make a backup of the partition table using

sfdisk -d /dev/sda > sda.out

Then go for it:

sfdisk /dev/sda -O sda-partition-sectors.save

You will see something like this

Checking that no-one is using this disk right now ...
OK

Disk /dev/sda: 1018 cylinders, 124 heads, 62 sectors/track
Old situation:
Units = cylinders of 3936256 bytes, blocks of 1024 bytes, counting from 0

   Device Boot Start     End   #cyls    #blocks   Id  System
/dev/sda1          0+      5       6-     23063+  83  Linux
/dev/sda2          6    1017    1012    3890128   83  Linux
/dev/sda3          0       -       0          0    0  Empty
/dev/sda4          0       -       0          0    0  Empty
Input in the following format; absent fields get a default value.
<start> <size> <type [E,S,L,X,hex]> <bootable [-,*]> <c,h,s> <c,h,s>
Usually you only need to specify <start> and <size> (and perhaps <type>).

/dev/sda1 :

Now it is asking you to give the new details for the 'sda1' partition. So you have to give the numbers of sda2 here. So, I put '6 1012' here and press Enter:

    /dev/sda1 :6 1012
    /dev/sda1          6    1017    1012    3890128   83  Linux
    /dev/sda2 :

Now check if the numbers printed after you pressed Enter are exactly the same as those printed earlier for sda2. If it is okay, continue with giving the new numbers for sda2:

    /dev/sda2 :0
    /dev/sda2          0+      5       6-     23063+  83  Linux
    /dev/sda3 :

This time it was enough to enter "0" in my case - but you have to make sure the numbers aren't messed up in yours.

Next, continue with the other partitions in the same manner. If you already reached the end of the disk, pressing Enter is enough. Finally, check again that all the numbers are okay and save the partition table (or not). If you messed something up, have a look at man sfdisk and the descriptions of '-d', '-O' and '-I' options.

Notice also, that once you've made the crazy changes, you might need to run 'sync' so that the partitions are re-read before you try to mount them.

Linux – Partition table not recognized by Linux kernel

For some reason your kernel fails to read the partition table:

[ 8775.030291] end_request: I/O error, dev sdb, sector 0
[ 8775.030300] quiet_error: 30 callbacks suppressed
[ 8775.030306] Buffer I/O error on device sdb, logical block 0
[ 8775.033781] ldm_validate_partition_table(): Disk read failed.

Thus, it can't create devices for partitions as it did not read the partition table. Later when you try to see the partition table with parted or fdisk the IO is performed successfully.

Try to use partprobe /dev/sdX when your kernel did not recognized the partitions at boot time.

man partprobe:

PARTPROBE(8)                                                         GNU Parted Manual                                                        PARTPROBE(8)

NAME
       partprobe - inform the OS of partition table changes

SYNOPSIS
       partprobe [-d] [-s] [devices...]

DESCRIPTION
       This manual page documents briefly the partprobe command.

       partprobe  is  a  program  that informs the operating system kernel of partition table changes, by requesting that the operating system re-read the
       partition table.

Best Answer

Related Solutions

How to Change Partition Number from sda1 to sda2

Linux – Partition table not recognized by Linux kernel

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