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Asked: 2009-07-06 04:10:43 +0800 CST

Reread partition table without rebooting?

  • 772

Sometimes, when resizing or otherwise mucking about with partitions on a disk, cfdisk will say:

Wrote partition table, but re-read table failed. Reboot to update table.

(This also happens with other partitioning tools, so I'm thinking this is a Linux issue rather than a cfdisk issue.) Why is this, and why does it only happens sometimes, and what can I do to avoid it?

Note: Please assume that none of the partitions I am actually editing are opened, mounted or otherwise in use.

Update:

cfdisk uses ioctl(fd, BLKRRPART, NULL) to tell Linux to reread the partition table. Two of the other tools recommended so far (hdparm -z DEVICE, sfdisk -R DEVICE) does exactly the same thing. The partprobe DEVICE command, on the other hand, seems to use a new ioctl called BLKPG, which might be better; I don't know. (It also falls back on BLKRRPART if BLKPG fails.)

BLKPG seems to be a "this partition has changed; here is the new size" operation, and it looked like partprobe called it individually on all the partitions on the device passed, so it should work if the individual partitions are unused. However, I have not had the opportunity to try it.

linux partition fdisk

15 Answers

  1. Best Answer

    IMHO the most reliable/best answer is

    partprobe /dev/sdX
    • 79

  2. Rereading partition table information doesn't always work, but try

    hdparm -z /dev/sda

    or

    sfdisk -R /dev/sda

    If it works the values in /proc/partitions will change.

    • 22

  3. I (the original questioner) had a situation a few days ago when none of the other answers (including partprobe /dev/sdX, currently the accepted and highest-voted answer) worked. What did work, however, was this:

    blockdev --rereadpt /dev/sdX

    (I don't know why this worked and the others didn't, but I'm happy it did work, as it saved me a reboot on a busy server.)

    • 15

  4. On Centos7 :

    According to https://access.redhat.com/solutions/199573

    You should try :

    partx -u <partition>

    It worked for me.

    • 14

  5. Note: Please assume that none of the partitions I am actually editing are opened, mounted or otherwise in use.

    Given that assumption, the partition table can be successfully rescanned, and the issue won't arise. If you're getting that error, it's because the partition table is currently in use, and hence can't be re-scanned without creating inconsistencies.

    • 8

  6. It is not based on partition that you are editing.

    Suppose you have only one harddisk (/dev/sda) and two partitions (/dev/sda1, /dev/sda2) and you have mounted only one partition (/dev/sda1). If you delete or change anything about other partition which is not even mounted (/dev/sda2) you will get the error that re-reading of partition table failed and kernel will use old table.

    But if you have two harddisks (/dev/sda, /dev/sdb) and none of the partitions of (/dev/sdb) are in use. Then you can add / delete / resize /edit partitions of /dev/sdb and they will be re-read without any problem. But even if one partition of /dev/sdb was mounted during change. Then kernel will keep using old table.

    • 6

  7. With all mount points unmounted, running Yocto 2.4: 

    partprobe /dev/sda

    Still failed to re-load the partition table after partitions had been deleted on the device. Also tried -- and failed were:

    udevadm trigger --subsystem-match=block; udevadm settle
hdparm -z /dev/sda
blockdev --rereadpt /dev/sda

    All reported similar "BLKRRPART failed : device or resource busy..." errors instructing me to reboot. Is this failure of previously working methods possibly due to the fact that udev is now under systemd control? Thinking along those lines I tried:

    systemctl restart systemd-udevd.service

    And suddenly my disk is available again, without a reboot!

    • 5

  8. i'm on centos 6.5 x64 ; kernel 2.6.32 . and i'm testing the fdisk trick to resize.

    /dev/sda1 /boot
/dev/sda2 /

    All the following commands did not make kernel reread partition :

    • partprobe /dev/sda (warning : kernel failed to reread ....)
    • hdparm -z /dev/sda (BLKRRPART failed : device or resource busy)
    • blockdev -rereadpt /dev/sda (BLKRRPART failed : device or resource busy)
    • sfdisk -R /dev/sda (BLKRRPART failed : device or resource busy)

    i still need a reboot to make it work

    • 4

  9. When a command like blockdev --rereadpt /dev/sdX fails with

    blockdev: ioctl error on BLKRRPART: Device or resource busy

    this usually means that some (old) partition is indeed still somehow used by the kernel.

    Possible causes/fixes:

    1. an sdX partition - say sdX1 - is still mounted - check with mount and umount it
    2. /dev/sdX1 is part of a software raid - check cat /proc/mdstat and possibly stop the relevant arrays, e.g. mdadm --stop /dev/md126
    3. /dev/sdX1 is part of an LVM physical volume - check with pvdisplay/vgdisplay and possibly deactivate with vgchange
    4. /dev/sdX1 is part of some device mapping - e.g. via cryptsetup - check /dev/mapper and lsblk and possibly remove the mapping (e.g. cryptsetup luksClose)
    5. Race condition with some udev probing - check running processes with ps and possibly kill one

    If one tool - say blockdev --rereadpt fails usually similar ones like (partx -uv, kpartx, partprobe, kpartprobe) fail in a similar way until the root cause is eliminated.

    • 4

  10. You can also try:

    echo 1 > /sys/block/sdX/device/rescan

    (But might not work, see the comment below)

    • 3