I added a new (logical) partition to my primary hard disk. There was no way I could udev make to recognize that partition. The recommended way to use hdparm yielded:

Actually I had to reboot the computer as to have the new partition show up in /dev/hdparm

Rebooting after a partition addition? What did I miss?

jlinkels

Whenever I've created, modified or deleted a partition with linux fdisk, after writing the changes and exiting fdisk,there is a message stating partition table will be re-synced on reboot.

I may be wrong here, but I think that a reboot is normal to let the kernel know about the partition changes.

partprobe might work - or not. I've had both it and hdparm -z fail to do the job.
Reboot is a surefire fix - if not always convenient.

If disk is in use, I've always had to reboot. If you want real freedom, then try LVM. Very convenient as well if you tend to change fs sizes often.

Why would it be normal to tell the kernel such things only during a reboot? One should be able to tell the kernel changes at all times. Only when the kernel itself needs to be reloaded, e.g. after installing a new one a reboot might be needed.

I heard about that one, but it is not available in Debian, or it was hidden too well. OK, I know the world is larger than just Debian but I was reluctant to install a non-Debian package. It seems like I have to find it anyway.

LVM would need some thorough study, but I heard many advantages of using it. Might do someday.

Thanks all
jlinkels

Are the physical partitions already used up? Why a logical partition called hda? I can understand an logical partition name of hda4 or hda5, given that the first 3 or so partitions are physical.
I'm no expert but I've done some partitioning, especially today, as I'm installing a new linux distro or three. The name hda may be referring to the mbr or the drive as a whole.
Best of luck.

Changing partitioning on the fly under a running OS is like reaching out the window and scraping the bugs off your airplanes windshield while flying. Chances of a successful and uneventful outcome are slim, no matter how many people brag that they've done it. It's always safer to land the airplane first.

Mangling partition tables of a disk that the OS isn't running on, is quite fine, and has worked for me 99% of the time. (Just once I made a typo, and had to cancel out of sfdisk before committing)

Mangling the partition table of the disk the OS is running on, is a little more hazardous, as you need to perform the reboot ASAP afterwards, or data can be read from / written to areas that the new partition table will not reflect until the reboot. Fun times.

I assume the "/dev/hda" mentioned is a typo and needs an actual partition number, as you can't add a logical partition as a device.

I don't see any harm in adding a partition to unpartitioned space. As long as the mounted partitions are not changed there should be nothing to worry. Non-mounted partitions do not take part in the kernel process in any way, regardless whether they are on the same device. And... how would you ever change partitions if the OS it not running?

jlinkels

Try "hdparm -z" or "partprobe".

There can only be 4 physical partitions on a hard disk as the partition table has only that much space to hold the description of the tables. Therefor usually one of the physical partitions is created to be extended. That is, it will be one physical partition, but it can be divided in an arbitrary number of logical partitions. You see only the logical ones, the OS takes car of that. The extended partition is always the last partition on disk, after you created the extended one, all space is used up and you only can create further logical ones, no physical ones.

jlinkels

You were doing o.k. till you got to this bit.
Not true at all.

(I presume you mean "primary")

Yes, I meant primary. sed s/physical/primary/g and it is correct again.

jlinkels

No, there is no problem there. You can certainly add the partition. But to start using it (making a new filesystem, mounting, etc.) then it's best to reboot first.

You change your partitions with that running OS, and then reboot. Attempting to continue on without a reboot is risky IMHO. It may work, it may not.

Whenever I'm doing major partitioning work (not just adding a new partition to unallocated space), I always do it from a LiveCD. First, I backup the entirety of Track Zero (so I include my bootloader stub) to an external USB thumbdrive. This is so I can recover/troubleshoot if things go bad. I don't find much need for partitioning work these days anyway - I started using LVM several years ago and love it.

Please keep such advise for windows forums ;p

It will work if you did it right and the disk was not already in use (which should be reported by the partitioning program).


Backup is a good thing and I would recommend it as well. But I can't see anything safer doing the operation from a life CD. Of course you need one if you screw up

Yes, LVM is easy and somehow safer (warns you if you try to do something really stupid although not foolproof). And you don't need a reboot.