mknod: does the creation of a block device write data into the device?

stf92 · 11-19-2013, 09:13 AM

Kernel 3.6.29, Slackware 14.0.

Hi: /dev/sda4, in my system, is an extended partition, to allocate two logical partitions, /dev/sda5 and /dev/sda6. Now I get

Code:

root@server:~# ls -l /dev/sda
brw-rw---- 1 root disk 8, 0 2013-11-19 08:37 /dev/sda
root@server:~# ls -l /dev/sda5
/bin/ls: cannot access /dev/sda5: No such file or directory
root@server:~# ls -l /dev/sda6
/bin/ls: cannot access /dev/sda6: No such file or directory
root@server:~# 
root@server:~# fdisk -l
fdisk: unable to seek on /dev/sda: invalid argument

[/code]

You can see /dev/sda is a _block device_ according to ls, that is, it exists. If I use mknod to have /dev/sda5, /dev/sda6 again, shall I be destroying my data on the logical partitions?

gnashley · 11-19-2013, 09:17 AM

What does 'ls -l /dev/sd*' show? mknod doesn't write any data at all. Did you create the sda node with mknod?

guanx · 11-19-2013, 09:21 AM

Quote:

Originally Posted by stf92

Code:

fdisk: unable to seek on /dev/sda: invalid argument

The position fdisk wants to read from is beyond the end of the device. You device has a size of zero. Check dmesg for more information.

stf92 · 11-19-2013, 09:22 AM

Left blank intentionally

stf92 · 11-19-2013, 09:25 AM

Quote:

Originally Posted by gnashley

What does 'ls -l /dev/sd*' show? mknod doesn't write any data at all. Did you create the sda node with mknod?

Thanks so much.

Code:

root@server:~# ls -l /dev/sda*
brw-rw---- 1 root disk 8, 0 2013-11-19 08:37 /dev/sda
brw-rw---- 1 root disk 8, 1 2013-11-19 08:37 /dev/sda1
brw-rw---- 1 root disk 8, 2 2013-11-19 08:37 /dev/sda2
brw-rw---- 1 root disk 8, 3 2013-11-19 08:37 /dev/sda3
brw-rw---- 1 root disk 8, 4 2013-11-19 08:37 /dev/sda4
root@server:~#

Quote:

Originally Posted by gnashley

Did you create the sda node with mknod?

No, I did not.

stf92 · 11-19-2013, 09:55 AM

Quote:

Originally Posted by guanx

The position fdisk wants to read from is beyond the end of the device. You device has a size of zero. Check dmesg for more information.

Thanks. I know what happens, I think. I told FDISK from a modern free DOS distro to allocate a logical partition on sda4, an extended partition. He seemed to do everything OK. I now see he did not. I followed the advice in the cfdisk about letting the particular O.S. to do the partition. The first time I installed FreeDOS I partitioned sda4 with linux fdisk and everything went OK!

TobiSGD · 11-19-2013, 10:28 AM

OFFTOPIC: Kernel 3.6 is EOL and totally unsupported for quite some time, I recommend to switch to one of the longterm kernels 3.4 or 3.10.

stf92 · 11-20-2013, 11:54 AM

Everything fine now. I sacrificed some unimportant files I had there and backup the other, after which a DISKPART'ed the extended partition and recreated the two logical partitions. After running lilo and booting the devices where created again. Thanks allthesame for you advices.

@TobiSGD: thanks for your notice.