Question

I’m writing some code to read and interpret the MBR and then the FAT of a pen drive formatted with fat32, everything is going fine, I now want to write to the device at a specific position, so after closing the device I’d opened to read, I try again like this:

dr = file("/dev/disk5","r+")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
 IOError: [Errno 16] Resource busy: '/dev/disk5'

So i close everything up, and restart the interpreter with sudo (sudo python), and retry all with the same results.

what can I do in order to be able to open the device for write access?
thanks
EDIT with some more code.

import sys,os
disk = file("/dev/disk5",'rb')
disk.seek(0)
sector_size=512
first_sector = disk.read(1*sector_size)
fat_part_list = (first_sector[-66:])[:64]
part1=fat_part_list[:16]
#more code here in order to analyse the first partition information in the MBR and get the required offset to actually read the partition itself.
#now for instance lets say I want to write here in sector 1 byte 0 ( so basically at seek(0).
disk.close()#close the device
disk = file("/dev/disk5","r+")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  IOError: [Errno 16] Resource busy: '/dev/disk5'

in fact you could simply see the problem as this:

http://pastie.org/2521541

never got the formating to work properly…

it all seems like an privileges error, but running the interpreter with sudo yields no changes.

Answer 1

You should unmount the block device before opening it in Python.