Retrieving free space in linux / partitioning

[Wimnat]

I installed Red Hat linux and when it came to partitioning, i left 20 GB of free space because i wasn't quite sure how i wanted to split that 20 GB up at the time.

Now i have decided i want a 10GB and 2x 5GB partitions. No problem - fdisk is the answer. Or so i thought. For some reason fdisk refuses to let me touch the free space. I'm not at all sure why. Any ideas?

[root@tigpr8 mnt]# df -m
Filesystem 1M-blocks Used Available Use% Mounted on
/dev/hda2 35971 17840 16304 53% /
/dev/hda1 97 15 78 16% /boot
none 1004 0 1004 0% /dev/shm

[root@tigpr8 mnt]# fdisk /dev/shm
You will not be able to write the partition table.

Unable to read /dev/shm

[root@tigpr8 mnt]# fdisk shm

Unable to open shm

[dylunio]

/dev/shm isn't your free space it's something special that linux uses (though I'm not sure what for). To find out the partitions that fdisk can partition:

fdisk -l

and you'll run

fdisk /dev/hda

to edit the partitons on hda, which in your case will be adding partitions.