Using fdisk (cont'd)
Creating Partitions
I'm going to do two examples that are hopefully pretty
illustrative and will help you figure out the magic behind fdisk.
Creating a swap partition
I'm not sure if you can run a Linux system without a swap
partition or not, but I wouldn't ever want to. So, this is
one of the more important partitions. It has no special
restrictions on it, really. Actually, for older (2.0) kernels
some of them can only handle swap partitions that are not any
larger than 128MB. But, by now those kernels are rarely in
use anymore and ought to be upgraded anyway.
In this example, I'm going to create a swap partition of
256MB at the end of my drive. So, once I'm in fdisk, I want
to choose the "n" option for "add a new partition". This is
what I get:
Command (m for help): n
Command action
l logical (5 or over)
p primary partition (1-4)
I sort of explained the difference between these two earlier.
Since I don't have any more room for another primary
partition (partitions 1-3 contain all of my cylinders), I
have to make it a logical partition, so I choose "l".
l
First cylinder (1351-2491, default 1351):
Unless you have a good reason for leaving space between your
partitions (and they do exist), it's almost always best to
choose the default, which is the first available cylinder.
You can actually type it in or just hit Enter.
Using default value 1351
Last cylinder or +size or +sizeM or +sizeK (1351-2491,
default 2491):
Now here's the best feature of fdisk. You don't have to
calculate the cylinders you want a partition to take up,
you can just give it a size in MB or KB and it will get it
as close as possible for you. Since I want this to be a
256MB swap partition I enter "+256M" (without quotes):
Last cylinder or +size or +sizeM or +sizeK (1351-2491,
default 2491): +256M
Command (m for help):
And now I'm back at a command prompt. Let's print out
the partition table again (p) and see if that change took
place:
Command (m for help): p
Disk /dev/hdb: 255 heads, 63 sectors, 2491 cylinders
Units = cylinders of 16065 * 512 bytes
Device Boot Start End Blocks Id System
/dev/hdb1 * 1 195 1566306 a5 BSD/386
/dev/hdb2 196 212 136552+ 82 Linux swap
/dev/hdb3 213 2491 18306067+ 5 Extended
/dev/hdb5 213 474 2104514+ 83 Linux
/dev/hdb6 475 506 257039+ 83 Linux
/dev/hdb7 507 532 208844+ 83 Linux
/dev/hdb8 795 925 1052257 83 Linux
/dev/hdb9 926 1056 1052257 83 Linux
/dev/hdb10 1057 1088 257008+ 83 Linux
/dev/hdb11 1089 1350 2104483+ 83 Linux
/dev/hdb12 533 794 2104483+ 83 Linux
/dev/hdb13 1351 1383 265041 83 Linux
Command (m for help):
Well, I now have a 259MB partition at the end. But,
there's a problem. It's a "Linux" partition (ID = 83)
and not a "Linux swap" partition (ID = 82).
After a quick look at the list of commands (m), I see
the "t" option - "change a partition's system id". This
sounds right, so let's give it a shot.
Command (m for help): t
Partition number (1-13):
Of course, we just created partition #13, so I choose
that one:
Partition number (1-13): 13
Hex code (type L to list codes):
Now I look up and see that the hex code (ID) for "Linux
swap" is 82, but I just want to make sure, so I hit "L",
and surely enough, you can see that 82 is indeed "Linux
swap", so we enter in 82:
Hex code (type L to list codes): 82
Changed system type of partition 13 to 82 (Linux swap)
Excellent! Now let's print the partition table again
just to make sure that the changes took effect. I get
this line for our partition:
/dev/hdb13 1351 1383 265041 82 Linux swap
Wonderful. We have created a Linux swap partition. Now
in order for it to actually be written onto the hard
drive we must write the partition table to the disk.
That is option "w" - "write table to disk and exit".
When I call it I get this:
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
WARNING: If you have created or modified any DOS 6.x
partitions, please see the fdisk manual page for additional
information.
So, now we have a new partition on our disk for swap.
All that's left now is to actually set up the swap
"filesystem" on it so that the system can read and write
to it correctly. I'm not going to cover that in this
particular NHF though I plan on writing another one
about it.
[- next page: ext2 and deleting partitions -]
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