Saturday, January 03, 2009

automated disk partitioning with sfdisk

I discovered sfdisk a few years ago (part of util-linux) and have been using it in automation scripts ever since.  sfdisk is like fdisk, but is scriptable.  So for example, to list the partitions on a disk: 
[root@host]# sfdisk -l /dev/sdc

Disk /dev/sdc: 121601 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start     End   #cyls    #blocks   Id  System
/dev/sdc1          0+ 121600  121601- 976760001   83  Linux
/dev/sdc2          0       -       0          0    0  Empty
/dev/sdc3          0       -       0          0    0  Empty
/dev/sdc4          0       -       0          0    0  Empty
To list them in a dump format, suitable as input to sfdisk (for cloning, saving or for some wacky awesome script): 
[root@host ]# sfdisk -d /dev/sdc
# partition table of /dev/sdc
unit: sectors

/dev/sdc1 : start=       63, size=1953520002, Id=83
/dev/sdc2 : start=        0, size=        0, Id= 0
/dev/sdc3 : start=        0, size=        0, Id= 0
/dev/sdc4 : start=        0, size=        0, Id= 0
You can use that dump in a fashion like this to clone a disks's partition map:
sfdisk -d /dev/sdc | sfdisk /dev/sdd
Or for saving it and using it later:
sfdisk -d /dev/sdc > partition.sfdisk
sfdisk /dev/sdc

# posted by Nathan : 1/03/2009 08:20:00 PM
Comments:
Yeah sfdisk is pretty trick! I actually used it back in the day @ mp3 for flipping our file system partition type from ext2 to reiserfs in our kickstart scripts.

#!/bin/sh

### Need to compile reiser tools before this will work

# Formats /usr1 as a reiserfs partition
# creates a swap partition

#detect drive interface type
grep 301 /proc/cmdline >/dev/null && export DTYPE=hda DPART=hda3
grep 801 /proc/cmdline >/dev/null && export DTYPE=sda DPART=sda3

#Make /usr1 reiserfs
umount /usr1 && \
/sbin/sfdisk --change-id /dev/$DTYPE 3 83 && \
echo "y" | /sbin/mkreiserfs -q /dev/$DPART || exit 1
# posted by Blogger tsaavik : 12:47 PM
 
Could it be that the last line of your posting is missing the input redirection of the previously generated partition file?

So this erroneous line:
sfdisk /dev/sdc
should better read:
sfdisk /dev/sdc < partition.sfdisk

Nevertheless, thanks a lot for your blog!
Cheers,
Gerhard
# posted by Anonymous Anonymous : 3:08 AM
 

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