Difference between revisions of "Allocating a Windows Disk Partition to RHEL 6"

Revision as of 21:32, 1 February 2016

In the previous chapter we looked at how to install Red Hat Enterprise Linux 6 on the same disk as Windows. This so called "dual boot" configuration allows the user to have both operating systems installed on a single disk drive with the option to boot one or the other when the system is powered on. Performing this type of installation was covered in Installing RHEL 6 with Windows in Dual Boot Environment.

This chapter is intended for users who have decided they like RHEL 6 enough to delete Windows entirely from the disk, and use the resulting space for Linux. In the following sections we will work through this process step by step.

Deleting the Windows Partition from the Disk

The first step in freeing up the Windows partition for use by RHEL is to delete that partition. Before doing so, however, it is imperative that any data you need to keep is backed up from both the Windows and RHEL partitions. Having done that, it is safe to proceed with this chapter.

In order to remove the Windows partition we first need to identify it using the fdisk tool:

# fdisk -l

Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x4eb978f9

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      102400    7  HPFS/NTFS
Partition 1 does not end on cylinder boundary.
/dev/sda2              13        1400    11141120    7  HPFS/NTFS
/dev/sda3            1400        1464      512000   83  Linux
/dev/sda4            1464        2611     9214976    5  Extended
/dev/sda5            1464        2611     9213952   8e  Linux LVM

In the above example output the system contains one physical disk drive referenced by device name /dev/sda. On that disk drive are three partitions accessed via the device names /dev/sda1 through /dev/sda5 respectively. Based on the values in the System column, there are two NTFS partitions. The first is very small and marked as bootable so clearly contains the boot record. The second, much larger, NTFS partition is the one containing the Windows operating system and user data that we plan to remove. Note that a FAT partition also indicates the presence of a Windows installation.

To remove the partition, start the fdisk tool using the device name of the disk containing the partition (/dev/sda in this instance) and follow the instructions to switch out from DOS mode and to display sectors:

# fdisk /dev/sda

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
         switch off the mode (command 'c') and change display units to
         sectors (command 'u').

Command (m for help): c
DOS Compatibility flag is not set

Command (m for help): u
Changing display/entry units to sectors

Command (m for help):

Next, display the partition table information for the disk drive using the p command:

Command (m for help): p

Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x4eb978f9

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS
/dev/sda2          206848    22489087    11141120    7  HPFS/NTFS
/dev/sda3        22489088    23513087      512000   83  Linux
/dev/sda4        23513088    41943039     9214976    5  Extended
/dev/sda5        23515136    41943039     9213952   8e  Linux LVM

Make a note of the start and end addresses of the partition we will be deleting (/dev/sda2 in this instance).

At the command prompt, delete the Windows partition (which is partition 2 on our example system):

Command (m for help): d
Partition number (1-5): 2

Command (m for help):

Now that we have deleted the Windows partition we now need to create the new RHEL partition in the vacated disk space. The partition number must match the number of the partition removed (in this case 2) and is going to be a primary partition. It will also be necessary to enter the Start and End sectors of the partition exactly as reported for the old partition (fdisk will typically offer the correct values by default, though it is wise to double check):

Command (m for help): n
Command action
   l   logical (5 or over)
   p   primary partition (1-4)
p
Selected partition 2
First sector (206848-41943039, default 206848):
Using default value 206848
Last sector, +sectors or +size{K,M,G} (206848-22489087, default 22489087):
Using default value 22489087

Having made these changes the next step is to check that the settings are correct:

Command (m for help): p

Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x4eb978f9

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS
/dev/sda2          206848    22489087    11141120   83  Linux
/dev/sda3        22489088    23513087      512000   83  Linux
/dev/sda4        23513088    41943039     9214976    5  Extended
/dev/sda5        23515136    41943039     9213952   8e  Linux LVM
To commit the changes we now need to write the new partition information to disk and quit from the fdisk tool:
Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.

WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.

If you see a warning similar to the one indicated in the above output you will need to reboot your RHEL 6 system to be sure the new partition table information is picked up by the system kernel before proceeding.

Formatting the Unallocated Disk Partition

In order to make the new partition suitable for use by RHEL 6, it needs to have a file system created on it. The default file system type for the current releases of RHEL 6 is ext4. Creation of the file system performed using the mkfs command as follows:

# mkfs -t ext4 /dev/sda2
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
696320 inodes, 2785280 blocks
139264 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2852126720
85 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208

Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 22 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

Editing the Boot Menu

The next step is to modify the boot menu. Since this was originally a dual boot system, the menu is configured to provide the option of booting either Windows or RHEL. Now that the Windows partition is gone, we need to remove this boot option. This is achieved by editing the menu.lst as follows:

su - 
gedit /boot/grub/menu.lst

Towards the bottom of the grub.conf file you will see a section similar to:

title Windows
        rootnoverify (hd0,0)
        chainloader +1

Delete this section from the file. Also check to see the default= value to make sure the default is not set to the partition which was just deleted. Save the file once the changes have been made.

Mounting the New Partition

Finally, we need to mount the new partition. In this example we will mount it in a directory named /data. You are free, however, to mount the new partition using any valid mount point you desire or to use it as part of a logical volume. First we need to create the directory to act as the mount point:

su - 
mkdir /data

Secondly, we need to edit the mount table so that the partition is automatically mounted each time system starts:

gedit /etc/fstab

At the bottom of the /etc/fstab file, add the following line to mount the new partition (modifying the /dev/sda2 device to match your environment):

/dev/sda2 /data ext4 defaults 0 0

Finally, we can manually mount the new partition (note that on subsequent reboots this will not be necessary as the partition will automount as a result of the setting we added to the /etc/fstab file above).

mount /data

To check the partition, try running the following command to display the available space:

df -h /data

You should see output similar to:

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              11G  155M  9.8G   2% /data