This post gives the details for creating a new partition after installed the operating system, Maximum Linux can allow to  create four primary partitions only, but you can have to create much number of logical partitions dividing from one of the primary partitions.

Normally creating partitions are look like,



  Device Boot      Start         End      Blocks   Id  System

/dev/sda1   *        2048      526335      262144   83  Linux

/dev/sda2          526336    57870335    28672000   8e  Linux LVM

/dev/sda3        57870336    58918911      524288   82  Linux swap / Solaris


Above partitions have been created three primary partitions, file systems are Linux, Linux LVM and Linux Swap. I would like to be add another two portions and the options are available can make only one primary , so create an extended partition, We can use fdisk command,

More fdisk commands : http://thelinuxfaq.com/147-how-to-create-swap-partition-in-centos-rhel-ubuntu

Note : When you create a extended ask first sector -> "Press Enter" button and Last Sector -> "Press Enter" button.
 
# fdisk -cu /dev/sda

Command (m for help): p

Disk /dev/sda: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 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: 0xf9b75ce8

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      526335      262144   83  Linux
/dev/sda2          526336    57870335    28672000   8e  Linux LVM
/dev/sda3        57870336    58918911      524288   82  Linux swap / Solaris

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
e
Selected partition 4
First sector (58918912-488397167, default 58918912):
Using default value 58918912
Last sector, +sectors or +size{K,M,G} (58918912-488397167, default 488397167):
Using default value 488397167


Command (m for help): p

Disk /dev/sda: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 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: 0xf9b75ce8

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      526335      262144   83  Linux
/dev/sda2          526336    57870335    28672000   8e  Linux LVM
/dev/sda3        57870336    58918911      524288   82  Linux swap / Solaris
/dev/sda4        58918912   488397167   214739128    5  Extended

 

There are four partitions has been created, including Extended partition the Extended ID is 5. I will create two partitions with 10G space from extended partition.

Note : When you create a partition ask first sector -> "Press Enter" button and Last Sector -> give your required space  value (Example : +10G or +500M )
 
Command (m for help): n
First sector (58920960-488397167, default 58920960):
Using default value 58920960
Last sector, +sectors or +size{K,M,G} (58920960-488397167, default 488397167): +10G

Command (m for help): n
First sector (79894528-488397167, default 79894528):
Using default value 79894528
Last sector, +sectors or +size{K,M,G} (79894528-488397167, default 488397167): +10G

Command (m for help): p

Disk /dev/sda: 250.1 GB, 250059350016 bytes
255 heads, 63 sectors/track, 30401 cylinders, total 488397168 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: 0xf9b75ce8

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      526335      262144   83  Linux
/dev/sda2          526336    57870335    28672000   8e  Linux LVM
/dev/sda3        57870336    58918911      524288   82  Linux swap / Solaris
/dev/sda4        58918912   488397167   214739128    5  Extended
/dev/sda5        58920960    79892479    10485760   83  Linux
/dev/sda6        79894528   100866047    10485760   83  Linux


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.

Once created the partitions rebooting the system.
# init 6

Have to decide create two directories in root the name of redhat and centos, mount that partition to this directories.


# mkdir /redhat

# mkdir /centos

You need to format these file system to  ext4 using mkfs.ext4 command,


# mkfs.ext4 /dev/sda5



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

655360 inodes, 2621440 blocks

131072 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=2684354560

80 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



Writing inode tables: done                            

Creating journal (32768 blocks): done

Writing superblocks and filesystem accounting information: done



This filesystem will be automatically checked every 26 mounts or

180 days, whichever comes first.  Use tune2fs -c or -i to override.

Same as
# mkfs.ext4 /dev/sda5

# Mount the device sda4 and sda5 to that directory


# mount /dev/sda5 /redhat/

# mount /dev/sda6 /centos/

Check your disk partition space,


# df -h



Filesystem            Size  Used Avail Use% Mounted on

/dev/mapper/vol0-root

                       18G  7.5G  9.4G  45% /

tmpfs                 1.8G  260K  1.8G   1% /dev/shm

/dev/sda1             248M   69M  167M  30% /boot

/dev/sda5             9.9G  151M  9.2G   2% /redhat

/dev/sda6             9.9G  151M  9.2G   2% /centos

The two partition set on after reboot add the line in /etc/fstab file,


/dev/sda5        /redhat       ext4     defaults     0         0

/dev/sda6        /centos       ext4     defaults     0         0

or Add with UUID

How to unmount the partition:

Before unmount the partition remove file system configuration line from /etc/fstab file and run below command


# umount /dev/sda5

# umount /dev/sda6

or


# umount /redhat

# umount /centos

Error :


# umount /dev/sda5



umount: /redhat: device is busy.

        (In some cases useful info about processes that use

         the device is found by lsof(8) or fuser(1))

If you get an above error you are currently working on that directory.