Using Disk Partitions

Disk Partitions in Oracle Linux

Oracle Linux requires one partition for the root file system. Further, two other partitions are typically reserved for swap space and the boot file system. On x86 and x86_64 systems, the system BIOS can access only the first 1024 cylinders of the disk at boot time. Configuring a separate boot partition in this region on the disk enables the GRUB bootloader to access the kernel image and other files that are required to boot the system.

For hard disks with a master boot record (MBR), the partitioning scheme supports up to 4 primary partitions. In turn, a primary partition can further be divided into up to 11 logical partitions. The primary partition that contains the logical partitions is known as an extended partition. The MBR scheme supports disks up to 2 TB in size.

On hard disks with a GUID Partition Table (GPT), you can configure up to 128 partitions. The GPT partition scheme doesn't use the concept of extended or logical partitions. If the disk's size is larger than 2 TB, use GPT to configure the device's partitions.

Note:

When you partition a block storage device, align the primary and logical partitions on one-megabyte (1048576 bytes) boundaries. If partitions, file system blocks, or RAID stripes are incorrectly aligned and overlap the boundaries of the underlying storage's sectors or pages, the device controller would modify twice as many sectors or pages than if correct alignment is used. This recommendation applies to most block storage devices, including hard disk drives, solid state drives (SSDs), LUNs on storage arrays, and host RAID adapters.

Partitioning Disks by Using fdisk

To create and manage hard disks that use MBRs, use the fdisk command. Alternatively, you can use the cfdisk utility, which is a text-based, graphical version of fdisk.

Before running fdisk, complete the following requirements first:

Unmount any mounted partition on the disk.
Disable any partition that's being used as swap space by using the swapoff command.
Backup the data on the disk to be configured.

fdisk can be used either interactively or directly with command line options and arguments.

Note:

The two modes can differ in the options they support to perform specific actions. To list supported options while in interactive mode, enter m at the mode's prompt. For supported options in the command line mode, type:

fdisk -h

To run the fdisk command interactively, specify only the name of the disk device as an argument, for example:

sudo fdisk /dev/sda

Welcome to fdisk (util-linux 2.32.1)
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help):

The following commands are useful for managing partitions:

p: Displays the current partition table.
n: Initiates the process for creating new partitions.
t: Changes the partition type.

Tip:

To list all the supported partition types, enter l.
w: Commits changes you made to the partition table, then exits the interactive session.
q: Disregards any configuration changes you made and exits the session.
m: Displays all the supported commands in the interactive mode.

For more information, see the cfdisk(8) and fdisk(8) manual pages.

Displaying the Partition Table

To display the partition table, enter p at the fdisk prompt, for example:

Command (m for help): p

Disk /dev/sda: 36.5 GiB, 39191576576 bytes, 76546048 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
Disklabel type: dos
Disk identifier: 0x67fb0c7a

Device     Boot   Start      End  Sectors  Size Id Type
/dev/sda1  *       2048  1026047  1024000  500M 83 Linux
/dev/sda2       1026048 76546047 75520000   36G 8e Linux LVM

Command (m for help):

The output contains device information summary such as disk size, disklabel type, and partition details. The partition details are specified under the following field names:

Device

Lists the current partitions on the device.

Boot

Identifies the boot partition with an asterisk (*). This partition contains the files that the GRUB bootloader needs to boot the system. Only one partition can be bootable.

Start and End

Lists the start and end offsets in sectors that mark a sector's boundaries. All partitions are aligned on one-megabyte boundaries.

Sectors

Displays sector sizes.

Size

Displays partition sizes.

Id and Type

Indicates a representative number and its corresponding representative number.

Oracle Linux typically supports the following types:

5 Extended: An extended partition that can contain up to four logical partitions.
82 Linux swap: Swap space partition.
83 Linux: Linux partition for a file system that's not managed by LVM. This is the default partition type.
8e Linux LVM: Linux partition that's managed by LVM.

Creating Partitions

The following example shows how to use the different fdisk interactive commands to partition a disk. 2 partitions are created on /dev/sdb. The first partition is assigned 2 GB while the second partition uses all the remaining disk space.

sudo fdisk /dev/sdb

The command runs a menu-based system where you must select the appropriate responses to configure the partition. Example inputs are displayed in the following interactive session:

...
Command (m for help): n
Partition type
   p   primary (0 primary, 0 extended, 4 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-32767999, default 2048): <Enter>
Last sector, +sectors or +size{K,M,G,T,P} (2048-32767999, default 32767999): +2G

Created a new partition 1 of type 'Linux' and of size 2 GiB.

Command (m for help): n
Partition type
   p   primary (1 primary, 0 extended, 3 free)
   e   extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2): 2
First sector (4196352-32767999, default 4196352): <Enter>
Last sector, +sectors or +size{K,M,G,T,P} (4196352-32767999, default 32767999): <Enter>

Created a new partition 2 of type 'Linux' and of size 13.6 GiB.

Command (m for help): p
Disk /dev/sdb: 15.6 GiB, 16777216000 bytes, 32768000 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
Disklabel type: dos
Disk identifier: 0x460247f0

Device     Boot   Start      End  Sectors  Size Id Type
/dev/sdb1          2048  4196351  4194304    2G 83 Linux
/dev/sdb2       4196352 32767999 28571648 13.6G 83 Linux

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

Partitioning Disks by Using parted

To create and manage hard disks that use GPTs, use the parted command. The command enables you to perform typical partition operations as fdisk. However, parted is more advanced because it supports a larger set of commands and more disk label types including GPT disks.

Before running parted, complete the following requirements first:

Unmount any mounted partition on the disk.
Disable any partition that's being used as swap space by using the swapoff command.
Backup the data on the disk to be configured.

You can use parted either interactively or directly with command line arguments. To run parted interactively, specify only the name of the disk device as an argument, for example:

sudo parted /dev/sdb

GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted)

The following commands are useful for managing partitions:

print: Displays the current partition table.
mklabel: Creates a partition type according to the label you choose.
mkpart: Starts the process for creating new partitions.
quit: Exits the session.

Note:

In interactive sessions, changes are committed to disk immediately. Unlike fdisk, the parted utility doesn't have an option for quitting without saving changes.
help: Displays all the supported commands in the interactive mode.

Creating Partitions

The following example shows how to use the different parted commands to create 2 disk partitions. The first partition is assigned 2 GB while the second partition uses all the remaining disk space.

sudo parted /dev/sdb

The command runs a menu-based system where you must select the appropriate responses to configure the partition. Example inputs are displayed in the following interactive session:

GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 16.8GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start  End  Size  Type  File system  Flags

(parted) mkpart
Partition type?  primary/extended? primary
File system type?  [ext2]? <Enter>
Start? 1
End? 2GB
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 16.8GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  2000MB  1999MB  primary  ext2         lba

(parted) mkpart
Partition type?  primary/extended? primary
File system type?  [ext2]? <Enter>
Start? 2001
End? -0
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 16.8GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  2000MB  1999MB  primary  ext2         lba
 2      2001MB  16.8GB  14.8GB  primary  ext2         lba

(parted) quit

Note:

Unless you specify otherwise, the size for the Start and End offsets is in megabytes. To use another unit of measure, type the value and the unit together, for example, 2GB. To assign all remaining disk space to the partition, enter -0 for the End offset as shown in the example.

Customizing Labels

By default, parted creates msdos-labeled partitions. When partitioning with this label, you're also prompted for the partition type. Partition types can be primary, extended, or logical.

To use a different label, you would need to specify that label first with the mklabel command before creating the partition. Depending on the label, you would be prompted during the partitioning process for information, such as the partition name, as shown in the following example:

sudo parted /dev/sdb

The command runs a menu-based system where you must select the appropriate responses to configure the partition. Example inputs are displayed in the following interactive session:

GNU Parted 3.2
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) mklabel
New disk label type? gpt
Warning: The existing disk label on /dev/sdb will be destroyed and all data on
this disk will be lost. Do you want to continue?
Yes/No? yes
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 16.8GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start  End  Size  File system  Name  Flags

(parted) mkpart
Partition name?  []? Example
File system type?  [ext2]? linux-swap
Start? 1
End? 2GB
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 16.8GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system     Name     Flags
 1      1049kB  2000MB  1999MB  linux-swap(v1)  Example

(parted) quit

To know which types of file systems and labels are supported by parted, consult the GNU Parted User Manual at https://www.gnu.org/software/parted/manual/, or enter info parted to view the online user manual. For more information, see the parted(8) manual page.

Automatic Device Mappings for Partitions and File Systems

Device mappings are handled automatically on Oracle Linux, by the kernel and the udev service. In the case of disk devices, the kernel automatically creates device mappings for disks and their partitions using a non persistent naming scheme in the form of /dev/sdxy, for example /dev/sda1. A problem with this approach is that the device naming scheme depends on the order in which devices are detected, which means that device names can change easily. Typically, device names change when changes to the boot process exist or when storage devices or their related controllers fail.

Avoid using the non persistent disk or partition names when configuring mount points in /etc/fstab.

Udev is a subsystem that works with the kernel to monitor hardware or device changes and manages events related to changes. Storage devices, partitions, and file systems are all allocated unique identifiers that the udev subsystem can read and use to automatically configure device mappings that you can use to identify the device or partition that you intend to work use. Device mappings for storage devices managed by udev are stored in /dev/disks and you can identify a device by various identifiers, including the unique partition UUID, file system UUID, or the partition label.

When configuring mount points in /etc/fstab, use the file system UUID or, if set, the partition label, for example:

UUID=8980b45b-a2ce-4df6-93d8-d1e72f3664a0 /boot   xfs     defaults        0 0
LABEL=home  /home  xfs  defaults 0 0

Note that because file systems can span multiple devices, defining mount points against the file system UUID is preferable to using a partition UUID or label. File system UUIDs are assigned when the file system is created and is stored as part of the file system itself. If you copy the file system to a different device, the file system retains the same file system UUID. However, if you reformat a device by using the mkfs command, the device loses the file system UUID and a new UUID is generated.

Listing Device Mapping Information

You can use the lsblk command to list device information for any block device attached to the system:

Tip:

Use the -o +UUID option to display the UUIDs for each device and partition listed, or use the -f option to get a display of important file system information.

lsblk -f

Output might appear as follows, indicating a tree of file system mappings:

NAME               FSTYPE      FSVER    LABEL UUID                                   FSAVAIL FSUSE% MOUNTPOINTS
sda                                                                                                 
├─sda1             vfat        FAT16          DDD4-C455                                94.5M     5% /boot/efi
├─sda2             xfs                        8980b45b-a2ce-4df6-93d8-d1e72f3664a0      1.5G    26% /boot
└─sda3             LVM2_member LVM2 001       LzsEPR-Mnbk-kQZY-eV3n-9u1T-lFXZ-x7ANgD                
  ├─ocivolume-root xfs                        26029274-0a04-4dc5-b794-2576b9a16884     28.6G    25% /
  └─ocivolume-oled xfs                        3cbc8301-6f0e-4947-bbe6-f3669b9e6985      9.9G     1% /var/oled

You can also use the udevadm info command to obtain information about any udev mappings on the system. For example:

sudo udevadm info /dev/sda3

Output might appear as follows, listing all the device links that udev has created for the device and any other information that udev has on the device:

P: /devices/pci0000:00/0000:00:04.0/virtio1/host2/target2:0:0/2:0:0:1/block/sda/sda3
N: sda3
L: 0
S: disk/by-partuuid/18b918a1-16ca-4a07-91c6-455c6dc59fac
S: oracleoci/oraclevda3
S: disk/by-id/wwn-0x60170f5736a64bd7accb6a5e66fe70ee-part3
S: disk/by-path/pci-0000:00:04.0-scsi-0:0:0:1-part3
S: disk/by-id/scsi-360170f5736a64bd7accb6a5e66fe70ee-part3
S: disk/by-id/lvm-pv-uuid-LzsEPR-Mnbk-kQZY-eV3n-9u1T-lFXZ-x7ANgD
E: DEVPATH=/devices/pci0000:00/0000:00:04.0/virtio1/host2/target2:0:0/2:0:0:1/block/sda/sda3
E: DEVNAME=/dev/sda3
E: DEVTYPE=partition
E: DISKSEQ=9
E: PARTN=3
E: MAJOR=8
E: MINOR=3
E: SUBSYSTEM=block
E: USEC_INITIALIZED=20248855
E: ID_SCSI=1
E: ID_VENDOR=ORACLE
E: ID_VENDOR_ENC=ORACLE\x20\x20
E: ID_MODEL=BlockVolume
E: ID_MODEL_ENC=BlockVolume\x20\x20\x20\x20\x20
E: ID_REVISION=1.0
E: ID_TYPE=disk
E: ID_SERIAL=360170f5736a64bd7accb6a5e66fe70ee
E: ID_SERIAL_SHORT=60170f5736a64bd7accb6a5e66fe70ee
E: ID_WWN=0x60170f5736a64bd7
E: ID_WWN_VENDOR_EXTENSION=0xaccb6a5e66fe70ee
E: ID_WWN_WITH_EXTENSION=0x60170f5736a64bd7accb6a5e66fe70ee
E: ID_BUS=scsi
E: ID_PATH=pci-0000:00:04.0-scsi-0:0:0:1
E: ID_PATH_TAG=pci-0000_00_04_0-scsi-0_0_0_1
E: ID_PART_TABLE_UUID=a0b1f7d8-e84b-461f-a016-c3fcfed369c3
E: ID_PART_TABLE_TYPE=gpt
E: ID_SCSI_INQUIRY=1
E: ID_FS_UUID=LzsEPR-Mnbk-kQZY-eV3n-9u1T-lFXZ-x7ANgD
E: ID_FS_UUID_ENC=LzsEPR-Mnbk-kQZY-eV3n-9u1T-lFXZ-x7ANgD
E: ID_FS_VERSION=LVM2 001
E: ID_FS_TYPE=LVM2_member
E: ID_FS_USAGE=raid
E: ID_PART_ENTRY_SCHEME=gpt
E: ID_PART_ENTRY_UUID=18b918a1-16ca-4a07-91c6-455c6dc59fac
E: ID_PART_ENTRY_TYPE=e6d6d379-f507-44c2-a23c-238f2a3df928
E: ID_PART_ENTRY_NUMBER=3
E: ID_PART_ENTRY_OFFSET=4401152
E: ID_PART_ENTRY_SIZE=100456415
E: ID_PART_ENTRY_DISK=8:0
E: SCSI_TPGS=0
E: SCSI_TYPE=disk
E: SCSI_VENDOR=ORACLE
E: SCSI_VENDOR_ENC=ORACLE\x20\x20
E: SCSI_MODEL=BlockVolume
E: SCSI_MODEL_ENC=BlockVolume\x20\x20\x20\x20\x20
E: SCSI_REVISION=1.0
E: SCSI_IDENT_LUN_NAA_REGEXT=60170f5736a64bd7accb6a5e66fe70ee
E: UDISKS_IGNORE=1
E: DEVLINKS=/dev/disk/by-partuuid/18b918a1-16ca-4a07-91c6-455c6dc59fac 
   /dev/oracleoci/oraclevda3
   /dev/disk/by-id/wwn-0x60170f5736a64bd7accb6a5e66fe70ee-part3 
   /dev/disk/by-path/pci-0000:00:04.0-scsi-0:0:0:1-part3
   /dev/disk/by-id/scsi-360170f5736a64bd7accb6a5e66fe70ee-part3
   /dev/disk/by-id/lvm-pv-uuid-LzsEPR-Mnbk-kQZY-eV3n-9u1T-lFXZ-x7ANgD
E: TAGS=:systemd:
E: CURRENT_TAGS=:systemd:

Manually Mapping Partition Tables to Devices

The kpartx utility maps to device files the partitions of any block device or file that contains a partition table. The command reads the partition table, creates device files for the partitions, and stores the device files in /dev/mapper. Each device file represents a disk volume or a disk partition on a device or within an image file.

For more information, see the kpartx(8) manual page.

Creating Device Mappings by Using kpartx

The -a option creates the device mappings. The following example uses the disk partitions that were created in Creating Partitions as basis for creating the mapping. The example begins by showing the partition table:

Display the partition table.

sudo fdisk -l /dev/sdb

...
Device     Boot   Start      End  Sectors  Size Id Type
/dev/sdb1          2048  3907583  3905536  1.9G 83 Linux
/dev/sdb2       3907584 32767999 28860416 13.8G 83 Linux

Map the partitions.

sudo kpartx -av /dev/sdb

add map sdb1 (253:2): 0 3905536 linear 8:16 2048
add map sdb2 (253:3): 0 28860416 linear 8:16 3907584

Display /dev/mapper contents.

ls /dev/mapper

control  sdb1  sdb2  vg_main-lv_root  vg_main-lv_swap

Listing Partition Mappings For a Device by Using kpartx

To list the partitions in the device, use the -l option.

In the following example, the first column of the output identifies the device files in /dev/mapper.

sudo kpartx -l /dev/sdb

sdb1 : 0 3905536 /dev/sdb 2048
sdb2 : 0 28860416 /dev/sdb 3907584

The kpartx command also works with image files such as an installation image. For example, for an image file system.img, you can do the following:

sudo kpartx -a system.img

sudo kpartx -l system.img

loop0p1 : 0 204800 /dev/loop0 2048
loop0p2 : 0 12288000 /dev/loop0 206848
loop0p3 : 0 4096000 /dev/loop0 212494848
loop0p4 : 0 2 /dev/loop0 16590848

The output of the previous command shows that the drive image contains four partitions.

Removing Partition Mappings by Using kpartx

If a partition isn't in use you can remove the device mapping for the partition by using the -d option:

sudo kpartx -d system.img
ls /dev/mapper

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