A.3. Partition Naming Schemes and Mount Points

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A common source of confusion for users unfamiliar with Linux is the matter of how partitions are used and accessed by the Linux operating system. In DOS/Windows, it is relatively simple: Each partition gets a "drive letter." You then use the correct drive letter to refer to files and directories on its corresponding partition. This is entirely different from how Linux deals with partitions and, for that matter, with disk storage in general. This section describes the main principles of partition naming scheme and the way how partitions are accessed in Red Hat Enterprise Linux.

A.3.1. Partition Naming Scheme

Red Hat Enterprise Linux uses a naming scheme that is file-based, with file names in the form of /dev/xxyN.
Device and partition names consist of the following:
This is the name of the directory in which all device files reside. Because partitions reside on hard disks, and hard disks are devices, the files representing all possible partitions reside in /dev/.
The first two letters of the partition name indicate the type of device on which the partition resides, usually sd.
This letter indicates which device the partition is on. For example, /dev/sda for the first hard disk, /dev/sdb for the second, and so on.
The final number denotes the partition. The first four (primary or extended) partitions are numbered 1 through 4. Logical partitions start at 5. So, for example, /dev/sda3 is the third primary or extended partition on the first hard disk, and /dev/sdb6 is the second logical partition on the second hard disk.


Even if Red Hat Enterprise Linux can identify and refer to all types of disk partitions, it might not be able to read the file system and therefore access stored data on every partition type. However, in many cases, it is possible to successfully access data on a partition dedicated to another operating system.

A.3.2. Disk Partitions and Mount Points

In Red Hat Enterprise Linux each partition is used to form part of the storage necessary to support a single set of files and directories. This is done by associating a partition with a directory through a process known as mounting. Mounting a partition makes its storage available starting at the specified directory (known as a mount point).
For example, if partition /dev/sda5 is mounted on /usr/, that would mean that all files and directories under /usr/ physically reside on /dev/sda5. So the file /usr/share/doc/FAQ/txt/Linux-FAQ would be stored on /dev/sda5, while the file /etc/gdm/custom.conf would not.
Continuing the example, it is also possible that one or more directories below /usr/ would be mount points for other partitions. For instance, a partition (say, /dev/sda7) could be mounted on /usr/local/, meaning that /usr/local/man/whatis would then reside on /dev/sda7 rather than /dev/sda5.

A.3.3. How Many Partitions?

At this point in the process of preparing to install Red Hat Enterprise Linux, you must give some consideration to the number and size of the partitions to be used by your new operating system. However, there is no one right answer to this question. It depends on your needs and requirements.
Keeping this in mind, Red Hat recommends that, unless you have a reason for doing otherwise, you should at least create the following partitions: swap, /boot/, and / (root).
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