What is linux native partition

5.9. Partitions

A hard disk can be divided into several partitions. Each partition functions as if it were a separate hard disk. The idea is that if you have one hard disk, and want to have, say, two operating systems on it, you can divide the disk into two partitions. Each operating system uses its partition as it wishes and doesn’t touch the other ones. This way the two operating systems can co-exist peacefully on the same hard disk. Without partitions one would have to buy a hard disk for each operating system.

Floppies are not usually partitioned. There is no technical reason against this, but since they’re so small, partitions would be useful only very rarely. CD-ROMs are usually also not partitioned, since it’s easier to use them as one big disk, and there is seldom a need to have several operating systems on one.

5.9.1. The MBR, boot sectors and partition table

The information about how a hard disk has been partitioned is stored in its first sector (that is, the first sector of the first track on the first disk surface). The first sector is the master boot record (MBR) of the disk; this is the sector that the BIOS reads in and starts when the machine is first booted. The master boot record contains a small program that reads the partition table, checks which partition is active (that is, marked bootable), and reads the first sector of that partition, the partition’s boot sector (the MBR is also a boot sector, but it has a special status and therefore a special name). This boot sector contains another small program that reads the first part of the operating system stored on that partition (assuming it is bootable), and then starts it.

The partitioning scheme is not built into the hardware, or even into the BIOS. It is only a convention that many operating systems follow. Not all operating systems do follow it, but they are the exceptions. Some operating systems support partitions, but they occupy one partition on the hard disk, and use their internal partitioning method within that partition. The latter type exists peacefully with other operating systems (including Linux), and does not require any special measures, but an operating system that doesn’t support partitions cannot co-exist on the same disk with any other operating system.

5.9.2. Extended and logical partitions

The original partitioning scheme for PC hard disks allowed only four partitions. This quickly turned out to be too little in real life, partly because some people want more than four operating systems (Linux, MS-DOS, OS/2, Minix, FreeBSD, NetBSD, or Windows/NT, to name a few), but primarily because sometimes it is a good idea to have several partitions for one operating system. For example, swap space is usually best put in its own partition for Linux instead of in the main Linux partition for reasons of speed (see below).

To overcome this design problem, extended partitions were invented. This trick allows partitioning a primary partition into sub-partitions. The primary partition thus subdivided is the extended partition; the sub-partitions are logical partitions. They behave like primary partitions, but are created differently. There is no speed difference between them. By using an extended partition you can now have up to 15 partitions per disk.

The partition structure of a hard disk might look like that in Figure 5-2. The disk is divided into three primary partitions, the second of which is divided into two logical partitions. Part of the disk is not partitioned at all. The disk as a whole and each primary partition has a boot sector.

Figure 5-2. A sample hard disk partitioning.

5.9.3. Partition types

The partition tables (the one in the MBR, and the ones for extended partitions) contain one byte per partition that identifies the type of that partition. This attempts to identify the operating system that uses the partition, or what it uses it for. The purpose is to make it possible to avoid having two operating systems accidentally using the same partition. However, in reality, operating systems do not really care about the partition type byte; e.g., Linux doesn’t care at all what it is. Worse, some of them use it incorrectly; e.g., at least some versions of DR-DOS ignore the most significant bit of the byte, while others don’t.

There is no standardization agency to specify what each byte value means, but as far as Linux is concerned, here is a list of partition types as per the fdisk program.

5.9.4. Partitioning a hard disk

There are many programs for creating and removing partitions. Most operating systems have their own, and it can be a good idea to use each operating system’s own, just in case it does something unusual that the others can’t. Many of the programs are called fdisk, including the Linux one, or variations thereof. Details on using the Linux fdisk given on its man page. The cfdisk command is similar to fdisk, but has a nicer (full screen) user interface.

When using IDE disks, the boot partition (the partition with the bootable kernel image files) must be completely within the first 1024 cylinders. This is because the disk is used via the BIOS during boot (before the system goes into protected mode), and BIOS can’t handle more than 1024 cylinders. It is sometimes possible to use a boot partition that is only partly within the first 1024 cylinders. This works as long as all the files that are read with the BIOS are within the first 1024 cylinders. Since this is difficult to arrange, it is a very bad idea to do it; you never know when a kernel update or disk defragmentation will result in an unbootable system. Therefore, make sure your boot partition is completely within the first 1024 cylinders.

However, this may no longer be true with newer versions of LILO that support LBA (Logical Block Addressing). Consult the documentation for your distribution to see if it has a version of LILO where LBA is supported.

Some newer versions of the BIOS and IDE disks can, in fact, handle disks with more than 1024 cylinders. If you have such a system, you can forget about the problem; if you aren’t quite sure of it, put it within the first 1024 cylinders.

Each partition should have an even number of sectors, since the Linux filesystems use a 1 kilobyte block size, i.e., two sectors. An odd number of sectors will result in the last sector being unused. This won’t result in any problems, but it is ugly, and some versions of fdisk will warn about it.

Changing a partition’s size usually requires first backing up everything you want to save from that partition (preferably the whole disk, just in case), deleting the partition, creating new partition, then restoring everything to the new partition. If the partition is growing, you may need to adjust the sizes (and backup and restore) of the adjoining partitions as well.

Since changing partition sizes is painful, it is preferable to get the partitions right the first time, or have an effective and easy to use backup system. If you’re installing from a media that does not require much human intervention (say, from CD-ROM, as opposed to floppies), it is often easy to play with different configuration at first. Since you don’t already have data to back up, it is not so painful to modify partition sizes several times.

There is a program for MS-DOS, called fips , which resizes an MS-DOS partition without requiring the backup and restore, but for other filesystems it is still necessary.

The fips program is included in most Linux distributions. The commercial partition manager «Partition Magic» also has a similar facility but with a nicer interface. Please do remember that partitioning is dangerous. Make sure you have a recent backup of any important data before you try changing partition sizes «on the fly». The program parted can resize other types of partitions as well as MS-DOS, but sometimes in a limited manner. Consult the parted documentation before using it, better safe than sorry.

5.9.5. Device files and partitions

Each partition and extended partition has its own device file. The naming convention for these files is that a partition’s number is appended after the name of the whole disk, with the convention that 1-4 are primary partitions (regardless of how many primary partitions there are) and number greater than 5 are logical partitions (regardless of within which primary partition they reside). For example, /dev/hda1 is the first primary partition on the first IDE hard disk, and /dev/sdb7 is the third extended partition on the second SCSI hard disk.

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Partitions: Planning Your Linux Installation¶

This article will explain some of the terms involved with partitioning your hard drive, as well as some concepts you will need to understand before installing Linux, and will help you determine what partitions you need to create for Linux.

What is a partition?В¶

Imagine your company is moving into a new building that is set up like a warehouse. There are no internal walls, it’s just one big room for everybody to work in. Chances are, the first thing the boss is going to do is build himself an office (he wouldn’t want to associate with you workers), so he’ll have a partition set up, an internal wall to separate him from you. Next, each worker will get a cubicle in the big room with smaller partitions to separate you from the person next to you.

Hard drives work the same way. The disk gets partitioned into smaller, separate pieces which can belong to different owners. In our case, Windows might own some and Linux will own others. On hard drives though, the word “partition” does not refer to the wall itself, it refers to the separated space. So we say Linux is installed “on” the first partition.

What is a file system?В¶

Ever go looking for a book in the library? In order to find what you’re looking for, you must understand the library’s file system, or method of organization. Fiction books are easy, they use a simple type of file system commonly known as alphabetical by author. Nonfiction books can be tougher because they use a different type of file system, the Dewey Decimal System. What if you don’t understand the Dewey Decimal System? What if you only know the title of a book and you don’t know whether it’s fiction or non-fiction? How can we find our book now? Luckily there is a librarian to help us, and she has created a card catalog (or in most libraries now, a computerized catalog) listing all the books available and where to find them.

Now, picture your hard drive as the library. Like the library, your hard drive can have different file systems. The operating system is your librarian, who has provided the directory tree (sometimes also referred to as “the file system”, with a slightly different meaning) as a catalog of the files available.

Unfortunately, the world of computers is not as standardized as our libraries. In computers, every librarian or operating system has its own type of file system, and other operating systems often don’t know how to read it. Lucky for us, Linux is a versatile operating system and it does understand the file system used by Windows 95 and Windows 98, as well as many others.

Planning your partitions¶

Each distribution’s installation guide contains (or should contain) a section on partitioning your hard drive. I have noticed, however, that the manuals often include far more detail than is necessary in a typical desktop installation, and can be confusing to new users.

Personally, I favor the KISS principle (Keep It Simple, Stupid), especially for beginners. If you are installing a server that will serve multiple user’s simultaneously and provide myriad services, you will want to read these manual sections as well as the Partition Mini-HOWTO, an excellent document detailing the reasons one might want to create the seven or more partitions sometimes recommended in these primers.

For a single-user desktop system, you can ignore just about all of that. Desktop systems for personal use don’t have most of the complications that require so many partitions. For a healthy Linux installation, I recommend three partitions: swap, root, and home.

Swap¶

You need one partition that will be used as Linux swap space. This is space on your hard drive that can be used as virtual memory. Virtual memory allows your computer to run large programs and perform complex tasks even if it does not have enough physical RAM to do the job. (It is a lot slower, but it works.)

The amount of swap space required is a matter of religious argument among geeks and hackers, and entire volumes could be written about the subject. To keep it simple, create one swap partition that is 50% to 100% the size of the physical RAM in your system. If you are short on RAM with plenty of drive space, go large. If you’re short on drive space and have lots of RAM, go small.

root (/)В¶

The root file system is represented by a forward slash (/). It is the top of the directory tree, and contains Linux and everything that you install with Linux. (See The Linux (Virtual) File System for details). This is roughly equivalent to your “C:” drive under DOS or Windows. You must create a partition for the root directory. (Don’t confuse this with the “root” user account, who is the administrator of the system. That’s a different kind of root!)

The size of your root partition will vary depending on what you install or plan to install. Check your distribution’s documentation, and reserve enough space for a maximum installation, plus at least 100MB more for temporary space and installation of new software. If you plan to download and try out lots of software, leave more space. If you have a small hard drive, you can trim back on your installed packages to save space.

In general, you should be fine with a root partition between 2GB and 8GB.

/home¶

The third and final partition you should create will hold your /home directory. This is the place where all the user-specific files, your data in other words, are stored. It is roughly equivalent to the “My Documents” folder on a MS Windows desktop (if you have MS Office installed). On a multi-user system, each user will have her own directory under /home .

Strictly speaking, it is not necessary to create a separate partition for /home . If you do not, it will reside on the root partition like everything else. If you are cramped for space, you may need to configure your machine this way.

The reason I recommend creating a separate partition is that you are a new user. You are going to want to play with things, experiment, push the limits of your system. Before long, you will break something so badly that you will need to reinstall, or you’ll just want to reinstall with different options, or try a different Linux distribution. Having /home on a separate partition makes it very easy to wipe out and reinstall Linux without losing any of your data.

Don’t think to yourself, “I’ll be careful, I won’t need to reinstall.” Wrong. You will definitely hose up your system at least once, and for the novice, reinstalling is often the easiest way to fix it. I had ten years of computer experience and worked in technical support when I started with Linux, so I knew my way around a PC, and I had to reinstall twice. Just plan on it and make it easy on yourself. Keep your data on a separate /home partition, or keep it backed up on some other medium, and be sure to create the boot floppies when prompted to do so during the installation process. They have saved my system more than once.

And don’t get the wrong impression here. This reinstall problem is only because you are a new user, still learning. Six months from now your system will be purring like a nursing kitten, and you’ll go weeks or months without rebooting, let alone reinstalling.

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