Learn Linux, 101
Create partitions and filesystems
Divide and conquer your disk space
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Overview
In this article, learn about disk partitions and Linux filesystems. Learn to:
- Create a partition
- Use
mkfscommands to set up ext2, ext3, ext4, xfs, Reiser v3,and vfat filesystems - Create and manage swap space
This article helps you prepare for Objective 104.1 in Topic 104 of the Linux Professional Institute's Junior Level Administration (LPIC-1) exam 101. The objective has a weight of 2.
Note: This article includes material for the LPI Exam 101: Objective Changes as of July 2, 2012. We have added
basic information on ext4 filesystems. We have also added some basic
information on the gdisk command and the GUID Partition Table
(GPT). The new code listings and figures were all done on a 64-bit Fedora
17 system.
Prerequisites
To get the most from the articles in this series, you should have a basic knowledge of Linux and a working Linux system on which you can practice the commands covered in this article. Sometimes different versions of a program will format output differently, so your results may not always look exactly like the listings and figures shown here.
You should also be familiar with the material in our article, "Learn Linux 101: Hard disk layout."
Block devices and partitions
Our article, "Learn Linux 101: Learn Linux, 101: Hard disk layout," introduced
you to hard drive layouts, partitions, and some basic use of the
fdisk and gdisk commands to view partition
information. You learned about the Master Boot Record (MBR), partition
tables, partitions, including primary, extended, and
logical partitions. You were also introduced to GUID
Partition Tables (GPT), a new format used to address the size limitations
inherent in the MBR layout. Finally, you learned that a Linux filesystem
contains files that are arranged on a disk or other block
storage device in directories.
As with many other systems,
directories on a Linux system may contain other directories called
subdirectories. That article also discussed the
considerations that guide you in making choices about partitioning.
Note: This article focuses on the LPI requirements related
to the fdisk command and partitioning using MB layouts. It
includes some gdisk command information in Creating an ext4 filesystem. Refer to the earlier article and its
resources for more information on GPT.
We'll start this article with a review of block devices and partitions, and
then show you more about the fdisk command, which is used to
create, modify, or delete partitions on block devices. You will also learn
about the various forms of the mkfs command (mkfs stands for
make filesystem); mkfs commands are used to
format partitions as a particular filesystem type.
Note: In addition to the tools and filesystems required for the LPI exams, you may encounter or need other tools and filesystems. Find a brief summary of some other available tools in Other tools and filesystems.
Block devices
A block device is an abstraction layer for any storage device that can be formatted in fixed-size blocks; individual blocks may be accessed independently of access to other blocks. Such access is often called random access.
The abstraction layer of randomly accessible fixed-size blocks allows programs to use these block devices without worrying about whether the underlying device is a hard drive, floppy, CD, solid-state drive, network drive, or some type of virtual device such as an in-memory file system.
Examples of block devices include the first IDE hard drive on your system
(/dev/sda or /dev/hda) or the second SCSI, IDE, or USB drive (/dev/sdb).
Use the ls -l command to display /dev entries. The first
character on each output line is b for a
block device, such as floppy, CD drive, IDE hard
drive, or SCSI hard drive; and c for a
character device, such as a or terminal (tty) or the
null device. See the examples in .
Linux block and character devices
[ian@echidna ~]$ ls -l /dev/loop1 /dev/null /dev/sd[ab] /dev/sr0 /dev/tty0 brw-rw----. 1 root disk 7, 1 2010-06-14 07:25 /dev/loop1 crw-rw-rw-. 1 root root 1, 3 2010-06-14 07:25 /dev/null brw-rw----. 1 root disk 8, 0 2010-06-14 07:25 /dev/sda brw-rw----. 1 root disk 8, 16 2010-06-14 07:25 /dev/sdb brw-rw----+ 1 root cdrom 11, 0 2010-06-14 07:25 /dev/sr0 crw--w----. 1 root root 4, 0 2010-06-14 07:25 /dev/tty0
Partitions
For some block devices, such as floppy disks and CD or DVD discs, it is common to use the whole media as a single filesystem. However, with large hard drives, and even with USB memory keys, it is more common to divide, or partition, the available space into several different partitions.
Partitions can be different sizes, and different partitions may have different filesystems on them, so a single disk can be used for many purposes, including sharing it between multiple operating systems. For example, I use test systems with several different Linux distributions and sometimes a Windows® system, all sharing one or two hard drives.
You will recall from the article, "Learn Linux 101: Learn Linux, 101: Hard disk layout," that hard drives have a geometry, defined in terms of cylinders, heads, and sectors. Even though modern drives use logical block addressing (LBA), which renders geometry largely irrelevant, the fundamental allocation unit for partitioning purposes is usually still the cylinder.
Displaying partition information
Partition information is stored in a partition table on the disk.
The table lists information about the start and end of each partition,
information about its type, and whether it is marked bootable or
not. To create and delete partitions, you edit the partition table using a
program specially designed for the job. For the LPI exam, you need to know
about the fdisk program, so that is what is covered here,
although several other tools could be used. We will mention some at the
end of this article.
The fdisk command with the -l option is used to
list partitions. Add a device name, such as /dev/sda, if you want to look
at the partitions on a particular drive. Note that partitioning tools
require root access. shows the partitions on the primary hard
drives of two of my systems.
Listing partitions with fdisk
[root@attic4 ~]# fdisk -l /dev/sda Disk /dev/sda: 640.1 GB, 640135028736 bytes 255 heads, 63 sectors/track, 77825 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: 0x00064a1a Device Boot Start End Blocks Id System /dev/sda1 1 127 1020096 83 Linux /dev/sda2 128 1402 10241437+ 82 Linux swap / Solaris /dev/sda3 * 46340 56538 81920000 83 Linux /dev/sda4 1403 46339 360956422 5 Extended /dev/sda5 1403 10420 72437053+ 83 Linux /dev/sda6 10421 19344 71681998+ 83 Linux /dev/sda7 19345 28350 72340663+ 83 Linux /dev/sda8 28351 37354 72324598+ 83 Linux /dev/sda9 37355 46339 72171981 83 Linux Partition table entries are not in disk order [root@echidna ~]# fdisk -l /dev/sda Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x000de20f Device Boot Start End Blocks Id System /dev/sda1 * 1 9111 73184076 7 HPFS/NTFS /dev/sda2 9634 9730 779152+ 83 Linux /dev/sda3 9731 116679 859067842+ 5 Extended /dev/sda5 9731 20917 89859546 83 Linux /dev/sda6 20918 39644 150424596 83 Linux /dev/sda7 39645 53905 114551451 83 Linux
Notes:
- The header information shows the disk size and geometry. Most large disks using LBA have 255 heads per cylinder and 63 sectors per track, making a total of 16065 sectors, or 8225280 bytes per cylinder.
- In the second example, the first primary partition (/dev/sda1) is marked bootable (or active). This enables the standard DOS PC master boot record to boot the partition. This flag has no significance for the LILO or GRUB boot loaders. The first example uses GRUB as the boot loader, and the fact that /dev/sda3 is marked bootable is probably an accident of the history of my use of this drive.
- The Start and End columns show the starting and ending cylinder for each partition. These must not overlap and should generally be contiguous, with no intervening space.
- The Blocks column shows the number of 1K (1024 byte) blocks in the partition. For most disks in use at the time of writing, the sector size is 512 bytes, so the maximum number of blocks in a partition is therefore half of the product of the number of cylinders (End + 1 - Start) and the number of sectors per cylinder. A trailing + sign indicates that not all sectors in the partition are used.
- The Id field indicates the intended use of the partition. Type 82 is a Linux swap partition, and type 83 is a Linux data partition. There are approximately 100 different partition types defined. The second disk is shared between several operating systems, including Windows/XP, hence the presence of Windows NTFS (and possibly FAT32) partitions.
Partitioning with fdisk
You have just seen how to display partition information using the
fdisk command. This command also provides a menu-driven
environment for editing the partition table to create or remove
partitions.
Warnings
Before you start modifying partitions, there are some important things to remember. You risk losing your existing data if you do not follow these guidelines.
- Back up important data before you start, as with any operation that may cause data loss.
- Do not change partitions that are in use. Plan your actions and execute them carefully. Booting a live distribution from CD, DVD, or USB is one good way to ensure that no hard drive partitions are in use.
- Know your tool. The
fdiskcommand does not commit any changes to your disk until you tell it to. Other tools, includingparted, may commit changes as you go. - Stop if you do make a mistake. Partitioning tools write the partition table. Unless the tool you are using also includes the ability to move, resize, format, or otherwise write to the data area of your disk, your data will not be touched. If you do make a mistake, stop as quickly as possible and seek help. You may still be able to restore your previous partition table definitions and thus recover your partitions and data.
Start fdisk
To start fdisk in interactive mode, simply give the name of a
disk, such as /dev/hda or /dev/sdb, as a parameter. The following example
boots a Knoppix live DVD. You will need root authority, and you will see
output similar to .
Starting interactive fdisk
knoppix@Microknoppix:~$ su - root@Microknoppix:~# fdisk /dev/sda The number of cylinders for this disk is set to 121601. There is nothing wrong with that, but this is larger than 1024, and could in certain setups cause problems with: 1) software that runs at boot time (e.g., old versions of LILO) 2) booting and partitioning software from other OSs (e.g., DOS FDISK, OS/2 FDISK) Command (m for help):
Most modern disks have more than 1024 cylinders, so you will usually see
the warning shown in . Type m to display a list of
available one-letter commands as shown in .
Help in fdisk
Command (m for help): m Command action a toggle a bootable flag b edit bsd disklabel c toggle the dos compatibility flag d delete a partition l list known partition types m print this menu n add a new partition o create a new empty DOS partition table p print the partition table q quit without saving changes s create a new empty Sun disklabel t change a partition's system id u change display/entry units v verify the partition table w write table to disk and exit x extra functionality (experts only) Command (m for help):
Use the p command to display the existing partition on this
particular disk;
shows the output.
Displaying the existing partition table
Command (m for help): p Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x000de20f Device Boot Start End Blocks Id System /dev/sda1 * 1 9111 73184076 7 HPFS/NTFS /dev/sda2 9634 9730 779152+ 83 Linux /dev/sda3 9731 116679 859067842+ 5 Extended /dev/sda5 9731 20917 89859546 83 Linux /dev/sda6 20918 39644 150424596 83 Linux /dev/sda7 39645 53905 114551451 83 Linux Command (m for help):
This particular disk is a 1TB disk with a Windows/XP partition of a little under 80GB. It is a primary partition, and it is marked bootable, as is typical for a Windows system.
Adding partitions
Let's now use part of the free space to add some partitions.
- We will create a swap partition as /dev/sda4. This will be a primary partition, filling the 521 cylinder gap between the end of /dev/sda1 and the start of /dev/sda2. Don't even begin to wonder what crazy things cause this gap to exist; I created the gap deliberately so I could write this article.
- We will create a 40GB logical partition as /dev/sda8.
- Finally, we will create a small 2000MB logical partition for sharing data between the Linux and Windows systems. This will eventually be formatted as FAT32 (or vfat). It will be /dev/sda9.
Creating our partitions
Let's start by using the n command to create a new partition;
see .
Creating our first partition
Command (m for help): n
Command action
l logical (5 or over)
p primary partition (1-4)
p
Selected partition 4
First cylinder (9112-121601, default 9112):
Using default value 9112
Last cylinder, +cylinders or +size{K,M,G} (9112-9633, default 9633): +521
Command (m for help): p
Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000de20f
Device Boot Start End Blocks Id System
/dev/sda1 * 1 9111 73184076 7 HPFS/NTFS
/dev/sda2 9634 9730 779152+ 83 Linux
/dev/sda3 9731 116679 859067842+ 5 Extended
/dev/sda4 9112 9633 4192965 83 Linux
/dev/sda5 9731 20917 89859546 83 Linux
/dev/sda6 20918 39644 150424596 83 Linux
/dev/sda7 39645 53905 114551451 83 Linux
Partition table entries are not in disk order
Command (m for help):We took the default for the first cylinder and specified the value of +521
for the number of cylinders. You can see from that our partition is approximately
4GB in size. Since it is a primary partition, it must be numbered from 1
through 4. It is a good idea to assign partition numbers sequentially;
some tools complain if this is not done and fdisk warns us
that our partition table entries are no longer in disk order.
Notice also that our new partition was assigned a type of 83, for a Linux data partition. Think of this as an indicator to the operating system of the intended use of the partition. The eventual use should match this, but at this point we don't even have the partition formatted, let alone have any data on it. We'll create out other partitions first, then look at how to change the partition type.
You may have noticed that when we entered the n subcommand to
create a new partition, the only choices were 'l' for logical and 'p' for
primary. You will only see options for the remaining possible types of
partitions. You would see 'e' for extended if the drive did not already
have an extended partition. Also note that our extended partition
(/dev/sda3) is type 5.
Now let's define the 40GB Linux partition and the 2000MB FAT32 partition.
This time we will simply specify sizes of +40G and +2000M, indicating 40GB
and 2000MB, respectively. We let fdisk calculate the number
of cylinders for us. The results are shown in .
Creating our data partitions
Command (m for help): n
First cylinder (53906-116679, default 53906):
Using default value 53906
Last cylinder, +cylinders or +size{K,M,G} (53906-116679, default 116679): +40G
Command (m for help): n
First cylinder (59129-116679, default 59129):
Using default value 59129
Last cylinder, +cylinders or +size{K,M,G} (59129-116679, default 116679): +2000M
Command (m for help): p
Disk /dev/sda: 1000.2 GB, 1000204886016 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000de20f
Device Boot Start End Blocks Id System
/dev/sda1 * 1 9111 73184076 7 HPFS/NTFS
/dev/sda2 9634 9730 779152+ 83 Linux
/dev/sda3 9731 116679 859067842+ 5 Extended
/dev/sda4 9112 9633 4192965 83 Linux
/dev/sda5 9731 20917 89859546 83 Linux
/dev/sda6 20918 39644 150424596 83 Linux
/dev/sda7 39645 53905 114551451 83 Linux
/dev/sda8 53906 59128 41953716 83 Linux
/dev/sda9 59129 59384 2056288+ 83 Linux
Partition table entries are not in disk order
Command (m for help):Changing partition type
Before we leave fdisk, we will change the partition types for
the swap and vfat partitions. We do this using the t
subcommand to set the partition type. We set /dev/sda4 to type 82 (Linux
swap) and /dev/sda9 to type 9 (FAT32). If you want to see the full list of
supported types, enter L as you see in .
Changing partition types
Command (m for help): t Partition number (1-9): 4 Hex code (type L to list codes): 82 Changed system type of partition 4 to 82 (Linux swap / Solaris) Command (m for help): t Partition number (1-9): 9 Hex code (type L to list codes): b Changed system type of partition 9 to b (W95 FAT32) Command (m for help):
Saving our partition table
So far, we have just been doing an in-memory edit of a partition table. We
could use the q command to quit without saving changes. If
something is not how you want it, you can use the d command
to delete one or more partitions so you can redefine them. If you are
happy with your setup, use the v command to verify your
setup, and then the w command to write the new partition
table and exit. See . If you run fdisk -l again, you
will see that Linux now knows about the new partitions. Unlike in some
operating systems, it is not always necessary to reboot to see the
changes. A reboot may be required if, for example, /dev/hda3 became
/dev/hda2 because the original /dev/hda2 was deleted. If a reboot is
needed, fdisk should tell you to do so.
Saving the partition table
Command (m for help): v 999521580 unallocated 512-byte sectors Command (m for help): w The partition table has been altered! Calling ioctl() to re-read partition table. WARNING: If you have created or modified any DOS 6.x partitions, please see the fdisk manual page for additional information. Syncing disks. root@Microknoppix:~# fdisk -l /dev/sda Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x000de20f Device Boot Start End Blocks Id System /dev/sda1 * 1 9111 73184076 7 HPFS/NTFS /dev/sda2 9634 9730 779152+ 83 Linux /dev/sda3 9731 116679 859067842+ 5 Extended /dev/sda4 9112 9633 4192965 82 Linux swap / Solaris /dev/sda5 9731 20917 89859546 83 Linux /dev/sda6 20918 39644 150424596 83 Linux /dev/sda7 39645 53905 114551451 83 Linux /dev/sda8 53906 59128 41953716 83 Linux /dev/sda9 59129 59384 2056288+ b W95 FAT32 Partition table entries are not in disk order
More on fdisk
You may notice that we did not change the bootable flag on any partition. As our disk stands now, it still has the Windows Master Boot Record (MBR) and will therefore boot the first primary partition that is marked bootable (the NTFS partition in our example).
Neither LILO nor GRUB uses the bootable flag. If either of these is installed in the MBR, then it can boot the Windows/XP partition. You could also install LILO or GRUB into your /boot partition (/dev/hda2) and mark that partition bootable and remove the bootable flag from /dev/hda1. Leaving the original MBR can be useful if the machine is later returned to being a Windows-only machine.
You can also use fdisk to fix the partition order in the
partition table if you need to. This will usually change the partition
numbers, so you may have other work to do to restore your system to a
working system. To make this change, use the f subcommand to
switch to expert mode and then the f subcommand to fix the
partition order, as shown in . If you just want to see what the new
partition order would be without changing it, you can use the
q subcommand to quit as we have done in this example, rather
than writing the updated partition table to disk.
Fixing the partition table order.
Command (m for help): p Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x000de20f Device Boot Start End Blocks Id System /dev/sda1 * 1 9111 73184076 7 HPFS/NTFS /dev/sda2 9634 9730 779152+ 83 Linux /dev/sda3 9731 116679 859067842+ 5 Extended /dev/sda4 9112 9633 4192965 82 Linux swap / Solaris /dev/sda5 9731 20917 89859546 83 Linux /dev/sda6 20918 39644 150424596 83 Linux /dev/sda7 39645 53905 114551451 83 Linux /dev/sda8 53906 59128 41953716 83 Linux /dev/sda9 59129 59384 2056288+ b W95 FAT32 Partition table entries are not in disk order Command (m for help): x Expert command (m for help): f Done. Expert command (m for help): r Command (m for help): p Disk /dev/sda: 1000.2 GB, 1000204886016 bytes 255 heads, 63 sectors/track, 121601 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Disk identifier: 0x000de20f Device Boot Start End Blocks Id System /dev/sda1 * 1 9111 73184076 7 HPFS/NTFS /dev/sda2 9112 9633 4192965 82 Linux swap / Solaris /dev/sda3 9634 9730 779152+ 83 Linux /dev/sda4 9731 116679 859067842+ 5 Extended /dev/sda5 9731 20917 89859546 83 Linux /dev/sda6 20918 39644 150424596 83 Linux /dev/sda7 39645 53905 114551451 83 Linux /dev/sda8 53906 59128 41953716 83 Linux /dev/sda9 59129 59384 2056288+ b W95 FAT32 Command (m for help): q
You have now seen one way to add partitions to a Linux workstation. Other choices you might make are covered in the article, "Learn Linux, 101: Find and place system files."
Filesystem types
Linux supports several different filesystems. Each has strengths and weaknesses and its own set of performance characteristics. One important attribute of a filesystem is journaling, which allows for much faster recovery after a system crash. Generally, a journaling filesystem is preferred over a non-journaling one when you have a choice. You may also want to consider whether your chosen filesystem supports Security Enhanced Linux (or SELinux). Following is a brief summary of the types you need to know about for the LPI exam. See Resources for additional background information.
The ext2 filesystem
The ext2 filesystem (also known as the second extended filesystem) was developed to address shortcomings in the Minix filesystem used in early versions of Linux. It has been used extensively on Linux for many years. There is no journaling in ext2, and it has largely been replaced by ext3 and more recently ext4.
The ext3 filesystem
The ext3 filesystem adds journaling capability to a standard ext2 filesystem and is therefore an evolutionary growth of a very stable filesystem. It offers reasonable performance under most conditions and is still being improved. Because it adds journaling on top of the proven ext2 filesystem, it is possible to convert an existing ext2 filesystem to ext3 and even convert back again if required.
The ext4 filesystem started as extensions to ext3 to address the demands of ever larger file systems by increasing storage limits and improving performance. To preserve the stability of ext3, it was decided in June 2006 to fork the extensions into a new filesystem, ext4. The ext4 filesystem, was released in December 2008 and included in the 2.6.28 kernel. Some of the changes from ext3 are:
- File systems up to 1 exabyte with files up to 16 terabytes
- The use of extents to replace block mapping as a means of improving performance
- Journal checksums to improve reliability
- Faster file system checking because unallocated blocks can be skipped during checks.
- Delayed allocation and multiblock allocators to improve performance and reduce file fragmentation.
- Timestamp changes that provide finer granularity, a new creation date (which will require eventual updates to many other libraries and utilities to become fully useful). A further timestamp change addresses the year 2038 problem which is caused by storing timestamps as signed 32-bit integers.
The ReiserFS filesystem
ReiserFS is a B-tree-based filesystem that has very good overall performance, particularly for large numbers of small files. ReiserFS also scales well and has journaling. It is no longer in active development, does not support SELinux and has largely been superseded by Reiser4.
The XFS filesystem
XFS is a filesystem with journaling. It comes with robust features and is optimized for scalability. XFS aggressively caches in-transit data in RAM, so an uninterruptible power supply is recommended if you use XFS.
The swap filesystem
Swap space must be formatted for use as swap space, but it is not generally considered a filesystem.
The vfat filesystem
This filesystem (also known as FAT32) is not journaled and lacks many features required for a full Linux filesystem implementation. It is useful for exchanging data between Windows and Linux systems as it can be read by both Windows and Linux. Do not use this filesystem for Linux, except for sharing data between Windows and Linux. If you unzip or untar a Linux archive on a vfat disk, you will lose permissions, such as execute permission, and you will lose any symbolic links that may have been stored in the archive.
The ext3 filesystem is mature and was used as the default filesystem on many distributions. The ext4 filesystem is replacing it as the default filesystem on several distributions, including Red Hat enterprise Linux 6. Fedora 17 and Ubuntu 12.10. The ReiserFS filesystem was used for many years as the default on some distributions, including SUSE, but is less used today.
Creating filesystems
Linux uses the mkfs command to create filesystems and
mkswapcommand to make swap space.
The mkfs command is
actually a front end to several filesystem-specific commands such as
mkfs.ext3 for ext3, mkfs.ext4 for ext4 and
mkfs.reiserfs for ReiserFS.
What filesystem support is already installed on your system? Use the
ls /sbin/mk* command to find out. An example is
shown in .
Filesystem creation commands
[ian@echidna ~]$ ls /sbin/mk* /sbin/mkdosfs /sbin/mkfs.ext2 /sbin/mkfs.ntfs /sbin/mke2fs /sbin/mkfs.ext3 /sbin/mkfs.vfat /sbin/mkfs /sbin/mkfs.ext4 /sbin/mkfs.xfs /sbin/mkfs.btrfs /sbin/mkfs.ext4dev /sbin/mkhomedir_helper /sbin/mkfs.cramfs /sbin/mkfs.msdos /sbin/mkswap
You will notice various forms of some commands. For example, you will usually find that the files mke2fs, mkfs.ext2, and mkfs.ext3 are identical, as are mkreiserfs and mkfs.reiserfs. Filesystems that may be needed to boot the system will usually use hard links to provide the different names for the same file. Filesystems that cannot be used for the / filesystem in Linux, such as vfat or msdos, may use symbolic links instead. The article "Learn Linux, 101: Create and change hard and symbolic links" will help you learn about these different kinds of links.
There are a few common options for all mkfs commands. Options
that are specific to the type of filesystem being created are passed to
the appropriate creation command, based on the type of filesystem
specified in the -type option. Our examples use
mkfs -type, but you may use the other forms
directly with equal effect. For example, you may use
mkfs -type ext2,
mk2fs, or mkfs.ext2. For the manual pages for a
specific filesystem, use the appropriate mkfs command as the
name, for example, man mkfs.ext3. Many of the
values displayed in the output examples below can be controlled by options
to mkfs.
Now that we have created all our partitions, we will reboot the Fedora 12 system and format the filesystems using that rather than the somewhat slower live Knoppix DVD. Of course, you could continue to use the Knoppix system if you wished. Remember that you need root authority to create filesystems.
Creating an ext3 filesystem
Let's format the /dev/sda8 partition as ext3 using the mkfs
command as shown in .
Creating an ext3 filesystem
[root@echidna ~]# mkfs -t ext3 /dev/sda8
mke2fs 1.41.9 (22-Aug-2009)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
2624496 inodes, 10488429 blocks
524421 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
321 block groups
32768 blocks per group, 32768 fragments per group
8176 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 20 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override. Note that a journal is created with ext3. If you wish to add a journal to
an existing ext2 system, use the tune2fs command with the
-j option.
A useful option for ext2, ext3, and
ext4 filesystems is the -L option with a name, which assigns
a label to the partition. This can
be used instead of the device name when mounting filesystems; it provides
some level of insulation against changes that may need to be reflected in
various control files. To display
or set a label for an existing ext2, ext3, or ext3 filesystem, use the
e2label command. Labels
are limited to a maximum size of 16 characters.
A more recent development is to use a Universally Unique
Identifier, or UUID, rather than a label. A UUID is a
128-bit identifier usually displayed as 32 hexadecimal digits and four
hyphens. Most Linux filesystems generate an UUID automatically when the
filesystem is formatted. Use the blkid command (which does
not need root authority) as shown in to see the UUID for the partition we just
formatted. UUIDs are more likely to be unique than labels and are
especially useful for hot-plugged devices such as USB drives.
Displaying a UUID using blkid
[ian@echidna ~]$ blkid /dev/sda8 /dev/sda8: UUID="87040def-920e-4525-9c81-c585ddc46384" SEC_TYPE="ext2" TYPE="ext3"
Creating an ext4 filesystem
Step outside the traditional MBR layout for a moment and format a USB flash
drive using the GUID Partition Table (GPT) layout to learn how it works.
Then create a Linux partition on the drive with the gdisk
command. Finally, create an ext4 filesystem on the new partition with the
mkfs command.
With gdisk, look at a typical USB flash drive (also known as
USB thumb drives or USB keys). They are commonly shipped with a FAT32
filesystem spanning the whole drive and they usually are not partitioned.
shows how
gdisk displays information for a drive that is not already in
GPT layout.
Using gdisk to display information on a non-GPT disk
[root@attic4 ~]# gdisk -l /dev/sdc GPT fdisk (gdisk) version 0.8.4 Partition table scan: MBR: MBR only BSD: not present APM: not present GPT: not present *************************************************************** Found invalid GPT and valid MBR; converting MBR to GPT format. *************************************************************** Warning! Main partition table overlaps the first partition by 2 blocks! Try reducing the partition table size by 8 entries. (Use the 's' item on the experts' menu.) Warning! Secondary partition table overlaps the last partition by 33 blocks! You will need to delete this partition or resize it in another utility. Disk /dev/sdc: 62530624 sectors, 29.8 GiB Logical sector size: 512 bytes Disk identifier (GUID): D7900F13-839B-49B2-9C43-4367528DC381 Partition table holds up to 128 entries First usable sector is 34, last usable sector is 62530590 Partitions will be aligned on 32-sector boundaries Total free space is 0 sectors (0 bytes) Number Start (sector) End (sector) Size Code Name 1 32 62530623 29.8 GiB 0700 Microsoft basic data
First note that you must run gdisk as root or use
sudo, depending on how your system is set up. Secondly note
that gdisk wants to convert the existing format to GPT and
warns you about this. Because you used the -l option to
simply list the partitions, no action is performed.
Now run gdisk in interactive mode. List the available
commands, then the known partition types before you create a new empty
GUID partition table and finally a Linux partition. You'll display the new
information and then quit gdisk. shows the interaction.
Using gdisk to create a GUID Partition Table (GPT) and a partition
[root@attic4 ~]# gdisk /dev/sdc
GPT fdisk (gdisk) version 0.8.4
Partition table scan:
MBR: MBR only
BSD: not present
APM: not present
GPT: not present
***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format.
THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by typing 'q' if
you don't want to convert your MBR partitions to GPT format!
***************************************************************
Warning! Main partition table overlaps the first partition by 2 blocks!
Try reducing the partition table size by 8 entries.
(Use the 's' item on the experts' menu.)
Warning! Secondary partition table overlaps the last partition by
33 blocks!
You will need to delete this partition or resize it in another utility.
Command (? for help): ?
b back up GPT data to a file
c change a partition's name
d delete a partition
i show detailed information on a partition
l list known partition types
n add a new partition
o create a new empty GUID partition table (GPT)
p print the partition table
q quit without saving changes
r recovery and transformation options (experts only)
s sort partitions
t change a partition's type code
v verify disk
w write table to disk and exit
x extra functionality (experts only)
? print this menu
Command (? for help): l
0700 Microsoft basic data 0c01 Microsoft reserved 2700 Windows RE
4200 Windows LDM data 4201 Windows LDM metadata 7501 IBM GPFS
7f00 ChromeOS kernel 7f01 ChromeOS root 7f02 ChromeOS reserved
8200 Linux swap 8300 Linux filesystem 8301 Linux reserved
8e00 Linux LVM a500 FreeBSD disklabel a501 FreeBSD boot
a502 FreeBSD swap a503 FreeBSD UFS a504 FreeBSD ZFS
a505 FreeBSD Vinum/RAID a800 Apple UFS a901 NetBSD swap
a902 NetBSD FFS a903 NetBSD LFS a904 NetBSD concatenated
a905 NetBSD encrypted a906 NetBSD RAID ab00 Apple boot
af00 Apple HFS/HFS+ af01 Apple RAID af02 Apple RAID offline
af03 Apple label af04 AppleTV recovery af05 Apple Core Storage
be00 Solaris boot bf00 Solaris root bf01 Solaris /usr & Mac Z
bf02 Solaris swap bf03 Solaris backup bf04 Solaris /var
bf05 Solaris /home bf06 Solaris alternate se bf07 Solaris Reserved 1
bf08 Solaris Reserved 2 bf09 Solaris Reserved 3 bf0a Solaris Reserved 4
bf0b Solaris Reserved 5 c001 HP-UX data c002 HP-UX service
ef00 EFI System ef01 MBR partition scheme ef02 BIOS boot partition
fd00 Linux RAID
Command (? for help): o
This option deletes all partitions and creates a new protective MBR.
Proceed? (Y/N): y
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-62530590, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-62530590, default = 62530590) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
Command (? for help): p
Disk /dev/sdc: 62530624 sectors, 29.8 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): B321C1C5-795A-4836-9E16-D7D45DD8F3F2
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 62530590
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)
Number Start (sector) End (sector) Size Code Name
1 2048 62530590 29.8 GiB 8300 Linux filesystem
Command (? for help): qYour final task is to create an ext4 filesystem on your new partition,
/ev/sdc1. With the -L option of mkfs, label the
partition and also show the GUID using the blkid command as
you did for the ext3 partition above. illustrates this.
Creating an ext4 partition
[root@attic4 ~]# mkfs -t ext4 -L IAN-USB32 /dev/sdc1 mke2fs 1.42.3 (14-May-2012) Filesystem label=IAN-USB32 OS type: Linux Block size=4096 (log=2) Fragment size=4096 (log=2) Stride=0 blocks, Stripe width=0 blocks 1957888 inodes, 7816324 blocks 390816 blocks (5.00%) reserved for the super user First data block=0 Maximum filesystem blocks=4294967296 239 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, 4096000 Allocating group tables: done Writing inode tables: done Creating journal (32768 blocks): done Writing superblocks and filesystem accounting information: done [root@attic4 ~]# blkid /dev/sdc1 /dev/sdc1: UUID="b3a3c2bc-ea8d-40c6-967e-927006f55416" TYPE="ext4" LABEL="IAN-USB32"
To see all the parameters that you can specify when creating an ext4
partition, consult the man pages for mkfs.ext4.
Creating an XFS filesystem
Let's now reformat the partition we just formatted as ext3 using the XFS
filesystem. Our Fedora 12 system uses SELinux (Security Enhanced Linux),
so we should specify larger inodes than the default of 256 using the
-i parameter. Recommended value is 512. Notice that the XFS
formatter notifies you if it finds a recognized filesystem already on the
partition. Note also that the UUID was reassigned by the XFS format.
Creating an XFS filesystem
[root@echidna ~]# mkfs -t xfs -i size=512 /dev/sda8
mkfs.xfs: /dev/sda8 appears to contain an existing filesystem (xfs).
mkfs.xfs: Use the -f option to force overwrite.
[root@echidna ~]# mkfs -t xfs -f -i size=512 /dev/sda8
meta-data=/dev/sda8 isize=512 agcount=4, agsize=2622108 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=10488429, imaxpct=25
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal log bsize=4096 blocks=5121, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
[root@echidna ~]# blkid /dev/sda8
/dev/sda8: UUID="1b6798f2-f07f-4d5e-af06-2470df37ddb3" TYPE="xfs"You can label an XFS system using the -L option with a name.
You can use the xfs_admin command with the -L
option to add a label to an existing XFS filesystem. Use the
-l option of xfs_admin to display a label.
Unlike ext2, ext3, and ReiserFS, XFS labels have a maximum length of 12
characters.
Creating a ReiserFS filesystem
You create a ReiserFS filesystem using the mkfs command with
the -t reiserfs option or the mkreiserfs
command. ReiserFS does not support SELinux and is being replaced by
Resier4
You can label a ReiserFS system using the -l (or
--labeloption with a name). You can use the
reiserfstune command to add a label or display the label on
an existing ReiserFS filesystem. Labels are limited to a maximum length of
16 characters.
You may need to install the ReiserFS package on your system to use ReiserFS as it may not be included in a default install. See the man or info pages for more details.
Creating a vfat filesystem
We'll now create the FAT32 (vfat) filesystem on /dev/sda9.
Creating a vfat filesystem
[root@echidna ~]# mkfs -t vfat /dev/sda9 mkfs.vfat 3.0.9 (31 Jan 2010) [root@echidna ~]# blkid /dev/sda9 /dev/sda9: LABEL="" UUID="CF72-99A8" TYPE="vfat"
UUIDs for vfat filesystems are shorter than normal UUIDs and therefore
somewhat less likely to be unique. If you want a label instead, use the
dosfslabel command. Labels for DOS partitions are limited to
11 characters in length.
Creating swap space
Now let's create some swap space on the /dev/sda4 partition using the
mkswap command as shown in .
Creating swap space
[root@echidna ~]# mkswap /dev/sda4 Setting up swapspace version 1, size = 4192960 KiB no label, UUID=8f5a3a05-73ef-4c78-bc56-0e9b1bcc7fdb
Note that recent versions of mkswap show you the generated
UUID.
Unlike regular filesystems, swap partitions aren't mounted. Instead, they
are enabled using the swapon command. Your Linux system's
startup scripts will take care of automatically enabling your swap
partitions.
Other tools and filesystems
The following tools and filesystems are not part of the LPI objectives for this exam. This very brief overview touches on some of the tools and filesystems that you may encounter.
Partitioning tools
Many Linux distributions include the cfdisk or
sfdisk commands. The cfdisk command provides a
more graphical interface than fdisk, using the ncurses library functions
as shown in . The
sfdisk command is intended for programmer use and can be
scripted. Use it if you know what you are doing.
Using cfdisk
Another popular tool for working with the partition table is
parted, which can resize and format many partition types as
well as create and destroy them. While parted cannot resize
NTFS partitions, ntfsresize can. The qtparted
tool uses the Qt toolkit to provide a graphical interface. It includes the
parted functions as well as ntfsresize
functions.
The gparted tool is another graphical partitioning tool,
designed for the GNOME desktop. It uses the GTK+GUI library, and is shown
in . (See Resources for links to both
qtparted and gparted.)
You may have to install the above packages in order to use them as they may not be part of your default install.
Using gparted
Earlier you saw the gdisk command which is quite similar in
operation to fdisk. Use the gdisk command for
GPT disks and the fdisk command for the more traditional MBR
layout. Both parted and gparted can handle GPT
layout as well as MBR layout, so you might find it more convenient to use
one of these tools to handle both types.
Many distributions allow you to partition your disk, and sometimes shrink an existing Windows NTFS or FAT32 partition, as part of the installation process. Consult the installation documentation for your distribution.
Logical volume manager
The logical volume manager (or LVM) for Linux allows you to combine multiple physical storage devices into a single volume group. For example, you might add a partition to an existing volume group, rather than having to carve out contiguous space large enough for your desired filesystem. The article "Learn Linux 101: Hard disk layout" has more information and an example of creating filesystems with LVM.
RAID
RAID (Redundant Array of Independent Disks) is a technology for providing a reliable data storage using low-cost disks that are much less expensive than the disks found on high-end systems. There are several different types of RAID, and RAID may be implemented in hardware or software. Linux supports both hardware and software RAID.
More filesystems
You will probably encounter filesystems besides those discussed above.
IBM's Journaled File System (JFS), currently used in IBM
enterprise servers, is designed for high-throughput server environments.
It is available for Linux and is included in several distributions. To
create JFS filesystems, use the mkfs.jfs command.
The btrfs (B-Tree file system) was initially developed by Oracle and is available under the GPL license. It is a new copy-on-write filesystem for Linux aimed at implementing advanced features while focusing on fault tolerance, repair, and easy administration. This may not be installed by default, so you will probably have to install a package, such as btrfs-progs to enable btrfs support.
There are other filesystems too, such as the cramfs filesystem often used on embedded devices.