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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.
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."
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.
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 Listing 1.
Listing 1. 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 |
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.
Listing 2 shows the partitions on the
primary hard drives of two of my systems.
Listing 2. 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.
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.
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.
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 Listing 3.
Listing 3. 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 Listing 3. Type
m to display a list of available one-letter
commands as shown in Listing 4.
Listing 4. 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; Listing 5 shows the output.
Listing 5. 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.
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.
Let's start by using the n command to create a
new partition; see Listing 6.
Listing 6. 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 Listing 6 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 Listing 7.
Listing 7. 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):
|
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 Listing 8.
Listing 8. 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): |
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 Listing 9. 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.
Listing 9. 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 |
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 Listing 10. 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.
Listing 10. 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."
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 (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 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.
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.
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.
Swap space must be formatted for use as swap space, but it is not generally considered a 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.
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 Listing 11.
Listing 11. 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.
Let's format the /dev/sda8 partition as ext3 using the
mkfs command as shown
in Listing 12.
Listing 12. 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 Listing 13 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.
Listing 13. Displaying a UUID using blkid
[ian@echidna ~]$ blkid /dev/sda8 /dev/sda8: UUID="87040def-920e-4525-9c81-c585ddc46384" SEC_TYPE="ext2" TYPE="ext3" |
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.
Listing 14 shows how gdisk displays
information for a drive that is not already in GPT layout.
Listing 14. 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.
Listing 15 shows the interaction.
Listing 15. 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): q
|
Your 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. Listing 16 illustrates this.
Listing 16. 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.
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.
Listing 17. 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.
We'll now create the FAT32 (vfat) filesystem on /dev/sda9.
Listing 18. 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.
Now let's create some swap space on the /dev/sda4 partition using the
mkswap command as shown in
Listing 19.
Listing 19. 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.
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.
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
Figure 1. The
sfdisk command is intended for programmer use
and can be scripted. Use it if you know what you are doing.
Figure 1. 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 Figure 2.
(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.
Figure 2. 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.
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 (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.
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.
Learn
- Use the developerWorks roadmap for
LPIC-1 to find the developerWorks articles to help you study for
LPIC-1 certification based on the April 2009 objectives.
- At the LPIC
Program site, find detailed objectives, task lists, and sample
questions for the three levels of the Linux Professional Institute's Linux
system administration certification. In particular, see their April 2009
objectives for LPI exam 101 and LPI exam 102.
Always refer to the LPIC Program site for the latest objectives.
Note the Exam 101: Objective Changes as of July 2, 2012.
- Review the entire LPI exam prep series on
developerWorks to learn Linux fundamentals and prepare for system
administrator certification based on earlier LPI exam objectives prior to
April 2009.
- Visit the home of the Filesystem Hierarchy Standard (FHS).
- Learn about the Linux Standard Base (LSB), a Free Standards Group (FSG) project to develop a standard binary operating environment.
- Learn about the Anatomy of ext4.
- Learn about the btrfs file system (B-Tree file system).
- Learn about the Reiser4 file system, the successor to ReiserFS.
- The Linux Documentation Project has a variety of useful documents, especially its HOWTOs.
- In the developerWorks Linux zone, find hundreds of how-to articles and tutorials, as well as downloads, discussion
forums, and a wealth of other resources for Linux developers and
administrators.
- Stay current with developerWorks technical events and webcasts focused on a variety of IBM products and IT industry topics.
- Attend a free developerWorks Live! briefing to get up-to-speed quickly on IBM products and tools, as well as IT industry trends.
- Watch developerWorks on-demand demos ranging from product installation and setup demos for beginners, to advanced functionality for experienced developers.
- Follow developerWorks on
Twitter, or subscribe to a feed of Linux tweets on developerWorks.
Get products and technologies
-
Evaluate
IBM products in the way that suits you best: Download a product
trial, try a product online, use a product in a cloud environment, or
spend a few hours in the SOA Sandbox learning how to implement Service Oriented
Architecture efficiently.
Discuss
- Participate in the discussion forum.
- Get involved in the developerWorks
community. Connect with other developerWorks users while exploring
the developer-driven blogs, forums, groups, and wikis.
Ian Shields works on a multitude of Linux projects for the developerWorks Linux zone. He is a Senior Programmer at IBM at the Research Triangle Park, NC. He joined IBM in Canberra, Australia, as a Systems Engineer in 1973, and has since worked on communications systems and pervasive computing in Montreal, Canada, and RTP, NC. He has several patents and has published several papers. His undergraduate degree is in pure mathematics and philosophy from the Australian National University. He has an M.S. and Ph.D. in computer science from North Carolina State University. Learn more about Ian in Ian's profile on developerWorks Community.
