Transcript Linux+ Guide to Linux Certification

Chapter 9 Part III
Linux File System Administration
Disk devices are represented by device files that
reside in the /dev directory
Device file – a file used by Linux commands that
represent a specific device on the system
Character devices - Transfer data to and from the
system one character or data bit at a time
Block devices
• Storage devices that transfer to and from the
system in chunks of many bits by caching the
information in RAM
• Can transfer information must faster than character
devices?
The /dev Directory
List 1st floppy & 1st SCSI tape device
$ ls –l /dev/fd0 /dev/tst0
brw-rw---- 1 root floppy 2, 0 Aug 30 2001 /dev/fd0
crw-rw---- 1 root disk
9, 0 Apr 4 2001 /dev/st0
Major number floppy 2, scsi tape 9
• Used by the kernel to identify what device driver to call to
interact properly with a given category of hardware
Minor number 0 on both
• Used by the kernel to identify which specific device, within a
given category, to use a driver to communicate with
• The b indicates block devices
• The c indicates character devices
The /dev Directory
Table 6-1 (continued): Common device files
Filesystems
Filesystem
• The organization imposed on a physical storage medium
that is used to manage the storage and retrieval of data
Formatting
• The process where a filesystem is placed on a disk drive
Create the ext2 format file system on floppy device 0
$ mkfs –t ext2 /dev/fd0
or
$ mkfs /dev/fd0 (ext2 is default filesystem for mkfs)
To list devices currently used on the system.
$ cat /proc/devices
Working with Floppy Disks
• Floppy disks must be prepared before they are used in
Linux
• Each disk device must be formatted with a filesystem prior
to being used to store files
Table 6-3: Commands used to create filesystems
Table 6-3: Commands used to create filesystems
Filesystem Types
Table 6-2: Common Linux filesystems
Filesystem Types
Table 6-2 (continued): Common Linux filesystems
Mounting
Mounting
• Process used to associate a device with a directory in the
logical directory tree such that users may store data on that
device
Mount point
• Directory in a file structure to which something is mounted
Mount floppy to default mount point (directory)
$ mount /dev/fd0
Mount floppy to specified mount point (directory)
$ mount /dev/fd0 /flopper
Working with Floppy Disks
Table 6-4:
Commands useful when mounting and unmounting filesystems
Mounting
Figure 6-1: The directory structure prior to mounting
Mounting
Figure 6-2: The directory structure after mounting a floppy device
Mounting
• When the Linux filesystem is first turned
on, a filesystem present on the hard drive
is mounted to the / directory
• Root filesystem
– Filesystem that contains the most files that
make up the operating system
– Should have enough free space to prevent
errors and slow performance
Working with Floppy Disks
Figure 6-6:
Viewing the
contents of a
CD-ROM in
a GUI
environment
Working with Floppy Disks
Figure 6-7:
Unmounting
a CD-ROM
device in a
GUI
environment
Working with CD-ROMs
• Linux systems have an ATAPI compliant IDE
CD-ROM drive that attaches to the
mainboard via an IDE ribbon cable
– These CD-ROMs act as a normal IDE hard disk,
and must be configured on of the four
configurations below, as seen with their
associated device files:
•
•
•
•
Primary master (/dev/hda)
Primary slave (/dev/hdb)
Secondary master (/dev/hdc)
Secondary slave (/dev/hdd)
Working with Hard Disks
• IDE hard disk drives attach to the
mainboard with an IDE cable and must be
configured on one of four configurations,
each of which has a different device file:
– Primary master (/dev/hda)
– Primary slave (/dev/hdb)
– Secondary master (/dev/hdc)
– Secondary slave (/dev/hdd)
Working with Hard Disks
• SCSI hard disks are well-suited to Linux
servers that require a great deal of storage
space for programs and user files
• Different device files associated with SCSI
hard disks:
– First SCSI hard disk drive (/dev/sda)
– Second SCSI hard disk drive (/dev/sdb)
– Third SCSI hard disk drive (/dev/sdc)
Working with Hard Disks
• Different device files associated with SCSI
hard disks (continued):
– Fourth SCSI hard disk drive (/dev/sdd)
– Fifth SCSI hard disk drive (/dev/sde)
– Sixth SCSI hard disk drive (/dev/sdf)
– And so on
Hard Disk Partitioning
• Recall that hard disks have the largest
storage capacity of any device used to
store information on a regular basis
– This poses some problems, because as the
size of a disk increases, organization
becomes more difficult and the chance of
error increases
• Partition
– A physical division of a hard disk drive
Hard Disk Partitioning
• It is good practice to use more than just two
partitions on Linux system as this division
can be useful to:
– Segregate different types of data
– Allow for the use of more than one type of
filesystem on one hard disk drive
– Reduce the chance the filesystem corruption will
render a system unusable
– Speed up access to stored data by keeping
filesystems as small as possible
Hard Disk Partitioning
• Tracks
– Area on a hard disk that form a concentric
circle of sectors
• Sector
– Smallest unit of data storage on a hard disk
• Block
– Unit of data commonly used by filesystem
commands
Hard Disk Partitioning
• Cylinder
– Series of tracks
on a hard disk
that are written
to
simultaneously
by the magnetic
heads in a hard
disk drive
Figure 6-8: The physical areas of a hard disk
Hard Disk Partitioning
Table 6-5:
Common hard disk partition device files for /dev/had and /dev/sda
Hard Disk Partitioning
Figure 6-9: A sample Linux partitioning strategy
Hard Disk Partitioning
Figure 6-10: A sample dual-boot Linux partitioning strategy
Working with Hard Disk
Partitions
• Disk Druid is an easy-to-use partitioning
tool used with Red Hat Linux, specifically
designed for installation only
• To create partitions after installations, you
use the fdisk command
• To use the fdisk command, you simply
specify the hard disk partition as an
argument
Disk Usage
• There may be several filesystems mounted to the
directory tree
• The more filesystems that are used, the less likely it
is that a corrupted filesystem may interfere with
normal system operations
• Conversely, using more filesystems typically results
in less hard disk space per filesystem and may
result in system errors if certain filesystems fill up
with data
• The easiest method for monitoring free space by
mounted filesystem is to use the df (disk free space)
command
Checking Filesystems for Errors
• Filesystem corruption
– Errors in a filesystem structure that prevent
the retrieval of stored data
• Syncing
– Process of writing data to the hard disk drive
that was stored in RAM
• Bad blocks
– Those areas of a storage medium used by
filesystem commands
Checking Filesystems for Errors
Table 6-6: Common options to the fsck command
Hard Disk Quotas
• Soft limits
– Limit imposed that can be exceeded for a
certain period of time
• Hard limit
– Limit imposed that cannot be exceeded
Chapter Summary
• Disk devices are represented by device
files that reside in the /dev directory
• Each disk drive must contain a filesystem,
which is then mounted to the Linux
directory tree for usage using the mount
command
• Hard disks must be partitioned into distinct
sections before filesystems are created on
those partitions
Chapter Summary
• There are many different filesystems
available to Linux
• It is important to monitor disk usage using
the df, du, and dumpe2fs commands to
avoid running out of storage space
• If hard disk space is limited, you can use
hard disk quotas to limit the space that
each user has on filesystems