Chapter 8 working with the bash shell
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Chapter 8: Working with the BASH Shell. The /dev directory. Each device is represented as files in /dev Devices are divided into two types Character Block The first character in the long listing indicates the type of the device

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Chapter 8: Working with the BASH Shell

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Chapter 8 working with the bash shell

Chapter 8: Working with the BASH Shell


The dev directory

The /dev directory

  • Each device is represented as files in /dev

  • Devices are divided into two types

    • Character

    • Block

  • The first character in the long listing indicates the type of the device

  • Major and minor numbers replace the size. Major for the type of the device and minor for the device itself

  • If a device file is corrupted or deleted you can use mknod to re-create it if you know the type, major and minor numbers. $mknod /dev/fd10 b 2 10

  • Otherwise, you can use: $/dev/MAKEDEV fd0

  • The file /proc/devices contains a list of used devices


Common device files

Common Device Files


File systems

File Systems

  • An advantage of Linux is that you can use several files systems at the same time, thus

  • Each partition can have its own file system

  • Mounting means making the data available

  • A storage device can be mounted to any directory in the system

  • It is common to use directories under /mnt

  • Mounting will temporary covers up all the content of the mount point for the duration of mounting

  • To mount and un-mount devices, use the mount/ unmount commands

  • The file system table (fstab) contains various information about currently mounted devices


Common file systems

Common File Systems


Floppy disks

Floppy Disks

  • To format a floppy disk (i.e. creating a file system) you use the mkfs commands

  • mkfs takes a –t option to specify the file system type and you need to specify the device file to be used

  • $ mkfs –t ext3 fd4

  • The default file system is ext2

  • A list of variant to mkfs is given in Table 6-3

  • A disk should be mounted to be accessible

  • The command mount lists currently mounted file systems

  • Similar effect can be achieved by viewing the mount table. $cat /etc/mtab

  • After mounting, use the mount point as the root dir.


Floppy disks cont

Floppy Disks (cont.)

  • When an ext2 is created on a device, a directory called lost+found is created by default

  • To check if amount directory is not used by any users, you use the fuser: $fuser –u /mnt/floppy

  • You need to unmount the floppy disk before ejecting it. To do so, use $unmount /mnt/floppy

  • The unmount commands accepts the device to be un-mounted or the mount point directory

  • You can use the fuser to check if any process is using the mount directory which will prevent the device from being un-mounted

  • The file-systems table is used to mount devices at boot time and in case the mount command does not have enough arguments


Floppy disks cont1

Floppy Disks (cont.)

  • The /etc/fstab has six fields: Device to mount, mount point, type, mount options, dump#, fsck#

    • The dump# determines if the Fs is to be backed up or not

    • The fsck# determines if FS is to be checked at boot or not

  • The mount can take fewer arguments

  • Example: $mount /dev/fd0 or $mount /mnt/floppy

  • Contents of /etc/fstab

  • Generally, floppy disks are mounted automatically when using a GUI environment such as the KDE or the GNOME


Cd roms

CD-ROMs

  • They are different than floppies in which they usually use IDE controller

  • Thus, they use similar naming convention like IDE hard disks (hda for primary master, etc.)

  • Besides, they typically use the iso9660 filesystem, thus they are mounted with

    • -t iso9660 option for the filesystem type

    • -r for read-only

  • $mount –r –t iso9660 /dev/cdrom / mnt/cdrom

  • They can be un-mounted using unmount

  • CD-ROM can NOT be ejected unless properly un-mounted.


Hard disks

Hard Disks

  • They are usually partitioned with different FS why

    • Separate different data types

    • Use of more than FS

    • Improve system reliability (FS corruption)

    • Enhance system performance

  • The MBR stores info about all particitions

  • Hard disk structure: Tracks, sectors, cylinder

  • Physical and logical partitions

  • Partitioning hard disks:

    • During installation: using Druid

    • After installation: Using fdisk

  • The machine might need to be rebooted to manually reload the new partition info


Maintenance commands

Maintenance Commands

  • Monitoring disk usage using disk free space (df)

  • It gives results in terms of block numbers

  • The –h option prints results measured in MB & GB

  • It only views mounted file systems

  • To get info about a specific directory use du (Directory Usage)

  • It, du, gives results in KB

  • The option –s give summary and can be used with –h

  • To view total number of i-nodes and the number of free ones use: dumpe2fs –h /dev/sda0


Maintenance commands cont

Maintenance Commands (cont)

  • Disk quotas

  • Soft limit and hard limit

  • Setting quotas (quotaon/quotaoff)

  • Editing quota (edquota)

  • List quota values for all users (repquota)

  • Checking quota values for individual users (quota –v <user>)


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