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Guidance to the Certification of Linux - PPT


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objectives
Objectives
  • Identify the structure and types of device files in the /dev directory
  • Understand common filesystem types and their features
  • Mount and unmount filesystems to and from the Linux directory tree
  • Create and manage filesystems on floppy disks, CDs, DVDs, USB storage devices, FireWire storage devices, and hard disk partitions
  • Create and use ISO images
objectives continued
Objectives (continued)
  • Use the LVM to create and manage logical volumes
  • Monitor free space on mounted filesystems
  • Check filesystems for errors
  • Use hard disk quotas to limit user space usage
the dev directory
The /dev Directory
  • Device file: file representing a system device
    • Typically found in /dev directory
    • Specifies how to transfer data to and from the device
  • Character devices: transfer data to and from system character by character
  • Block devices: transfer chunks or blocks of data using physical memory as a buffer
    • Fast data transfer
    • Floppy disks, CD-ROMs, DVDs, USB flash drives, hard disk drives
the dev directory continued
The /dev Directory (continued)
  • Major number: points to the device’s driver in the Linux kernel
  • Minor number: indicates the particular device
  • Device file type (block or character), major number, and minor number make up the unique characteristics of a device file
the dev directory continued1
The /dev Directory (continued)
  • mknod command: can be used to re-create a corrupted device file
    • Must know file type, major, and minor numbers
  • /dev/MAKEDEV command: can be used to re-create a device file based on its common name
    • Useful if don’t know some of the information required for the mknod command
filesystems
Filesystems
  • Filesystem: organization and management imposed on physical storage media
  • Formatting: creating a filesystem on a device
mounting
Mounting
  • Mounting: making a device accessible to users via the logical directory tree
  • Mount point: directory to which a device is attached
    • The mounted device temporarily covers up the contents of the mount point
    • Any existing directory can be a mount point
  • In order to prevent making files inaccessible, create empty directories used specifically for mounting devices
mounting continued
Mounting (continued)

Figure 5-1: The directory structure prior to mounting

mounting continued1
Mounting (continued)

Figure 5-2: The directory structure after mounting a floppy device

mounting continued2
Mounting (continued)
  • Root filesystem: when Linux filesystem is first turned on, a filesystem on the hard drive is mounted to the / directory
    • Contains most OS files
  • mount command: used to mount devices to mount point directories
    • When used with no options or arguments, lists currently mounted filesystems
  • umount command: used to unmount devices from mount point directories
working with floppy disks
Working with Floppy Disks
  • Disk devices must be prepared before use
    • Formatted with a filesystem
  • mkfs (make filesystem) command: Used to format a disk device with a filesystem
    • –t option: Specifies filesystem type
    • Default is ext2 filesystem
  • To mount or unmount floppies, must ensure that no user is currently using the mount point directory
    • Use mount command with no options or arguments to get list of currently mounted filesystems
    • Once mounted, use as any other directory
working with floppy disks continued
Working with Floppy Disks (continued)
  • mkfs -t ext3 /dev/hda1
  • mke2fs
  • mkfs.ext3
  • mkfs.msdos
  • mkfs.vfat

Table 5-3: Commands used to create filesystems

working with floppy disks continued1
Working with Floppy Disks (continued)
  • fuser command: With the –u option, lists users using a directory
  • /etc/fstab file: Used to mount devices at boot time
    • Also consulted when users do not specify enough mount command arguments
    • Six fields:
  • <device to mount>
  • <mount point>
  • <type>
  • <mount options>
  • <dump#>
  • <fsck#>
working with floppy disks continued2
Working with Floppy Disks (continued)
  • mount
    • Mount <filesystem> <target>
  • umount
    • umount <target>

Table 5-4: Useful commands when mounting and unmounting filesystems

working with cds dvds and iso images
Working with CDs, DVDs, and ISO Images
  • Most software is packaged on CDs and DVDs
  • Can be mounted using the mount command and unmounted using umount command
    • Different device file - depend on the technology used by the drive itself.
  • For PATA drives, use one of the following:
    • Primary master (/dev/hda)
    • Primary slave (/dev/hdb)
    • Secondary master (/dev/hdc)
    • Secondary slave (/dev/hdd)
working with cds dvds and iso images continued
Working with CDs, DVDs, and ISO Images (continued)
  • For SATA or SCSI drives, Linux may use many different names, depending on the actual CD or DVD drive
  • To make identification of CD/DVD drive easier, Fedora Linux includes symbolic links within the /dev directory:
    • /dev/cdrom – symbolic link to first CD-ROM drive
    • /dev/cdrw – symbolic link to first CD-RW drive
    • /dev/dvd – symbolic link to first DVD-ROM drive
    • /dev/dvdrw – symbolic link to first DVD-RW drive
working with cds dvds and iso images continued1
Working with CDs, DVDs, and ISO Images (continued)
  • CDs and DVDs Typically use iso9660 filesystem type and are read only when accessed using Linux
    • Mount with –r (read-only) option
  • Cannot be ejected until properly unmounted
  • In GUI environment, CD or DVD automatically mounted to a directory underneath the /media directory
    • Named for the label on the CD or DVD
    • System places shortcut on desktop
working with cds dvds and iso images continued2
Working with CDs, DVDs, and ISO Images (continued)

Figure 5-3: Accessing a DVD within the GNOME desktop environment

working with cds dvds and iso images continued3
Working with CDs, DVDs, and ISO Images (continued)
  • iso9660 filesystem can be used to create ISO images that contain other files
    • Can be mounted as a loopback device using the mount command
  • mkisofs command: Used to create ISO image from directory
    • Receives at least two arguments:
      • Filename to be created
      • Directory used to create the ISO image
working with hard disks
Working with Hard Disks
  • Three types of hard disks: PATA, SATA, and SCSI
  • PATA HDDs must be configured in one of the following:
    • Primary master (/dev/hda)
    • Primary slave (/dev/hdb)
    • Secondary master (/dev/hdc)
    • Secondary slave (/dev/hdd)
  • Different device file for each
working with hard disks continued
Working with Hard Disks (continued)
  • SATA and SCSI hard disks are well-suited to Linux servers
    • Faster access speed
    • Multiple hard drives can be attached to a controller
  • Associated with different device files
    • First SCSI HDD (/dev/sda)
    • Second SCSI HDD (/dev/sdb)
    • Third SCSI HDD (/dev/sdc)
    • And so on
standard hard disk partitioning
Standard Hard Disk Partitioning
  • Partition: physical division of an HDD; can have its own filesystem
  • Linux requires at least two partitions; root and swap
  • Good practice to use more than two partitions
    • Segregate different types of data
    • Allow for use of multiple filesystem types on one HDD
    • Reduce chance that filesystem corruption will render a system unusable
    • Speed up access to stored data
standard hard disk partitioning continued
Standard Hard Disk Partitioning (continued)
  • Track: area on a hard disk that forms a concentric circle
  • Sector: portion of a track containing information
  • Block: combination of sectors
  • Cylinder: series consisting of the same concentric track on all of the metal platters inside a HDD
  • Partition definitions stored in first readable sector of the hard disk
    • Master Boot Record (MBR) or master boot block (MBB)
standard hard disk partitioning continued1
Standard Hard Disk Partitioning (continued)

Figure 5-4: The physical areas of a hard disk

standard hard disk partitioning continued2
Standard Hard Disk Partitioning (continued)

Table 5-5: Common hard disk partition device files for /dev/hda and /dev/sda

standard hard disk partitioning continued3
Standard Hard Disk Partitioning (continued)

Table 5-5 (continued): Common hard disk partition device files for /dev/hda and /dev/sda

standard hard disk partitioning continued4
Standard Hard Disk Partitioning (continued)

Figure 5-5: A sample Linux partitioning strategy

standard hard disk partitioning continued5
Standard Hard Disk Partitioning (continued)

Figure 5-6: A sample dual-boot Linux partitioning strategy

working with standard hard disk partitions
Working with Standard Hard Disk Partitions
  • fdisk command: Create partitions after installation
    • Specify hard disk partition as an argument
    • Variety of options for fdisk prompt to achieve different tasks
  • cfdisk command: Interactive graphical utility for creating, manipulating and deleting partitions
  • Reboot computer after using the fdisk and cfdisk commands to ensure proper reloading into memory
working with standard hard disk partitions continued
Working with Standard Hard Disk Partitions (continued)
  • Edit /etc/fstab file to allow system to mount new filesystems automatically at boot time
  • mkswap command: Prepare the swap partition
  • swapon command: Activate the swap partition
  • swapoff command: Deactivate the swap partition
  • Edit /etc/fstab file to ensure that new swap partition is activated as virtual memory
working with the lvm
Working with the LVM
  • Logical Volume Manager (LVM): Used to create volumes
    • Volumes can contain filesystems and can be mounted to directories
    • More flexible than standard partitions – allows use of free space across multiple hard disks
    • Has error correction abilities
  • LVM components: physical volumes (PVs), volume group (VG), and logical volumes (LVs)
working with the lvm continued1
Working with the LVM (continued)
  • pvcreate command: used to create PVs
  • pvdisplay command: used to display detailed information about each PV
  • vgcreate command: used to create a VG that uses the space in PVs
    • Arguments are name of the VG and PVs to be used
  • Physical Extent: block size for saving data in a VG
    • Should be set when creating a VG
    • Can use vgcreate -s to set the PE
working with the lvm continued2
Working with the LVM (continued)
  • vgdisplay command: used to display detailed information about each VG
  • lvcreate command: used to create LVs from available space in a VG
  • lvdisplay command: used to display information about each LV
  • Work with mount points of LVs as would work with any other had disk partition device file
    • Edit /etc/fstab to ensure that LVs are automatically mounted at system startup
working with the lvm continued3
Working with the LVM (continued)
  • pvscan, vgscan, and lvscan commands: Display information about PVs, VGs, and LVs, respectively
  • vgextend command: used to add a new PV to an existing VG
  • lvextend command: used to increase the size of an LV, e.g., to use space extended onto an existing VG
working with usb and firewire based storage devices
Working with USB and FireWire-Based Storage Devices
  • Most removable storage devices emulate SCSI protocol in the firmware of the device
  • Devices are automatically mounted to a new directory under the /media directory named for the label on the device
  • Easy to work with removable storage devices using a GUI interface
    • If you want to use commands, must know the device file and mount point directory
monitoring filesystems
Monitoring Filesystems
  • Check mounted filesystems periodically
    • Errors
    • Disk Space usage
    • Inode usage
  • Minimizes problems that due to damaged filesystems
disk usage
Disk Usage
  • Using more filesystems typically results in less hard disk space per filesystem
    • Errors when filesystems fill up with data
    • Periodically remove obsolete files such as old log files to make room for new ones
  • df (disk free space) command: Monitor free space used by mounted filesystems
    • –h option: More user friendly
    • To get information about different filesystems, you must mount them prior to using df command
disk usage continued
Disk Usage (continued)
  • du (directory usage) command: view size of a directory and contents in Kilobytes
    • –s option: Summarizes output
    • –h option: More user friendly
  • dumpe2fs command: view total number of inodes and free inodes for ext2, ext3, or ext4 filesystem
    • Use –h option
checking filesystems for errors
Checking Filesystems for Errors
  • Filesystem corruption: errors in filesystem structure preventing retrieval of data
    • Commonly occurs due to improper system shutdown
  • Syncing: process of writing data stored in RAM to the HDD
  • Bad blocks: unusable areas of a disk
    • Cannot hold a magnetic charge
checking filesystems for errors continued
Checking Filesystems for Errors (continued)
  • fsck (filesystem check) command: check a filesystem for errors
    • Filesystem must be unmounted
    • –f option used to perform full check
  • e2fsck command: Check ext2, ext3, and ext4 filesystems
    • -c option checks for bad blocks
  • tune2fs command: Used to change filesystem parameters
    • -i option sets interval to forcing full system check
checking filesystems for errors continued1
Checking Filesystems for Errors (continued)

Table 5-6: Common options to the fsck command

hard disk quotas
Hard Disk Quotas
  • If several users on a system, must be enough hard disk space for each user’s files
  • Hard disk quotas: user limits on filesystem usage
    • Restrict number of files/directories or total disk space usage
  • Soft limit: user may exceed quota briefly
  • Hard limit: limit cannot be exceeded
hard disk quotas continued
Hard Disk Quotas (continued)
  • quotaon and quotaoff commands: toggle quotas on and off
  • edquota command: edit user quotas
  • repquota command: report user quotas
  • quota command: allows regular users to view their own quotas and current usage
summary
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
  • Many different filesystems available to Linux
summary continued
Summary (continued)
  • The LVM can be used to create logical volumes from the free space within multiple partitions
  • USB and FireWire storage devices are recognized as SCSI disks by the Linux system
  • 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