Linux Unix Day 2

8/2/2019 Linux Unix Day 2

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Linux File system


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Linux File system

Super block: The superblock contains information about the

filesystem as a whole, such as its size

Inode block: Contains all information about a file, except its name.Also includes the number for data blocks for that block.

Data block: Used to store data in the file.

Directory block: A directory entry consists of a filename and the

number of the inode which represents the file.

Indirection block: These dynamically allocated blocks are indirect

blocks; the name indicates that in order to find the data block, onehas to find its number in the indirect block first.


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Directories

/

etc home bin usr lib

dev boot/ - first of mount point in linux

/etc - keep linux default configuration/boot - keep important linux booting files

/dev - keep all device files

/usr - keep all user binary and X library/home - keep user home directory

/var - keeping mail, log file and printer spooling


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Directories

Directory

Used to organize other files into a logical tree structure

Absolute pathname

Pathname from the root directory to a certain file or

directory

Root

The top level directory

Referred to using the / character


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Directories

~ metacharacter

Can be used to refer to the current users

home directory

Can be used to specify another users homedirectory by appending a username at the

end of the ~ metacharacter

Relative pathname

Pathname of a target directory relative to your

current directory in the tree


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Shells

Shell accepts commands, interprets them and pass them tokernel.

bash

Most commonly used shell.

csh

Syntax is very familiar to the C- proramminglanguage

ksh

korn shell

tcsh


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Linux Basics

Navigation and searching


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Navigation

ls Lists the entries of a directory

lsa lists all, including system files.

mkdir cd PATH

cd takes the user to its home

pwd cp file 1 file2


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Navigation

mv file1 file2

moves files or rename file

rm file removes a filermdir dir removes a directory

cat file prints the contents

whoami mank help or --help


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File types

Text files

Store information in a readable text format

Binary data files

Store information associated with executable

programs

Executable program files

Directory files


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File types

Linked filesAssociated with another file

Special device files

Represent system devicesNamed pipes

Identify channel that passes information

between processesSocket files

Allow a process on another computer to writeto a local file


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Displaying content of a text file

Log files

File that contains past system event

cat commandtac command

Linux command that displays a file to the

screen beginning with the last line of the fileand ending with the first line of the file


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headcommand

By default, displays the first 10 lines (including blank lines)

of a text file to the terminal screen

Can also take a numeric option specifying a differentnumber of lines to display

tail command

By default, displays the last 10 lines (including blank lines)

of a text file to the terminal screen

Can also take a numeric option specifying a different

number of lines to display


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more command

less command

Displays a text file page-by-page on the terminal

Better thanmore

Exit with q

Themore and less commands can also be used in

conjunction with the output of other commandsIf output is too large to fit on terminal screen, use |

metacharacter, e.g. ls -l | more


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Searching files

updatedb

locate file

findname file*findname * size +500k

grep string file

ls grep|newgrep b.*g file


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Searching files

which commandCommand used to locate files that exist

within directories listed in the PATH

variablePATH variable

Lists directories on system where executable

files are located

Allows executable files to be run without

specifying absolute or relative path


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Manipulation

vi file

opens a file in current directory for editing.

commands: :q :q!

:w

:wq

/ -searching string

Select some text to copy it, and right click pastes it.


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Manipulation

emacsEmacs is more than "just an editor" -- it provides a fully integrateduser environment offering the sort of facilities outlined below. Issue shell comands

Read and send mail

Read news Access the internet

Write and test programs

Maintain a calendar

Play a game!

nano gedit


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Linux Devices

/etc


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The /dev Directory

Device file

File representing a device

Typically found in the /dev directory

Character devices Transfer data to and from the system one data bit

at a time

Block devices Transfer to and from the system in chunks ofmany bits by caching the information in RAM

Represented by block device files

Fast data transfer


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The /dev Directory

BlockDefault CD-ROM/DVD-ROM drive/dev/cdrom

BlockFirst primary partition on the first SCSI hard disk drive/dev/sda1

BlockFirst primary partition on the fourth IDE hard disk drive(secondary slave)

/dev/hdd1

BlockFirst primary partition on the third IDE hard disk drive

(secondary master)

/dev/hdc1

BlockFirst primary partition on the first IDE hard disk drive

(primary master)

/dev/hda1

BlockFirst primary partition on the second IDE hard disk drive

(primary slave)

/dev/hdb1

Second floppy disk on the system

First floppy disk on the system

Description

Block/dev/fd1

Block/dev/fd0

Block or

CharacterDevice File

Common device files


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The /dev Directory

Major number

Used by the kernel to identify what device

driver to call to interact properly with agiven category of hardware

Minor number

Used by the kernel to identify whichspecific hardware device, within a givencategory, to use a driver to communicatewith


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The /dev Directory Device file type (block or character),

major number, and minor number makeup a device files unique characteristics

lrwxrwxrwx 1 root root 8 May 2 11:33 cdrom -> /dev/hdc

brw-rw---- 1 root disk 3, 0 Feb 23 2004 hda

brw-rw---- 1 root disk 3, 1 Feb 23 2004 hda1

mknodcommand

Can be used to re-create a corrupted

device file Must know file type, major, and minor

numbers


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Filesystem Types

Third extended filesystem; a variation on ext2 that allows

for journaling and thus has a faster startup and recovery

time

ext3

Second extended filesystemcurrently the most common

filesystem used on Linux, it supports Access Control Lists

(individual user permissions). It retains its name from being

the new version of the original extended filesystem, based

on the Minix filesystem

ext2

Compact disc filesystemused to view all tracks and data

on a CD-ROM as normal files

cdfs

Boot File Systema small bootable filesystem used to hold

the files necessary for system startup; it is commonly used

on UNIX systems

bfs

DescriptionFilesystem

Common Linux filesystems


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Filesystem Types

The DOS FAT filesystemmsdos

The DOS FAT filesystem with long file name supportvfat

The MINIX filesystemfilesystem used by Linus Torvalds

in the early days of Linux development

minix

Hierarchical File Systema filesystem native to Apple

Macintosh computers

hfs

The CD-ROM filesystemoriginated from the International

Standards Organization recommendation 9660 and used

to access data stored on CD-ROMs

iso9660

High Performance File Systeman IBM-proprietary OS/2

filesystem that provides long file name support and is

optimized to manipulate data on large disk volumes

hpfs




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Filesystem Types

New Technology File Systema Microsoft-proprietary

filesystem developed for its NT4 and Windows 2000

operating systems, currently available as a read-only

filesystem under Linux

ntfs

The Veritas filesystema journaling filesystem that offers

large file support, supports Access Control Lists (individual

user permissions), and is commonly used by major

versions of UNIX

vxfs

The Universal Disk Format filesystemA filesystem used

by software systems that write to a CD-R, CD-RW or DVD

udf

The REISERFS filesystema journaling filesystem similar

to ext3 more suited for use with databases

reiserfs




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Mounting Mounting

Making a device accessible to users via thelogical directory tree

Term originated in the 1960s, wheninformation was stored on large tape reelsthat had to be mounted on computers tomake the data available

Mount point

Directory in a file structure to which a deviceis attached

Any existing directory can be a mount point


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Mounting/

mnt root

floppy cdrom

homedata etc

mary bob sue

The filesystem prior to mounting


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Mounting/

mnt root homedata etc

mary bob sue

The directory structure after mounting a floppy device

/mnt


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Mounting/

mnt root

cdrom

homedata etc

mary bob sue

The directory structure after mounting a floppy device

correctly

floppy

/mnt/floppy


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Mounting

When the Linux filesystem is firstturned on, a filesystem present on the

hard drive is mounted to the / directory Root filesystem

Filesystem that contains files that start up

the operating system Should have enough free space to

prevent errors and slow performance


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Mounting

mount command

Used to mount devices to mount point

directories With no options or arguments, lists

currently mounted filesystems

umount command Used to unmount devices from mount

point directories


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Working with Floppy Disks

When transferring small amounts ofinformation from computer tocomputer, it is commonplace to usefloppy disk removable media to storethe files However, 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


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mkfs (make filesystem) command

Used to format a disk with a filesystem

t option: Specifies filesystem type Default is ext2 filesystem

To mount or unmount floppies, must

ensure that no user is currently usingthe mount point directory


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fuser command

With the u option, lists users using a

directory Most (almost all) floppy disks today

come preformatted with the DOS FATfilesystem

Will work just fine for Linux when mountedcorrectly

(Work on Macs as well)


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Used to create a REISERFS filesystemmkfs.reiserfs

mkreiserfs

Used to create a CD-ROM filesystemmkisofs

Used to create an ext3 filesystem (j = journaling)mkfs.ext3

mke2fs -j

Used to create an ext2 filesystemmkfs.ext2mke2fs

Used to create a DOS FAT filesystemmkfs.msdos

mkdosfs

mkfs.vfat

Used to create filesystems of most typesmkfs

DescriptionCommand

Commands used to create filesystems


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/etc/fstab file

Used to mount devices at boot time

Also consulted when users do not specifyenough mount command arguments

Six fields: Device to mount, mount point,

type, mount options, dump#, fsck#


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Unmounts a from

its directory

umount

or

umount

Displays the users using aparticular directory

fuser -u

Mounts a of a

certain to a directory

mount -t

Displays mounted

filesystems

mount

DescriptionCommand

Useful commands when mounting and unmountingfilesystems


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Mounting a

floppy deviceusing a GUI

environment


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Unmounting a

floppy devicein

a GUI

environment


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Working with CD-ROMs

CD-ROMs are normally mounted as/dev/cdromdespite occupying one of

the hard drive block device designations Typically use iso9660 filesystem type

and are not writable

Mount with

r(read-only) option

Cannot be ejected until properlyunmounted


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Viewing the

contents of aCD-ROM

device in

a GUI

environment


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Unmounting a

CD-ROMdevice in

a GUI

environment


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Working with Hard Disks

IDE hard disk drives attach to themainboard with an IDE cable and mustbe configured on one of four

configurations, each of which has adifferent device file:

Primary master (/dev/hda)

Primary slave (/dev/hdb)

Secondary master (/dev/hdc)

Secondary slave (/dev/hdd)


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Working with Hard Disks

SCSI hard disks well-suited to Linuxservers

Faster access speed

Multiple hard drives can be attached to acontroller

Associated with different device files

First SCSI HDD (/dev/sda)

Second SCSI HDD (/dev/sdb)

Third SCSI HDD (/dev/sdc) and so on.


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Hard Disk Partitioning

As disk size increases, organizationbecomes more difficult and chance oferror increases

Partition

A physical division of a hard disk drive

Can have its own filesystem


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It is good practice to use more than justtwo partitions

Segregates different types of data Allows for use of multiple filesystem types on one

HDD

Reduces the chance the filesystem corruption

will render a system unusable Speeds up access to stored data by keeping

filesystems as small as possible


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Tracks

Area on a hard disk that form a concentriccircle of sectors

Sector

Smallest unit of data storage on a harddisk

Block

Unit of data commonly used by filesystemcommands


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Cylinder

Series of tracks on a hard disk that are

written to simultaneously by the magneticheads in a hard disk drive

Partition definitions stored in first readablesector of the hard disk

Master Boot Record (MBR) or master boot block(MBB)


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Track

Sector

Block

The physical

areas of a harddrive


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Common hard disk partition device files for

/dev/hda and /dev/sda

SCSI Device Name

(assuming /dev/sda1)

IDE Device Name

(assuming /dev/hda1)

Partition

/dev/sdan/dev/hdannth logical drive in the extended partition

/dev/sda9/dev/hda95th logical drive in the extended partition

/dev/sda8/dev/hda84th logical drive in the extended partition

/dev/sda7/dev/hda73rd logical drive in the extended partition

/dev/sda6/dev/hda62nd logical drive in the extended partition

/dev/sda5/dev/hda51st logical drive in the extended partition

/dev/sda4/dev/hda44th primary partition

/dev/sda3/dev/hda33rd primary partition

/dev/sda2/dev/hda22nd primary partition

/dev/sda1/dev/hda11st primary partition


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Hard Disk Partitioninghda1primary

hda5logical

MBR(MBB)

Freespace

swap1GB

hda5 + free space = hda2extended

A sample Linux partitioning strategy

/ (Linux)

9GB


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Hard Disk Partitioninghda1primary

hda7logical

MBR(MBB)

Freespace

Swap1GB

hda5 + hd6 + hd7 + free space= hda2(extended)

A sample dual-boot Linux partitioning strategy

hda5logical

hda6logical

C:\win984GB

/home5GB

/ (Linux)

9GB


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Working with Hard Disk

Partitions Disk Druid is an easy-to-use partitioningtool used with Red Hat Linux, specifically

designed for installation only fdisk command

Used to create partitions after installation

Specify hard disk partition as an argument


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Working with Hard Disk Partitions

tune2fs command

Create a journal file on the filesystem

Convert ext2 to ext3

Edit /etc/fstab file to allow system

to mount new filesystems automatically

at boot time


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Monitoring Filesystems

Check mounted filesystemsperiodically

Errors

Disk Space usage

Inode usage


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Disk Usage

Using more filesystems typically resultsin less hard disk space per filesystem

Errors when filesystems fill up with data

e.g., free space on / filesystem falls below 10%

df (disk free space) command

Monitor free space used by mounted

filesystems

h option: More user friendly


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Disk Usage

du (directory usage) command

View size of a directory and contents in

Kilobytes s option: Summarizes output

dumpe2fs command

View total number of inodes and freeinodes for ext2 or ext3 filesystem

Use h option


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Checking Filesystems for

Errors Filesystem corruption Errors in a filesystem structure that prevent the

retrieval of stored 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


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Errors fsck (filesystem check) command

Check a filesystem for errors

Filesystem must be unmounted

f option used to perform full check

e2fsck command

Check ext2 and ext3 filesystems

reiserfsck

Check reiserfs filesystems


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Errors

Common options to the fsck command

Displays verbose output-V

Checks all filesystems in /etc/fstab that have a 1 or 2 in

the sixth but skips field the / filesystem

-AR

Performs a full filesystem check and displays a progressline

-Cf

Checks all filesystems in /etc/fstab that have a 1 or 2 in thesixth field

-A

Allows fsck to repair any errors automatically-a

Performs a full filesystem check-f

DescriptionOption


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Hard Disk Quotas

If several users on a system, must be enoughhard disk space for each users files

Hard disk quotas

User limits on filesystem usage Restrict number of files/directories or total disk

space usage

Soft limits

Limit imposed that can be exceeded for a certainperiod of time

Hard limit

Limit imposed that cannot be exceeded


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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 quotas andcurrent usage


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Errors

Common options to the fsck command

Displays verbose output-V

Checks all filesystems in /etc/fstab that have a 1 or 2 in

the sixth but skips field the / filesystem

-AR

Performs a full filesystem check and displays a progressline

-Cf

Checks all filesystems in /etc/fstab that have a 1 or 2 in thesixth field

-A

Allows fsck to repair any errors automatically-a

Performs a full filesystem check-f

DescriptionOption

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