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In order to check the free and usage space per file system and directory and each sub directory we have two command

1. df
2. du

the ‘df’ command reports on a per file system basis. It report total disk space , disk space used , disk space free

#df –h

-h : used multipliers such as G or M for gigabytes and Megabytes

The ‘du’ command reports the number of kilobytes contained by the items within a directory

#du –s

#du –h

-s : used to request only the summary directory information

#du –s /etc

A symbolic link point to another file. We can display the link name and the referenced file by ‘ls –l’

#ls –l pf

lrwxrwxrwx 1 root root pf->/etc/passwd

file type: l for symbolic link

the content of the symbolic link is the name of the file that is referenced

Syntax:

Ln –s filename [linkname]

Example:

Ln –s /etc/passwd password

There are seven fundamental file type

- : regular file

d : symbolic link

b : block special file

c : character special file

p : named file

s : socket

character special file are used to communicate with hardware one character at a time. Block special file is used to communicate with hardware a block of data at a time : 512 bytes, 1024 bytes, 2048 bytes

ls –l /dev |less { to check c and b files}

named pipe type of file that passes data between processes. It stores no data itself socket file are used for inter process communication.

The standard Output of command , which normally display on the terminal can be redirected into a file. Similarly standard error, which normally display on the terminal can be redirected into a file.

Common redirection operator

> : command>file : output command to file

>> : command>>file : Append output of command to file

< : command>file : receive input from file

2> : command2>file : error from command to file

2>> : command2>>file : append

Example:

#find /etc –name passwd

this command will search for all file name passwd in /etc and its subdirectories

now we can redirtect the standard outpout

#find /etc –name passwd > output

output is a file where command output will be stored. Standard error is still displayed on the screen

#cat output

If the target file of the file redirection with > already exists, the existing file will be overwritten. To append data to an existing file use >> to redirect instead of >

#find /etc –name passwd >> output

Redirecting standard Error

We can redirect standard error with 2>

#find /etc –name passwd 2>errorfile

standard output is displayed on the screen , redirect further standard error, appending to the same file with 2>>

#find /etc/ -name passwd 2>>errorfile

#cat errorfile

There are three type of user account in Red hat Linux

1. Super user or Administrative account
2. Regular user account
3. service account

1. Super User created automatically at the time of installation
2. Regular user Account;

1. Using command line method ‘useradd’ or ‘adduser’ command
2. Graphical method by using Red hat user manager utility

a.

# adduser user_name (Recommended : minimum 6 character used in password)

# passwd user_name

Example:

#adduser rakesh

#passwd rakesh

Now open the file /etc/passwd to check the entry of user

#vi /etc/passwd

it contain 7 entry of each user

1. Username
2. Password
3. userid
4. groupid
5. blank (User information field ) comment
6. home directory
7. login shell

password entry for each user will be stored in /etc/shadow

# vi /etc/shadow

now in order to check the Userid, Group we use /etc/login.def

# vi /etc/login.def

when any user account is created then user will get userid, groupid automatically from /etc/login.def

5^th field is used for user information or comment

6^th field is used for home directory. When any user is created its default home directory is created inside /home

/home/rakesh

7^th field is login shell. Default shell for user is /bin/bash

different shells are used

ksh, sh, csh, tcsh,zsh

shell is an user interface between user and O.S. linux command shell is a prompt that allow us to interact with our system by executing various command.

In order to check the shell available use /etc/shells

# vi /etc/shells

in order to get the information about the group we need /etc/group

#vi /etc/group

it contain four field

1. Group name
2. password
3. GroupId
4. Member of group

# finger : this command is used to get the information about the user

Syntax:

#finger username

#finger rakesh

#id : this command is used to get userid, groupid of the user

syntax:

#id username

#id rakesh

Creating Group:

Syntax:

#groupadd groupname

#groupadd –g gid groupname

Example:

#groupadd raj

Exercise:

Create a user that should have uid=1000 shell=sh description and home directory as /data

Sol:

#useradd –u 1000 –c rakeshpundir –s /bin/sh –d /data rakesh

#passwd rakesh

Grpahically

System Setting :-> User & Group

OR

#system-config-user

Every user have two group one is elementary group or primary group and secondary group

-g : Primary Group

-G : Secondary Group

Creating Group

#groupadd g1

#groupadd g2

Steps:

1. adding group to the user

#usermod –g g1 –G g2 rakesh

2. To change id of the user

#usermod –u 1001 rakesh

3. change comment

#usermod –c rakeshsingh

4. change home directory

#usermod –d /rakesh-home rakesh –m

5. change shell

#usermod –s /bin/bash rakesh

6. change user login name

#usermod –l newname oldname

#usermod –l rajesh rakesh

7. Change Group name

#groupmod –n newname oldname

#groupmod –n group1 g1

8. change Group id

#groupmod –g 2005 group1

Vi is the standard file editor for Unix and Vim is the standard file editor for Linux

For Red hat Linux vi and Vim both are same

There are three mode of vi editor

1. command mode
2. insert mode
3. save and Exit Mode

1. Command mode is again divided into 3 mode

1. Cursor movement
2. Copy, paste, delete, undo
3. Text search

1. Cursor Movement

J : Down

K : UP

L : RIGHT

H : LEFT

2. Copy, paste delete, undo

dd : delete particular line

yy : copy particular line

u : Undo

p : paste

ndd : n is the number of line to be deleted

nyy : n is the number of line to be copied

3. Text Search

/text

example

/then

2. Insert Mode

Option I, insert, a ,o, O

i : insert mode start at the point where cursor is. Same is used with

insert option

a : insert mode start after one character

o : insert mode start after one line

O : insert mode start before one line

3. Save and Exit

:q : Quiet

:q! : forcely quiet

:wq! : save and forcely quiet

:wq : save and exit

All the device file are stored in /dev/

Hard disk ; /dev/hdx

Where x is

a : /dev/hda : Primary master

b : /dev/hdb : Primary slave

c : /dev/hdc : Secondary master

d : /dev/hdd : Secondary slave

In case of SCSI, Sata or USB we will use : /dev/sda

CD-rom:

/dev/cdrom

/dev/cdrom1

/dev/cdrecorder

Floppy:

/dev/fd0

/dev/fd1

to access partition of windows in linux

#mount –t vfat /dev/hdax /mnt

in order to check the label of any partition

#e2label /dev/hdax

where x is number

Mounting CD Rom

# mount –t auto /dev/hdc /media/cdrom

-t : file type

auto : file type

in order to check where cdrom is attached we can open the file fstab

#vi /etc/fstab

now in case of RHEl 3.0 we have to use command in order to unmount.

# umount /media/cdrom

and then eject the cdrom

in case of RHEL 4.0 we simply type

# eject

Mounting Floppy

#mount –t auto /dev/fd0 /media/floppy

in case of floppy we have to umount first then only we remove floppy otherwise all content of floppy may be lost or floppy may be physically damaged.

# umount /media/floppy

Mounting USB media :- directed by the kernel as SCSI device

/dev/sdax

Vi Editor:

Using vi , we can create or modify any file

Figure

Root : it is an home directory of super user (root) administrator

Etc : it is the location of all configuration file and directory used for server

configuration or system configuration

dev : it is a location of the device file

home : it is a location of home directory or regular users

proc : it is a virtual file system or directory not actually store on the disk and

contain system information

# cat /proc/meminfo

# cat /proc/cpuinfo

boot : contain kernel and boot related files

sys : it is also a virtual directory and contain system information

media : it is a mount point of removable disk like cdrom floppy usb drive etc.

tmp : it contain all temporary file

usr : it is used for software installation

lib : it contain all library files

bin : it is the location of all executable files or command or user command

/usr/bin also contain user command

sbin : it contain all system command or super user command /usr/sbin

mnt : it is a mount point for physical hard-disk or partition

opt : optional directory and used for temporary working

var : it is a variable file system or directory and contain all log and error

message

file system type:

Dos : Fat 16

95/Xp/2000 : FAT32

Xp/NT/2000 : NTFS

Linux : EXT2,EXT3

UNIX : VXFS

‘ll’ is used to display the information about the files and directory including date, time, users,group, size, name and permission.

Four symbols are used when displaying permission.

R : Read

W : Write

X : Execute

- : no permission

-rwxrwxrwx : files

drwxrwxrwx : directory

files and directory permission are symbolized by ten character.

If we want to change permission, then there are two methods:

1. symbolic
2. Numeric

Syntax:

Chmod mode directory/filename

Mode Option:

1. u,g,o
2. w,r,x
3. +,-
4. =

1. # chmod u+rwx file or directory : in case of user only
2. # chmod ug+rwx file or directoty : in case of user and group
3. # chmod u+w,g+r,o+x directory/file
4. # chmod u+rw,g+rw directory/file
5. # chmod u-r, g-w,o-rw directory/file
6. # chmod ugo+rwx file/directory
7. # chmod ugo-rwx file/directory

• + is used to add permission
• - is used remove permission

chmod ugo=rw directory/file

this command will assign read/write permission to u,g,o

suppose we have one file as

test.txt

permission : -r- - r- -r- -

chmod u=w,g=wx,o=w test.txt

this command will assign write to user, write/execute to group and write to other while remove the previous permission.

The main difference between +,= are + operator simply add the new permission with previous one and = assign the new permission while removing old (new permission overwrite an old)

In this method, calculation are based on following numbers

r=4 w=2 x=1 0= no permission

Example:

#chmod 777 file/directory

in this case user get 7 means that user has permission of read/write/execute, group get 7 means read/write/execute and ame for other

# chmod 531 file/directory

in this case user get 5 means that user has permission of read/execute, group get 3 means write/execute and other get 1 means that other has permission to execute.

#chmod 742 file/directory

7 : User : rwx

4 :Group : r

2 : Other : w

The command that are used to get the help are discussed as :

1. Whatis

Display a short description of command , it uses a database that is updated nightly. Often not available immediately after installation.

Syntax:

# Whatis cal

2. Help

Display usage summary and argument list

Syntax:

--help

Example:

#Date –help

3. Man and Info:

Both provide documentation for command. Almost every command has a “man” page. Collection of pages are called linux manual.

# man date

# info date

Viewing Text Page

Syntax:

#less [option] [filename]

Example:

# less abc.txt

scroll with arrows/PgUp /PgDown

/text : search for text

n : Next Match

Option:

-c : Clear before displaying

-s : Squeeze multiple blank lines into a single blank line

Simply we can also use “less” along with pipe | as

# ll |less