Unix Architecture:
·
Kernel:
The kernel is the heart of the
operating system. It interacts with hardware and most of the tasks like memory
management, and file management.
·
Shell:
When you type in a command at your
terminal, the shell interprets the command and calls the program that you want.
C Shell, Bourne Shell and Korn Shell are most famous shells
which are available with most of the Unix variants.
·
Files and Directories: All data in UNIX is organized into files. All files are organized
into directories. These directories are organized into a tree-like structure
called the file system.
ESSENTIAL UNIX Commands:
Command
|
Example
|
Description
|
ls
|
$ ls
$ ls -ltr
$ ls-a
|
Lists
files (not content) in current directory.
-ltr List current
directory in detailed format.
-a List current
directory including hidden files.
|
cd
|
$ cd
tempdir
$ cd ..
$ cd ~
jbk/web
|
Change
current directory.
Change
directory to tempdir
Move back one directory Move into jbk’s web directory |
mkdir
|
$ mkdir
trialdir
|
Make a directory
Make a
directory called graphics
|
rmdir
|
$ rmdir
trialdir
|
Remove
directory (must be empty)
|
pwd
|
$ pwd
|
Get
full path of your current directory
|
cat
|
$ cat
filename
|
Look at the content of file
|
vi
|
$ vi filename
|
Creates a new file if it
already does not exist, otherwise opens existing file.
Command mode- default mode of vi editor.
-Saving file
-Moving courser
k
h l
j
save the contents of the
editor is :w!
out of vi is :q! or :q.
save and exit together :wq!
or :wq.
Insert mode- to insert text into file
|
cat>
|
$ cat > demo.txt
This text print in above file.
|
Creating
file using cat
|
echo
|
$ echo 'The only winning move is not to play.' > demo.txt
|
Creating
file using echo
|
cp
|
$ cp
file1 web-docs
$ cp file1 file1.bak $ cp -r sourcedir targetdir
|
Copy
file.
Copy
file into directory
Make backup of file1 |
rm
|
$ rm
file1.bak
$ rm *.tmp
$ rm
–i file1.txt
|
Remove
or delete file
Remove all file
Confirmation
before file delete
|
mv
|
$ mv
old.html new.html
|
Move or
rename files.
|
more
|
$ more
index.html
|
Look at
file, one page at a time
|
lpr
|
$ lpr
index.html
|
Send
file to printer
|
man
|
$ man
ls
$ man
mv
|
Manual
pages (help) about command
|
cc
|
$ cc
HelloWorld.c
|
C
compiler. Will compile c program
|
cat /etc/issue
|
$ cat /etc/issue
|
To find
which version of linux using
|
useradd
|
$ useradd
kiran
$ useradd -g groupname username
$useradd
-g kiran umesh
$ groups
username
|
To add
user
To add
user in specific group
Will
show user belongs to which group
|
userdel
|
$ userdel
kiran
|
To
delete account from the system
|
groupadd
|
$ groupadd
developers
|
To add
group
|
passwd
|
$ passwd
kiran
|
Set
password to account
|
ps
|
$ ps
|
Snapshot
of current processes
|
tail
tail -f
|
$ tail
filename
$ tail
–n filename
$ tail -f filename
|
Shows
last few lines.
-n to
show last n lines
Shows
last 10 lines of file and monitor file for updates. i.e if line added to file
tail then continue to output and keep refreshing.
|
find
|
$ find
. *.txt
|
To find
files in current directory or its sub directories.
Here .
(period) represent current
directory
|
top
|
$ top
|
Display
all system processes
|
grep
|
$ grep "this" demo_file
$ grep "this" demo_*
$ grep -i "is" demo_file
|
To
search for specific string containing line in specific file.
To
search for specific string in multiple file
Case
insensitive search in file.
Please find below screenshot for details
About grep command
|
chmod (To change file or directory permissions):
While
using ls -l command it displays various information related to file
permission as follows: $ ls –l demo.txt
-rw-r--r-- 1 cliff
user 767392 Mar 6 14:28 demo.txt
^ ^ ^
^ ^ ^
^ ^ ^
^ ^
| | |
| | |
| | |
| |
| | |
| | owner group
size date time
name
| | |
| number of links to file or
directory contents
| | | permissions
for world
| | permissions for members of group
| permissions for owner of file:
permission r = read, w = write, x = execute - =no
Type of
file: - = normal file, d=directory, l = symbolic link, and others...
Each
permission is assigned a value, as the following table shows, and the total of
each set of permissions provides a number for that set.
Number
|
Octal Permission Representation
|
Ref
|
0
|
No
permission
|
---
|
1
|
Execute
permission
|
--x
|
2
|
Write
permission
|
-w-
|
3
|
Execute
and write permission: 1 (execute) + 2 (write) = 3
|
-wx
|
4
|
Read
permission
|
r--
|
5
|
Read
and execute permission: 4 (read) + 1 (execute) = 5
|
r-x
|
6
|
Read
and write permission: 4 (read) + 2 (write) = 6
|
rw-
|
7
|
All
permissions: 4 (read) + 2 (write) + 1 (execute) = 7
|
rwx
|
chmod
|
$ chmod
755 demo.txt
$ chmod
o+wx demo.txt
$ chmod
u-x demo.txt
$ chmod
g=rx demo.txt
$ chmod
o+wx,u-x,g=rx demo.txt
|
|
chown
|
$ chown
kiran filename
|
The
chown command changes the ownership of a file
|
chgrp
|
$ chgrp
developers filename
|
Changes
the group of the given file to developers group.
|
| (pipe symbol)
|
To sort students name we write:
$ who
> students.txt
$ sort < students .txt
Instead of it use pipe:
$ who
| sort
$ ls
–al | more
|
The
symbol | is the Unix pipe symbol.
Give
output of one command is input to other.
< (input
redirection)
> (output redirection)
This
is simple and fast.
|
tee
|
$ ls
| tee file
$ ls
| tee file1 file2
$ ls
| tee –a file
|
It
display the output and also saves it in the file at same time.
This
is useful when you wanted to know which data going to store in your file.
-a
instruct tee command to append data in file.
|
history
|
$ history
|
Record
(or history) of commands is kept for your login session.
|
sudo
|
$ programmers
ALL=(ALL) ALL
|
Allow
permitted user to execute a command as a superuser.
ALL:
Allow sudo access from any terminal (any machine).
(ALL):
Allow sudo command to be executed as any user.
ALL:
Allow all commands to be executed.
|
gzip
|
$ gzip readme
$ gzip –c readme
|
Compress
files and save them in .gz format, to occupy less space than original
Compress
the file named readme. Creates readme .gz
and deletes readme.
-c
keeps readme.
|
gunzip
|
$ gunzip readme.gz
|
Decompress
the .gz file
|
tar
|
$ tar –cvf /archives/data-history.tar data/notes |
Tape archive.
It create single file with the content of directory structure.
–cvf to view tar progress
–tvf to view content in tar file
|
rpm
|
$ rpm -ivh mozilla-mail-1.7.5-17.i586.rpm
$ rpm -Uvh mozilla-mail-1.7.6-12.i586.rpm
$ rpm -ev mozilla-mail
$ rpm -qa
|
Red Hat Package Manager.
RPM command is used for installing, uninstalling, upgrading RPM
packages on Linux system.
Package can be archive file
-ivh Install
the package
-Uvh
upgrade
the package
-ev erase
the package
-qa display installed packages
|
su
|
$ su kiran
$ su root
|
To change
the ownership of a login session to root or to any other user.
|
halt
reboot
poweroff
|
$ halt
$ reboot
$ poweroff
|
Reboot or stop the system
|
kill
|
$ kill processname
|
To kill running process
|
shutdown
|
$ shutdown -h now
$ shutdown -h 20:00
$ shutdown -r now
$ shutdown -c
|
Shutdown the system in a safe way. shutdown the machine immediately,
or schedule a shutdown using 24 hour format.
-h halt the system
-r reboot the system
-c cancel a running shutdown
|
|
||
awk
|
$ awk
'{print;}' employee.txt
$ awk '{print $2,$5;}' employee.txt
|
Awk
command is used to generate
Formatted
output.
It
uses search pattern is a regular
expression.
If the line has 4 words, it will be stored in $1, $2, $3 and $4
variabe.
NF represents total number of fields in a record.
$2,$5 will print 2nd and 5th colum
|
alias
|
$ alias
ls="ls -al"
$ alias
p="pwd"
p and
pwd now work same
|
Allow
user to give simple name for
Complex
commands combination
|
vim
|
Go to 143rd line of file
$ vim +143 filename.txt
Open file in read only format
$ vim -R filename
|
To
provide extra file handling features
|
sed
|
Replaces the word "unix" with "linux" in the file.
$ sed 's/unix/linux/' file.txt
Replaces the second occurrence of the word "unix" with "linux" in a line.
$ sed 's/unix/linux/2' file.txt
|
Sed command is mostly used to replace the text in a file
|
sort
|
$ sort
$ sort
names.txt
$ sort
-r names.txt
|
Used
to sort
-r
for descending order
|
whereis
|
|
To
find out where a specific Unix command exists
|
whatis
|
|
Single
line description about a command.
|
mysql
|
|
To
connect mysql database
|
Some basic Unix commands:
cal, date , time , who , whoami , sort , echo, df,
du, ping, logout
How to create and run perl
script:
1. Create
a new text file and type the following exactly as shown:
#!usr/bin/perl
print "Enter your name: ";
$ name=<STDIN>;
print "Hello, ${name} ... you will soon be a Perl creater!";
print "Enter your name: ";
$ name=<STDIN>;
print "Hello, ${name} ... you will soon be a Perl creater!";
Save it
as hello.pl to a location of your choice.
2. Back
at the command prompt, change to the directory where you saved your Perl
script.
$ cd c:\perl\scripts
$ perl
hello.pl
you'll be prompted to enter your name.
Enter your name: Kiran
Hello, Kiran
... you will soon be a Perl creater!
Hello, Kiran
... you will soon be a Perl creater!
-e
with perl allows you to run code from the command line, instead of
having to write your program to a file and then execute it.
$ perl -e
'print "Hello World\n";'
Output:
Hello
World
To protect your directory:
We need to create two files .htaccess
and .htpasswd in our directory
.htaccess file contains security
directives for the specific directory
.htpasswd file contains
the userids and associated encrypted passwords.
.htaccess file must
contain:
AuthUserFile
/users/www/userid/welcome_html/class1/.htpasswd
AuthGroupFile /dev/null
AuthName Private
AuthType Basic
<Limit GET>
require user USERID1 USERID2
</Limit>
AuthGroupFile /dev/null
AuthName Private
AuthType Basic
<Limit GET>
require user USERID1 USERID2
</Limit>
