Basic Commands :
The Commands which are basically use to operate an Operating System(O/S) is called Basic Commands. 1) pwd : present working directory ---> used to know the path of present user.
2) ls : list ------>It gives the list of files & Directories present in the path
3) ls -l or ll --------> Listing of all files along with attributes
4) ls -a ------> Lists all hidden files & directories
5) ls -r -------> lists all files & directories in reverse mode
6) ls -il---------> lists all files & directories along with inode numbers
7) ls -ld < directory name> ------> to view attributes of a particular directory
8) ls -R <directory.name> -------> to view tree structure of a directory
9) ls -a* ----------> to view all files & directories starts with a
10) man < command> ---------> to view entire options of a command
To create a file we have 3 methods :
1) touch
2) cat
3) vi(vim)
1) touch : With the help of touch command we can create an empty file.
syntax: touch < filename>
ex: touch f1
with this command we can create n number of files at a time.
syntax: touch <file1> <file2> <file3>
ex: touch mahesh raju naveen
2)cat: By using cat we can create data-files
syntax: cat > <filename>
ex: cat >mahesh
(edit data)
( ctrl+d)(to save)
To view content of a file
cat < filename>
To add data in existing file
cat >> <existing filename>
(enter-data)
(ctrl+d)
we cannot edit the written text through cat command. we can only add data to modify existing data we have to use editors. we have number of editors in linux
ex: gedit ,nano, kedit, kate, emacs ,vim ,etc...
Note : but we always use the best editor "vim" editor .
we can transfer an output as input for another file
ex: to view output of file1 file2 we use
cat file1 file2
In the same way, we can transfer output of that command as input for another file
ex: cat file1 file2 > file3
here we are giving file1 file2's data as input for file3 , by this data of file1&file2 will copied into file3.
How To Practice In Linux-System(command mode) :
1.ls -l for listing the files as well as directories those are kept in
the particular working directory
syntax
[root@bsrtech ~]#ls -l
2.ls -la same as 'ls -l'but by this command we can also see the hiden
files.
syntax
[root@bsrtech ~]#ls -la
3.ls -li same as 'ls -la' but it will also shows us the inode number of
each and every file
syntax
[root@bsrtech ~]#ls -li
4.ls by this command we can see only file name nothing else
syntax
[root@bsrtech ~]#ls
5.clear it will clear the screen(short cut ctl+l)
syntax
[root@bsrtech ~]#clear
6.exit to end a current session as well current terminal logging
syntax
[root@bsrtech ~]#exit
7.touch to create a new empty file
syntax
[root@bsrtech ~]#touch
8.cd to change the working/present directory
syntax
[root@bsrtech ~]#cd /home/mango
where '/home/mango' is the desired directory to be change from '/root'
9.cat to view the contents of a file and it is also used for creating a new file with some contents
syntax
[root@bsrtech ~]#cat <file name> to view file contents
[root@bsrtech ~]#cat > newfilename enter,then you can write something in the file and then to save the file contents press clt+d then enter
10.mkdir to make a new directory
syntax
[root@bsrtech ~]#mkdir newdirname
you can also create a directory at your desired path without changing your present working directory
syntax
[root@bsrtech ~]#mkdir /home/mango/newdirname
11.rm to remove a empty file
syntax
[root@bsrtech ~]#rm filename
12.rmdir to remove a empty directory
syntax
[root@bsrtech ~]#rmdir directoryname
13.rm [-i/-r/-f] to remove a directory with its subdirectories as well as its files that is to remove a directory which already contains some files in it
syntax
[root@bsrtech ~]#rm -i directory/filename
-i stands for interactively
-r stands for recursively
-f stands for forcefully
14.cp to copy something in a destination file or directory
syntax
[root@bsrtech ~]#cp sourcepath destinationpath
example: [root@bsrtech ~]#cp /home/mango/webmin.rpm /root/abcd
in this example the webmin.rpm file will be copied in /root/abcd directory
15.mv to move one file or directory from one place to another place, it is also used for renaming a directory or file.
syntax
[root@bsrtech ~]#mv source destination
[root@bsrtech ~]#mv oldfilename newfilename [to change the file name]
16.man to view the mannual page of commands for syntax
syntax
[root@bsrtech ~]#man commandname
17.info to view the information about any command
syntax
[root@bsrtech ~]#mkdir info
18.--help to view the help doccuments of a command
syntax
[root@bsrtech ~]#commandname --help
19.dir to view the subdirectories and filesn under the directory
syntax
[root@bsrtech ~]#dir
20.su - to become a super user
syntax
[mahesh@bsrtech ~]$su -
output wil be
[root@bsrtech ~]#
21.who by this command you can see the user name and their ip addresses
who have loged in on your server
syntax
[root@bsrtech ~]#who
22.whoami this command shows your current logged in terminal user name
syntax
[root@bsrtech ~]#whoami
23.who am i this command shows you the logged in terminal number and user name and more detailed information
syntax
[root@bsrtech ~]#who am i
24.pwd to view the present working directory
syntax
[root@nettech root]#pwd
25.rpm -ivh to intall a rpm package
syntax
[root@bsrtech ~]#rpm -ivh packagename.rpm
rpm stands for 'redhat package manager'
-i stands for install
-v stands for verbose mode
-h stands for with hash sign(#)
26.rpm -q to querry about any rpm package
syntax
[root@bsrtech ~]#rpm -q packagename
27.rpm -e to uninstall a rpm package
synatx
[root@bsrtech ~]#rpm -e package
28.find / -name to find any file or directory in linux file system
syntax
[root@bsrtech ~]#find / -name filename
29.su username to switch from one user to another users home directory
syntax
[root@bsrtech ~]#su mahesh
output will be
[mahesh@bsrtech ~]$cd
[mahesh@bsrtech ~]$
30.su - username to switch from one user to another user users home directory directly
syntax
[root@bsrtech ~]#su -mahesh
[mahesh@bsrtech ~]$
31.useradd to create a new user
synatx
[root@bsrtech ~]#useradd username
32.passwd to give a password of a user
syntax
[root@bsrtech ~]#passwd mahesh
output will be
give a password for user mahesh:(here you have to type a password for mahesh user)
confirm password:(again type the same password)
33.userdel to remove a user from linux
syntax
[root@bsrtech ~]#userdel mahesh
34. groupadd to add a new group
syntax
[root@bsrtech ~]#groupadd <groupname>
35.gruopdel to delete a group
syntax
[root@bsrtech ~]#groupdel <groupname>
36.chown to change the ownership of a file or directory
syntax
[root@bsrtech ~]#chown <ownername> <filename>
example:
[root@bsrtech ~]#ls -l
output
-rw------- 1 root root 1433 Sep 10 16:33 anaconda-ks.cfg
(permission) (links) (own) (group own) (size) (date) (File-name)
[root@bsrtech ~]#chown mahesh /file1
in this example /file1 file owner will be change to mahesh user
effect
[root@bsrtech /]##ls -l
-rw-r--r-- 2 mahesh root 4096 Sep 05 12:05 file1
37.chgrp to change the group ownership of a file or directory
syntax
[root@bsrtech ~]#chgrp <owner-of-group> <filename>
example
[root@bsrtech /]#ls -l
-rw-r--r-- 2 mahesh root 4096 Sep 05 12:05 file1
[root@bsrtech ~]#chgrp mahesh /file1
effect
[root@nettech /]#ls -l
-rw-r--r-- 2 mahesh root 4096 Sep 05 12:05 file1
38. chmod to change the permission of a file or directory
-rw-r--r-- 2 mahesh root 4096 Sep 05 12:05 file1
(permission) (links) (own) (group own) (size) (date) (File-name)
- stands for file
d stands for directory
r stands for read only permission READ=4
w stands for write only permission WRITE=2
x stands for execute only permission EXECUTE=1
drwxrw-rw-
FIRST OCTET FOR DENOTING THE DIRECTORY OR FILE OR LINK FILE ETC.
SECOND THREE OCTET FOR USER OR OWNER PERMISSION (rwx OR 7 IN OCTAL VALUE)
THIRD THREE OCTET FOR GROUP PERMISSION (rw- OR 6 IN OCTAL VALUE)
FORTH THREE OCTET FOR OTHERS PERMISSION (rw- OR 6 IN OCTAL VALUE)
SYNTAX
[root@bsrtech /]#chmod value file or directory-name
example
[root@bsrtech /]#ls -l
-rw-r--r-- 2 mahesh root 4096 Sep 05 12:05 file1
[root@bsrtech /]#chmod 666 /file1
[root@bsrtech /]#ls -l
-rw-rw-rw- 2 mahesh root 4096 Sep 05 12:05 file1
40.usermod to modify the user profile
synatx
[root@bsrtech ~]#usermod <parameter> <groupname> <username>
File Prompting Commands :
head : used to view first 10 lines of a file
syntax : head <filename>
ex: head /etc/passwd
To view 4 lines of a file
head -n <no of lines> <filename>
ex: head -4 /etc/passwd
Tail : is used to view last ten lines of a file
syntax: tail <filename>
ex: tail /etc/passwd
To view last 10 lines of a file
tail -10 /etc/passwd
more : used to see the content pagewise but we cannot scroll up
syntax: more < file name>
ex: more /etc/passwd
less: used to see the content pagewise we can scroll up&down
syntax: less <filename>
ex: less /etc/passwd
date: used to view current date&time
to change date
date <mm-dd-hr-min-year>
ex: date 120111452013
it means 12th month 01 date 11:45 11 hours 45 minutes 2013 year
or
date -s <content>
date -s "wed june 20 20:46:51 IST 2013"
cal : cal is used to view present months calender
cal to view a particular month,particular years calender
cal <Month> <year>
cal 5 1986 -------------> to view may 1986 calender
cal 2050 ----------------> to view entire 2050 year calender
| --------> this symbol is called as pipe it is used to link conmmands
ex: ls | grep pot
grep : is used to skip something specially from the output
here in example from output of ls we are grepping pot
ll | grep "^d" ---------> here from the out put of ll we are greping only directories
mkdir <directory name> -----> to create a directory
ex: mkdir mahesh
To create multiple directories :
mkdir <dir1> <dir2> <dir3>
ex: mkdir d1 d2 d3
To create nested directory
mkdir -p <dir1/dir2/dir3>
mkdir -p world/asia/india/ap/vskp/mahesh
To change the directory
cd < path of directory>
To change directory one level back
cd ..
To change directory two levels back
cd ../..
Removing a file or directory
to remove a file
rm <filename>
to remove an empty directory
rmdir <dir-name>
To remove directory recursively & forcefully
rm -rf -> to delete directory with out asking yes or no
copying a file
cp <sorce> <destination> -----> to copy a file
ex: cp file1 /etc/
cp -rf <source > <destination> ---> to copy entire directory along with subdirectories & files
ex: cp -rf mahesh /opt/
cp -a <source> <destination> -----> to copy a file or directory along with permissions
ex: cp -a Server /var/ftp/pub
To move a file or directory
mv < source> <destination>
mv mahesh /opt/users/
To rename a file or directory
mv <oldname> <newname>
To create chain commands
In linux we can execute "n" number of commands at a single command line
syntax: command1;command2;command3;
ex: date;cal2013;date 120111452013;mkdir mahesh;cd mahesh;cd
good
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