0003 SOME BASIC COMMANDS OF REDHAT LINUX

Linux have large command pool. Still here are some linux command useful for beginners with small description. Being this is written for beigners he command listed here may have some more uses than explained in this post, for more information you can get the help of relative commands using man or info commands.

1. TO CLEAR THE SCREEN
   
   #clear
   
   
2. TO CHECK DIRECTORY LISTINGS OR CONTENTS OF DIRECTORY.
   #ls
   bin boot dev etc home lib lost+found media mnt opt proc root sbin selinux srv sys tmp usr var
   
   To check long (detailed) directory listings
   #ls -l
   total 112
   
   drwxr-xr-x 2 root root 4096 2009-05-04 09:26 bin
   drwxr-xr-x 5 root root 4096 2009-04-15 11:46 boot
   drwxr-xr-x 14 root root 4880 2009-05-09 19:49 dev
   drwxr-xr-x 131 root root 12288 2009-05-09 21:10 etc
   
   
3. CREATIN NEW EMPTY FILE.
   #touch FILE_NAME
   
   e.g.
   #touch my_file.txt
   
   Above command will create a new empty file called "my_file.txt" if it does not exist. If it exists already it will just change the time stamp of the existing file.
   
   
4. CREATING A NEW FILE WITH SOME CONTENT
   
   #cat > FILE_NAME
   
   e.g.
   #cat > my_file.txt
   
   after firing the command you have to enter the data in the file. After finishing entering the data in the file you have to press d to save the contents of the file.
   
   
5. READING THE CONTENT OF EXISTING FILE
   
   #cat FILE_NAME
   
   e.g.
   
   #cat my_fiel.txt
   
   After firing this command, contents of the "my_file.txt" will be displayed and controlls will be returned to command prompt. If the contets of the file is too long to read on single screen then you can use command as follws.
   
   #cat my_file.txt | less
   or
   #less my_file.txt
   
   After firing the above command you can scrolle the output using up/down arrow keys. After finishing reading the file to quit you can press "q" to quit.
   
   
6. CREATING NEW DIRECTORY.
   
   To create the new directory the command is
   
   #mkdir NEW_DIR_NAME
   
   e.g. say you need to create a directory named "data"
   
   #mkdir data
   
   To print a message for each created directory
   # mkdir -v data
   
   
   To create a new directory with user dedined permissions
   # mkdir -m=MODE
   e.g.
   To create a directory say "videos" with user defined permissions "777"
   #mkdir -m=777 videos
   
   
7. CHANGING THE DIRECTORY
   
   #cd DIR_NAME
   
   e.g.
   To enter in the directory say "videos"
   #cd videos
   
   To exit from the directory i.e. to enter in parent directory
   #cd ..
   
   To switch to home directory immediately
   #cd ~
   
   To switch to previous directory immediately
   #cd -
   
   
8. DELETING OR REMOVING EXISTING FILE OR DIRECTORY.
   
   To remove/delete the existing file
   
   #rm FILE_NAME
   
   e.g. to remove a existing file say "my_file.txt"
   #rm my_file.txt
   
   To remove/delete existing directory
   #rm -rf
   e.g. say you want to remove a existing directory "videos"
   #rm -rf videos
   
   
9. COPING CONTENTS OF EXISTING FILE/DIRECTORY IN NEW FILE/DIRECTORY.
   
   To copy contents of file "file1" to file "file2"
   #cp file1 file2
   
   To copy all the contents of directory "videos" to directory "vsongs"
   #cp -Rv videos vsongs
   
   
   
10. RENAMING A FILE/DIRECTORY.
    
    To change the name of the file "file1" to new name "file1"
    #rename file file1
    
    to change th name of the directory "videos" to "video_song"
    #mv video video_song
    
    
    
11. CHANGING THE PERMISSIONS OF FILE/DIRECTORY
    #chmod MODE FILE_NAME
    
    e.g. To change the permissions of the file "my_file.txt" to 777
    #chmod 777 mt_file.txt
    
    To change permission of a directory named "video" with its all subdirectories and files to new permissions say 446
    #chmod -R 446 video
    
    
12. CHANGING THE USER OWNERSHIP OF THE FILE/DIRECTORY.
    
    #chown NEW_OWNER FILE_NAME
    
    e.g. To change owner of a file named "my_file.txt" to new owner (user) say "denis"
    #chown dnis my_file.txt
    
    e.g. To change owner of a directory named "video" to new owner (user) say "denis"
    #chown dnis video
    
    e.g. To change owner of a directory named "video" with its all subdirectories and files to new owner (user) say "denis"
    #chown -R dnis video
    
    
    
13. CHANGING THE GROUP OWNERSHIP OF THE FILE/DIRECTORY.
    
    #chgrp NEW_GROUP FILE_NAME
    
    e.g. To change group group of a file named "my_file.txt" to new group say "denis"
    # chgrp dnis my_file.txt
    
    e.g. To change group of a directory named "video" to new group say "denis"
    #chgrp dnis video
    
    e.g. To change group of a directory named "video" with its all subdirectories and files to new group say "denis"
    #chgrp -R dnis video
    
    
14. CHECKING FILE SYSTEMS DISK USES
    # df -h
    
    
    
15. GETTING REPORT OF DISK USES.
    #du -h
    
    
    
16. GETTING CURRENT WORKING DIRECTORY.
    #pwd
    
    
17. CREATING A SYMBOLIC LINK
    To creates a symbolic link named symlink that points to the file test
    
    #ln -s FILE_NAME SYMBOLIC_LINK_NAME
    
    e.g
    #ln -s test symlink
    
    Typing "ls -i test symlink" will show the two files are different with different inodes. Typing "ls -l test symlink" will show that.
    
    
18. GETTING WHICH USEERS ARE LOGGED IN.
    #who
    
    
19. LOCATING BINARIES AND MANUAL PAGES FOR COMMANDS
    
    To locate binaries and manual pages for the "ls" command.
    
    #locate ls
    
    
20. SHUTTING DOWN THE COMPUTER
    
    To shuts the system down to halt immediately.
    #shutdown -h now
    
    To shut the system down immediately and the system reboots.
    #shutdown -r now
    
    To reboot the system in 10 minutes and send the message to all users.
    #shutdown -r +10 "Rebooting in 10 minutes"
    
    To shut the system down and do a reboot at 1:00 in the afternoon.
    #shutdown -r 13:00
    
    
21. LOGGING OUT FROM THE TERMINAL
    
    #logout
    
    or press CTRL+D
    
    
22. CHECKING/SETTING DATE AND TIME
    
    To check date and time of the system
    #date
    
    

    list the time and date in the below format:

    DATE: 02/08/01
    TIME:16:44:55

    #date '+DATE: %m/%d/%y%nTIME:%H:%M:%S'
    
    To sate date and time of the systm
    #date -s "11/20/2003 12:48:00"
    
    
23. SETTING ALIASES
    
    Alias allows you to have a small more familiar command or name to execute a long string of commans.
    
    #alias ALIAS_NAME 'LONG_COMMAND'
    
    e.g. The follofing command will create a alias named "shutt" to command "shutdown -r now".
    
    #alias shutt 'shutdown -r now'
    
    
24. TO DISPLAY THE ARCHITECTURE OF THE PROCESSOR
    
    #arch
    
    
25. CHECKING CALENDER ON COMMAND LINE
    
    To check calendar for the current month and the year.
    #cal
    
    To check calendar for the specific month and the year say December of 2000.
    #cal 12 2000
    
    To display prev/current/next month calender.
    #cal -3
    
    To display a calendar for the current year.
    #cal -y
    
    
26. DNS LOOKUP
    
    To get IP of the hostname
    #dig www.gooogle.com
    
    To get hostname of the IP addresses
    #dig -x 192.168.1.1