Saturday, 28 January 2012



Using chmod  you can change the permission of single or multiple directories or files.
In unix, nothing works without proper permissions. To run any script ,the first thing you need to
do after writing it is to give execute permissions .

To view file permissions. use ls –lrt

Example 1)
/home/d456/$ ls –lrt

-rw-r--r--    1 d456  Readers  1181170    Apr 27    2011 apache_manual.tar.gz
-rw-r--r--    1 d456  Readers  1128480    Apr 27    2011 perl
-rw-r--r--    1 d456  Readers    70228       May  3    2011  IMP.txt

All the files have read and write permissions to the user read to the group and others.
-rw-r--r--     can be interpreted in octal notation as 110-100-100 or 644
To change the permissions of the file IMP. txt    with read and write to user and
 group, only read to  others (rw-rw--r--)  ,you can use:

D2-/home/d456/$ chmod  664  IMP.txt
D2-/home/d456/$ ls  –lrt
rw-r--r--     1  d456  Readers  1181170    Apr 27    2011  apache_manual.tar.gz
-rw-r--r--    1  d456  Readers  1128480    Apr 27    2011 perl
-rw-rw-r--  1  d456  Readers    70228       May  3    2011  IMP.txt
-rw-r--r--     1 d456  Readers  5748626    May 12   2011 sg245511.pdf

Example 2)
 you want to allow all users to  run the  script named
 /home/d476/$ chmod   a+x
/home/d476/$  ls  –lrt
-rwx -rx--rx--     1 d476   Readers  5748626    Jun  10   2011

Here a in ‘a+x’  represents all.similarly use ‘u’  is for user, ‘g ‘ for group , ‘o’’ for others ‘+’ to give permissions  and ‘-‘  to deny.

Example 3)
You may have to give  permissions  to all the files in a directory tree use –R option.
To give all files and directories  read ,write and  execute permissions in /home directory ,

D2- /home $ chmod   -R  777  *
chmod:  /home/ d476/relativity.txt       operation not permitted
chmod :  /home/ d476/         operation not permitted      

You will definitely get these errors if you are not an admin user  or logged in as a different user.

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