Tutorial 3

 

In this tutorial, we are going to exercise our knowledge on file permissions.

 

Why need to change file permissions?

• It protects files from accidental deletion or modification;

• It allows team members to read, modify, execute, and possibly even delete a file without having to send them a copy;

• When setting up your webpage on UNIX, you have to make the html files accessible or no one will be able to see it!

• ...

 

In order to carry out the following exercises, please follow the following instructions:

• Work in pairs;

• Logon a machine from cs1 to cs3 at utdallas.edu, type in your UTD netid and password one at a time followed by pressing the "Enter" key;

 

You can use either putty or Xmanager to access these UNIX machines.

 

For detail instructions on login, please refer back to Tutorial 1.

 

Create Directories and Files

 

The goal is to create three subdirectories with eight testfiles in each one to match the permissions, and your partner will try out some basic commands on the files:

    testdir1 group & other has no access
            testfile1.html group & other has no access
            testfile2.html group & other has read access
            testfile3.html group & other has write access
            testfile4.html group & other has execute access
            testfile5.html group & other has read and execute access
            testfile6.html group & other has read and write access
            testfile7.html group & other has write and execute access
            testfile8.html group & other has read, write, and execute access

    testdir2 group & other has read access
    // 8 files

    testdir3 group & other has write access
    // 8 files
 

Follow the steps below to create a subdirectory where you can work on this tutorial. First, create a new subdirectory:

{cs1:~} mkdir tutorial3
{cs1:~} ls -l
total 178
drwx------ 4 weiminma sn 1024 Jan 19 2008 aos
drwx--x--x 2 weiminma cs 512 Sep 8 12:24 tutorial3
drwx------ 16 weiminma sn 512 Sep 3 16:59 working_directory

 

Then change the permissions for group and other to read and execute on the subdirectory "tutorial3":

{cs1:~} chmod 755 tutorial3
{cs1:~} ls -l
total 176
drwx------ 4 weiminma sn 1024 Jan 19 2008 aos
drwxr-xr-x 2 weiminma cs 512 Sep 8 12:24 tutorial3
drwx------ 16 weiminma sn 512 Sep 3 16:59 working_directory
 

The commands that create the above three directories and eight files with above permissions are as follows. But first, we want to copy the directories and testfiles using the following commands:

 

{cs1:~} cd tutorial3
{cs1:~/tutorial3}

{cs1:~/tutorial3} cp -pr ~weiminma/course_related/TA_S08/CS5375/tutorials/Tutorial3/testdir1 .

{cs1:~/tutorial3} cp -pr ~weiminma/course_related/TA_S08/CS5375/tutorials/Tutorial3/testdir2 .

{cs1:~/tutorial3} cp -pr ~weiminma/course_related/TA_S08/CS5375/tutorials/Tutorial3/testdir3 .

 

Then we are going to see whether everything is ok by the following command:

 

{cs1:~/tutorial3} whoami

weiminma

{cs1:~/tutorial3} ls -lR

.:
total 6
drwxr-xr-x 2 weiminma cs 512 Sep 7 20:34 testdir1
drwxr-xr-x 2 weiminma cs 512 Sep 7 20:35 testdir2
drwxr-xr-x 2 weiminma cs 512 Sep 7 20:35 testdir3

./testdir1:
total 16
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:31 testfile1.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:32 testfile2.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:32 testfile3.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:32 testfile4.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:32 testfile5.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:33 testfile6.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:33 testfile7.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:33 testfile8.htm

./testdir2:
total 16
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile1.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile2.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile3.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile4.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile5.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile6.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:36 testfile7.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile8.htm

./testdir3:
total 16
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile1.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile2.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile3.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile4.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile5.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:37 testfile6.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:38 testfile7.htm
-rwxr-xr-x 1 weiminma cs 303 Sep 7 20:38 testfile8.htm
 

Change File Permissions

 

Now, we want to change the files' permission, and "chmod" is the command which can be used to change the file permissions. Its syntax is:

 

chmod [–R] mode file …

 

Permissions can be changed in different manner. The “mode” can be either absolute mode or symbolic mode. The “mode” consists of three parts:

1. User category (user, group, other)
2. The operation to be performed (assign or remove a permission)
3. The type of permission (read, write and execute)

 

For demonstration purpose, we will use the directories and files copied above. There are three copied subdirectories, i.e., "testdir1" to "testdir3", with the same permissions and each of these directories has eight files with the same permissions too. Their permissions can be viewed by the command shown above.

 

Now we want to change the subdirectories' permissions first, the commands to change them are as follows:

{cs1:~/tutorial3} chmod 700 testdir1