Linux/C2/File-Attributes/English
Title of script: The Linux File Attributes
Author: Shahid Ali Farooqui
Keywords: File permissions, ownership of a file, group, inode, soft and hard links.
Prerequisite: Please create empty files named as example1, example2, example3, example4,
example5, and testchown. Please also create empty directories named as test_chown and
directory1
Resources for the tutorial:File:Resources for file attributes.zip
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Display slide 1 | Welcome to this spoken tutorial on Linux File Attributes. |
Switch to terminal | The prerequisite for this tutorial is to create empty files named as example1, example2, example3, example4, example5, and testchown. Please create empty directories named as test_chown and directory1 also |
Display slide 2 | A file attribute is metadata that describes or is associated with a computer file. File attribute is the characteristics that describe a file, such as owner, file type, access permissions, etc. |
Display slide 3 | chown command is used to change the ownership of the file or directory. This is an admin command, root user only can change the owner of a file or directory. |
The syntax of chown command is chown space [options] space ownername space filename or directoryname | |
We may give following options with chown command.
-R : To change the permission on files that are in the subdirectories of the directory that you are currently in. -c : Change the permission for each file. -f : Prevents chown from displaying error messages. | |
Display slide 4 | Now we will look at some examples |
Switch to terminal | So go to the terminal. We will move to the directory where we have created empty files and folders. For that cd space Desktop slash file_attr and press enter |
Now type the command
$ ls space -l spacetestchown and press Enter.
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Here we can see the owner of the file 'testchown' is shahid | |
To change the owner of the file, type the command
press Enter | |
Enter the sudo password and press Enter again. Press enter | |
Now type
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Now we will see how to change owner of the proposal software directory
Type the command
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To change the owner of the directory, type the command
Enter the sudo password, if required and press Enter again. | |
I will clear the screen by pressing Clt+L for our convenience. Now type
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Display slide 5 | chmod command is used to change the access mode or permissions of one or more files. |
Syntax of the chmod command is
-c : Print information about files that are changed. -f : Do not notify user of files that chmod cannot change. | |
Display slide 6 | There are following types of access or permissions
r : Read w : Write x : Execute s : Set user (or group) ID |
Switch to terminal | Alternatively, we may specify permissions by a three-digit octal number. The first digit stands for owner permission, the second stands for group permission, and the third stands for other's permission. |
Permissions are calculated by adding the following octal values:
4 : Read 2 : Write 1 : Execute | |
Display slide 7 | Now we will look at some examples of chmod
Move to terminal and enter the command to add execute-by-user permission to file example1 Before that i will again clear the screen by pressing Clt+l. |
Now lets type
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Now type
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Now type the command
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Now type
and press Enter
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Display slide 8 | To assign read-only permission to file example1 for everyone type the command
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Now type the command
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To change the permission recursively and assign the read and execute access for everyone and also write access for the owner of the directory directory1 type the command
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Now type
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Display
slide 9 |
To give the user execute permission on file example2
Type the command
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Now type the command
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To add the write permissions to the group for file example3
type the command
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and now type
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To remove the write permissions for all type the command
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Now type
-r--r--r-- 1 shahid shahid 6 2010-12-14 00:31 example3
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Display slide 10 | Chgrp
chgrp command is used to change the group of one or more files to newgroup. Newgroup is either a group ID number or a group name located in /etc/group. Only the owner of a file or a privileged user may change the group. |
The syntax for the chgrp command is
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Switch to terminal | Lets go to terminal.
Now we will look at some examples of chgrp command. type the command $ ls space -l space example4
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To change the group permission , type the command
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Now type the command
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Display slide 11 | The inode number is a unique integer assigned to the device. Inode stores basic information about a regular file or a directory. All the files are hard links to inodes. Whenever a program refers to a file by name, the system actually uses the filename to search for the corresponding inode. |
We can use ls space -i command to see the inode number of a file.
type the command
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Display slide 12 | Inodes are associated with precisely one directory entry at a time.
Hard links are to associate multiple directory entries with a single inode. ln is the command to make link |
The syntax of ln command to create the hard link is
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Display slide 13 | Now we will look at some examples of hard links
$ ln space example1 space exampleln
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Switch to terminal | To display the inode number of both the files, type the command
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Display slide 14 | Soft link (symbolic link) is a special type of file that contains a reference to another file or directory in the form of an absolute or relative path. |
The syntax of ln command to create soft links is
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Display slide 15 | Now we will look at some examples of soft links |
To create the soft link, type the command
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Switch to terminal | Now, to display the inode number and list of both the files, type the command
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Display slide 16 | So in this tutorial we have learnt about the Linux Files Attributes like changing permission, ownership and group of a file.
We also learnt about the inode, soft and hard links of a file. This brings me to the end of this tutorial. Spoken Tutorials are a part of the Talk to a Teacher project, supported by the National Mission on Education through ICT. More information on the same is available at the following link http://spoken-tutorial.org /NMEICT-Intro . This is Anusha Kadambala and Shahid from IIT Bombay signing off . Thanks for joining. |