BOSS-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

Visual Cue	Narration
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. -rw-r--r-- 1 shahid shahid 0 2010-12-14 16:28 testchown
	Here we can see the owner of the file 'testchown' is shahid
	To change the owner of the file, type the command $ sudo space chown space anusha space testchown press Enter
	Enter the sudo password and press Enter again. Press enter
	Now type $ ls space -l space testchown and press Enter Here we can see the new owner of the file is anusha.
	Now we will see how to change owner of the proposal software directory Type the command $ ls -l press Enter Here we can see the owner of the directory 'test_chown' is shahid
	To change the owner of the directory, type the command $ sudo space chown space minus capital R space anusha space test_chown which is directory name and press Enter Enter the sudo password, if required and press Enter again.
	I will clear the screen by pressing Clt+L for our convenience. Now type $ ls space -l press Enter Here we can see the new owner of the directory is anusha.
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 chmod space [options] space mode space filename We may give the following options with chmod command. -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 $ chmod space u+x space example1 press Enter
	Now type $ ls space -l space example1 press Enter to see the changes Here you can see to assign the read/write/execute permission by owner, read/execute permission by group, and execute-only permission by others to file example1
	Now type the command $ chmod space 751 space example1 press Enter
	Now type $ ls space -l space example1 and press Enter Here we can see that above command has assigned the read/write/execute permission by owner, read/execute permission by group, and execute-only permission by others to file example1.
Display slide 8	To assign read-only permission to file example1 for everyone type the command $ chmod space =r space example1 and press Enter
	Now type the command $ ls space -l space example1 press Enter Here we can see that the read only permission has been assigned to file example1 for everyone
	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 $ chmod space minus capital R space 755 space directory1 press Enter
	Now type $ ls space -l press Enter to see the changes
Display slide 9	To give the user execute permission on file example2 Type the command $ chmod space u+x space example2 press Enter
	Now type the command $ ls space -l space example2 and press Enter Here we can see that execute permission has been assigned to user on example2
	To add the write permissions to the group for file example3 type the command $ chmod space g+w space example3 press Enter
	and now type $ ls space -l space example3 press Enter Here we can see the write permission has been added to group
	To remove the write permissions for all type the command $ chmod space a-w space example3 press Enter
	Now type $ ls space -l space example3 press Enter Here we can see the write permission for all has been removed
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 chgrp space [options] space newgroup space files
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 press Enter Here we can see the group permission is for user shahid
	To change the group permission , type the command $ sudo space chgrp space rohit space example4 press Enter Enter the sudo password if required.
	Now type the command $ ls space -l space example4 press Enter Here we can see that the group has changed from shahid to rohit.
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 $ ls space -i space example5 press Enter Number written before the file is the inode number of the file.
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 ln space {source} space {link} Where, source is an existing file and link is the file to create.
Display slide 13	Now we will look at some examples of hard links Let me clear the screen again. Now type the command $ ln space example1 space exampleln press Enter
Switch to terminal	To display the inode number of both the files, type the command $ ls space -i space example1 space exampleln press Enter Here we can see that inode number of both the files are same, file exampleln is the hard link for file example1
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 ln space -s space {target-filename} space {symbolic-filename}
Display slide 15	Now we will look at some examples of soft links
	To create the soft link, type the command $ ln space -s space example1 space examplesoft press Enter
Switch to terminal	Now, to display the inode number and list of both the files, type the command $ ls space -li space example1 space examplesoft press Enter Here we can see that inode number of both the files are different and examplesoft is a softlink of example1.
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.

Contributors and Content Editors

Nancyvarkey, PoojaMoolya