BOSS-Linux/C2/File-System/English-timed

Time	Narration
00:00	Welcome to this spoken tutorial on Linux File System.
00:04	I am using Linux Operating system.
00:08	We assume that you know how to get started with the Linux operating system and have some basic idea about commands.
00:16	If you are interested, it is available through another spoken tutorial on the following website http://spoken-tutorial.org
00:28	Also note that linux is case sensitive.
00:32	All the commands used in this tutorial are in lower case unless otherwise mentioned.
00:41	In Linux, almost everything is a file.
00:44	So, what is a file? In real life, we know that a file is where we store our documents and papers.
00:54	Similarly, in Linux a file is a container for storing information.
01:00	Next, what is a directory?
01:03	A directory can be understood as a collection of files and other (sub)directories.
01:10	A directory helps us in organizing our files in a systematic manner.
01:16	This is like what we call folders in Windows.
01:20	It allows different users to have their own directories with their files which others cannot access or modify.
01:30	Also, if there are no directories, all the files on the system need to have unique names which would be very difficult to maintain.
01:41	These definitions of files and directories are good to get a general feel about them; they are not entirely accurate.
01:51	As well as its contents, a file has a name and some properties or “administrative information” that is, the file’s creation/modification date and its permissions.
02:05	Thus, properties are stored in the file’s inode- a special block of data in the file system that also contains the length of the file and where on the disk it’s stored.
02:20	The system uses the number of the file’s inode ; the directory structure just names the file for our benefit as it's easier for us to remember names than larger numbers.
02:35	Contrary to its oversimplified definition, a directory does not actually store other files, it itself is a file that holds the inode numbers and names of other files.
02:49	In fact, in Linux there are three kinds of files:
02:54	Regular Files or Ordinary files: It contains only data, as a stream of characters.
03:01	Directories: As we just saw in the previous slides.
03:07	Device Files: All hardware devices and peripherals are represented as files in Linux.
03:14	A CD, a Hard disk or even an usb stick, everything is a file in Linux. But why is this so? This helps to read and write these devices in a way similar to that for ordinary files.
03:32	All files in Linux are related. In short, all form a family much like we do.
03:39	A directory containing say- some files and sub-directories, will have a parent – child relationship with each other. This gives rise to the Linux File System Tree.
03:52	At the top is the root( denoted by a frontslash /). It contains all the other files and directories.
04:04	This also helps in easy navigation from one file or directory to other, if we know the correct path.
04:12	As we work with a Linux file system, it seems that we are moving along this tree.
04:18	One command and there you are... teleported from one place to other.
04:24	Sounds interesting!! Indeed it is, as we will see.
04:29	When we login into the Linux system, we are by default in a home directory.
04:36	Now, switch to the terminal.
04:39	To see the home directory , type at the command prompt: echo space dollar H-O-M-E in capital and press Enter.
04:53	This gives the path name of our home directory.
04:57	We can move around from one directory to other.
05:01	But, any time we can be in one directory and this directory is known as the current directory or working directory.
05:09	The pwd command helps us to see the current directory. pwd stands for present working directory.
05:18	Type at the command prompt pwd and press Enter. Now, this is our present working directory.
05:28	We have said that we can move from one directory to other.
05:32	But how do we do so? We have the cd command for this purpose.
05:39	You have to type the command cd followed by the path name of the directory you want to move to.
05:47	Let's again see our current directory by typing pwd at the command prompt and press Enter.
05:57	So, now we are placed in this directory.
06:01	Now, say we want to move to slash usr directory. So, type: cd space slash usr. Remember, here slash in linux means front-slash and press Enter.
06:17	Now lets see our current directory. Type pwd and press Enter.
06:24	Yes, we have moved to slash usr directory.
06:30	The problem here is, the path names can be very long; this is because these are Absolute Path names that enlist the entire path, starting from the root directory.
06:42	Instead, we may use Relative path names that begin from the current directory.
06:48	Here, we need to know two special characters. dot that represent the current directory and dot dot that represent the parent directory of the current directory.
07:02	Now, let us have a brief session on cd command.
07:06	The command cd, without any argument, is used to move back to the home directory.
07:13	Type at the command prompt cd and press Enter.
07:19	Now check our current directory by the pwd command.
07:23	So, now we are back in our home directory- /home/gnuhata [slash home slash gnuhata].
07:30	Now, let us move to music directory. Type at the command prompt cd space Music (M in capital) slash and press Enter.
07:43	Now check our current directory by the pwd command. pwd and press enter. See, we have moved /home/gnuhata/Music.
07:57	Let us go to the parent directory of Music. For that, you have to use cd command with dot dot.
08:04	Type at the command prompt: cd space dot dot and press Enter.
08:11	Now check our present directory by typing pwd. We are again in /home/gnuhata.
08:23	Now, let's try to move to a sub-directory of the current directory using dot.
08:30	Type at the command prompt: cd space dot slash Documents (D in capital) slash. Press Enter.
08:42	Check our current directory by typing pwd. We are at- /home/gnuhata/Documents.
08:53	Let me clear the screen by pressing control L. So you can see clearly.
08:58	To go back to our home directory by cd command, type cd and press Enter.
09:07	Again check our current directory by pwd command. We are back to /home/gnuhata.
09:17	We can combine any number of dot dot separated by slash in a relative path.
09:23	In this slide, we can see the file system hierarchy. Root or slash is at the top. home and bin are two sub-directories under root. username , here the directory named gnuhata, is a sub-directory under home.
09:43	So, now we are in /home/gnuhata. Now, how can we go to the bin directory?
09:51	Type at the command prompt: cd space dot dot slash dot dot slash bin and press Enter.
10:03	Check our current directory by the command pwd. We are at /bin (slash bin).
10:11	The first ".." (dot dot) takes us from /home/gnuhata (slash home slash gnuhata) to /home (slash home).
10:18	The next, takes us from slash home to root.
10:24	Now from root or slash, we have moved to /bin directory.
10:30	Go back to our home directory by the command cd.
10:34	To create a directory, we use the mkdir command.
10:40	You have to type the command and the name of directory to be created and a directory would be created under the current directory.
10:49	To create a directory named testdir, type the command: mkdir space testdir and press Enter.
11:01	This creates the testdir directory successfully.
11:05	Note that, there is no explicit notification of successful directory creation or removal.
11:13	If you do not get any error message, it denotes successful execution.
11:18	We can also use the relative or absolute path name to create a directory anywhere in the tree provided we have the permission to do so and a directory by that name does not already exist.
11:33	This process can be used for making multiple directories or even a hierarchy of directories.
11:39	Type: mkdir space test1 space test2 and press Enter. This will make two directories named test1 and test2 under the present directory.
11:57	Type: "'mkdir space testtree space testtree slash test3'".
12:11	This will make a directory testtree and another directory test3 which is a sub-directory under testtree.
12:20	So, we have created four directories namely testdir, test1, test2 and testtree in the current directory, out of which first three are empty and the last one contains a sub-directory namely test3.
12:40	Similar to the mkdir command is the rmdir command which is used for removing a directory or directories.
12:50	The command rmdir space test1 removes the test1 directory successfully.
13:00	A directory can be removed only if you are its owner, your current directory is hierarchically above the directory to be removed and the directory is empty.
13:13	Now type at the command prompt: '"cd space testtree slash test3"'.
13:25	So, we are now in test3 directory which is a sub-directory under testtree.
13:33	Let's try to remove the testdir directory by typing the command rmdir space testdir. Press Enter.
13:46	We see it can't be done because the current directory is not hierarchically above the directory to be removed.
13:54	So, we have to go to the directory which is hierarchically above testdir directory.
14:00	Type: "'cd space dot dot"' and press Enter.
14:06	Now, go back to our parent directory by typing the command "'cd space dot dot'".
14:13	Now, again try the previous command.
14:16	Type: "rmdir space testdir". Press Enter.
14:23	The testdir directory is successfully deleted. Note that, testdir directory was also empty.
14:32	Multiple directories or a hierarchy of directories can be removed at once. So, try to delete the testtree directory along with its sub-directory test3.
14:43	Type at the command prompt: rmdir space testtree space testtree slash test3 press Enter.
14:57	See, it is giving the error message that 'testree' directory cannot be removed because 'testtree' is not empty.
15:07	But one thing which you may miss is that testtree slash test3 has been deleted as it was empty.
15:16	To check that, type at the command prompt: cd space testtree and press Enter.
15:25	Now, type ls and press Enter. See, the directory contains nothing. So, 'test3' was deleted.
15:34	So, in this linux tutorial we have learnt about Linux Files and directories and how to work with Linux Directories. See them, move between them, make them, remove them.
15:48	This brings me to the end of this tutorial. Spoken Tutorials are part of the "Talk to a Teacher" project, supported by the National Mission on Education through ICT.
16:02	More information on this is available at the following link.
16:08	This is Anusha Kadambala, signing off. Thanks for joining.

Contributors and Content Editors

PoojaMoolya, Sandhya.np14