Difference between revisions of "BOSS-Linux/C2/File-System/English-timed"

|Welcome to this spoken tutorial on Linux File System.

|I am using Linux Operating system.

|We assume that you know how to get started with the Linux operating system and have some basic idea about commands.  

|If you are interested, it is available through another spoken tutorial, on the following website http://spoken-tutorial.org

|Also note that linux is case sensitive.

|In Linux almost everything is a file.  

|So what is a file? In real life we know that a file is where we store our documents and papers.  

|Similarly in Linux a file is a container for storing information.  

|Next what is a directory?  

|A directory helps us in organising our files in a systematic manner.  

|Also if there are no directories, all the files on the system need to have unique names,which would be very difficult to maintain.

|These definitions of files and directories are good to get a general feel about them, they are not entirely accurate.  

|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.  

|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.  

|The system uses the number of the file’s '''inode''' ; the directory structure just names the file for our benefit as its easier for us to remember names than larger numbers.

|Contrary to its oversimplified definition, a directory doesnot actually store other files ,it is itself a file that holds the inode numbers and names of other files.  

|In fact in Linux there are three kinds of files:

|Regular Files or Ordinary files: It contains only data , as a stream of characters.

|A CD, a Harddisk 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.

|All files in Linux are related, in short all form a family much like we do.  

|A directory containing say some files and subdirectories will have a parent – child relationship with each other. This gives rise to the Linux File System Tree.

|At the top is the root( denoted by a frontslash /). It contains all the other files and directories.  

|One command and there you are teleported from one place to other.

|Sounds interesting!! Indeed it is. As we will see.

|When we login into the Linux system we are by default in a home directory.  

|Now Switch to the terminal.

|To see the home directory , Type at the command prompt "'echo space dollar H-O-M-E in capital"' and press enter.

|This gives the pathname of our '''home''' directory.  

|But any time we can be in one directory and this directory is known as the current directory or working directory.  

|The '''pwd''' command helps us to see the current directory. '''pwd''' stands for present working directory.

|Type at the command prompt '"pwd'" and press enter. Now this is our present working directory.  

|You have to type the command '''cd''' followed by the pathname of the directory you want to move to.

|Lets again see our current directory by typing '''pwd''' at the command prompt and press enter.

|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.

|Now lets see our current directory. Type '''pwd''' and press enter.

|Yes we have moved to '''slash usr''' directory.  

|The problem here is the pathnames can be very long, this is because these are Absolute Pathnames that enlist the entire path staring from the root directory.

|Instead we may use Relative pathnames that begin from the current directory.  

|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.  

|Now let us have a brief session on '''cd''' command

|The command '''cd''' without any argument is used to move back that to the home directory.  

|Type at the command prompt "'cd'" and press enter.  

|So, now we are back in our home directory '''/home/gnuhata''' [ slash home slash gnuhata ]  

|Now let us move to music directory. Type at the command prompt "'cd space Music(M in capital) slash"' and press enter

|Now check our current directory by the '''pwd''' command. '''pwd''' and press enter. See, we have moved ''' /home/gnuhata/Music '''

|Let us go to the parent directory of Music. For that you have to use cd command with dot dot.  

|Type at the command prompt '''cd space dot dot''' and press enter.  

|Now check our present directory by typing '''pwd.''' We are again in '''/home/gnuhata'''

|Now lets try to move to a subdirectory of the current directory using dot.  

|Type at the command prompt '''cd space dot slash Documents(D in capital) slash'''. Press enter.

|Check our current directory by typing '''pwd.''' We are at ''' /home/gnuhata/Documents'''

|Let me clear the screen by pressing control L. So you can see clearly.

|To go back to our home directory by '''cd''' command. Type '''cd''' and press enter.

|Again check our current directory by '''pwd''' command. We are back to '''/home/gnuhata''' .  

|We can combine any number of dot dot separated by slash in a relative path .  

|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.'''

| So, now we are in '''/home/gnuhata.''' Now how can we go to the bin directory?  

|Type at the command prompt "'cd space dot dot slash dot dot slash bin'" and press enter.  

|Check our current directory by the command '''pwd.'''  We are at /bin (slash bin)

|The first .. (dot dot) takes us from /home/gnuhata (slash home slash gnuhata) to /home (slash home)

|The next takes us from '''slash home''' to root.  

|Now from root or slash, we have moved to /bin directory.

|To create a directory we use the '''mkdir''' command.  

|You have to type the command and name of directory to be created and a directory would be created under the current directory.

|To create a directory named '''testdir''', type the command '"mkdir space testdir'" and press enter.

|We can also use the relative or absolute pathname 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.

|Type "'mkdir space test1 space test2''' and press enter ,this will make two directories named '''test1''' and '''test2''' under the present directory.

|Type "'mkdir space testtree space testtree slash test3'".  

|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 subdirectory namely test3.  

|Similar to the '''mkdir''' is the '''rmdir''' command which is used for removing a directory or directories.

|The command "'rmdir space test1'" removes the '''test1''' directory successfully.  

|Now type at the command prompt '"cd space testtree slash test3"'

|So, we are now in '''test3''' directory which is a subdirectory under '''testtree.'''

|Lets try to remove the '''testdir''' directory by typing the command '"rmdir space testdir'". Press enter.  

|We see it can't be done, because the current directory is not hierarchically above the directory to be removed.

|So,we have to go to the directory which is hierarchically above '''testdir''' directory.  

|Type "'cd space dot dot"' and press enter.  

|Now, go back to our parent directory by typing the command "'cd space dot dot'".  

|Type "rmdir space testdir". Press enter.  

|Multiple directories or a hierarchy of directories can be removed at once.So, try to delete the '''testtree''' directory along with its subdirectory '''test3.'''  

|Type at the command prompt '"rmdir space testtree space testtree slash test3'" press enter.

|See, it is giving the error message that '''testree''' directory cannot be removed because testtree is not empty.  

|To check that, type at the command prompt "'cd space testtree"' and press enter.

|Now type "'ls'" and press enter. See, the directory contains nothing. So, '''test3''' was deleted.

|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.  

|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 this is available at the following link  

|This is Anusha Kadambala signing off. Thanks for joining.