We have already learnt about UNIX directories, special files which contain file names and/or sub directory. Let us look at some of the standard UNIX directories. Typically UNIX Directory System consists of the following standard directories:
Home Directory: It is that directory in which a user logs in when he connects to the UNIX system. A user cannot change the location of the Home Directory.
Current directory: It is the directory where the user is currently in and is issuing commands to the system.
By default, at the login time the Home Directory and current directory are one are the same? Later, one can change his current directory.
/etc: This directory stores all the utility files which are used for System Administration. Password is one of such administration file which is used by the system to maintain security.
/user: This directory stores all the user Home Directories. /user directory apart from storing user home directories store some of the UNIX commands.
/bin: It is this directory, where UNIX stores all the most commonly used commands of UNIX System.
/Lib: This directory contains, all the library files, which are used for development of ‘C’ programs.
/dev: This directory stores all the device files.
/tmp: This directory stores all the temporary files are used for temporary storage during Execution of Commands.
Thus these standard directories which store specific files are one of the effective features of the UNIX file system.
Connecting to the UNIX System
The procedure for Connecting to the UNIX Systemby the users, so as to work on the platform is known as Login procedure.
An user can log in to the UNIX system from any terminal connected to the UNIX system, he need to respond to the login prompt, which looks as follows, and then five the password for authorization purpose. A user will get connection only when he is validated as an authorized user.
Login: <user name> (has to be typed by the user)
Password: <user has to type password>
When a user types the name of the Login and gives Password(which will not be visible on screen for security purposes). The UNIX system validates the user name and password as a measure of external security. The password is not mandatory, if one wants, it may be avoided, but it really defeats the security. Once it is found correct, a user will see the shell prompt (a ‘$’ for the bourne shell) which will give an indication, to the user that the system is ready to take Input and give Output to the user.
On verification of password you will get (it is correct)
If the password is incorrect or the user name is incorrect. The prompt will not come, as the access to the UNIX system is not granted.
When the work is over, to disconnect or Logout of the UNIX System, we have to press <control> and <D> key at a time, which will take you out of the UNIX system.
The UNIX users are categories as: Ordinary user and Super user
This classification is made for determining privileges to be given for various utilities of the UNIX system. In general every user is an ordinary user, who has restricted privileges for using the UNIX system.
Whereas Super user also known as Root/System Administrationis a privileged user, who has all the privileged and can administer all the other users as well as the system utilities. He has directory of the super user is the root (/). Form this directory he can do any action, therefore a super user has to be very careful, as his work with effect the total system. He has to know thoroughly what he is doing; else it costs the system performance.
Starting the UNIX System
Before working on the UNIX system from any terminal as well as console, one needs to start up the system. The start up of the UNIX System follows series of the steps, which have to be taken for the booting of the system. The following are the steps involved in the starting of the system:
Operating system has to be loaded. The file system has to be checked and cleaned. The mode of system operation has to be chosen.
Operating System Loading: This step involves in the loading of the UNIX Operating System from the hard disk into the primary memory. This is first step in starting the UNIX system. This can be done very easily, when the system is started, the system given the following prompt.
To Boot i.e., load the Operating System we need to press the <enter> key. Once the <enter> key is pressed, the UNIX system gets loaded into the memory. This process will consume some time (in seconds), before the operating system is completely loaded into the memory.
File System Check and Cleaning
This step involves the checking of the file system, and UNIX, checks the file system by itself, to see whether the root file system is in order or not. If the root system is in order, then the file system is thought to be clean and the system proceeds else if the root system is not clean, it will wait by displaying the message, so that the file system can be cleaned:
Proceed with cleaning (y or n)?
If we press ‘y, then the operating system starts cleaning itself i.e., Repairing Damaged Files or deleting files that cannot be repaired. This is done with the help of fsck, the file system check utility of the UNIX administration.
The Mode of the System Operating Chosen
Once the file system is cleaned one has to choose the mode of Operation of the UNIX System. UNIX operating system can run in two modes:
Normal Operation Mode, System Maintenance Mode
Normal Operation Mode: It is that mode which allows multiple users to log into the System and Work. This is the normal operation of the UNIX System.
System maintenance Mode: This is a single user mode, which will not allow multiple users. This Mode for the System Administration, where the system administration can log in to the UNIX system and carry on the maintenance. The mode of the operation of the system can be choose at the time of starting of the system, which can be done by responding to the following message/Prompt, which the system gives after the file the file system us Checked and Cleaned.
Type <control-d> to continue with normal start up. (Or give the root password for System Maintenance):
At this juncture if the user presses the, control + d> keys together the system starts up in the normal mode of operation. Then the system displays the start up message and login prompt (already learnt), so that users can long on to the system.
To get into the system maintenance mode, one has to press <enter> key after giving the Super/Root Password. After validation, if it is the authentic, then system gives root/super user prompt which is/#. After administration, once the super user logs out of the system maintenance mode by pressing <Control> and <d> keys together, the system gets into the Normal Operation mode automatically.
Define Meaning of the Shutdown Process
To stop the UNIX system, we cannot simply turn off the power we need to follow certain procedure to shutdown the system, so that the file system is in order. The Shutdown of the UNIX can be done from the super user login. The following commands can be used for shutting down the UNIX system:
Shutdown: This command is the most preferred and command for shutting down the UNIX system normally whenever this command is given, all the users who are currently working on the UNIX system will get the message that the system is going to shutdown and gives them time to finish and save their work. Once this command is given, then the system will prompt to take the number of minutes, it should wait to Shutdown the System, which is as follows:
Minutes till shutdown? (0-25):
Here we need to enter, the number of minutes from (0-15), so that the system waits for that time before shutting down the system.
The system after displaying the warning to all users working waits for them to Log out or Specified Time to elapse then the system is shutdown and the following message is displayed.
Normal system shutdown, Safe to power off, Press any key to Reboot
One has to act according to his need at this time, but a point has to be remembered that, once the shutdown command is given, it must never be interrupted by any means [usually pressing <break> or <del> key].
Haltsys: This command is used when no other users are logged on the system, as this command stops the system immediately. When this command is issued, even if the users are logged into the system, they are logged out automatically and their work in progress is not saved and is lost. Therefore we need to be careful while using this command.
Once this command is issued the system shutdown with following messages being displayed:
Normal System Shutdown, safe to power off, press any key to Reboot
One can act accordingly to either switch off the power or restart the system.