Logging in / Logging out of Linux

Linux systems allow many users to work simultaneously. A user normally works at a user terminal. You have to establish connection to the Linux system, the system after showing some information; will show Login prompt(prompt is a helping message), which is the location where you enter your user name. Your Login name is nothing but user (your) name.

You need not be frightened by the word Login, which simply means user here.

Assume a house with many rooms and one person occupies one room and each room contains invaluable treasure. How will you safeguard each room of that house? The entire house should be locked inside and a watchman should be employed. The arrangement is that you should tell him your name and your identity code. He has a list of names and matching identity codes for each individual. If the name and the identity code match with any of the name and its identity code, then and only then, he will allow you to enter into your room. If the name and the identity code do not match with any of the names and the corresponding identity codes then you will be asked to repeat your name and identity code. This process continues until user says the

valid name and identity code.

The same process happens in Linux also. When you connect to the Linux system, you will be asked to enter your Login name at the Login prompt, you have to enter your Login name and you will be shown the Password prompt. You have to enter your password. To keep your password a secret, the Linux system will not display your password.

The system compares these two items with the system files. If the match is not found, then you should enter these two items. Ofcourse, if the match is found you will be shown the following prompt;

[ilamathi@localhost ilamathi] $

Here you assume your login name is ilamathi.

You should be careful about the lower case and upper case letters because the system is case sensitive. The verification process does not allow any unauthorized person to access any of your directories or files. Normally, not necessarily, the name of the user is the Login name.

The Home Directory is assigned to the user when he/she enters into the system for the first time, by the System Administrator ( SA ). You will learn about SA later.

Logout Process

If you come out of the system without closing your /home directory then the other people may tamper with your work. So it is mandatory to Logout of the Linux system. Entering exit or logout at the command prompt will end your current Linux session then the system displays the Login prompt on the screen for other users.

Changing the password

Suppose you have an uneasy feeling that someone knows your password. Then you have to spend sleepless nights. The Linux operating system has its own method of solving your problem. It allows you to change your password. A user can change his/her password with the passwd command. The steps followed by the user, ilamathi, to change her password are depicted below. The actual prompt is similar to the one shown here.

Example:

[ilamathi@localhost ilamathi]$ passwd ( the user enters his/her password)

Changing password for ilamathi (current ) password: (User enters the current password)

New password: (User enters the new passeord)

Retype new password: (User re-enters the new password) passwd: all authentication tokens updated successfully [ilamathi@localhost ilamathi]$ _

The passwd command asks for the old password. This command is essential to check up the authenticity of the user, otherwise the mischief mongers will play havoc on the work of the other people. Again the system demands that the user should make up his/her mind about the new password. That is why it asks the new password twice.

Example:

[ilamathi@localhost ilamathi]$ passwd

Changing password for ilamathi

( current ) password:(User enters the current password) New passwd:(User enters the new passeord)

Retype new password: (User misspells the new password) Sorry, passwords do not match

New password:

If you commit a mistake in typing the current password (that is the password that you want to change) then you may not be an authenticated user. So, there is a suspicion that you are trying to change someone else’s password. Therefore you will not be allowed to change the password. If two entries of the new password do not match then the system is in a dilemma. The system does not know which is to be accepted. So, your new password is outrightly rejected. Hence you should be careful about the old as well as the new passwords.

Some of the rules for changing the password:

The password should not be less than six characters in length.

When changing a password, the new password should differ from the old password by at least three positions

The password should be different from the user’s Login name.

The new password cannot be the same as the old password. It is ridiculous to change the password with same password.

Since the SA can execute control over the entire system, SA can change the password of any user of the Linux system.