Carreer:Networking Programming in Unix (C programming Language) Post: 302232999

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Top Forums UNIX for Dummies Questions & Answers Carreer:Networking Programming in Unix (C programming Language) Post 302232999 by ovais245 on Friday 5th of September 2008 07:05:26 PM

09-05-2008

Registered User

Write or study a small program that mimics the most common login procedures in UNIX.
You have two options here. Either, you write it yourself according to the specification
below, or you copy the file
/cab/cestud/work/edu/course/EDA263_Computer_Security/
lib/login_linux/login_linux.c into your home directory. If you choose to write
it yourself the following should be implemented.
- The program begins with displaying ”login:” and takes the username as input.
7
- Then the program writes ”Password:” and waits for the password to be entered,
which should not be visible on the terminal (use the function getpass(3) that
among other things will see to that the text is not ”echoed” on the terminal).
- The program queries the system’s user database to see if the username exists. If
this is the case it encrypts the entered password (with a known algorithm) and
ensures it corresponds to the stored encrypted password belonging to the actual
user. Suitable library routines are getpwnam(3), crypt(3) and strncmp(3).
- If the username does not exist, or if the password is wrong, the program displays
”Login incorrect” and restarts from the beginning, otherwise it writes something
like ”Welcome to this System!” and terminates.
Test that your program works by compiling and running it.

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LEARN ABOUT DEBIAN

passwd

PASSWD(5)						   File Formats and Conversions 						 PASSWD(5)

NAME

       passwd - the password file

DESCRIPTION

       /etc/passwd contains one line for each user account, with seven fields delimited by colons (":"). These fields are:

       o   login name

       o   optional encrypted password

       o   numerical user ID

       o   numerical group ID

       o   user name or comment field

       o   user home directory

       o   optional user command interpreter

       The encrypted password field may be blank, in which case no password is required to authenticate as the specified login name. However, some
       applications which read the /etc/passwd file may decide not to permit any access at all if the password field is blank. If the password
       field is a lower-case "x", then the encrypted password is actually stored in the shadow(5) file instead; there must be a corresponding line
       in the /etc/shadow file, or else the user account is invalid. If the password field is any other string, then it will be treated as an
       encrypted password, as specified by crypt(3).

       The comment field is used by various system utilities, such as finger(1).

       The home directory field provides the name of the initial working directory. The login program uses this information to set the value of
       the $HOME environmental variable.

       The command interpreter field provides the name of the user's command language interpreter, or the name of the initial program to execute.
       The login program uses this information to set the value of the $SHELL environmental variable. If this field is empty, it defaults to the
       value /bin/sh.

FILES

       /etc/passwd
	   User account information.

       /etc/shadow
	   optional encrypted password file

       /etc/passwd-
	   Backup file for /etc/passwd.

	   Note that this file is used by the tools of the shadow toolsuite, but not by all user and password management tools.

SEE ALSO

       crypt(3), getent(1), getpwnam(3), login(1), passwd(1), pwck(8), pwconv(8), pwunconv(8), shadow(5), su(1), sulogin(8).

shadow-utils 4.1.5.1						    05/25/2012								 PASSWD(5)