Introduction
The concept of a user on a Linux system is fairly rigidly defined and more numeric than you might think. At the login prompt, you type in some string of characters (e.g., shawkins or root) called your user name. The system takes this string, compares it to the entries in the /etc/passwd file, and finds the encrypted password associated with that user. It then prompts you for a password. Whatever string you type in is encrypted, and the result of the encryption is compared with the password string stored in /etc/ passwd. If the strings match, the system acknowledges your right to log in.
The login program sets your user id and group id and forks (creates a copy of itself); then, the copy turns into whatever shell is specified as your ...
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