Sunday, November 27, 2011

Choosing a Password and Password Files

Choosing a Password:

Passwords must be constructed to meet the following requirements:

  • Each password must have atleast PASSLENGTH characters as set in /etc/default/passwd file.PASSLENGTH must contain a minimum of 6 characters, but only the first 8 characters are significant.
  • Each  password must contain at least 2 alphabetic characters and atleast 1 numeric or special character.
  • Each password must differ from the user's login name and any reverse or circular shift of that login name. For comparison purposes, an upper case letter and its corresponding lower case letter are equivalent .
  • New passwords must differ from the old by atleast 3 characters.

Password Files:

The passwd  command uses the files /etc/shadow, /etc/passwd and /etc/oshadow.
The file /etc/passwd contains the following information for each user:
  • login name
  • dummy password
  • numerical user ID
  • numerical group ID
  • comment
  • initial working directory
  • program to be used as the shell
passwd is an ASCII file . Each field within each user's entry is separarted from the next by a colon. The comment field  can contain any information that the user desires. each user is separated from the next by a new-line. If the shell field is null, /usr/bin/sh is used.

This file has user login information and general read permission. It can therefore be used , to map numerical user ID's to names.
The password field consists of the character x.Password information is contained in the file /etc/shadow.

The next command will be the echo command.

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