UNIX Password Security: Each userid on the system is unique (First 8 
characters is maximum used, but password can be longer)

Good password criteria: (1) you can remember it 
	(2) No names or attributes about you or yours in any language 
	(3) Mix upper and lower case 
	(4) mix numbers and printable characters 
	(5) consider using pairs of words with punctuation
	(6) consider using mnemonics: 1st character of each word of the 
		first line of a poem.

passwd(1)               - change login password
/etc/passwd(5)          - password file
/etc/group(5)           - group file

$ cat /etc/passwd


Each data line has information separated by : to indicate the field.

e.g.

  1   2  3   4       5             6             7  <--field
rkatz:x:531:535:Robert Katz:/home/cis/rkatz:/bin/bash

field 1 is the userid
field 2 is the encrypted password placeholder for comparison when you log in
field 3 is the userid number (uid)
field 4 is the group id number (gid)
field 5 is the actual name field (gecos)
field 6 is the home directory for this userid
field 7 is the program that the login program will launch

$ cat /etc/group

Each data line has information separated by : to indicate the field.

e.g.

    1  2 3     4                                        <--field 
daemon:x:2:root,bin,daemon

field 1 is the group name
field 2 is the null password area (not used)
field 3 is the group id number (gid)
field 4 is at least one userid's in this group (comma separated list)

The passwd program permits you to change your current 
password for a new one. When you type it, it will not display
what you typed. Therefore you must type it exactly the same
way twice in order to verify that what you typed is really the
new password.  To use it, you must also type your old password so
your friends and strangers won't change your password and not
tell you what they did.

Questions? Robert Katz: rkatz@ned.highline.edu
Last Update July 9, 2002