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Top Forums UNIX for Dummies Questions & Answers shadow file Post 59686 by S.Vishwanath on Wednesday 29th of December 2004 05:12:42 AM
Old 12-29-2004
HI,

Unix Stores passwords in a text file. Usually passwords were
stored in /etc/passwd file. So any body can see the contents of
the passwd file. Also can look into the password string (ofcourse
they are encrypted (cypher text). Which could only be
understood by the passed program.

This gave some space for the world community to start guessing
and re-coining the passwords for some definite kind of password
text.

Hence in order to avoid / give no chance to the password visibility,
a file called /etc/shadow was being provided which has one and only one permission, and passwords are now being stored in this file instead.
i.e. Read permission on the file only for
root/superuser. Hence no body will be able to see the contents
of this /etc/shadow file other than the root user.

Well, now you may feel that, why shouldn't we apply the only root user
read permission for the /etc/passwd file?

Actually the /etc/passwd file will have -r--r--r type of permission (i.e., read only for all).
This read only for all is required because,
when a valid user loggs on successfully to the unix box, he will be
put into some specific directory (home directory), and his required
shell is loaded for him to interect with the Unix World.
So, all the infromation regarding the users Home Dirctory, his/her preferrd shell etc.,
are stored in this file. So, when the user logs
in, login program should be able to read and load all this information from this file,
before user is allowed to work in his way.

For more details type man passwd and go through it.
 

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LEARN ABOUT OPENSOLARIS

pwconv

pwconv(1M)						  System Administration Commands						pwconv(1M)

NAME

       pwconv - installs and updates /etc/shadow with information from /etc/passwd

SYNOPSIS

       pwconv

DESCRIPTION

       The pwconv command creates and updates /etc/shadow with information from /etc/passwd.

       pwconv relies on a special value of 'x' in the password field of /etc/passwd. This value of 'x' indicates that the password for the user is
       already in /etc/shadow and should not be modified.

       If the /etc/shadow file does not exist, this command will create /etc/shadow with  information  from  /etc/passwd.  The	command  populates
       /etc/shadow  with  the  user's  login  name,  password,	and  password  aging  information. If password aging information does not exist in
       /etc/passwd for a given user, none will be added to  /etc/shadow. However, the last changed information will always be updated.

       If the  /etc/shadow file does exist, the following tasks will be performed:

	   Entries that are in the  /etc/passwd file and not in the /etc/shadow file will be added to the /etc/shadow file.

	   Entries that are in the  /etc/shadow file and not in the /etc/passwd file will be removed from /etc/shadow.

	   Password attributes (for example, password and aging information)  that exist in an /etc/passwd entry will be moved to the  correspond-
	   ing entry in  /etc/shadow.

       The pwconv command can only be used by the super-user.

FILES

       /etc/opasswd

       /etc/oshadow

       /etc/passwd

       /etc/shadow

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       passwd(1), passmgmt(1M), usermod(1M), passwd(4), attributes(5)

DIAGNOSTICS

       pwconv exits with one of the following values:

       0    SUCCESS.

       1    Permission denied.

       2    Invalid command syntax.

       3    Unexpected failure.  Conversion not done.

       4    Unexpected failure.  Password file(s) missing.

       5    Password file(s) busy.  Try again later.

       6    Bad entry in /etc/shadow file.

SunOS 5.11							    9 Mar 1993								pwconv(1M)
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