check Linux password from /etc/shadow and C language

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LEARN ABOUT SUSE

shadow

SHADOW(5)							File Formats Manual							 SHADOW(5)

NAME

       shadow - encrypted password file

DESCRIPTION

       shadow contains the encrypted password information for user's accounts and optional the password aging information. Included is

	    Login name

	    Encrypted password

	    Days since Jan 1, 1970 that password was last changed

	    Days before password may be changed

	    Days after which password must be changed

	    Days before password is to expire that user is warned

	    Days after password expires that account is disabled

	    Days since Jan 1, 1970 that account is disabled

	    A reserved field

       The  password  field must be filled. The encryped password consists of 13 to 24 characters from the 64 characters alphabet a thru z, A thru
       Z, 0 thru 9, . and /. Optionally it can start with a "$" character. This means the encrypted password was generated using another (not DES)
       algorithm. For example if it starts with "$1$" it means the MD5-based algorithm was used.

       Refer to crypt(3) for details on how this string is interpreted.

       The  date  of  the  last  password change is given as the number of days since Jan 1, 1970. The password may not be changed again until the
       proper number of days have passed, and must be changed after the maximum number of days.  If the minimum number of days required is greater
       than the maximum number of day allowed, this password may not be changed by the user.

       An  account is considered to be inactive and is disabled if the password is not changed within the specified number of days after the pass-
       word expires.  An account will also be disabled on the specified day regardless of other password expiration information.

       This information supercedes any password or password age information present in /etc/passwd.

       This file must not be readable by regular users if password security is to be maintained.

FILES

       /etc/passwd    - user account information
       /etc/shadow    - encrypted user passwords

SEE ALSO

       chage(1), login(1), passwd(1), su(1), passwd(5), pwconv(8), pwunconv(8), sulogin(8)

AUTHOR

       Julianne Frances Haugh (jockgrrl@ix.netcom.com)

																	 SHADOW(5)

Programming