✏ EDIT: shadow.h

/* Copyright (C) 1996-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

/* Declaration of types and functions for "shadow" storage of hashed
   passphrases.  The shadow database is like the user database, but is
   only accessible with special privileges, so that malicious users
   cannot retrieve everyone else's hashed passphrase to brute-force at
   their convenience.  */

#ifndef _SHADOW_H
#define _SHADOW_H	1

#include <features.h>

#include <paths.h>

#define __need_size_t
#include <stddef.h>

#include <bits/types/FILE.h>

/* Paths to the user database files.  */
#define	SHADOW _PATH_SHADOW

__BEGIN_DECLS

/* A record in the shadow database.  */
struct spwd
  {
    char *sp_namp;		/* Login name.  */
    char *sp_pwdp;		/* Hashed passphrase.  */
    long int sp_lstchg;		/* Date of last change.  */
    long int sp_min;		/* Minimum number of days between changes.  */
    long int sp_max;		/* Maximum number of days between changes.  */
    long int sp_warn;		/* Number of days to warn user to change
				   the password.  */
    long int sp_inact;		/* Number of days the account may be
				   inactive.  */
    long int sp_expire;		/* Number of days since 1970-01-01 until
				   account expires.  */
    unsigned long int sp_flag;	/* Reserved.  */
  };

/* Open database for reading.

This function is not part of POSIX and therefore no official
   cancellation point.  But due to similarity with an POSIX interface
   or due to the implementation it is a cancellation point and
   therefore not marked with __THROW.  */
extern void setspent (void);

/* Close database.

/* Get next entry from database, perhaps after opening the file.

/* Get shadow entry matching NAME.

/* Read shadow entry from STRING.

/* Read next shadow entry from STREAM.

/* Write line containing shadow entry to stream.

#ifdef __USE_MISC
/* Reentrant versions of some of the functions above.

These functions are not part of POSIX and therefore no official
   cancellation point.  But due to similarity with an POSIX interface
   or due to the implementation they are cancellation points and
   therefore not marked with __THROW.  */
extern int getspent_r (struct spwd *__result_buf, char *__buffer,
		       size_t __buflen, struct spwd **__result);

extern int getspnam_r (const char *__name, struct spwd *__result_buf,
		       char *__buffer, size_t __buflen,
		       struct spwd **__result);

extern int sgetspent_r (const char *__string, struct spwd *__result_buf,
			char *__buffer, size_t __buflen,
			struct spwd **__result);

extern int fgetspent_r (FILE *__stream, struct spwd *__result_buf,
			char *__buffer, size_t __buflen,
			struct spwd **__result);
#endif	/* misc */

/* The simple locking functionality provided here is not suitable for
   multi-threaded applications.  */

/* Request exclusive access to /etc/passwd and /etc/shadow.  */
extern int lckpwdf (void) __THROW;

/* Release exclusive access to /etc/passwd and /etc/shadow.  */
extern int ulckpwdf (void) __THROW;

__END_DECLS

#endif /* shadow.h */

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