/* General shadow password file API */
       #include <shadow.h>

       struct spwd *getspnam(const char *name);

       struct spwd *getspent(void);

       void setspent(void);

       void endspent(void);

       struct spwd *fgetspent(FILE *stream);

       struct spwd *sgetspent(const char *s);

       int putspent(const struct spwd *p, FILE *stream);

       int lckpwdf(void);

       int ulckpwdf(void);

       /* GNU extension */
       #include <shadow.h>

       int getspent_r(struct spwd *spbuf,
               char *buf, size_t buflen, struct spwd **spbufp);

       int getspnam_r(const char *name, struct spwd *spbuf,
               char *buf, size_t buflen, struct spwd **spbufp);

       int fgetspent_r(FILE *stream, struct spwd *spbuf,
               char *buf, size_t buflen, struct spwd **spbufp);

       int sgetspent_r(const char *s, struct spwd *spbuf,
               char *buf, size_t buflen, struct spwd **spbufp);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getspent_r(), getspnam_r(), fgetspent_r(), sgetspent_r():
           _BSD_SOURCE || _SVID_SOURCE

       Long ago it was considered safe to have encrypted passwords openly vis-
       ible in the password file.  When computers got faster  and  people  got
       more  security-conscious,  this  was  no  longer  acceptable.  Julianne
       Frances Haugh implemented the shadow  password  suite  that  keeps  the
       encrypted  passwords  in  the shadow password database (e.g., the local
       shadow password file /etc/shadow, NIS,  and  LDAP),  readable  only  by

       The  functions described below resemble those for the traditional pass-
       word database (e.g., see getpwnam(3) and getpwent(3)).

       The sgetspent() function parses the supplied string  s  into  a  struct

       The putspent() function writes the contents of the supplied struct spwd
       *p as a text line in the shadow password file format to stream.  String
       entries with value NULL and numerical entries with value -1 are written
       as an empty string.

       The lckpwdf() function is intended to protect against multiple simulta-
       neous  accesses of the shadow password database.  It tries to acquire a
       lock, and returns 0 on success, or -1 on  failure  (lock  not  obtained
       within  15  seconds).  The ulckpwdf() function releases the lock again.
       Note that there is no protection against direct access  of  the  shadow
       password file.  Only programs that use lckpwdf() will notice the lock.

       These were the functions that formed the original shadow API.  They are
       widely available.

   Reentrant versions
       Analogous to the reentrant functions for the password  database,  glibc
       also  has  reentrant  functions  for the shadow password database.  The
       getspnam_r() function is  like  getspnam()  but  stores  the  retrieved
       shadow  password  structure  in  the  space  pointed to by spbuf.  This
       shadow password structure  contains  pointers  to  strings,  and  these
       strings  are stored in the buffer buf of size buflen.  A pointer to the
       result (in case of success) or NULL (in case no entry was found  or  an
       error occurred) is stored in *spbufp.

       The  functions getspent_r(), fgetspent_r(), and sgetspent_r() are simi-
       larly analogous to their nonreentrant counterparts.

       Some non-glibc systems also have functions with these names, often with
       different prototypes.

       The shadow password structure is defined in <shadow.h> as follows:

           struct spwd {
               char *sp_namp;     /* Login name */
               char *sp_pwdp;     /* Encrypted password */
               long  sp_lstchg;   /* Date of last change
                                     (measured in days since
                                     1970-01-01 00:00:00 +0000 (UTC)) */
               long  sp_min;      /* Min # of days between changes */
               long  sp_max;      /* Max # of days between changes */
               long  sp_warn;     /* # of days before password expires
                                     to warn user to change it */
               long  sp_inact;    /* # of days after password expires
                                     until account is disabled */
               long  sp_expire;   /* Date when account expires
                                     (measured in days since
                                     1970-01-01 00:00:00 +0000 (UTC)) */
               unsigned long sp_flag;  /* Reserved */

       error number is returned.

       EACCES The caller does not have permission to access the  shadow  pass-
              word file.

       ERANGE Supplied buffer is too small.

              local shadow password database file

              lock file

       The  include  file  <paths.h>  defines the constant _PATH_SHADOW to the
       pathname of the shadow password file.

       For  an  explanation  of  the  terms  used   in   this   section,   see

       |Interface     | Attribute     | Value                          |
       |getspnam()    | Thread safety | MT-Unsafe race:getspnam locale |
       |getspent()    | Thread safety | MT-Unsafe race:getspent        |
       |              |               | race:spentbuf locale           |
       |setspent(),   | Thread safety | MT-Unsafe race:getspent locale |
       |endspent(),   |               |                                |
       |getspent_r()  |               |                                |
       |fgetspent()   | Thread safety | MT-Unsafe race:fgetspent       |
       |sgetspent()   | Thread safety | MT-Unsafe race:sgetspent       |
       |putspent(),   | Thread safety | MT-Safe locale                 |
       |getspnam_r(), |               |                                |
       |sgetspent_r() |               |                                |
       |lckpwdf(),    | Thread safety | MT-Safe                        |
       |ulckpwdf(),   |               |                                |
       |fgetspent_r() |               |                                |
       In  the above table, getspent in race:getspent signifies that if any of
       the functions setspent(3), getspent(3), getspent_r(3),  or  endspent(3)
       are used in parallel in different threads of a program, then data races
       could occur.

       The shadow password database and its associated API are  not  specified
       in POSIX.1.  However, many other systems provide a similar API.
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