shadow(3) — Linux manual page


SHADOW(3)                     Library Calls                    SHADOW(3)

NAME         top

       shadow, getspnam - encrypted password file routines

SYNTAX         top

       #include <shadow.h>

       struct spwd *getspent();

       struct spwd *getspnam(char *name);

       void setspent();

       void endspent();

       struct spwd *fgetspent(FILE *fp);

       struct spwd *sgetspent(char *cp);

       int putspent(struct spwd *p, FILE *fp);

       int lckpwdf();

       int ulckpwdf();

DESCRIPTION         top

       shadow manipulates the contents of the shadow password file,
       /etc/shadow. The structure in the #include file is:

           struct spwd {
                 char      *sp_namp; /* user login name */
                 char      *sp_pwdp; /* encrypted password */
                 long int       sp_lstchg; /* last password change */
                 long int       sp_min; /* days until change allowed. */
                 long int       sp_max; /* days before change required */
                 long int       sp_warn; /* days warning for expiration */
                 long int       sp_inact; /* days before account inactive */
                 long int       sp_expire; /* date when account expires */
                 unsigned long int   sp_flag; /* reserved for future use */

       The meanings of each field are:

       •   sp_namp - pointer to null-terminated user name

       •   sp_pwdp - pointer to null-terminated password

       •   sp_lstchg - days since Jan 1, 1970 password was last changed

       •   sp_min - days before which password may not be changed

       •   sp_max - days after which password must be changed

       •   sp_warn - days before password is to expire that user is
           warned of pending password expiration

       •   sp_inact - days after password expires that account is
           considered inactive and disabled

       •   sp_expire - days since Jan 1, 1970 when account will be

       •   sp_flag - reserved for future use

DESCRIPTION         top

       getspent, getspname, fgetspent, and sgetspent each return a
       pointer to a struct spwd.  getspent returns the next entry from
       the file, and fgetspent returns the next entry from the given
       stream, which is assumed to be a file of the proper format.
       sgetspent returns a pointer to a struct spwd using the provided
       string as input.  getspnam searches from the current position in
       the file for an entry matching name.

       setspent and endspent may be used to begin and end, respectively,
       access to the shadow password file.

       The lckpwdf and ulckpwdf routines should be used to insure
       exclusive access to the /etc/shadow file.  lckpwdf attempts to
       acquire a lock using pw_lock for up to 15 seconds. It continues
       by attempting to acquire a second lock using spw_lock for the
       remainder of the initial 15 seconds. Should either attempt fail
       after a total of 15 seconds, lckpwdf returns -1. When both locks
       are acquired 0 is returned.

DIAGNOSTICS         top

       Routines return NULL if no more entries are available or if an
       error occurs during processing. Routines which have int as the
       return value return 0 for success and -1 for failure.

CAVEATS         top

       These routines may only be used by the superuser as access to the
       shadow password file is restricted.

FILES         top

           Secure user account information.

SEE ALSO         top

       getpwent(3), shadow(5).

COLOPHON         top

       This page is part of the shadow-utils (utilities for managing
       accounts and shadow password files) project.  Information about
       the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, send it to  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-15.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

shadow-utils 4.11.1            12/22/2023                      SHADOW(3)