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 disabled

       ·   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 2020-07-14.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-06-19.)  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 4.6                 07/14/2020                        SHADOW(3)