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GETPWNAM(3P)               POSIX Programmer's Manual              GETPWNAM(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       getpwnam, getpwnam_r -- search user database for a name
SYNOPSIS
       #include <pwd.h>
       struct passwd *getpwnam(const char *name);
       int getpwnam_r(const char *name, struct passwd *pwd, char *buffer,
           size_t bufsize, struct passwd **result);
DESCRIPTION
       The getpwnam() function shall search the user  database  for  an  entry
       with a matching name.
       The getpwnam() function need not be thread-safe.
       Applications  wishing to check for error situations should set errno to
       0 before calling getpwnam().  If getpwnam() returns a null pointer  and
       errno is non-zero, an error occurred.
       The  getpwnam_r() function shall update the passwd structure pointed to
       by pwd and store a pointer to that structure at the location pointed to
       by result.  The structure shall contain an entry from the user database
       with a matching name.  Storage referenced by the structure is allocated
       from  the  memory  provided with the buffer parameter, which is bufsize
       bytes in size. A call to sysconf(_SC_GETPW_R_SIZE_MAX)  returns  either
       -1 without changing errno or an initial value suggested for the size of
       this buffer.  A null pointer shall be returned at the location  pointed
       to by result on error or if the requested entry is not found.
RETURN VALUE
       The  getpwnam() function shall return a pointer to a struct passwd with
       the structure as defined in <pwd.h> with a matching entry if  found.  A
       null  pointer shall be returned if the requested entry is not found, or
       an error occurs. On error, errno shall be set to indicate the error.
       The application shall not modify the  structure  to  which  the  return
       value  points,  nor any storage areas pointed to by pointers within the
       structure. The returned pointer, and  pointers  within  the  structure,
       might  be  invalidated  or  the structure or the storage areas might be
       overwritten by a subsequent call to getpwent(),  getpwnam(),  or  getp-
       wuid().
       The  getpwnam_r()  function  shall  return  zero  on  success or if the
       requested entry was not found and no error has occurred.  If  an  error
       has occurred, an error number shall be returned to indicate the error.
ERRORS
       These functions may fail if:
       EIO    An I/O error has occurred.
       EINTR  A signal was caught during getpwnam().
       EMFILE All  file  descriptors  available  to  the process are currently
              open.
       ENFILE The maximum allowable number of files is currently open  in  the
              system.
       The getpwnam_r() function may fail if:
       ERANGE Insufficient storage was supplied via buffer and bufsize to con-
              tain the data to be referenced by the  resulting  passwd  struc-
              ture.
       The following sections are informative.
EXAMPLES
       Note  that  sysconf(_SC_GETPW_R_SIZE_MAX)  may return -1 if there is no
       hard limit on the size of the buffer needed to  store  all  the  groups
       returned.  This  example shows how an application can allocate a buffer
       of sufficient size to work with getpwnam_r().
           long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
           size_t len;
           if (initlen == -1)
               /* Default initial length. */
               len = 1024;
           else
               len = (size_t) initlen;
           struct passwd result;
           struct passwd *resultp;
           char *buffer = malloc(len);
           if (buffer == NULL)
               ...handle error...
           int e;
           while ((e = getpwnam_r("someuser", &result, buffer, len, &resultp))
                   == ERANGE)
               {
               size_t newlen = 2 * len;
               if (newlen < len)
                   ...handle error...
               len = newlen;
               char *newbuffer = realloc(buffer, len);
               if (newbuffer == NULL)
                   ...handle error...
               buffer = newbuffer;
               }
           if (e != 0)
               ...handle error...
           free (buffer);
   Getting an Entry for the Login Name
       The following example uses the getlogin() function to return  the  name
       of the user who logged in; this information is passed to the getpwnam()
       function to get the user database entry for that user.
           #include <sys/types.h>
           #include <pwd.h>
           #include <unistd.h>
           #include <stdio.h>
           #include <stdlib.h>
           ...
           char *lgn;
           struct passwd *pw;
           ...
           if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
               fprintf(stderr, "Get of user information failed.\n"); exit(1);
           }
           ...
APPLICATION USAGE
       Three names associated with the current process can be determined: get-
       pwuid(geteuid()) returns the name associated with the effective user ID
       of the process; getlogin() returns the name associated with the current
       login activity; and getpwuid(getuid()) returns the name associated with
       the real user ID of the process.
       The getpwnam_r() function is thread-safe and returns values in a  user-
       supplied  buffer  instead of possibly using a static data area that may
       be overwritten by each call.
       Portable applications should take into account that it is usual for  an
       implementation  to return -1 from sysconf() indicating that there is no
       maximum for _SC_GETPW_R_SIZE_MAX.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       getpwuid(), sysconf()
       The Base Definitions volume of POSIX.1-2008, <pwd.h>, <sys_types.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                         GETPWNAM(3P)