getpwuid(3p) — Linux manual page


GETPWUID(3P)              POSIX Programmer's Manual             GETPWUID(3P)

PROLOG         top

       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         top

       getpwuid, getpwuid_r — search user database for a user ID

SYNOPSIS         top

       #include <pwd.h>

       struct passwd *getpwuid(uid_t uid);
       int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
           size_t bufsize, struct passwd **result);

DESCRIPTION         top

       The getpwuid() function shall search the user database for an entry
       with a matching uid.

       The getpwuid() function need not be thread-safe.

       Applications wishing to check for error situations should set errno
       to 0 before calling getpwuid().  If getpwuid() returns a null pointer
       and errno is set to non-zero, an error occurred.

       The getpwuid_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 uid.  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         top

       The getpwuid() 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

       If successful, the getpwuid_r() function shall return zero;
       otherwise, an error number shall be returned to indicate the error.

ERRORS         top

       These functions may fail if:

       EIO    An I/O error has occurred.

       EINTR  A signal was caught during getpwuid().

       EMFILE All file descriptors available to the process are currently

       ENFILE The maximum allowable number of files is currently open in the

       The getpwuid_r() function may fail if:

       ERANGE Insufficient storage was supplied via buffer and bufsize to
              contain the data to be referenced by the resulting passwd

       The following sections are informative.

EXAMPLES         top

       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 getpwuid_r().

           long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
           size_t len;
           if (initlen == −1)
               /* Default initial length. */
               len = 1024;
               len = (size_t) initlen;
           struct passwd result;
           struct passwd *resultp;
           char *buffer = malloc(len);
           if (buffer == NULL)
               ...handle error...
           int e;
           while ((e = getpwuid_r(42, &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 Root User
       The following example gets the user database entry for the user with
       user ID 0 (root).

           #include <sys/types.h>
           #include <pwd.h>
           uid_t id = 0;
           struct passwd *pwd;

           pwd = getpwuid(id);

   Finding the Name for the Effective User ID
       The following example defines pws as a pointer to a structure of type
       passwd, which is used to store the structure pointer returned by the
       call to the getpwuid() function. The geteuid() function shall return
       the effective user ID of the calling process; this is used as the
       search criteria for the getpwuid() function. The call to getpwuid()
       shall return a pointer to the structure containing that user ID

           #include <unistd.h>
           #include <sys/types.h>
           #include <pwd.h>
           struct passwd *pws;
           pws = getpwuid(geteuid());

   Finding an Entry in the User Database
       The following example uses getpwuid() to search the user database for
       a user ID that was previously stored in a stat structure, then prints
       out the user name if it is found. If the user is not found, the
       program prints the numeric value of the user ID for the entry.

           #include <sys/types.h>
           #include <pwd.h>
           #include <stdio.h>
           struct stat statbuf;
           struct passwd *pwd;
           if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
               printf(" %-8.8s", pwd->pw_name);
               printf(" %-8d", statbuf.st_uid);


       Three names associated with the current process can be determined:
       getpwuid(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 getpwuid_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         top




SEE ALSO         top

       getpwnam(3p), geteuid(3p), getuid(3p), getlogin(3p), sysconf(3p)

       The Base Definitions volume of POSIX.1‐2008, pwd.h(0p),

COPYRIGHT         top

       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 Electrical 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 .

       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 .

IEEE/The Open Group                 2013                        GETPWUID(3P)

Pages that refer to this page: pwd.h(0p)find(1p)endpwent(3p)getlogin(3p)getlogin_r(3p)getpwnam(3p)getpwnam_r(3p)