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. If the requested entry was not
       found, errno shall not be changed. 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 getpwuid().  The returned pointer, and
       pointers within the structure, might also be invalidated if the
       calling thread is terminated.

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

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 open.

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

       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 structure.

       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 value.

           #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.1‐2017, pwd.h(0p),

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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               2017                      GETPWUID(3P)

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