# getpwuid

## 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



           getpwuid, getpwuid_r — search user database for a user ID
    


## SYNOPSIS



           #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



           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



           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
           error.
    


## ERRORS



           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



           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;
               else
                   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);
               else
                   printf(" %-8d", statbuf.st_uid);
    


## APPLICATION USAGE



           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



           None.
    


## FUTURE DIRECTIONS



           None.
    


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