The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


getpwuid, getpwuid_r - search user database for a user ID


#include <pwd.h>

struct passwd *getpwuid(uid_t

[TSF] [Option Start] int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
bufsize, struct passwd **result); [Option End]


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

The getpwuid() function need not be reentrant. A function that is not required to be reentrant is not required to 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.

[TSF] [Option Start] 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. The maximum size needed for this buffer can be determined with the {_SC_GETPW_R_SIZE_MAX} sysconf() parameter. A NULL pointer shall be returned at the location pointed to by result on error or if the requested entry is not found. [Option End]


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 return value may point to a static area which is overwritten by a subsequent call to getpwent(), getpwnam(), or getpwuid().

[TSF] [Option Start] If successful, the getpwuid_r() function shall return zero; otherwise, an error number shall be returned to indicate the error. [Option End]


The getpwuid() and getpwuid_r() functions may fail if:

An I/O error has occurred.
A signal was caught during getpwuid().
{OPEN_MAX} file descriptors are currently open in the calling process.
The maximum allowable number of files is currently open in the system.

The getpwuid_r() function may fail if:

[TSF] [Option Start] Insufficient storage was supplied via buffer and bufsize to contain the data to be referenced by the resulting passwd structure. [Option End]

The following sections are informative.


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.






getpwnam(), geteuid(), getuid(), getlogin(), the Base Definitions volume of IEEE Std 1003.1-2001, <limits.h>, <pwd.h>, <sys/types.h>


First released in Issue 1. Derived from System V Release 2.0.

Issue 5

Normative text previously in the APPLICATION USAGE section is moved to the RETURN VALUE section.

The getpwuid_r() function is included for alignment with the POSIX Threads Extension.

A note indicating that the getpwuid() function need not be reentrant is added to the DESCRIPTION.

Issue 6

The getpwuid_r() function is marked as part of the Thread-Safe Functions option.

The Open Group Corrigendum U028/3 is applied, correcting text in the DESCRIPTION describing matching the uid.

In the SYNOPSIS, the optional include of the <sys/types.h> header is removed.

In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a static data area.

IEEE PASC Interpretation 1003.1 #116 is applied, changing the description of the size of the buffer from bufsize characters to bytes.

End of informative text.

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