man getpwuid () - search user database for a user ID

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 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.

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.

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. 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().

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

ERRORS

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

EIO
An I/O error has occurred.
EINTR
A signal was caught during getpwuid().
EMFILE
{OPEN_MAX} file descriptors are currently open in the calling process.
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

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.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

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

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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
http://www.opengroup.org/unix/online.html .