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GETPWUID(3P) POSIX Programmer's Manual GETPWUID(3P)
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.
getpwuid, getpwuid_r — search user database for a user ID
#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);
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.
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
getpwuid().
If successful, the getpwuid_r() function shall return zero;
otherwise, an error number shall be returned to indicate the error.
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.
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);
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.
None.
None.
getpwnam(3p), geteuid(3p), getuid(3p), getlogin(3p), sysconf(3p)
The Base Definitions volume of POSIX.1‐2008, pwd.h(0p),
sys_types.h(0p)
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 http://www.unix.org/online.html .
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 GETPWUID(3P)
Pages that refer to this page: pwd.h(0p), find(1p), endpwent(3p), getlogin(3p), getpwnam(3p)