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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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GETPWNAM(3P) POSIX Programmer's Manual GETPWNAM(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.
getpwnam, getpwnam_r — search user database for a name
#include <pwd.h>
struct passwd *getpwnam(const char *name);
int getpwnam_r(const char *name, struct passwd *pwd, char *buffer,
size_t bufsize, struct passwd **result);
The getpwnam() function shall search the user database for an
entry with a matching name.
The getpwnam() function need not be thread-safe.
Applications wishing to check for error situations should set
errno to 0 before calling getpwnam(). If getpwnam() returns a
null pointer and errno is non-zero, an error occurred.
The getpwnam_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 name. 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 getpwnam() 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.
The getpwnam_r() function shall return zero on success or if the
requested entry was not found and no error has occurred. If an
error has occurred, 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 getpwnam().
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 getpwnam_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 getpwnam_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 = getpwnam_r("someuser", &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 Login Name
The following example uses the getlogin() function to return the
name of the user who logged in; this information is passed to the
getpwnam() function to get the user database entry for that user.
#include <sys/types.h>
#include <pwd.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
...
char *lgn;
struct passwd *pw;
...
if ((lgn = getlogin()) == NULL || (pw = getpwnam(lgn)) == NULL) {
fprintf(stderr, "Get of user information failed.\n"); exit(1);
}
...
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 getpwnam_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.
getpwuid(3p), sysconf(3p)
The Base Definitions volume of POSIX.1‐2017, pwd.h(0p),
sys_types.h(0p)
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 http://www.opengroup.org/unix/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 2017 GETPWNAM(3P)
Pages that refer to this page: pwd.h(0p), endpwent(3p), getlogin(3p), getpwuid(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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