GETPWNAM


HOME

GETPWNAM

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
FILES
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO
COLOPHON

NAME

getpwnam, getpwnam_r, getpwuid, getpwuid_r − get password file entry

SYNOPSIS

#include <sys/types.h>
#include <pwd.h>

struct passwd *getpwnam(const char *name);

struct passwd *getpwuid(uid_t uid);

int getpwnam_r(const char *name, struct passwd *pwd,
char *
buf, size_t buflen, struct passwd **result);

int getpwuid_r(uid_t uid, struct passwd *pwd,
char *
buf, size_t buflen, struct passwd **result);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getpwnam_r(), getpwuid_r():

_POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE || _POSIX_SOURCE

DESCRIPTION

The getpwnam() function returns a pointer to a structure containing the broken-out fields of the record in the password database (e.g., the local password file /etc/passwd, NIS, and LDAP) that matches the username name.

The getpwuid() function returns a pointer to a structure containing the broken-out fields of the record in the password database that matches the user ID uid.

The passwd structure is defined in <pwd.h> as follows:

struct passwd {
char *pw_name; /* username */
char *pw_passwd; /* user password */
uid_t pw_uid; /* user ID */
gid_t pw_gid; /* group ID */
char *pw_gecos; /* user information */
char *pw_dir; /* home directory */
char *pw_shell; /* shell program */
};

See passwd(5) for more information about these fields.

The getpwnam_r() and getpwuid_r() functions obtain the same information as getpwnam() and getpwuid(), but store the retrieved passwd structure in the space pointed to by pwd. The string fields pointed to by the members of the passwd structure are stored in the buffer buf of size buflen. A pointer to the result (in case of success) or NULL (in case no entry was found or an error occurred) is stored in *result.

The call

sysconf(_SC_GETPW_R_SIZE_MAX)

returns either −1, without changing errno, or an initial suggested size for buf. (If this size is too small, the call fails with ERANGE, in which case the caller can retry with a larger buffer.)

RETURN VALUE

The getpwnam() and getpwuid() functions return a pointer to a passwd structure, or NULL if the matching entry is not found or an error occurs. If an error occurs, errno is set appropriately. If one wants to check errno after the call, it should be set to zero before the call.

The return value may point to a static area, and may be overwritten by subsequent calls to getpwent(3), getpwnam(), or getpwuid(). (Do not pass the returned pointer to free(3).)

On success, getpwnam_r() and getpwuid_r() return zero, and set *result to pwd. If no matching password record was found, these functions return 0 and store NULL in *result. In case of error, an error number is returned, and NULL is stored in *result.

ERRORS

0 or ENOENT or ESRCH or EBADF or EPERM or ...

The given name or uid was not found.

EINTR

A signal was caught.

EIO

I/O error.

EMFILE

The maximum number (OPEN_MAX) of files was open already in the calling process.

ENFILE

The maximum number of files was open already in the system.

ENOMEM

Insufficient memory to allocate passwd structure.

ERANGE

Insufficient buffer space supplied.

FILES

/etc/passwd

local password database file

ATTRIBUTES

Multithreading (see pthreads(7))
The getpwnam() and getpwuid() functions are not thread-safe.

The getpwnam_r() and getpwuid_r() functions are thread-safe.

CONFORMING TO

SVr4, 4.3BSD, POSIX.1-2001. The pw_gecos field is not specified in POSIX, but is present on most implementations.

NOTES

The formulation given above under "RETURN VALUE" is from POSIX.1-2001. It does not call "not found" an error, and hence does not specify what value errno might have in this situation. But that makes it impossible to recognize errors. One might argue that according to POSIX errno should be left unchanged if an entry is not found. Experiments on various UNIX-like systems show that lots of different values occur in this situation: 0, ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM, and probably others.

The pw_dir field contains the name of the initial working directory of the user. Login programs use the value of this field to initialize the HOME environment variable for the login shell. An application that wants to determine its user’s home directory should inspect the value of HOME (rather than the value getpwuid(getuid())−>pw_dir) since this allows the user to modify their notion of "the home directory" during a login session. To determine the (initial) home directory of another user, it is necessary to use getpwnam("username")−>pw_dir or similar.

EXAMPLE

The program below demonstrates the use of getpwnam_r() to find the full username and user ID for the username supplied as a command-line argument.

#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

int
main(int argc, char *argv[])
{
struct passwd pwd;
struct passwd *result;
char *buf;
size_t bufsize;
int s;

if (argc != 2) {
fprintf(stderr, "Usage: %s username\n", argv[0]);
exit(EXIT_FAILURE);
}

bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
if (bufsize == −1) /* Value was indeterminate */
bufsize = 16384; /* Should be more than enough */

buf = malloc(bufsize);
if (buf == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}

s = getpwnam_r(argv[1], &pwd, buf, bufsize, &result);
if (result == NULL) {
if (s == 0)
printf("Not found\n");
else {
errno = s;
perror("getpwnam_r");
}
exit(EXIT_FAILURE);
}

printf("Name: %s; UID: %ld\n", pwd.pw_gecos, (long) pwd.pw_uid);
exit(EXIT_SUCCESS);
}

SEE ALSO

endpwent(3), fgetpwent(3), getgrnam(3), getpw(3), getpwent(3), getspnam(3), putpwent(3), setpwent(3), passwd(5)

COLOPHON

This page is part of release 3.69 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man−pages/.







Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.





Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.


Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.





Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.


Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.





Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.


Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.