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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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getpwent_r(3) Library Functions Manual getpwent_r(3)
getpwent_r, fgetpwent_r - get passwd file entry reentrantly
Standard C library (libc, -lc)
#include <pwd.h>
int getpwent_r(size_t size;
struct passwd *restrict pwbuf,
char buf[restrict size], size_t size,
struct passwd **restrict pwbufp);
int fgetpwent_r(size_t size;
FILE *restrict stream, struct passwd *restrict pwbuf,
char buf[restrict size], size_t size,
struct passwd **restrict pwbufp);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getpwent_r(),
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE || _SVID_SOURCE
fgetpwent_r():
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_SVID_SOURCE
The functions getpwent_r() and fgetpwent_r() are the reentrant
versions of getpwent(3) and fgetpwent(3). The former reads the
next passwd entry from the stream initialized by setpwent(3). The
latter reads the next passwd entry from stream.
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 */
};
For more information about the fields of this structure, see
passwd(5).
The nonreentrant functions return a pointer to static storage,
where this static storage contains further pointers to user name,
password, gecos field, home directory and shell. The reentrant
functions described here return all of that in caller-provided
buffers. First of all there is the buffer pwbuf that can hold a
struct passwd. And next the buffer buf of size size that can hold
additional strings. The result of these functions, the
struct passwd read from the stream, is stored in the provided
buffer *pwbuf, and a pointer to this struct passwd is returned in
*pwbufp.
On success, these functions return 0 and *pwbufp is a pointer to
the struct passwd. On error, these functions return an error
value and *pwbufp is NULL.
ENOENT No more entries.
ERANGE Insufficient buffer space supplied. Try again with larger
buffer.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────┬───────────────┬────────────────────────────────┐
│ Interface │ Attribute │ Value │
├───────────────┼───────────────┼────────────────────────────────┤
│ getpwent_r() │ Thread safety │ MT-Unsafe race:pwent locale │
├───────────────┼───────────────┼────────────────────────────────┤
│ fgetpwent_r() │ Thread safety │ MT-Safe │
└───────────────┴───────────────┴────────────────────────────────┘
In the above table, pwent in race:pwent signifies that if any of
the functions setpwent(), getpwent(), endpwent(), or getpwent_r()
are used in parallel in different threads of a program, then data
races could occur.
Other systems use the prototype
struct passwd *
getpwent_r(struct passwd *pwd, char buf[.size], int size);
or, better,
int
getpwent_r(struct passwd *pwd, char buf[.size], int size,
FILE **pw_fp);
None.
These functions are done in a style resembling the POSIX version
of functions like getpwnam_r(3).
The function getpwent_r() is not really reentrant since it shares
the reading position in the stream with all other threads.
#define _GNU_SOURCE
#include <pwd.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#define BUFLEN 4096
int
main(void)
{
struct passwd pw;
struct passwd *pwp;
char buf[BUFLEN];
int i;
setpwent();
while (1) {
i = getpwent_r(&pw, buf, sizeof(buf), &pwp);
if (i)
break;
printf("%s (%jd)\tHOME %s\tSHELL %s\n", pwp->pw_name,
(intmax_t) pwp->pw_uid, pwp->pw_dir, pwp->pw_shell);
}
endpwent();
exit(EXIT_SUCCESS);
}
fgetpwent(3), getpw(3), getpwent(3), getpwnam(3), getpwuid(3),
putpwent(3), passwd(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-06-28 getpwent_r(3)
Pages that refer to this page: fgetpwent(3), getpwent(3), genhomedircon(8)
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HTML rendering created 2025-09-06 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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