Checking username: getpwnam / getpwnam_r: No such file or directory - c

Question

I'm trying to make a web logging and I use getpwnam() function to check username existing. But for valid username getpwnam returns error: No such file or directory. So I tried getpwnam_r(), but it also failed with the same error. I'm running on embedded arm linux and I use /etc/passwd for password storing (I don't have /etc/shadow). My test program is:
#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);
}
Password file can be written only by root:
/ # ls -l /etc/passwd
-rw-r--r-- 1 root root 207 Jan 1 00:29 /etc/passwd
/ #
I also tried to run my program (test) with root rights, but it also failed when I gave it an existing username.
/ # /tmp/test admin
getpwnam_r: No such file or directory
/ #
1) So, what I forgot about, or what should do additionally?
2) Do I need to use /etc/shadow file for storing passwords for system users?
Update:
My passwd file is:
~ # cat /etc/passwd
root:b6MVch7fPLasN:0:0:root:/home/root:/bin/ash
admin:8Mt/Jtxcyg8AY:1000:1000:admin:/tmp:/tmp/cli
user:5v4HoPrA9NtUo:1001:1000:user:/tmp:/tmp/cli
~ #
Thanks in advance! Bakir

Answer 1

1) The search service or method used in the password database (/etc/passwd) is defined in /etc/nsswitch.conf. To use this service getpwnam function calls shared library in the lib directory: /lib/libnss_SERVICE.so.x, where SERVICE is the search method. In my case compat is default method because of absent of /etc/nsswitch.conf. So, I was need to add libnss_compat.so.2 to /lib.
strace is useful thing!
Many thanks to osqx and alk!