getpwent_r - Linux

Overview

getpwent_r is a C library function that retrieves the next password entry from the system password file /etc/passwd. It is typically used to iterate through all user accounts on the system.

Syntax

int getpwent_r(struct passwd *result, struct passwd *buffer, char *buf, size_t bufsize, struct passwd **resultp);

Options/Flags

None

Examples

Simple example

#include <pwd.h>
int main() {
    struct passwd *pw;
    while ((pw = getpwent_r())) {
        printf("Username: %s, UID: %d\n", pw->pw_name, pw->pw_uid);
    }
    endpwent();
    return 0;
}

Complex example

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

int main() {
    struct passwd *pw;
    struct passwd *pw_result;
    char buffer[512];

    while ((pw = getpwent_r(pw_result, buffer, sizeof(buffer), &pw_result))) {
        printf("Username: %s, UID: %d\n", pw->pw_name, pw->pw_uid);
    }
    endpwent();
    return 0;
}

Common Issues

• Result buffer too small: If the buffer passed to getpwent_r is too small to hold the next password entry, the function will return NULL and set errno to ERANGE.
• Password file not accessible: If the system password file /etc/passwd is not accessible, getpwent_r will return NULL and set errno to EACCES.

Integration

getpwent_r can be combined with other Linux commands and tools to gather information about user accounts. For example:

getpwent_r | grep "username"

This command will print information about users whose username matches "username".

Related Commands

• getpwuid_r: Get password entry by user ID
• getpwnam_r: Get password entry by username