CODEWITHSUNDEEP
cunix
Ricenwind
Ricenwind

Reputation: 3

How to print groups of all local users?

I want to print all groups of users stored in /etc/passwd. Seems easy enough, I can just use getpwent() and getgrouplist(). I came with this code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <pwd.h>
#include <unistd.h>
#include <grp.h>

int main(int argc, char** argv){

    struct passwd* user;
    int nGroups = 20;
    gid_t* groups;
    groups = malloc(nGroups * sizeof(gid_t));
    struct group* gr;
    while(user = getpwent()){
        printf("%s : ", user->pw_name);
        getgrouplist(user->pw_name, user->pw_gid, groups, &nGroups);
        int i;
        for(i = 0; i < nGroups; ++i){
            gr = getgrgid(groups[i]);
            if(gr){
                printf("%s ", gr->gr_name);
            }  
        }
        printf("\n");
    }

    free(groups);
    return 0;
}

It gives me this output:

root : root 
daemon : daemon 
bin : bin 
.
.
.
pulse : pulse root 
ricenwind : ricenwind adm root root root root root root 
vboxadd : daemon

which is clearly wrong, as for example using

groups ricenwind

gives me:

ricenwind : ricenwind adm cdrom sudo dip plugdev lpadmin sambashare

Upvotes: 0

Views: 1024

Answers (2)

Naveen Dharman
Naveen Dharman

Reputation: 1

You can achieve this using a simple bash script as

!/bin/bash

grep "/bin/bash" /etc/passwd

it would do the result,bcoz all the local user will have /bin/bash or /bin/sh as their shell

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409166

If you read the getgrouplist manual page you will see

Up to *ngroups of these groups are returned in the array groups.

The ngroups argument is not only set by the function, it's also used by the function to know how many structures you have allocated for the groups argument.

You need to "reset" the nGroups variable before calling getgrouplist, otherwise the old value set by the previous call to the function will be used:

nGroups = 20;
getgrouplist(user->pw_name, user->pw_gid, groups, &nGroups);

Upvotes: 1

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