Quick question, linux programming

Quick and stupid question but I don't really know where to begin to search for this...

In linux, what function should I use to convert a uid to a user name, or a user name to a uid for comparason purposes?


Hopefully some of you linux gurus can help me out here :D

In what language are you thinking ?

Or do you mean the command line..
In that case

Code:

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id -u username

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gives you the uid of a user.
I don't know if there is an easy way to get a username for an id.. but

Code:

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grep :uid: /etc/passwd | cut -d ":" -f 1

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should do the trick

sorry i should have specified...

I'm editing the debian pmount utility to work with gentoo, hal, and gvm, instead of using fstab-sync which is unsafe and just didn't work period for me, and want to allow users in the plugdev group to unmount devices. So far I can get the gid of the mounting user through /etc/mtab, and can get a vector of user names in that group through getgrgid(). I would like to check to see if the calling user (getuid()) is in the group that mounted the volume to allow that user to unmount it.

is there a way to use either method in c, or preferrebly a function that i can call to get either an id or a user name?

upon further googling, getpwnam() looks promising, i'll get back to you if it works

Thanks!

Hi

You almost found the correct function. I just did an illustration:

Code:

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

int main(int argv, char *argc[]){
    struct passwd *pw;
    uid_t uid;

    pw=getpwnam(argc[1]);
    if (pw)        // assuming it is a username
                printf("%s found %d:%d\n",argc[1],pw->pw_uid,pw->pw_gid);
    else{        // trying ID
        uid=atoi(argc[1]);
        pw=getpwuid(uid);
        if (pw)        // assuming it is a uid
                printf("%s found %d:%d\n",pw->pw_name,pw->pw_uid,pw->pw_gid);
    }
   
    return 0;
}

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Start the above little program with either a username or the uid.
Of course, you simple can modify it using uid=getuid();

Cheers.

Thanks a bunch sec_ware that did the trick :D