On unix.. Know if the user is in a specific system group ?

[Benoit Lefebvre]

I'm doing a program that needs to know if the user is in a specific
group in the system.

How do I do it ? :-)

I'm desesperate and I'm starting to think about executing a shell
command to find the answer.

Anyone ever made that ? I can't find anything when searching with
google.

Thanks,
--Ben

[Walter Roberson]

In article <11**********************@o80g2000hse.googlegroups .com>,
Benoit Lefebvre <be*************@gmail.comwrote:

>I'm doing a program that needs to know if the user is in a specific
group in the system.

>How do I do it ? :-)

>I'm desesperate and I'm starting to think about executing a shell
command to find the answer.

Try comp.unix.programmer (who might perhaps refer you to getgroups())
--
Is there any thing whereof it may be said, See, this is new? It hath
been already of old time, which was before us. -- Ecclesiastes

[Rob Hoelz]

ro******@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote:

In article <11**********************@o80g2000hse.googlegroups .com>,
Benoit Lefebvre <be*************@gmail.comwrote:

I'm doing a program that needs to know if the user is in a specific
group in the system.

How do I do it ? :-)

I'm desesperate and I'm starting to think about executing a shell
command to find the answer.

Try comp.unix.programmer (who might perhaps refer you to getgroups())

getgroups() isn't POSIX standard *I think*; it's a convenience function
provided by a lot of unixes. I think what you want is getgrnam
or getgrgid, depending on if you're specifying group name or ID.

[Robert Gamble]

On Sep 6, 12:50 pm, Rob Hoelz <[e-mail]:

[e-mail] (Walter Roberson) wrote:

In article <[e-mail] .com>,
Benoit Lefebvre <[e-mail]:

>I'm doing a program that needs to know if the user is in a specific
>group in the system.

>How do I do it ? :-)

>I'm desesperate and I'm starting to think about executing a shell
>command to find the answer.

Try comp.unix.programmer (who might perhaps refer you to getgroups())

getgroups() isn't POSIX standard *I think*; it's a convenience function
provided by a lot of unixes.

getgroups() is POSIX, setgroups() is not.

Robert Gamble

[Benoit Lefebvre]

On Sep 6, 12:50 pm, Rob Hoelz <[e-mail]:

[e-mail] (Walter Roberson) wrote:

In article <[e-mail] .com>,
Benoit Lefebvre <[e-mail]:

>I'm doing a program that needs to know if the user is in a specific
>group in the system.

>How do I do it ? :-)

>I'm desesperate and I'm starting to think about executing a shell
>command to find the answer.

Try comp.unix.programmer (who might perhaps refer you to getgroups())

getgroups() isn't POSIX standard *I think*; it's a convenience function
provided by a lot of unixes. I think what you want is getgrnam
or getgrgid, depending on if you're specifying group name or ID.

Thanks, you aligned me in the right direction with getgrnam

I started with these sources :
http://samba.org/ftp/tridge/nsswitch-tests/getgrnam.c

And here is what I came up with:

It's checking if the user that runs the script from sudo is in the
tempsa group or not.
Because the environment variable "SUDO_USER" is generated by sudo just
before running this command, I know I can trust it.
This program will only be run directly from SUDO from some users

--8<----------------------------------------
struct group *gr;
int nolog;

gr = getgrnam("tempsa");

nolog = 1;
if (gr->gr_mem != NULL) {
int i =0;
while(gr->gr_mem[i] != NULL) {
if (!strcmp(gr->gr_mem[i],getenv("SUDO_USER"))) {
nolog = 0;
}
i++;
}
}
--------------------------------------------

thanks,
--Ben

[Walter Roberson]

In article <11*********************@y42g2000hsy.googlegroups. com>,
Benoit Lefebvre <be*************@gmail.comwrote:

>And here is what I came up with:

>It's checking if the user that runs the script from sudo is in the
tempsa group or not.
Because the environment variable "SUDO_USER" is generated by sudo just
before running this command, I know I can trust it.
This program will only be run directly from SUDO from some users

And will you enforce that, by ensuring that the binary will
be inaccessible to anyone who hasn't already sudo'd to the proper
group? And if it -is- inaccessible to all but the proper people,
then why bother checking the group??

struct group *gr;
int nolog;

gr = getgrnam("tempsa");

nolog = 1;
if (gr->gr_mem != NULL) {
int i =0;
while(gr->gr_mem[i] != NULL) {
if (!strcmp(gr->gr_mem[i],getenv("SUDO_USER"))) {
nolog = 0;
}
i++;
}
}

Once you have found a nolog condition, what is the point
in continuing in the loop? If you used

while(nolog && gr->gr_mem[i] != NULL)

then you would not bother with the test if you've already passed;
or, better yet, use a break; after the nolog = 0;
--
Is there any thing whereof it may be said, See, this is new? It hath
been already of old time, which was before us. -- Ecclesiastes

[Keith Thompson]

Rob Hoelz <ho***@wisc.eduwrites:

ro******@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote:

>In article <11**********************@o80g2000hse.googlegroups .com>,
Benoit Lefebvre <be*************@gmail.comwrote:

>I'm doing a program that needs to know if the user is in a specific
group in the system.

>How do I do it ? :-)

>I'm desesperate and I'm starting to think about executing a shell
command to find the answer.

Try comp.unix.programmer (who might perhaps refer you to getgroups())

getgroups() isn't POSIX standard *I think*; it's a convenience function
provided by a lot of unixes. I think what you want is getgrnam
or getgrgid, depending on if you're specifying group name or ID.

This kind of speculation is exactly why comp.unix.programmer is a
better place to discuss this. The experts over there are much more
likely to know the answer -- and if they don't, the other experts will
quickly correct them.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Mark McIntyre]

On Thu, 06 Sep 2007 08:43:59 -0700, in comp.lang.c , Benoit Lefebvre
<be*************@gmail.comwrote:

>I'm doing a program that needs to know if the user is in a specific
group in the system.

How do I do it ? :-)

grep /etc/group username

>Anyone ever made that ? I can't find anything when searching with
google.

comp.unix.progammer maybe?
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

[Keith Thompson]

Mark McIntyre <ma**********@spamcop.netwrites:

On Thu, 06 Sep 2007 08:43:59 -0700, in comp.lang.c , Benoit Lefebvre
<be*************@gmail.comwrote:

>>I'm doing a program that needs to know if the user is in a specific
group in the system.

How do I do it ? :-)

grep /etc/group username

Nope.

>>Anyone ever made that ? I can't find anything when searching with
google.

comp.unix.progammer maybe?

Yup.

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

[Al Balmer]

On Fri, 07 Sep 2007 00:28:50 +0100, Mark McIntyre
<ma**********@spamcop.netwrote:

>On Thu, 06 Sep 2007 08:43:59 -0700, in comp.lang.c , Benoit Lefebvre
<be*************@gmail.comwrote:

>>I'm doing a program that needs to know if the user is in a specific
group in the system.

How do I do it ? :-)

grep /etc/group username

grep: can't open username

(works better t'other way round.:)

>

>>Anyone ever made that ? I can't find anything when searching with
google.

comp.unix.progammer maybe?

Yes.

--
Al Balmer
Sun City, AZ