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comp.lang.ruby

Super User Can't Change UID?

James Gray

1/27/2009 11:12:00 PM

Why would the super user not be able to switch UID's?

$ sudo ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
Password:
-e:1:in `uid=': Operation not permitted (Errno::EPERM)
from -e:1

Tips of TFM I should go R are welcome. :)

James Edward Gray II
13 Answers

Michel Boaventura

1/27/2009 11:22:00 PM

0

This works on my gentoo without any problem. Try to became root and
try to run to see if it's another problem.

2009/1/27 James Gray <james@grayproductions.net>:
> Why would the super user not be able to switch UID's?
>
> $ sudo ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
> Password:
> -e:1:in `uid=': Operation not permitted (Errno::EPERM)
> from -e:1
>
> Tips of TFM I should go R are welcome. :)
>
> James Edward Gray II
>
>
>

James Gray

1/27/2009 11:26:00 PM

0

On Jan 27, 2009, at 5:21 PM, Michel Boaventura wrote:

> This works on my gentoo without any problem. Try to became root and
> try to run to see if it's another problem.

It doesn't seem to work for me that way either:

$ sudo sh
Password:
sh-3.2# ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
-e:1:in `uid=': Operation not permitted (Errno::EPERM)
from -e:1

James Edward Gray II

James Gray

1/28/2009 12:42:00 AM

0

On Jan 27, 2009, at 5:11 PM, James Gray wrote:

> Why would the super user not be able to switch UID's?
>
> $ sudo ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
> Password:
> -e:1:in `uid=': Operation not permitted (Errno::EPERM)
> from -e:1

Another data point on this odd issue: Apple's bundled Ruby (I'm on OS
X) works:

$ sudo /usr/bin/ruby -r etc -e 'Process.uid =
Etc.getpwnam("james").uid'
Password:
$

It's just the Ruby I built that fails. How could I have messed this
up in the build?

James Edward Gray II

Rob Biedenharn

1/28/2009 12:46:00 AM

0

On Jan 27, 2009, at 6:26 PM, James Gray wrote:

> On Jan 27, 2009, at 5:21 PM, Michel Boaventura wrote:
>
>> This works on my gentoo without any problem. Try to became root and
>> try to run to see if it's another problem.
>
> It doesn't seem to work for me that way either:
>
> $ sudo sh
> Password:
> sh-3.2# ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
> -e:1:in `uid=': Operation not permitted (Errno::EPERM)
> from -e:1
>
> James Edward Gray II
>


It works for me on Ubuntu and Mac OS X also.

-Rob

Rob Biedenharn http://agileconsult...
Rob@AgileConsultingLLC.com

James Gray

1/28/2009 2:35:00 AM

0

On Jan 27, 2009, at 6:45 PM, Rob Biedenharn wrote:

> It works for me on Ubuntu and Mac OS X also.

Were you using Apple's bundled Ruby or something you compiled?

James Edward Gray II

Rob Biedenharn

1/28/2009 3:00:00 AM

0

On Jan 27, 2009, at 9:34 PM, James Gray wrote:

> On Jan 27, 2009, at 6:45 PM, Rob Biedenharn wrote:
>
>> It works for me on Ubuntu and Mac OS X also.
>
> Were you using Apple's bundled Ruby or something you compiled?
>
> James Edward Gray II


Apple's /usr/bin/ruby. (I'd answered before I saw your
clarification.) I also just ran it fine with macruby.

$ sudo macruby -r etc -e 'puts Process.pid,Process.uid; sleep 2;puts
"now"; Process.uid = Etc.getpwnam("rab").uid; puts Process.uid; sleep 2'
Password:
26951
0
now
501

I don't suppose that really helps you much.

-Rob

Rob Biedenharn http://agileconsult...
Rob@AgileConsultingLLC.com

James Gray

1/28/2009 3:06:00 AM

0

On Jan 27, 2009, at 9:00 PM, Rob Biedenharn wrote:

> On Jan 27, 2009, at 9:34 PM, James Gray wrote:
>
>> On Jan 27, 2009, at 6:45 PM, Rob Biedenharn wrote:
>>
>>> It works for me on Ubuntu and Mac OS X also.
>>
>> Were you using Apple's bundled Ruby or something you compiled?
>>
>> James Edward Gray II
>
> Apple's /usr/bin/ruby. (I'd answered before I saw your
> clarification.) I also just ran it fine with macruby.

It also seems to work in my locally compiled 1.9:

$ sudo ruby_dev -r etc -ve 'Process.uid = Etc.getpwnam("james").uid'
Password:
ruby 1.9.1 (2008-12-30 patchlevel-0 revision 21203) [i386-
darwin9.6.0]

James Edward Gray II

Ezra Zygmuntowicz

1/28/2009 4:16:00 AM

0


On Jan 27, 2009, at 7:06 PM, James Gray wrote:

> On Jan 27, 2009, at 9:00 PM, Rob Biedenharn wrote:
>
>> On Jan 27, 2009, at 9:34 PM, James Gray wrote:
>>
>>> On Jan 27, 2009, at 6:45 PM, Rob Biedenharn wrote:
>>>
>>>> It works for me on Ubuntu and Mac OS X also.
>>>
>>> Were you using Apple's bundled Ruby or something you compiled?
>>>
>>> James Edward Gray II
>>
>> Apple's /usr/bin/ruby. (I'd answered before I saw your
>> clarification.) I also just ran it fine with macruby.
>
> It also seems to work in my locally compiled 1.9:
>
> $ sudo ruby_dev -r etc -ve 'Process.uid = Etc.getpwnam("james").uid'
> Password:
> ruby 1.9.1 (2008-12-30 patchlevel-0 revision 21203) [i386-
> darwin9.6.0]
>
> James Edward Gray II
>

It fails for me on my self compiled ruby 1.8.6 on osx but the built
in ruby and my gentoo ruby works fine. No clue why.

-Ezra

Daniel Berger

1/28/2009 5:18:00 AM

0

James Gray wrote:
> Why would the super user not be able to switch UID's?
>
> $ sudo ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
> Password:
> -e:1:in `uid=': Operation not permitted (Errno::EPERM)
> from -e:1
>
> Tips of TFM I should go R are welcome. :)

I seem to recall that setreuid() is busted on OS X, 10.4.x anyway. I
think it's fixed in 10.5, but I can't confirm.

I know this has come up before. Check the the ruby-core archives.

Regards,

Dan

Daniel Berger

1/28/2009 2:01:00 PM

0

James Gray wrote:
> On Jan 27, 2009, at 5:11 PM, James Gray wrote:
>
>> Why would the super user not be able to switch UID's?
>>
>> $ sudo ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
>> Password:
>> -e:1:in `uid=': Operation not permitted (Errno::EPERM)
>> from -e:1
>
> Another data point on this odd issue: Apple's bundled Ruby (I'm on OS
> X) works:
>
> $ sudo /usr/bin/ruby -r etc -e 'Process.uid = Etc.getpwnam("james").uid'
> Password:
> $
>
> It's just the Ruby I built that fails. How could I have messed this up
> in the build?

Are you on 10.4.x?

If I had to guess, I'd bet Apple replaced setreuid() with seteuid(), but
that's a guess.

I've never really understood the way OS X manages users. My own account
is not in /etc/passwd, but shows up in NetInfo.

Regards,

Dan