How can i call a function which is usually used by root?

[wk]

I want write a c program.And a common user(not in root group) will run this program.
In this program,I call fread(/dev/sdc...) and fwrite(/dev/sdc),but this call will return "permission no allow".If I use the root user,will be ok.
How to change to the authority to root's?

I know the  root's password.

[Andreas Waldenburger]

On Tue, 2 Dec 2008 17:20:43 +0800 "wk"  wrote:
> I want write a c program.And a common user(not in root group) will
> run this program. In this program,I call fread(/dev/sdc...) and
> fwrite(/dev/sdc),but this call will return "permission no allow".

Why do you work with the devices? Can't you just operate on the
directories where those drives are mounted?

And if you absolutely have to use the device files, then you could
always change their permissions. Not that that's recommended, just
saying.

regards,
/W

[Paul Black]

2008/12/2 Wildemar Wildenburger wrote:
> And if you absolutely have to use the device files, then you could
> always change their permissions. Not that that's recommended, just
> saying.

Changing permissions is not wise as it allows a user to bypass filesystem
permissions.

A possibility is for the OP to read up on setuid and setgid; that offers the
potential to restrict a user to what a program will allow rather than
allowing unfettered access to a device (assuming no security holes in the
application).

[Paul W. Frields]

On Tue, Dec 02, 2008 at 01:53:56PM +0000, Paul Black wrote:
> 2008/12/2 Wildemar Wildenburger wrote:
> > And if you absolutely have to use the device files, then you could
> > always change their permissions. Not that that's recommended, just
> > saying.
>
> Changing permissions is not wise as it allows a user to bypass filesystem
> permissions.
>
> A possibility is for the OP to read up on setuid and setgid; that offers the
> potential to restrict a user to what a program will allow rather than
> allowing unfettered access to a device (assuming no security holes in the
> application).

I think most programmers tend to make it the user's prerogative to run
the program using 'sudo' or 'su -c' to inherit the proper privileges.
In other words, the permission error you're getting is something
normal users should expect when they try to run against a device to
which they don't have access.  Elevating their privilege automatically
inside a program is generally frowned upon.

[bruce]

hi...

check out how to handle/setup a superuser group (sudo) which allows a normal
user to assume the role/privs of the root/superuser for a specifically
defined task.

should handle your issue, if i understand what you're attempting. there
should be examples on the 'net as well..

-----Original Message-----
From: [e-mail]
[mailto:[e-mail]]On Behalf Of wk
Sent: Tuesday, December 02, 2008 1:21 AM
To: fedora-list
Subject: How can i call a function which is usually used by root?

I want write a c program.And a common user(not in root group) will run this
program.
In this program,I call fread(/dev/sdc...) and fwrite(/dev/sdc),but this call
will return "permission no allow".If I use the root user,will be ok.
How to change to the authority to root's?

I know the  root's password.

[Fred Silsbee]

--- On Tue, 12/2/08, bruce  wrote:
> From: bruce 
> Subject: RE: How can i call  a function which is usually used by root?
> To: "'Community assistance, encouragement, and advice for using Fedora.'" 
> Date: Tuesday, December 2, 2008, 4:04 PM
> hi...
>
> check out how to handle/setup a superuser group (sudo)
> which allows a normal
> user to assume the role/privs of the root/superuser for a
> specifically
> defined task.
>
> should handle your issue, if i understand what you're
> attempting. there
> should be examples on the 'net as well..
>
> -----Original Message-----
> From: [e-mail]
> [mailto:[e-mail]]On Behalf Of wk
> Sent: Tuesday, December 02, 2008 1:21 AM
> To: fedora-list
> Subject: How can i call a function which is usually used by
> root?
>
> I want write a c program.And a common user(not in root
> group) will run this
> program.
> In this program,I call fread(/dev/sdc...) and
> fwrite(/dev/sdc),but this call
> will return "permission no allow".If I use the
> root user,will be ok.
> How to change to the authority to root's?
>
> I know the  root's password.
>
> -- 
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study the following... s bit is what you want:

consider the function passwd...allows the user to alter a file owned by root

How does one set the sticky bit and set UID bits with chmod?

octal digit>      1            2           3           4 
     octal value

4             set UID         r           r           r

2             set GID         w           w           w

1             sticky bit      x           x           x

r   read 
w   write 
x   execute 
s   set UID or set GID 
t   set sticky bit

chmod u+st  filename 
chmod -R does down the tree