Programming Forums > Application Development > C

MegaArcon · Mar 29th, 2006, 2:27 PM

Hi all,

I was wondering if anybody out there could tell me how to change a user id. I'm writing a c wrapper for a java program. Since java does not seem to have any way to do a change uid, I figured I'd write a c wrapper to call the program and use c to do a change uid. However, I don't know how....I just heard that it could be done.

Thanks for any and all help

OpenLoop · Mar 29th, 2006, 2:32 PM

and user id is ???

nnxion · Mar 29th, 2006, 2:54 PM

So you are root? I'm pretty sure it can't be done when you're not root. I'm not sure if you can when you are.

@OpenLoop: it's a *nix thing, the system can tell who is logged on by the userid (often shortened to UID, like Process ID is shortened to PID).

MegaArcon · Mar 29th, 2006, 3:15 PM

I could be root if it was required. Basically, the user would log in to a web interface and ask to do an operation. The web server is run by a different user (apache). So, before I get the server to call the operation, I wanted to change the user id to the logged in user and then change back to apache after it was complete.

However, should root be required, I do have a module that can run a process as root. So, I could get that process to run my c program which will change to the given uid and then change back.

nnxion · Mar 29th, 2006, 4:29 PM

http://www.hmug.org/man/2/setuid.php

Go down on that page, so you can read the "standards" section.

Check your system's man pages on setuid though for more information.

MegaArcon · Mar 30th, 2006, 7:49 AM

Cool, thanks. I'll play around with that and come back if I need further help. ^_^

jim mcnamara · Mar 30th, 2006, 11:15 AM

setuid() and setgid() are what you're looking for.

"setuid" programs require great care in coding to be secure. Since you didn't know what setuid was, I'd be inclined to think that you need to do a lot reading. setuid on net-exposed systems is a security risk.

Mar 29th, 2006, 2:27 PM	#1
MegaArcon Programmer Join Date: Aug 2005 Posts: 66 Rep Power: 0	changing a user id. Hi all, I was wondering if anybody out there could tell me how to change a user id. I'm writing a c wrapper for a java program. Since java does not seem to have any way to do a change uid, I figured I'd write a c wrapper to call the program and use c to do a change uid. However, I don't know how....I just heard that it could be done. Thanks for any and all help __________________ Isn't that just the way life goes? If it's worth doing, it's NP-Hard. Todd Wareham - Memorial University of Newfoundland

Mar 29th, 2006, 2:54 PM	#3
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	So you are root? I'm pretty sure it can't be done when you're not root. I'm not sure if you can when you are. @OpenLoop: it's a *nix thing, the system can tell who is logged on by the userid (often shortened to UID, like Process ID is shortened to PID). __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

Mar 29th, 2006, 3:15 PM	#4
MegaArcon Programmer Join Date: Aug 2005 Posts: 66 Rep Power: 0	I could be root if it was required. Basically, the user would log in to a web interface and ask to do an operation. The web server is run by a different user (apache). So, before I get the server to call the operation, I wanted to change the user id to the logged in user and then change back to apache after it was complete. However, should root be required, I do have a module that can run a process as root. So, I could get that process to run my c program which will change to the given uid and then change back. __________________ Isn't that just the way life goes? If it's worth doing, it's NP-Hard. Todd Wareham - Memorial University of Newfoundland

Mar 29th, 2006, 4:29 PM	#5
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	http://www.hmug.org/man/2/setuid.php Go down on that page, so you can read the "standards" section. Check your system's man pages on setuid though for more information. __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

Mar 30th, 2006, 7:49 AM	#6
MegaArcon Programmer Join Date: Aug 2005 Posts: 66 Rep Power: 0	Cool, thanks. I'll play around with that and come back if I need further help. ^_^ __________________ Isn't that just the way life goes? If it's worth doing, it's NP-Hard. Todd Wareham - Memorial University of Newfoundland

Mar 29th, 2006, 2:32 PM	#2
OpenLoop Expert Programmer Join Date: May 2005 Location: East Lansing, MI Posts: 663 Rep Power: 4	and user id is ???

Mar 30th, 2006, 11:15 AM	#7
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	setuid() and setgid() are what you're looking for. "setuid" programs require great care in coding to be secure. Since you didn't know what setuid was, I'd be inclined to think that you need to do a lot reading. setuid on net-exposed systems is a security risk.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Programming Forums > Application Development > C

changing a user id.