How to restart Linux from inside a C++ program?

Question

I have a Qt 4 GUI where I need to have a option in a drop-down menu that allows the user to choose to restart the computer. I realize this might seem redunant with the ability to restart the computer in other ways, but the choice needs to stay there. I've tried using system() to call the following:

1. a suid-root shell script
2. a non-suid shell script
3. a suid-root binary program

and all of them just cause

reboot: must be superuser

to be printed. Using system() to call reboot directly does the same thing. I'm not especially attached to using system() to do this, but it seemed like the most direct choice.

How can I reboot the system from the GUI?

Gizmo

printf("Please push the reset button now"); – Scheldt

Have you tried running it as a superuser? – Escaut

There are lots of ways to do this in Windows, but most are not intentional – Levan

blogs.msdn.com/oldnewthing/archive/2010/03/24/9983984.aspx – Glandulous

This can be done within KDE apps. For instance, both KGet and KTorrent can told to turn off your computer when they've finished downloading. But I don't know if what they use to do that is KDE-specific or whether you can do it Qt without the KDE stuff. – Rodrigues

FYI, Linux ignores the suid bit on scripts, since there is a serious security problem with allowing suid scripts. See section 5.5.3 here: docstore.mik.ua/orelly/networking/puis/ch05_05.htm – Guyette

Answer 1

The reboot function is described in the Linux Programmer's Manual. Under glibc, you can pass the RB_AUTOBOOT macro constant to perform the reboot.

Note that if reboot is not preceded by a call to sync, data may be lost.

Using glibc in Linux:

#include <unistd.h>
#include <sys/reboot.h>

sync();
reboot(RB_AUTOBOOT);

Rickets

Answer 2

In Linux:

#define LINUX_REBOOT_CMD_POWER_OFF 0x4321fedc   

sync();
reboot(LINUX_REBOOT_CMD_POWER_OFF);

Dyeline

If you're using the glibc version, #include <sys/reboot.h> should be included in the above code... if so, just use the #define RB_POWER_OFF in that header file... – Pinprick

Answer 3

Have you tried running a shell script, using gksudo? Something like

gksudo shutdown -r

With any luck, that should pull up a modal dialogue to get user credentials.

Shul

Well, you don't really need to run it as a shell script, just execv it, or if you really want the PATH functionality that comes along with shell scripts, execvp. – Petromilli

Answer 4

This should do it on almost any linux system.

#include <unistd.h>
#include <sys/reboot.h>

int main () {
  sync();
  setuid(0);
  reboot(RB_AUTOBOOT);
  return(0);
}

Then just compile with gcc reboot.c -o reboot and do chmod a+s reboot on the binary. Then call reboot as any user and the system should reboot smoothly. The way you do this through your GUI varies, as in if your Desktop Environment was KDE for example, it's quite different than doing the same thing under Fluxbox.

Kelda

Answer 5

suid-ing shell scripts is just dangerous as already mentioned (which is why that didn't work).

I suspect that suid-ing the binary doesn't work because system spawns its subprocess with the user's actual uid and not the suid one, again for security reasons (it would let you substitute any binary for the one being called and run it as root).

You could put a copy of reboot in a location protected such that only users you want have permission to can execute it, and then suid-root THAT.

Alternately give them sudoer privilege to execute JUST the command you care about and system out to something like "ksh -c 'sudo reboot'"

Stephie

Answer 6

In binary try to call

setuid (0);

before system() call.

Meghannmegiddo

Thanks for the suggestion, but this didn't work when the program was called from another program. It does work if a program is called directly from the command line though. – Gizmo

Answer 7

how would you reboot the system from the command line on your system?

basically do

system( <however you wouuld do it from the command line> );

Chemosynthesis

Thanks for the suggestion, but that's what we've tried, and it doesn't work. – Gizmo