reboot Linux box from user space

Question

I need to reboot a Linux box from a user space process. I want to have the following behavior:

1. sync file systems
2. not attempt to gracefully stop processes, go to runlevel 5/6, etc., for I assume things are bad and that would fail

Can those requirements be achieved together at all?

I was planning to write a 'b' into proc/sysrq-trigger. Is there a better way? (No, that won't give me sync.)

Thanks!

Answer 1

I'm assuming you have root.

• the sysrq-trigger thing is fine, you just have to echo 's' a couple times into it first, which is an "Emergency Sync".
• You can also check out the '-n' option to shutdown(8). That's a canned way to do what you want. It just sends SIGTERM, SIGKILL, syncs and shuts down or reboots (-h or -r option.)

Hope that helps.

Answer 2

Well, do sync(1), kill -1, sync again, kill -9 -1, sync, poweroff -f.

That should do the trick, I guess!

Answer 3

This directly from sys/reboot.h :

#ifndef _SYS_REBOOT_H
#define _SYS_REBOOT_H   1

#include <features.h>

/* Perform a hard reset now.  */
#define RB_AUTOBOOT     0x01234567

/* Halt the system.  */
#define RB_HALT_SYSTEM  0xcdef0123

/* Enable reboot using Ctrl-Alt-Delete keystroke.  */
#define RB_ENABLE_CAD   0x89abcdef

/* Disable reboot using Ctrl-Alt-Delete keystroke.  */
#define RB_DISABLE_CAD  0

/* Stop system and switch power off if possible.  */
#define RB_POWER_OFF    0x4321fedc

__BEGIN_DECLS

/* Reboot or halt the system.  */
extern int reboot (int __howto) __THROW;

__END_DECLS

#endif  /* _SYS_REBOOT_H */

I believe RB_HALT_SYSTEM will handle all sync()s , etc. I usually do that myself, and finally trigger the reboot with RB_AUTOBOOT.

Answer 4

On an ordinary distro, the simplest way to do this is:

system("/sbin/reboot -f");

This will sync all filesystems, then reboot immediately. Note that sysrq b will NOT sync.