Forcing an immediate reboot

Forcing an immediate reboot

[Marc Perkel]

Is there any way to force an immediate reboot as if to push the reset 
button in software? Got a remote server that i need to reboot and 
shutdown isn't working.

Re: Forcing an immediate reboot

[Lee Revell]

On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
> Is there any way to force an immediate reboot as if to push the reset 
> button in software? Got a remote server that i need to reboot and 
> shutdown isn't working.

If it has Oopsed, and the "reboot" command does not work, then all bets
are off - kernel memory has probably been corrupted.

Get one of those powerstrips that you can telnet into and power cycle
things remotely.

Lee

Re: Forcing an immediate reboot

[Randy.Dunlap]

On Fri, 14 Oct 2005 18:46:46 -0700 Marc Perkel wrote:

> Is there any way to force an immediate reboot as if to push the reset 
> button in software? Got a remote server that i need to reboot and 
> shutdown isn't working.

What kernel version?
Does it have sysrq enabled?

If 2.6.x and Yes, then you should be able to do:
  echo b > /proc/sysrq-trigger

to cause a reboot.

---
~Randy

Re: Forcing an immediate reboot

[Danny ter Haar]

Marc Perkel  <marc@perkel.com> wrote:
>Is there any way to force an immediate reboot as if to push the reset 
>button in software? Got a remote server that i need to reboot and 
>shutdown isn't working.

reboot -nf

Doesn't sync
just plain reboot


Danny

Re: Forcing an immediate reboot

[Willy Tarreau]

On Fri, Oct 14, 2005 at 06:46:46PM -0700, Marc Perkel wrote:
> Is there any way to force an immediate reboot as if to push the reset 
> button in software? Got a remote server that i need to reboot and 
> shutdown isn't working.

If you can telnet it, simply use this :

# echo 1 >/proc/sys/kernel/sysrq
# echo b >/proc/sysrq-trigger

It's dirty and you'll have an fsck. But it will nearly always work.
I use it a lot in local on distros on which the shutdown process is
as long as the boot process (you know, the ones which display lots
of 'OK' or wait indefinitely for some dead services to stop, when
you really want them to reboot quickly).

Cheers,
Willy

Re: Forcing an immediate reboot

[Coywolf Qi Hunt]

On 10/15/05, Lee Revell <rlrevell@joe-job.com> wrote:
> On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
> > Is there any way to force an immediate reboot as if to push the reset
> > button in software? Got a remote server that i need to reboot and
> > shutdown isn't working.
>
> If it has Oopsed, and the "reboot" command does not work, then all bets
> are off - kernel memory has probably been corrupted.
>
> Get one of those powerstrips that you can telnet into and power cycle
> things remotely.
>

use reboot on panic.
--
Coywolf Qi Hunt
http://sosdg.org/~coywolf/

Re: Forcing an immediate reboot

[Coywolf Qi Hunt]

On 10/15/05, Willy Tarreau <willy@w.ods.org> wrote:
> On Fri, Oct 14, 2005 at 06:46:46PM -0700, Marc Perkel wrote:
> > Is there any way to force an immediate reboot as if to push the reset
> > button in software? Got a remote server that i need to reboot and
> > shutdown isn't working.
>
> If you can telnet it, simply use this :
>
> # echo 1 >/proc/sys/kernel/sysrq
> # echo b >/proc/sysrq-trigger
>
> It's dirty and you'll have an fsck. But it will nearly always work.

You may avoid the fsck by:

# echo s >/proc/sysrq-trigger
# echo u >/proc/sysrq-trigger

> I use it a lot in local on distros on which the shutdown process is
> as long as the boot process (you know, the ones which display lots
> of 'OK' or wait indefinitely for some dead services to stop, when
> you really want them to reboot quickly).
--
Coywolf Qi Hunt
http://sosdg.org/~coywolf/

Re: Forcing an immediate reboot

[Marc Perkel]

Coywolf Qi Hunt wrote:

>On 10/15/05, Lee Revell <rlrevell@joe-job.com> wrote:
>  
>
>>On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
>>    
>>
>>>Is there any way to force an immediate reboot as if to push the reset
>>>button in software? Got a remote server that i need to reboot and
>>>shutdown isn't working.
>>>      
>>>
>>If it has Oopsed, and the "reboot" command does not work, then all bets
>>are off - kernel memory has probably been corrupted.
>>
>>Get one of those powerstrips that you can telnet into and power cycle
>>things remotely.
>>
>>    
>>
>
>use reboot on panic.
>  
>

But it didn't panic. It was still running - filtering spam. But reboot 
wouldn't work and I couldn't kill anything that was running. So it never 
paniced.

Re: Forcing an immediate reboot

[Anton Altaparmakov]

On Fri, 14 Oct 2005, Lee Revell wrote:
> On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
> > Is there any way to force an immediate reboot as if to push the reset 
> > button in software? Got a remote server that i need to reboot and 
> > shutdown isn't working.
> 
> If it has Oopsed, and the "reboot" command does not work, then all bets
> are off - kernel memory has probably been corrupted.
> 
> Get one of those powerstrips that you can telnet into and power cycle
> things remotely.

If it has sysrq compiled in as root just do:

echo s > /proc/sysrq-trigger
echo u > /proc/sysre-trigger
echo s > /proc/sysrq-trigger
echo b > /proc/sysrq-trigger

This will "sync", "umount/remount read-only", "sync", "immediate hardware 
reboot".  Should always work...

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/

Re: Forcing an immediate reboot

[Coywolf Qi Hunt]

On 10/15/05, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
> On Fri, 14 Oct 2005, Lee Revell wrote:
> > On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
> > > Is there any way to force an immediate reboot as if to push the reset
> > > button in software? Got a remote server that i need to reboot and
> > > shutdown isn't working.
> >
> > If it has Oopsed, and the "reboot" command does not work, then all bets
> > are off - kernel memory has probably been corrupted.
> >
> > Get one of those powerstrips that you can telnet into and power cycle
> > things remotely.
>
> If it has sysrq compiled in as root just do:
>
> echo s > /proc/sysrq-trigger
> echo u > /proc/sysre-trigger
> echo s > /proc/sysrq-trigger

What the purpose of the second sync?

> echo b > /proc/sysrq-trigger
>
> This will "sync", "umount/remount read-only", "sync", "immediate hardware
> reboot".  Should always work...
--
Coywolf Qi Hunt
http://sosdg.org/~coywolf/

Re: Forcing an immediate reboot

[Anton Altaparmakov]

On Sat, 15 Oct 2005, Coywolf Qi Hunt wrote:
> On 10/15/05, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
> > On Fri, 14 Oct 2005, Lee Revell wrote:
> > > On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
> > > > Is there any way to force an immediate reboot as if to push the reset
> > > > button in software? Got a remote server that i need to reboot and
> > > > shutdown isn't working.
> > >
> > > If it has Oopsed, and the "reboot" command does not work, then all bets
> > > are off - kernel memory has probably been corrupted.
> > >
> > > Get one of those powerstrips that you can telnet into and power cycle
> > > things remotely.
> >
> > If it has sysrq compiled in as root just do:
> >
> > echo s > /proc/sysrq-trigger
> > echo u > /proc/sysre-trigger
> > echo s > /proc/sysrq-trigger
> 
> What the purpose of the second sync?

Allows any i/o initiated between the first sync and the remount r/o to 
complete.  Remember that r/o mounting doesn't stop i/o.  It only stops you 
from writing to the fs at the vfs layer.  Once a write/modification has 
entered the fs driver it will get written no matter what, unless the 
"reboot" sysrq is triggered in which case the kernel just reboots 
immediately.

Maybe it is just paranoia on my part but I have gotten used to hitting 
Alt+PrtScr+S, +U, +S, +B so I do it automatically.

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/

Re: Forcing an immediate reboot

[Denis Vlasenko]

[-- Attachment #1: Type: text/plain, Size: 244 bytes --]

On Saturday 15 October 2005 04:46, Marc Perkel wrote:
> Is there any way to force an immediate reboot as if to push the reset 
> button in software? Got a remote server that i need to reboot and 
> shutdown isn't working.

See atttached
--
vda

[-- Attachment #2: hardshutdown.c --]
[-- Type: text/x-csrc, Size: 2608 bytes --]

/* Including <unistd.h> makes sure that on a glibc system
   <features.h> is included, which again defines __GLIBC__ */

#include <unistd.h>
#include <stdio.h>	/* puts */
#include <time.h>	/* nanosleep */
#include <errno.h>

#include "linux_reboot.h" /* reboot magic */

#define USE_LIBC

#ifdef USE_LIBC

/* libc version */
#if defined __GLIBC__ && __GLIBC__ >= 2
#  include <sys/reboot.h>
#  define REBOOT(cmd) reboot(cmd)
#else
extern int reboot(int, int, int);
#  define REBOOT(cmd) reboot(LINUX_REBOOT_MAGIC1,LINUX_REBOOT_MAGIC2,(cmd))
#endif

int my_reboot(int cmd) {
	return REBOOT(cmd);
}

#else /* no USE_LIBC */

/* direct syscall version */
#include <linux/unistd.h>

#ifdef _syscall3
_syscall3(int,  reboot,  int,  magic, int, magic_too, int, cmd);
#else
/* Let us hope we have a 3-argument reboot here */
extern int reboot(int, int, int);
#endif

int my_reboot(int cmd) {
	return reboot(LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, cmd);
}

#endif


void do_reboot() {
	my_reboot(LINUX_REBOOT_CMD_RESTART);
}

void do_poweroff() {
	my_reboot(LINUX_REBOOT_CMD_POWER_OFF);
}

void do_halt() {
	my_reboot(LINUX_REBOOT_CMD_HALT);
}

void usage() {
	puts(
	    "Usage: hardshutdown -h|-r|-p [NN]\n"
	    "	NN - seconds to sleep before requested action"
	);
	exit(1);
}

enum action_t {
	SHUTDOWN,	// do nothing
	HALT,
	POWEROFF,
	REBOOT
};

int main(int argc, char *argv[]) {
	struct timespec t = {0,0};
	enum action_t action = SHUTDOWN;
	int c, i;
	char *prog, *ptr;

	//if(*argv[0] == '-') argv[0]++;	/* allow shutdown as login shell */
	prog = argv[0];
	if( (ptr=strrchr(prog,'/')) != 0 ) prog = ptr+1;

	/* All names (halt, reboot, shutdown)
	   refer to the same program with the same options,
	   only the defaults differ. */
	if(!strcmp("hardhalt", prog)) {
		action = HALT;
	} else if(!strcmp("hardpoweroff", prog)) {
		action = POWEROFF;
	} else if(!strcmp("hardreboot", prog)) {
		action = REBOOT;
	}
		
	for(c=1; c < argc; c++) {
		if(argv[c][0] >= '0' && argv[c][0] <= '9') {
			t.tv_sec = strtol(argv[c], NULL, 10);
			continue;
		}
		if(argv[c][0] != '-') {
			usage();
			return 1;
		}
		for(i=1; argv[c][i]; i++) {
			switch(argv[c][i]) {
			case 'h': 
				action = HALT;
				break;
			case 'p':
				action = POWEROFF;
				break;
			case 'r':
				action = REBOOT;
				break;
			default:
				usage();
				return 1;
			}
		}
	}

	if(action==SHUTDOWN) {
		usage();
		return 1;
	}

	chdir("/");
	while(nanosleep(&t,&t)<0)
		if(errno!=EINTR) break;

	switch(action) {
	case HALT:
		do_halt(); break;
	case POWEROFF:
		do_poweroff(); break;
	case REBOOT:
		do_reboot(); break;
	}
	return 1;
}

[-- Attachment #3: linux_reboot.h --]
[-- Type: text/x-objchdr, Size: 932 bytes --]

/*
 * Magic values required to use _reboot() system call.
 */

#define	LINUX_REBOOT_MAGIC1	0xfee1dead
#define	LINUX_REBOOT_MAGIC2	672274793
#define	LINUX_REBOOT_MAGIC2A	85072278
#define	LINUX_REBOOT_MAGIC2B	369367448


/*
 * Commands accepted by the _reboot() system call.
 *
 * RESTART     Restart system using default command and mode.
 * HALT        Stop OS and give system control to ROM monitor, if any.
 * CAD_ON      Ctrl-Alt-Del sequence causes RESTART command.
 * CAD_OFF     Ctrl-Alt-Del sequence sends SIGINT to init task.
 * POWER_OFF   Stop OS and remove all power from system, if possible.
 * RESTART2    Restart system using given command string.
 */

#define	LINUX_REBOOT_CMD_RESTART	0x01234567
#define	LINUX_REBOOT_CMD_HALT		0xCDEF0123
#define	LINUX_REBOOT_CMD_CAD_ON		0x89ABCDEF
#define	LINUX_REBOOT_CMD_CAD_OFF	0x00000000
#define	LINUX_REBOOT_CMD_POWER_OFF	0x4321FEDC
#define	LINUX_REBOOT_CMD_RESTART2	0xA1B2C3D4

[-- Attachment #4: mkdiet.sh --]
[-- Type: application/x-shellscript, Size: 72 bytes --]

documentation? (i learned something today ;-) )

[Damir Perisa]

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hi all,

Le Saturday 15 October 2005 09:48, Anton Altaparmakov a écrit :
 | If it has sysrq compiled in as root just do:
 |
 | echo s > /proc/sysrq-trigger
 | echo u > /proc/sysre-trigger
 | echo s > /proc/sysrq-trigger
 | echo b > /proc/sysrq-trigger
 |
 | This will "sync", "umount/remount read-only", "sync", "immediate
 | hardware reboot".  Should always work...

i'm impressed that i see that sysrq also works from procfs.... the 
"PrintScreen/SysRq" button on my keyboard from time to time does not work 
(old keyboard) and then it's pain hitting this key if you have to. 

great news that you can also pass sysrq requests using proc - i've learned 
something today... is this documented somewhere? maybe i'm bad in 
reading/finding docs but i think i'm not the only one here. can somebody 
point me to the links of docs where all this magic is specified? if not, 
i will try to start my own docs on how to use the linux kernel magic. 
mainly a collection of tricks like this and similar ones. 

thank you in advance + greetings,
Damir

-- 
  Customer: (angrily) "You said I would get 98 windows with this computer. 
Where are they?" 

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Re: documentation? (i learned something today ;-) )

[Benoit Boissinot]

On 10/15/05, Damir Perisa <damir.perisa@solnet.ch> wrote:
> hi all,
>
> Le Saturday 15 October 2005 09:48, Anton Altaparmakov a écrit:
>  | If it has sysrq compiled in as root just do:
>  |
>  | echo s > /proc/sysrq-trigger
>  | echo u > /proc/sysre-trigger
>  | echo s > /proc/sysrq-trigger
>  | echo b > /proc/sysrq-trigger
>  |
>  | This will "sync", "umount/remount read-only", "sync", "immediate
>  | hardware reboot". Should always work...
>
> i'm impressed that i see that sysrq also works from procfs.... the
> "PrintScreen/SysRq" button on my keyboard from time to time does not work
> (old keyboard) and then it's pain hitting this key if you have to.
>
> great news that you can also pass sysrq requests using proc - i've learned
> something today... is this documented somewhere? maybe i'm bad in
> reading/finding docs but i think i'm not the only one here. can somebody
> point me to the links of docs where all this magic is specified? if not,
> i will try to start my own docs on how to use the linux kernel magic.
> mainly a collection of tricks like this and similar ones.
>
> thank you in advance + greetings,
> Damir

it is mentionned in Documentation/sysrq.txt

On all -  write a character to /proc/sysrq-trigger.  eg:

                echo t > /proc/sysrq-trigger

regards,

Benoit

Re: Forcing an immediate reboot

[Marc Perkel]

Anton Altaparmakov wrote:

>On Fri, 14 Oct 2005, Lee Revell wrote:
>  
>
>>On Fri, 2005-10-14 at 18:46 -0700, Marc Perkel wrote:
>>    
>>
>>>Is there any way to force an immediate reboot as if to push the reset 
>>>button in software? Got a remote server that i need to reboot and 
>>>shutdown isn't working.
>>>      
>>>
>>If it has Oopsed, and the "reboot" command does not work, then all bets
>>are off - kernel memory has probably been corrupted.
>>
>>Get one of those powerstrips that you can telnet into and power cycle
>>things remotely.
>>    
>>
>
>If it has sysrq compiled in as root just do:
>
>echo s > /proc/sysrq-trigger
>echo u > /proc/sysre-trigger
>echo s > /proc/sysrq-trigger
>echo b > /proc/sysrq-trigger
>
>This will "sync", "umount/remount read-only", "sync", "immediate hardware 
>reboot".  Should always work...
>
>
>  
>
This worked great. If I had this last night it would probably have saved 
me a trip to San Jose. I especially like that it does the file system 
syncs. I've put it in a script I call "coldboot" and it is now one of my 
tools.

Very useful.

Documentation/files somewhere online?

[Damir Perisa]

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thank you for the quick reply, Benoit,

Le Saturday 15 October 2005 15:40, Benoit Boissinot a écrit :
 | On 10/15/05, Damir Perisa <damir.perisa@solnet.ch> wrote:
 | > Le Saturday 15 October 2005 09:48, Anton Altaparmakov a écrit:
 | >  | echo s > /proc/sysrq-trigger
 | > i'm impressed that i see that sysrq also works from procfs.... 
 |
 | it is mentionned in Documentation/sysrq.txt
 
oh ... i definitely have to read the Documentation/files more often for 
updates... last time i did, i didn't remember seeing proc magic in this 
one. 

is somebody keeping a online version of the kernel source docs (i mean the 
Documentation/* files) somewhere for surfing? i want to point people to 
pages with links without forcing them to download the sources to read 
what i tell them to.

often i'm asked questions about linux in general. an updated docs pages on 
the net would be helpful. of course if it does not exist, i can create 
one, but why re-inventing the wheel if it is easier to give credits to 
the first person who invented it and use it? ;-)

thanx + greetings,
Damir

-- 
The bureaucracy is expanding to meet the needs of an expanding 
bureaucracy.

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Re: Documentation/files somewhere online?

[Denis Vlasenko]

On Saturday 15 October 2005 17:52, Damir Perisa wrote:
> thank you for the quick reply, Benoit,
> 
> Le Saturday 15 October 2005 15:40, Benoit Boissinot a écrit :
>  | On 10/15/05, Damir Perisa <damir.perisa@solnet.ch> wrote:
>  | > Le Saturday 15 October 2005 09:48, Anton Altaparmakov a écrit:
>  | >  | echo s > /proc/sysrq-trigger
>  | > i'm impressed that i see that sysrq also works from procfs.... 
>  |
>  | it is mentionned in Documentation/sysrq.txt
>  
> oh ... i definitely have to read the Documentation/files more often for 
> updates... last time i did, i didn't remember seeing proc magic in this 
> one. 
> 
> is somebody keeping a online version of the kernel source docs (i mean the 
> Documentation/* files) somewhere for surfing? i want to point people to 
> pages with links without forcing them to download the sources to read 
> what i tell them to.

http://lxr.linux.no/source/Documentation/

> often i'm asked questions about linux in general. an updated docs pages on 
> the net would be helpful. of course if it does not exist, i can create 
> one, but why re-inventing the wheel if it is easier to give credits to 
> the first person who invented it and use it? ;-)
--
vda

Re: Documentation/files somewhere online?

[Michael Krufky]

Denis Vlasenko wrote:

>On Saturday 15 October 2005 17:52, Damir Perisa wrote:
>  
>
>>is somebody keeping a online version of the kernel source docs (i mean the 
>>Documentation/* files) somewhere for surfing? i want to point people to 
>>pages with links without forcing them to download the sources to read 
>>what i tell them to.
>>    
>>
>http://lxr.linux.no/source/Documentation/
>  
>
I think that using the -git web interface to Linus' tree on kernel.org 
is even better.

The following is a link to the top-level of the kernel source tree:

http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=tree

You will notice a Documentation tree link (3rd file object link from the 
top).

This will get you the most current Documentation at the moment from 
Linus' tree, and it also gives you the ability to see the history of 
changes.

Hope this helps.

-- 
Michael Krufky

Documentation/files online: available at git in webinterface

[Damir Perisa]

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Le Saturday 15 October 2005 17:13, Michael Krufky a écrit :
 | I think that using the -git web interface to Linus' tree on kernel.org
 | is even better.
 
great idea...

 | The following is a link to the top-level of the kernel source tree:
 |
 | 
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=tree
 
i totally forgot that git has a webinterface. how very useful! :D

 | Hope this helps.

it is even better: it's the solution. thank you!

greetings,
Damir

-- 
Everything bows to success, even grammar.

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Re: Forcing an immediate reboot

[Petr Vandrovec]

Anton Altaparmakov wrote:
> On Sat, 15 Oct 2005, Coywolf Qi Hunt wrote:
> 
>>On 10/15/05, Anton Altaparmakov <aia21@cam.ac.uk> wrote:
>>
>>>echo s > /proc/sysrq-trigger
>>>echo u > /proc/sysre-trigger
>>>echo s > /proc/sysrq-trigger
>>
>>What the purpose of the second sync?
> 
> 
> Allows any i/o initiated between the first sync and the remount r/o to 
> complete.  Remember that r/o mounting doesn't stop i/o.  It only stops you 
> from writing to the fs at the vfs layer.  Once a write/modification has 
> entered the fs driver it will get written no matter what, unless the 
> "reboot" sysrq is triggered in which case the kernel just reboots 
> immediately.
> 
> Maybe it is just paranoia on my part but I have gotten used to hitting 
> Alt+PrtScr+S, +U, +S, +B so I do it automatically.

Second sync is a must, otherwise remounting read-only is not written to 
the filesystem (at least in my case) so no fsck is saved.   But you can 
save first sync (before remount), and then you get nice sequence which 
even admins comming from Windows can remember - they have to use USB to 
safely reboot their Linux systems ;-)  (alt-sysrq-U, S, B)
								Petr