.\" Copyright (c) 2004 Poul-Henning Kamp .\" Copyright (c) 2003, 2004 Sean M. Kelly .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd January 2, 2018 .Dt WATCHDOG 4 .Os .Sh NAME .Nm watchdog .Nd "hardware and software watchdog" .Sh SYNOPSIS .In sys/watchdog.h .Sh DESCRIPTION The .Nm facility is used for controlling hardware and software watchdogs. .Pp The device .Pa /dev/fido supports several optional .Xr ioctl 2 calls for configuration, and responds to a single operational .Xr ioctl 2 call, .Dv WDIOCPATPAT . It takes a single argument which represents a timeout value specified as a power of two nanoseconds, or-ed with a flag selecting active or passive control of the watchdog. .Pp .Dv WD_ACTIVE indicates that the .Nm will be kept from timing out from userland, for instance by the .Xr watchdogd 8 daemon. .Dv WD_PASSIVE indicates that the .Nm will be kept from timing out from the kernel. .Pp The .Dv WDIOCPATPAT .Xr ioctl 2 call will return success if just one of the available .Xr watchdog 9 implementations supports setting the timeout to the specified timeout. This means that at least one watchdog is armed. By default, this will be a hardware watchdog if one is present, but if no hardware watchdog is able to process the request, a default software watchdog is enabled. If the call fails, for instance if none of .Xr watchdog 9 implementations support the timeout length, all watchdogs are disabled and must be explicitly re-enabled. .Pp To disable the watchdogs pass .Dv WD_TO_NEVER . If disarming the watchdog(s) failed an error is returned. The watchdog might still be armed! .Pp The optional configuration .Xr ioctl 2 commands are listed here, along with the type of the parameter used. Examples of their use can be found in .Xr watchdogd 8 . .Bl -tag -width "WDIOC_SETSOFTTIMEOUTACT int " .It Dv WDIOC_SETTIMEOUT Fa int set/reset the timer .It Dv WDIOC_GETTIMEOUT Fa int get total timeout .It Dv WDIOC_GETTIMELEFT Fa int get time left .It Dv WDIOC_GETPRETIMEOUT Fa int get the pre-timeout .It Dv WDIOC_SETPRETIMEOUT Fa int set the pre-timeout .It Dv WDIOC_SETPRETIMEOUTACT Fa int Set the action when a pre-timeout occurs (see .Li WD_SOFT_* below). .It Dv WDIOC_SETSOFT Fa int Use an internal software watchdog instead of hardware. There is also an external software watchdog, which is used by default if no hardware watchdog was attached. .It Dv WDIOC_SETSOFTTIMEOUTACT Fa int Set the action whan a soft timeout occurs. .El .Pp The actions that may be specified for the pre-timeout or the internal software watchdog are listed here. Multiple actions can be specified by ORing values together. .Bl -tag -width WD_SOFT_PRINT .It Dv WD_SOFT_PANIC panic .It Dv WD_SOFT_DDB enter debugger .It Dv WD_SOFT_LOG log(9) .It Dv WD_SOFT_PRINT printf(9) .El .Sh RETURN VALUES The .Dv WDIOCPATPAT .Xr ioctl 2 returns zero on success and non-zero on failure. .Bl -tag -width Er .It Bq Er EOPNOTSUPP No watchdog present in the kernel or none of the watchdogs supports the requested timeout value (timeout value other than 0). .It Bq Er EOPNOTSUPP Watchdog could not be disabled (timeout value of 0). .It Bq Er EINVAL Invalid flag combination passed. .El .Pp The configuration .Xr ioctl 2 operations return zero on success and non-zero on failure. .Sh EXAMPLES .Bd -literal -offset indent #include #include #define WDPATH "/dev/" _PATH_WATCHDOG int wdfd = -1; static void wd_init(void) { wdfd = open(WDPATH, O_RDWR); if (wdfd == -1) err(1, WDPATH); } static void wd_reset(u_int timeout) { if (ioctl(wdfd, WDIOCPATPAT, &timeout) == -1) err(1, "WDIOCPATPAT"); } /* in main() */ wd_init(); wd_reset(WD_ACTIVE|WD_TO_8SEC); /* potential freeze point */ wd_reset(WD_TO_NEVER); .Ed .Pp Enables a watchdog to recover from a potentially freezing piece of code. .Pp .Dl "options SW_WATCHDOG" .Pp in your kernel config forces a software watchdog in the kernel to be configured even if a hardware watchdog is configured, dropping to KDB or panicking when firing, depending on the KDB and KDB_UNATTENDED kernel configuration options. .Sh SEE ALSO .Xr watchdogd 8 , .Xr watchdog 9 .Sh HISTORY The .Nm code first appeared in .Fx 5.1 . .Sh AUTHORS .An -nosplit The .Nm facility was written by .An Poul-Henning Kamp Aq Mt phk@FreeBSD.org . The software watchdog code and this manual page were written by .An Sean Kelly Aq Mt smkelly@FreeBSD.org . Some contributions were made by .An Jeff Roberson Aq Mt jeff@FreeBSD.org . .Sh BUGS The .Dv WD_PASSIVE option has not yet been implemented.