Provided by: watchdog_5.16-1_amd64 bug


       watchdog - a software watchdog daemon


       watchdog    [-F|--foreground]    [-f|--force]    [-c    filename|--config-file   filename]
       [-v|--verbose] [-s|--sync] [-b|--softboot] [-q|--no-action]


       The Linux kernel can reset the system if serious  problems  are  detected.   This  can  be
       implemented  via  special watchdog hardware, or via a slightly less reliable software-only
       watchdog inside the kernel. Either way, there needs to be a daemon that tells  the  kernel
       the system is working fine. If the daemon stops doing that, the system is reset.

       watchdog is such a daemon. It opens /dev/watchdog, and keeps writing to it often enough to
       keep the kernel from resetting, at least once per minute. Each  write  delays  the  reboot
       time  another  minute.  After  a minute of inactivity the watchdog hardware will cause the
       reset. In the case of the software watchdog the ability to reboot will depend on the state
       of the machines and interrupts.

       The watchdog daemon can be stopped without causing a reboot if the device /dev/watchdog is
       closed correctly, unless your kernel is compiled with the CONFIG_WATCHDOG_NOWAYOUT  option


       The watchdog daemon does several tests to check the system status:

       •  Is the process table full?

       •  Is there enough free memory?

       •  Is there enough allocatable memory?

       •  Are some files accessible?

       •  Have some files changed within a given interval?

       •  Is the average work load too high?

       •  Has a file table overflow occurred?

       •  Is a process still running? The process is specified by a pid file.

       •  Do some IP addresses answer to ping?

       •  Do network interfaces receive traffic?

       •  Is the temperature too high? (Temperature data not always available.)

       •  Execute a user defined command to do arbitrary tests.

       •  Execute  one or more test/repair commands found in /etc/watchdog.d.  These commands are
          called with the argument test or repair.

       If any of these checks fail watchdog will cause a shutdown.  Should  any  of  these  tests
       except  the  user defined binary last longer than one minute the machine will be rebooted,


       Available command line options are the following:

       -v, --verbose
              Set verbose mode. Only implemented if compiled with SYSLOG feature. This mode  will
              log  each  several  infos in LOG_DAEMON with priority LOG_DEBUG.  This is useful if
              you want to see exactly what happened  until  the  watchdog  rebooted  the  system.
              Currently it logs the temperature (if available), the load average, the change date
              of the files it checks and how often it went to sleep. You can use  this  twice  to
              enable some more verbose debug message for testing.

       -s, --sync
              Try  to  synchronize  the filesystem every time the process is awake. Note that the
              system is rebooted if for any reason the synchronizing lasts longer than a minute.

       -b, --softboot
              Soft-boot the system if an error occurs during the main loop, e.g. if a given  file
              is  not  accessible  via  the  stat(2)  call.  Note that this does not apply to the
              opening of /dev/watchdog and /proc/loadavg, which are opened before the  main  loop
              starts. Now this is implemented by disabling the error re-try timer.

       -F, --foreground
              Run in foreground mode, useful for running under systemd (for example).

       -f, --force
              Force  the  usage  of  the  interval given or the maximal load average given in the
              config file. Without this option these values are sanity checked.

       -c config-file, --config-file config-file
              Use   config-file   as   the   configuration   file   instead   of   the    default

       -q, --no-action
              Do  not  reboot  or  halt the machine. This is for testing purposes. All checks are
              executed and the results are logged as usual, but no action is  taken.   Also  your
              hardware  card  or  the  kernel software watchdog driver is not enabled. NOTE: This
              still allows 'repair' actions to run, but the daemon  itself  will  not  attempt  a

       -X num, --loop-exit num
              Run  for  'num' loops then exit as if SIGTERM was received. Intended for test/debug
              (e.g. using valgrind for checking memory access). If the daemon  exits  on  a  loop
              counter and you have the CONFIG_WATCHDOG_NOWAYOUT option compiled for the kernel or
              device-driver then an unplanned reboot will follow - be warned!


       After watchdog starts, it puts itself into  the  background  and  then  tries  all  checks
       specified  in  its configuration file in turn. Between each two tests it will write to the
       kernel device to prevent a reset. After finishing all tests watchdog  goes  to  sleep  for
       some  time.  The  kernel  drivers  expects  a  write  to the watchdog device every minute.
       Otherwise the system will be reset.  watchdog will sleep for  a  configure  interval  that
       defaults to 1 second to make sure it triggers the device early enough.

       Under  high  system  load  watchdog might be swapped out of memory and may fail to make it
       back in in time. Under these circumstances the Linux kernel will  reset  the  machine.  To
       make  sure  you won't get unnecessary reboots make sure you have the variable realtime set
       to yes in the configuration file watchdog.conf.  This adds real time support to  watchdog:
       it  will lock itself into memory and there should  be no problem even under the highest of

       On system running out of memory the kernel will try  to  free  enough  memory  by  killing
       process. The watchdog daemon itself is exempted from this so-called out-of-memory killer.

       Also you can specify a maximal allowed load average. Once this load average is reached the
       system is rebooted. You may specify maximal load averages for 1 minute, 5  minutes  or  15
       minutes.  The default values is to disable this test. Be careful not to set this parameter
       too low. To set a value less then the predefined minimal value of 2, you have to  use  the
       -f option.

       You  can  also  specify  a  minimal amount of virtual memory you want to have available as
       free. As soon as more virtual memory is used action is taken by watchdog.  Note,  however,
       that watchdog does not distinguish between different types of memory usage. It just checks
       for free virtual memory.

       If you have a machine with temperature sensor(s)  you  can  specify  the  maximal  allowed
       temperature. Once this temperature is reached on any sensor the system is powered off. The
       default value is 90 C. Typically the temperature information is provided  by  the  sensors
       package  as  files  in  the  virtual  filesystem  /sys/device  and can be found using, for
       example, the command

           find /sys -name 'temp*input' -print

       These files hold the temperature in milli-Celsius. You can have multiple sensors  used  in
       the  config  file. For example to change to 75C maximum and to check two virtual files for
       the system temperature you might have this:

           max-temperature = 75
           temperature-sensor = /sys/class/hwmon/hwmon0/device/temp1_input
           temperature-sensor = /sys/class/hwmon/hwmon0/device/temp2_input

       The watchdog will issue warnings once the temperature increases 90%, 95% and  98%  of  the
       configured maximum temperature.

       When using file mode watchdog will try to stat(2) the given files. Errors returned by stat
       will not cause a reboot. For a reboot the stat call has to last at least the re-try  time-
       out  value  (default  1 minute).  This may happen if the file is located on an NFS mounted
       filesystem. If your system relies on an NFS mounted filesystem you might try this  option.
       However, in such a case the sync option may not work if the NFS server is not answering.

       watchdog  can  read  the  pid from a pid file and see whether the process still exists. If
       not, action is taken by watchdog.  So you can for instance restart the  server  from  your

       watchdog  will  try  periodically to fork itself to see whether the process table is full.
       This process will leave a zombie process until watchdog wakes up  again  and  catches  it;
       this is harmless, don't worry about it.

       In  ping mode watchdog tries to ping the given IPv4 addresses. These addresses do not have
       to be a single machine. It is possible to ping to a broadcast address instead to see if at
       least one machine in a subnet is still living.

       Do  not  use this broadcast ping unless your MIS person a) knows about it and b) has given
       you explicit permission to use it!

       watchdog will send out three ping packages and wait up to <interval> seconds for the reply
       with  <interval> being the time it goes to sleep between two times triggering the watchdog
       device. Thus a unreachable network will not cause a hard reset but a soft reboot.

       You can also test passively  for  an  unreachable  network  by  just  monitoring  a  given
       interface for traffic. If no traffic arrives the network is considered unreachable causing
       a soft reboot or action from the repair binary.

       watchdog can run an external command for user-defined tests. A return  code  not  equal  0
       means an error occurred and watchdog should react. If the external command is killed by an
       uncaught signal this is considered an error by watchdog too.  The command may take  longer
       than  the  time  slice  defined  for  the  kernel device without a problem. However, error
       messages are generated into the syslog facility. If you have enabled softboot on error the
       machine  will  be  rebooted  if  the  binary doesn't exit in half the time watchdog sleeps
       between two tries triggering the kernel device.

       If you specify a repair binary it will be started instead of shutting down the system.  If
       this binary is not able to fix the problem watchdog will still cause a reboot afterwards.

       If  the  machine  is  halted  an email is sent to notify a human that the machine is going
       down. Starting with version 4.4 watchdog will also notify  the  human  in  charge  if  the
       machine is rebooted.

       The re-try timer applies to most errors, except reset/reboot calls and too hot.  It allows
       a given error source to recover, and treats most tests in this way.  Exceptions  are  file
       handle  test,  load averages, and system memory. If set to the minimum time of 1 second it
       will still allow a single re-try at any polling interval of the system.


       A soft reboot (i.e. controlled shutdown and reboot) is initiated for every error  that  is
       found.  Since there might be no more processes available, watchdog does it all by himself.
       That means:

       1.  Kill all processes with SIGTERM.

       2.  After a short pause kill all remaining processes with SIGKILL.

       3.  Record a shutdown entry in wtmp.

       4.  Save the random seed from /dev/urandom.  If the device is non-existant or there is  no
           filename for saving this step is skipped.

       5.  Turn off accounting.

       6.  Turn off quota and swap.

       7.  Unmount all partitions

       8.  Finally reboot.


       If  the  return  code  of  the  check binary is not zero watchdog will assume an error and
       reboot the system. Be careful with this if you  are  using  the  real-time  properties  of
       watchdog since watchdog will wait for the return of this binary before proceeding. An exit
       code smaller than 245 is interpreted as an system error code (see  errno.h  for  details).
       Values of 245 or larger than are special to watchdog:

       255    (based  on  -1  as unsigned 8-bit number) Reboot the system. This is not exactly an
              error message but a command to watchdog.  If the return code is this  the  watchdog
              will not try to run a shutdown script instead.

       254    Reset  the  system. This is not exactly an error message but a command to watchdog.
              If the return code is this the watchdog will  attempt  to  hard-reset  the  machine
              without  attempting  any  sort  of  orderly stopping of process, unmounting of file
              systems, etc.

       253    Maximum load average exceeded.

       252    The temperature inside is too high.

       251    /proc/loadavg contains no (or not enough) data.

       250    The given file was not changed in the given interval.

       249    /proc/meminfo contains invalid data.

       248    Child process was killed by a signal.

       247    Child process did not return in time.

       246    Free for personal watchdog-specific use (was -10 as an unsigned 8-bit number).

       245    Reserved for an unknown result, for example a slow background test  that  is  still
              running so neither a success nor an error.


       The  repair binary is started with one parameter: the error number that caused watchdog to
       initiate the boot process. After trying to repair the system the binary should exit with 0
       if  the  system  was  successfully  repaired  and thus there is no need to boot anymore. A
       return value not equal 0 tells watchdog to reboot. The return code of  the  repair  binary
       should  be  the error number of the error causing watchdog to reboot. Be careful with this
       if you are using the real-time properties since watchdog will wait for the return of  this
       binary before proceeding.

       The  configuration  file parameter repair-maximum controls the number of successive repair
       attempts that report 0 (i.e. success) but fail to clear  the  tested  fault.  If  this  is
       exceeded  then a reboot takes place. If set to zero then a reboot can always be blocked by
       the repair program reporting success.


       Executables placed in the test directory are discovered by watchdog  on  startup  and  are
       automatically  executed.   They  are  bounded  time-wise  by the test-timeout directive in

       These executables are called with either "test" as the first argument (if a test is  being
       performed)  or  "repair" as the first argument (if a repair for a previously-failed "test"
       operation on is being performed).

       As with test binaries and repair binaries, expected exit codes for a  successful  test  or
       repair operation is always zero.

       If  an executable's test operation fails, the same executable is automatically called with
       the "repair" argument as well as the return code of the previously-failed test operation.

       For example, if the following execution returns 42:

           /etc/watchdog.d/my-test test

       The watchdog daemon will attempt to repair the problem by calling:

           /etc/watchdog.d/my-test repair 42

       This enables administrators and application developers  to  make  intelligent  test/repair
       commands.   If the "repair" operation is not required (or is not likely to succeed), it is
       important that the author of the command return a non-zero value so the machine will still
       reboot as expected.

       Note  that the watchdog daemon may interpret and act upon any of the reserved return codes
       noted in the Check Binary section prior to calling a given command in "repair" mode.

       As for the repair binary, the configuration parameter  repair-maximum  also  controls  the
       number  of successive repair attempts that report success (return 0) but fail to clear the


       None known so far.


       The original code is an example written by Alan Cox <>, the author
       of  the  kernel  driver. All additions were written by Michael Meskes <>.
       Johnie Ingram <> had the idea of testing the load average. He  also  took
       over  the  Debian  specific  work.  Dave  Cinege  <>  brought up some
       hardware watchdog issues and helped testing this stuff.


              The watchdog device.

              The pid file of the running watchdog.