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CRON(8)                     System Manager's Manual                    CRON(8)



NAME
       cron - clock daemon

SYNOPSIS
       /usr/etc/cron

DESCRIPTION
       cron  executes commands at specified dates and times.  Regularly sched-
       uled commands can be  specified  according  to  instructions  found  in
       crontab  files  in  the  directory /var/spool/cron/crontabs.  Users can
       submit their own crontab files using the crontab(1) command.   Commands
       that are to be executed only once may be submitted using the at(1) com-
       mand.

       cron only examines crontab files and at command  files  during  process
       initialization  and  when  a  file  changes  using crontab or at.  This
       reduces the overhead of checking for new or changed files at  regularly
       scheduled intervals.

       Since  cron never exits, it should only be executed once.  This is nor-
       mally done by running cron from the initialization process through  the
       file  /etc/rc;  see  init(8).  /var/spool/cron/FIFO is a FIFO file that
       crontab and at use to communicate with cron; it is also used as a  lock
       file to prevent the execution of more than one cron.

FILES
       /var/spool/cron          main cron directory
       /var/spool/cron/FIFO     FIFO for sending messages to cron
       /var/spool/cron/crontabs directory containing crontab files

SEE ALSO
       at(1), crontab(1), sh(1), queuedefs(5), init(8), syslogd(8)

DIAGNOSTICS
       cron  logs  various errors to the system log daemon, syslogd(8), with a
       facility code of cron.  The messages are listed here, grouped by sever-
       ity level.

   Err Severity
       Can't create /var/spool/cron/FIFO: reason
              cron  was  unable  to  start  up  because  it  could  not create
              /var/spool/cron/FIFO.

       Can't access /var/spool/cron/FIFO: reason
              cron was  unable  to  start  up  because  it  could  not  access
              /var/spool/cron/FIFO.

       Can't open /var/spool/cron/FIFO: reason
              cron   was  unable  to  start  up  because  it  could  not  open
              /var/spool/cron/FIFO.

       Can't start cron - another cron may  be  running  (/var/spool/cron/FIFO
       exists)
              cron found that /var/spool/cron/FIFO already existed when it was
              started; this normally means that cron had already been started,
              but it may mean that an earlier cron terminated abnormally with-
              out removing /var/spool/cron/FIFO.

       Can't stat /var/spool/cron/FIFO: reason
              cron could not get the status of /var/spool/cron/FIFO.

       Can't change directory to directory:reason
              cron could not change to directory.

       Can't read directory:reason
              cron could not read directory.

       error reading message: reason
              An error occurred when cron tried to read a control message from
              /var/spool/cron/FIFO.

       message received -- bad format
              A    message    was    successfully    read    by    cron   from
              /var/spool/cron/FIFO, but the message was not of a  form  recog-
              nized by cron.

       SIGTERM
              received  cron  was told to terminate by having a SIGTERM signal
              sent to it.

       cron could not unlink /var/spool/cron/FIFO: reason
              cron was  told  to  terminate,  but  it  was  unable  to  unlink
              /var/spool/cron/FIFO before it terminated.

       ******* CRON ABORTED ********
              cron  terminated,  either due to an error or because it was told
              to.

       Can't open queuedefs file file:reason
              cron could not open a queuedefs file.

       I/O error reading queuedefs file file:reason
              An I/O error occurred while cron was reading a queuedefs file.

       Using default queue definitions
              An error occurred while trying to read  a  queuedefs  file;  the
              default queue definitions will be used.

       Can't allocate numberbytes of space
              An internal error occurred in cron while trying to allocate mem-
              ory.

   Info Severity
       queue queue max run limit reached
              There were more jobs running or to be run  in  the  queue  queue
              than  the maximum number specified.  cron will wait until one of
              the currently-running jobs completes before starting  to  run  a
              new one.

       MAXRUN (25) procs reached
              There were more than 25 jobs running or to be run by cron.  cron
              will wait until one  of  the  currently-running  jobs  completes
              before starting to run a new one.

       *** cron started ***
              cron started running.

       >>  CMD:  pid queue command job
              A  cron  job  was  started, in queue queue, with process ID pid.
              command is the command to be run.  For at or batch jobs, job  is
              the job number.

       >> user pid queue time job
              A  cron  job  was  started  for  user user, in queue queue, with
              process ID pid, at the date and time  time.   For  at  or  batch
              jobs, job is the job number.

       <&lt; user pid queue time job status
              A cron job completed for user user, in queue queue, with process
              ID pid, at the date and time time.  For at or batch jobs, job is
              the  job number.  If the command terminated with a non-zero exit
              status or a signal, status indicates the exit status or signal.

   Notice Severity
       Can't fork
              An attempt to fork (2) to  run  a  new  job  failed;  cron  will
              attempt again after a 30-second delay.

   Warning Severity
       Can't stat queuedefs file file:reason
              cron  could  not  get the status of a queuedefs file in order to
              determine whether it has  changed.   cron  will  assume  it  has
              changed and will reread it.



                                6 December 1988                        CRON(8)