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Manual page for CRON(8)

cron - clock daemon

SYNOPSIS

/usr/etc/cron

DESCRIPTION

cron executes commands at specified dates and times. Regularly scheduled 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 command.

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 normally 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 severity 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 without 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 recognized 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 memory.

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.
< 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.


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Created by unroff & hp-tools. © by Hans-Peter Bischof. All Rights Reserved (1997).

Last modified 21/April/97