166 lines
4.6 KiB
Groff
166 lines
4.6 KiB
Groff
|
.TH CRON 8
|
||
|
|
.SH NAME
|
||
|
|
cron \- clock daemon
|
||
|
|
.SH SYNOPSIS
|
||
|
|
.B cron
|
||
|
|
.RB [ \-d\c
|
||
|
|
.RI [ level ]]
|
||
|
|
.SH DESCRIPTION
|
||
|
|
The
|
||
|
|
.B cron
|
||
|
|
daemon executes tasks that must be repeated every now and then (cron jobs),
|
||
|
|
and tasks that must be run just once (at jobs). It is normally used to run
|
||
|
|
daily or weekly system maintenance scripts. What it needs to run and when
|
||
|
|
is specified in a number of "cron tables", or crontab files for short.
|
||
|
|
These tables are:
|
||
|
|
.PP
|
||
|
|
.RS
|
||
|
|
.nf
|
||
|
|
.ft B
|
||
|
|
/usr/lib/crontab
|
||
|
|
/usr/local/lib/crontab
|
||
|
|
/var/lib/crontab
|
||
|
|
/var/opt/\fIname\fP/lib/crontab\ \ \fR(Minix-vmd only)\fB
|
||
|
|
/usr/spool/crontabs/\fIuser\fP
|
||
|
|
.ft R
|
||
|
|
.fi
|
||
|
|
.RE
|
||
|
|
.PP
|
||
|
|
These files follow the usual pattern: One for the standard things, one for
|
||
|
|
local tasks per organization, one for tasks per system, and one crontab per
|
||
|
|
installed package. (Cron reads
|
||
|
|
.B /usr/lib/packages
|
||
|
|
to find names of installed packages, it doesn't just grab everything in
|
||
|
|
.BR /var/opt .)
|
||
|
|
The last set of files fall outside the normal pattern, they are per user
|
||
|
|
crontabs that one can create with the
|
||
|
|
.BR crontab (1)
|
||
|
|
command. The file names in
|
||
|
|
.B /usr/spool/crontabs/
|
||
|
|
are login names of the file owners.
|
||
|
|
.PP
|
||
|
|
The format of a crontab file is described in
|
||
|
|
.BR crontab (5).
|
||
|
|
.SS "AT jobs"
|
||
|
|
.B Cron
|
||
|
|
also takes care of the execution of jobs issued by
|
||
|
|
.BR at (1)
|
||
|
|
that are found in
|
||
|
|
.BR /usr/spool/at/ .
|
||
|
|
Cron simply runs the AT job as if there were an "sh at-job" as a cron job at
|
||
|
|
the appropriate time under the user-id of the owner of the script. The
|
||
|
|
script takes care of the rest. See
|
||
|
|
.BR at (1)
|
||
|
|
for the details.
|
||
|
|
.SS "Job I/O"
|
||
|
|
Standard input, output and error are the same as cron's if the job is
|
||
|
|
started by the system crontabs or from package crontabs. This means that
|
||
|
|
output from system jobs usually ends up on the console and in the log file.
|
||
|
|
Output from personal cron jobs or at jobs are mailed to the owner of the
|
||
|
|
job. No mail is sent if the job is silent.
|
||
|
|
.SH OPTIONS
|
||
|
|
.TP 5
|
||
|
|
[\fB\-d\fR[\fIlevel\fR]]
|
||
|
|
Set the debug level, by default 1. Makes
|
||
|
|
.B cron
|
||
|
|
print info on what it happens to be doing. Level 1 just tells about sleep
|
||
|
|
times and what job is executed, level 2 also shows the internal crontab
|
||
|
|
data on a table load. (With time fields translated to match those of
|
||
|
|
.BR "struct tm" ,
|
||
|
|
see
|
||
|
|
.BR ctime (3).)
|
||
|
|
.SS SIGNALS
|
||
|
|
.B Cron
|
||
|
|
takes the following actions when sent one of the following signals:
|
||
|
|
.TP 12
|
||
|
|
.B SIGHUP
|
||
|
|
Reload the crontab tables if they changed since the last time they were
|
||
|
|
loaded, and reexamine the AT job spool. Used by
|
||
|
|
.BR at (1)
|
||
|
|
and
|
||
|
|
.BR crontab (1).
|
||
|
|
.TP
|
||
|
|
.B SIGUSR1
|
||
|
|
Increase the debug level by 1.
|
||
|
|
.TP
|
||
|
|
.B SIGUSR2
|
||
|
|
Turn debugging off.
|
||
|
|
.SH ENVIRONMENT
|
||
|
|
.B Cron
|
||
|
|
sets the environment variables
|
||
|
|
.BR USER ,
|
||
|
|
.BR LOGNAME ,
|
||
|
|
.BR HOME ,
|
||
|
|
and
|
||
|
|
.BR SHELL
|
||
|
|
to the user's login name (2x), home directory, and shell if a job is
|
||
|
|
executed for a given user. The working directory is set to the user's home
|
||
|
|
directory. Everything else is inherited from
|
||
|
|
.BR cron ,
|
||
|
|
exactly as
|
||
|
|
.B cron
|
||
|
|
got it when it started. Note that commands are always passed to
|
||
|
|
.BR /bin/sh ,
|
||
|
|
not to the user's shell.
|
||
|
|
.PP
|
||
|
|
System cron jobs are in principle executed with
|
||
|
|
.BR cron 's
|
||
|
|
environment, use
|
||
|
|
.B "\-u root"
|
||
|
|
or the crontab file
|
||
|
|
.B /usr/spool/crontabs/root
|
||
|
|
if you want to give root the same treatment as ordinary users.
|
||
|
|
.SH FILES
|
||
|
|
.TP 25n
|
||
|
|
.B /usr/lib/crontab
|
||
|
|
Main Minix crontab file.
|
||
|
|
.TP
|
||
|
|
.B /usr/local/lib/crontab
|
||
|
|
Local jobs for all systems in an organization.
|
||
|
|
.TP
|
||
|
|
.B /var/lib/crontab
|
||
|
|
System specific jobs.
|
||
|
|
.TP
|
||
|
|
.B /var/opt/\fIname\fP/lib/crontab
|
||
|
|
Per package jobs for Minix-vmd.
|
||
|
|
.TP
|
||
|
|
.B /usr/lib/packages
|
||
|
|
List of installed packages.
|
||
|
|
.TP
|
||
|
|
.B /usr/spool/crontabs/\fIuser\fP
|
||
|
|
Per user jobs.
|
||
|
|
.TP
|
||
|
|
.B /usr/spool/at/*
|
||
|
|
Jobs issued by
|
||
|
|
.BR at (1).
|
||
|
|
.TP
|
||
|
|
.B /usr/run/cron.pid
|
||
|
|
Process id of cron when cron is running. Used by
|
||
|
|
.BR at (1)
|
||
|
|
and
|
||
|
|
.BR crontab (1)
|
||
|
|
to send cron a hangup signal.
|
||
|
|
.SH "SEE ALSO"
|
||
|
|
.BR at (1),
|
||
|
|
.BR crontab (1).
|
||
|
|
.SH NOTES
|
||
|
|
A job is not reissued until a previous instance of it has exited. The next
|
||
|
|
time to execute is computed from the previous time it ran. If job issuing
|
||
|
|
lags behind on the system time then the next time to run it is computed from
|
||
|
|
the current system time.
|
||
|
|
.SH BUGS
|
||
|
|
.B Cron
|
||
|
|
doesn't like it if the system time is changed. If set forward then cron
|
||
|
|
will react when it next wakes up by running all jobs within the skipped time
|
||
|
|
once or twice before it catches up. Setting the clock backwards makes cron
|
||
|
|
play dead until the system time passes the old time. (Changing the system
|
||
|
|
time is bad idea anyway, and not just because of cron.)
|
||
|
|
.PP
|
||
|
|
Jobs that fall in the missing hour in a change to Daylight Saving Time are
|
||
|
|
skipped. Nothing is done in the extra hour on the change out of DST.
|
||
|
|
.SH AUTHOR
|
||
|
|
Kees J. Bot (kjb@cs.vu.nl)
|
||
|
|
|
||
|
|
.\"
|
||
|
|
.\" $PchId: cron.8,v 1.3 2000/07/17 18:49:18 philip Exp $
|