| 1 | .TH CRON 8
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| 2 | .SH NAME
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| 3 | cron \- clock daemon
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| 4 | .SH SYNOPSIS
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| 5 | .B cron
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| 6 | .RB [ \-d\c
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| 7 | .RI [ level ]]
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| 8 | .SH DESCRIPTION
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| 9 | The
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| 10 | .B cron
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| 11 | daemon executes tasks that must be repeated every now and then (cron jobs),
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| 12 | and tasks that must be run just once (at jobs). It is normally used to run
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| 13 | daily or weekly system maintenance scripts. What it needs to run and when
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| 14 | is specified in a number of "cron tables", or crontab files for short.
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| 15 | These tables are:
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| 16 | .PP
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| 17 | .RS
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| 18 | .nf
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| 19 | .ft B
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| 20 | /usr/lib/crontab
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| 21 | /usr/local/lib/crontab
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| 22 | /var/lib/crontab
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| 23 | /var/opt/\fIname\fP/lib/crontab\ \ \fR(Minix-vmd only)\fB
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| 24 | /usr/spool/crontabs/\fIuser\fP
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| 25 | .ft R
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| 26 | .fi
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| 27 | .RE
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| 28 | .PP
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| 29 | These files follow the usual pattern: One for the standard things, one for
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| 30 | local tasks per organization, one for tasks per system, and one crontab per
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| 31 | installed package. (Cron reads
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| 32 | .B /usr/lib/packages
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| 33 | to find names of installed packages, it doesn't just grab everything in
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| 34 | .BR /var/opt .)
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| 35 | The last set of files fall outside the normal pattern, they are per user
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| 36 | crontabs that one can create with the
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| 37 | .BR crontab (1)
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| 38 | command. The file names in
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| 39 | .B /usr/spool/crontabs/
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| 40 | are login names of the file owners.
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| 41 | .PP
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| 42 | The format of a crontab file is described in
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| 43 | .BR crontab (5).
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| 44 | .SS "AT jobs"
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| 45 | .B Cron
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| 46 | also takes care of the execution of jobs issued by
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| 47 | .BR at (1)
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| 48 | that are found in
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| 49 | .BR /usr/spool/at/ .
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| 50 | Cron simply runs the AT job as if there were an "sh at-job" as a cron job at
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| 51 | the appropriate time under the user-id of the owner of the script. The
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| 52 | script takes care of the rest. See
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| 53 | .BR at (1)
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| 54 | for the details.
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| 55 | .SS "Job I/O"
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| 56 | Standard input, output and error are the same as cron's if the job is
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| 57 | started by the system crontabs or from package crontabs. This means that
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| 58 | output from system jobs usually ends up on the console and in the log file.
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| 59 | Output from personal cron jobs or at jobs are mailed to the owner of the
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| 60 | job. No mail is sent if the job is silent.
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| 61 | .SH OPTIONS
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| 62 | .TP 5
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| 63 | [\fB\-d\fR[\fIlevel\fR]]
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| 64 | Set the debug level, by default 1. Makes
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| 65 | .B cron
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| 66 | print info on what it happens to be doing. Level 1 just tells about sleep
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| 67 | times and what job is executed, level 2 also shows the internal crontab
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| 68 | data on a table load. (With time fields translated to match those of
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| 69 | .BR "struct tm" ,
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| 70 | see
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| 71 | .BR ctime (3).)
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| 72 | .SS SIGNALS
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| 73 | .B Cron
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| 74 | takes the following actions when sent one of the following signals:
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| 75 | .TP 12
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| 76 | .B SIGHUP
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| 77 | Reload the crontab tables if they changed since the last time they were
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| 78 | loaded, and reexamine the AT job spool. Used by
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| 79 | .BR at (1)
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| 80 | and
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| 81 | .BR crontab (1).
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| 82 | .TP
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| 83 | .B SIGUSR1
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| 84 | Increase the debug level by 1.
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| 85 | .TP
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| 86 | .B SIGUSR2
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| 87 | Turn debugging off.
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| 88 | .SH ENVIRONMENT
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| 89 | .B Cron
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| 90 | sets the environment variables
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| 91 | .BR USER ,
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| 92 | .BR LOGNAME ,
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| 93 | .BR HOME ,
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| 94 | and
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| 95 | .BR SHELL
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| 96 | to the user's login name (2x), home directory, and shell if a job is
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| 97 | executed for a given user. The working directory is set to the user's home
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| 98 | directory. Everything else is inherited from
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| 99 | .BR cron ,
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| 100 | exactly as
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| 101 | .B cron
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| 102 | got it when it started. Note that commands are always passed to
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| 103 | .BR /bin/sh ,
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| 104 | not to the user's shell.
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| 105 | .PP
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| 106 | System cron jobs are in principle executed with
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| 107 | .BR cron 's
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| 108 | environment, use
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| 109 | .B "\-u root"
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| 110 | or the crontab file
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| 111 | .B /usr/spool/crontabs/root
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| 112 | if you want to give root the same treatment as ordinary users.
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| 113 | .SH FILES
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| 114 | .TP 25n
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| 115 | .B /usr/lib/crontab
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| 116 | Main MINIX 3 crontab file.
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| 117 | .TP
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| 118 | .B /usr/local/lib/crontab
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| 119 | Local jobs for all systems in an organization.
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| 120 | .TP
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| 121 | .B /var/lib/crontab
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| 122 | System specific jobs.
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| 123 | .TP
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| 124 | .B /var/opt/\fIname\fP/lib/crontab
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| 125 | Per package jobs for Minix-vmd.
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| 126 | .TP
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| 127 | .B /usr/lib/packages
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| 128 | List of installed packages.
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| 129 | .TP
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| 130 | .B /usr/spool/crontabs/\fIuser\fP
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| 131 | Per user jobs.
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| 132 | .TP
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| 133 | .B /usr/spool/at/*
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| 134 | Jobs issued by
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| 135 | .BR at (1).
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| 136 | .TP
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| 137 | .B /usr/run/cron.pid
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| 138 | Process id of cron when cron is running. Used by
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| 139 | .BR at (1)
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| 140 | and
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| 141 | .BR crontab (1)
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| 142 | to send cron a hangup signal.
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| 143 | .SH "SEE ALSO"
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| 144 | .BR at (1),
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| 145 | .BR crontab (1).
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| 146 | .SH NOTES
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| 147 | A job is not reissued until a previous instance of it has exited. The next
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| 148 | time to execute is computed from the previous time it ran. If job issuing
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| 149 | lags behind on the system time then the next time to run it is computed from
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| 150 | the current system time.
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| 151 | .SH BUGS
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| 152 | .B Cron
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| 153 | doesn't like it if the system time is changed. If set forward then cron
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| 154 | will react when it next wakes up by running all jobs within the skipped time
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| 155 | once or twice before it catches up. Setting the clock backwards makes cron
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| 156 | play dead until the system time passes the old time. (Changing the system
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| 157 | time is bad idea anyway, and not just because of cron.)
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| 158 | .PP
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| 159 | Jobs that fall in the missing hour in a change to Daylight Saving Time are
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| 160 | skipped. Nothing is done in the extra hour on the change out of DST.
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| 161 | .SH AUTHOR
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| 162 | Kees J. Bot (kjb@cs.vu.nl)
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| 163 |
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| 164 | .\"
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| 165 | .\" $PchId: cron.8,v 1.3 2000/07/17 18:49:18 philip Exp $
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