[cc]mc |
.hd cron "time driven command processor" 08/22/84
cron
.ds
'Cron' allows the system administrator to have shell files executed
automatically at a given time. It does this by creating phantoms to
execute the file. The attributes (name, project, and associated groups)
of the phantom can be specified,
along with the time, by the administrator. 'Cron' must be started
from the system console to retain the privileges needed to spawn phantoms
for alternate user numbers. It could be started as a final step in
the boot procedure by phantoming it from the boot initialization file
(c_config or primos.comi).
.sp
'Cron' gets its information from the file "=cronfile=". It periodically
(currently, every minute) wakes up and reads the information in this
file. If it finds a job that should be run, it collects the attributes
(name, project, and groups) that the job is to have, creates a temporary
file in the directory "=crondir=" to hold the commands, copies the file
to execute into the temporary file, and calls 'sph' to attempt to
spawn the executing process. Before the spawn attempt, 'cron' prints
information, on STDOUT, as to what file is being phantomed for
whom, and the attributes of the phantom.
.sp
The file "=cronfile=" contains a line for each job to be processed.
Each line contains a sequence of space seperated sequences of numbers
that describe the time and day to phantom the process, the user name
and project name to phantom, the name of the file to phantom, and the
list of groups the phantom should have. Each space seperated time
description may contain up to 10 comma seperated fields indicating
multiple times when this job is to be run. The times specify, in order,
the minute, hour, day, day of the month, and month that
a command is to be run. If a time does not matter, it can
specified by a '*' in the appropriate column. In addition
to the job descriptions, the file may contain
comments by simply placing a '#' in the first column of the line.
For example, if "=cronfile=" contained
.sp
.nf
.ne 2
.in +5
# min hrs  day dat mth user   proj file          groups
    0 6,18  *   *   *  jeff   lab  //acct/fix    guru
.in -5
.fi
.sp
then the first line would be ignored (because of the '#' in column 1)
and the second line would cause the shell file "//acct/fix" to be
executed by "jeff" under project "lab" with the ".guru" group at
6am and 6pm every day. A more complicated example would be
.sp
.nf
.ne 2
.in +5
# min hrs  day dat mth user   proj file          groups
   15  *   1,7  *   12 arnold lab  //system/die  scum
.in -5
.fi
.sp
which would have "arnold" with project "lab" and group ".scum"
run the file "//system/die" every 15 minutes after the hour
on weekends (Sunday = 1, Saturday = 7) during the month of
December (January = 1, December = 12). Another example might
be a program to be run on the first day of the year, to send
a happy new year message to everyone. This might look like
.sp
.nf
.ne 2
.in +5
# min hrs  day dat mth user   proj file
   0   0    *   1   1  system lab  //message
.in -5
.fi
.sp
which would run "//message" on January 1 at midnight.
.sp
When specifying the time, care must be taken to prevent a command
from being over-executed. If in the second example the entry
had been
.sp
.nf
.ne 2
.in +5
# min hrs  day dat mth user   proj file          groups
   *   *   1,7  *   12 arnold lab  //system/die  scum
.in -5
.fi
.sp
then the file would have been executed every minute during the weekends
in December.
.me
"can't open =cronfile=" when "=cronfile=" does not exist or is
unreadable.
.sp
"can't open <file>" when the file to spawn does not exist or ir
unreadable.
.sp
"can't create <file>" when it can't create temporary files in
the directory "=crondir=".
.sp
Any message that 'sph' can generate.
.es
cron
.bu
Locally supported until Prime supports EPF's and the SPAWN$
subroutine call.
.sp
Generates lots of output if "=cronfile=" does not exist.
.sa
sph (5)
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