cron

cron

[Alex Snow]

Hi All.
Does anyone know the syntax of the crontab file? I cant seem to find it.
what I'm aiming to do is run a job every 15 mins or so but I cant seem to
find the syntax and what all the fields are.

--
A message from the system administrator: "I've upped my priority, now up yours!"

Re: cron

[Adam Myrow]

The syntax of the crontab file is downright odd, but it's been this way in
just about every Unix system or Linux system I've encountered.

The first entry is the minute or minutes on which you want your cron job
to run.  For every 15 minutes, you would use "0,15,30,45, in the first
field.  The second field is the hour.  It is expressed in 24-hour notation
from 0 to 23.  The third field is the day of the month you want to run the
cron job.  The fourth field is the month or months of the year to run the
cron job.  The fifth field is the day of the week from 0 for Sunday to 6
for Saturday.  All of these fields can take a single value, a
comma-separated list of values, a range, or an asterisk which means any.
For example, if you wanted the time announced every 15 minutes, and you
had a command called "saytime," you would put something like this in your
crontab file.

0,15,30,45 * * * * /usr/local/bin/saytime >/dev/null 2>&1

It is generally a good idea to include the full path to commands since the
path can be set up oddly when running a cron script.  You also generally
want to redirect both standard out and standard error somewhere.
Otherwise, any output gets mailed to the user who has the cron job.  This
is a good thing in some cases, but not so good in a lot of others.
Instead of /dev/null, you could use the ">> /var/log/saytime.log" to
append output to that file.  In the case of "saytime" it seldom produces
output other than an error saying that the device is busy, so we don't
really need to log it.  Check out the default crontab file.  It has some
cron entries already set up.  As I said, this applies to just about any
Unix system you can think of.  Some crontab programs will have special
features like being able to understand symbolic names like MON instead of
the numbers, but I stick with the most portable format.

Here is another example.  suppose you leave your computer on 24 hours a
day.  That Saytime program is keeping you up all night!  How to shut it up
while letting it run in the daytime?  Try this.

0,15,30,45 8-20 * * * /usr/local/bin/saytime >/dev/null 2>&1

Now, the cron entry will only run from 8 A.M. to 8 P.M.  I think you get
the idea.  These are just examples I made up off the top of my head.

Lastly, always use "crontab -e" to edit cron files.  If you don't like the
editor it starts with, set the environment variable "EDITOR" to point to
your favorite editor.  For example "export EDITOR='pico -t'" or "export
EDITOR=emacs."  Since some programs use VISUAL instead of EDITOR, I have
my .profile export both variables and give them the same value.  This
effects most news readers, and most other email readers besides Pine which
has its own option for setting an editor.  I hope this was helpful.

Re: cron

[Alex Snow]

Hi.
Thanks for the info!

--
A message from the system administrator: "I've upped my priority, now up yours!"
On Sat, 14 Jun 2003, Adam Myrow wrote:

> The syntax of the crontab file is downright odd, but it's been this way in
> just about every Unix system or Linux system I've encountered.
>
> The first entry is the minute or minutes on which you want your cron job
> to run.  For every 15 minutes, you would use "0,15,30,45, in the first
> field.  The second field is the hour.  It is expressed in 24-hour notation
> from 0 to 23.  The third field is the day of the month you want to run the
> cron job.  The fourth field is the month or months of the year to run the
> cron job.  The fifth field is the day of the week from 0 for Sunday to 6
> for Saturday.  All of these fields can take a single value, a
> comma-separated list of values, a range, or an asterisk which means any.
> For example, if you wanted the time announced every 15 minutes, and you
> had a command called "saytime," you would put something like this in your
> crontab file.
>
> 0,15,30,45 * * * * /usr/local/bin/saytime >/dev/null 2>&1
>
> It is generally a good idea to include the full path to commands since the
> path can be set up oddly when running a cron script.  You also generally
> want to redirect both standard out and standard error somewhere.
> Otherwise, any output gets mailed to the user who has the cron job.  This
> is a good thing in some cases, but not so good in a lot of others.
> Instead of /dev/null, you could use the ">> /var/log/saytime.log" to
> append output to that file.  In the case of "saytime" it seldom produces
> output other than an error saying that the device is busy, so we don't
> really need to log it.  Check out the default crontab file.  It has some
> cron entries already set up.  As I said, this applies to just about any
> Unix system you can think of.  Some crontab programs will have special
> features like being able to understand symbolic names like MON instead of
> the numbers, but I stick with the most portable format.
>
> Here is another example.  suppose you leave your computer on 24 hours a
> day.  That Saytime program is keeping you up all night!  How to shut it up
> while letting it run in the daytime?  Try this.
>
> 0,15,30,45 8-20 * * * /usr/local/bin/saytime >/dev/null 2>&1
>
> Now, the cron entry will only run from 8 A.M. to 8 P.M.  I think you get
> the idea.  These are just examples I made up off the top of my head.
>
> Lastly, always use "crontab -e" to edit cron files.  If you don't like the
> editor it starts with, set the environment variable "EDITOR" to point to
> your favorite editor.  For example "export EDITOR='pico -t'" or "export
> EDITOR=emacs."  Since some programs use VISUAL instead of EDITOR, I have
> my .profile export both variables and give them the same value.  This
> effects most news readers, and most other email readers besides Pine which
> has its own option for setting an editor.  I hope this was helpful.
>
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>

cron

[Ann Parsons]

Hi all,

Um, try man crontab  Their may be docs in /usr/docs too.

Ann P.

-- 
			Ann K. Parsons  
email:  akp@eznet.net 			ICQ Number:  33006854
WEB SITE:  http://home.eznet.net/~akp
"All that is gold does not glitter.  Not all those who wander are lost."  JRRT

Re: cron

[Ralph W. Reid]

Alex Snow staggered into view and mumbled:
>
>Hi All.
>Does anyone know the syntax of the crontab file? I cant seem to find it.
>what I'm aiming to do is run a job every 15 mins or so but I cant seem to
>find the syntax and what all the fields are.

Have you considered using `at' instead of editing that file manually?
For what you want to do, the `at' command line would look something
like this:

at now + 15 minutes

You can then enter a list of commands you would like to run, and then
terminate the list with a CTRL-D (end of file character) to get
things started.  You might also want to redirect any output from the
commands to keep from getting email every 15 minutes if the list ends
with `at now + 15 minutes'.  See the man page for `at' for more
details.  I hope this helps.

Have a _great_ day!

-- 
Ralph.  N6BNO.  Wisdom comes from central processing, not from I/O.
rreid@sunset.net  http://personalweb.sunset.net/~rreid
Opinions herein are either mine or they are flame bait.
SLOPE = (y2 - y1) / (x2 - x1)

Re: cron

[Alex Snow]

Hi.
Thanks for the info.

--
A message from the system administrator: "I've upped my priority, now up yours!"
On Sun, 15 Jun 2003, Ralph W. Reid wrote:

> Alex Snow staggered into view and mumbled:
> >
> >Hi All.
> >Does anyone know the syntax of the crontab file? I cant seem to find it.
> >what I'm aiming to do is run a job every 15 mins or so but I cant seem to
> >find the syntax and what all the fields are.
>
> Have you considered using `at' instead of editing that file manually?
> For what you want to do, the `at' command line would look something
> like this:
>
> at now + 15 minutes
>
> You can then enter a list of commands you would like to run, and then
> terminate the list with a CTRL-D (end of file character) to get
> things started.  You might also want to redirect any output from the
> commands to keep from getting email every 15 minutes if the list ends
> with `at now + 15 minutes'.  See the man page for `at' for more
> details.  I hope this helps.
>
> Have a _great_ day!
>
> --
> Ralph.  N6BNO.  Wisdom comes from central processing, not from I/O.
> rreid@sunset.net  http://personalweb.sunset.net/~rreid
> Opinions herein are either mine or they are flame bait.
> SLOPE = (y2 - y1) / (x2 - x1)
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>

Re: cron

[Thomas Stivers]

On 06/15/03  7:52 AM -0700, Ralph W. Reid wrote:
> Have you considered using `at' instead of editing that file manually?
> For what you want to do, the `at' command line would look something
> like this:
> 
> at now + 15 minutes
> 
> You can then enter a list of commands you would like to run, and then
> terminate the list with a CTRL-D (end of file character) to get
> things started.  You might also want to redirect any output from the
> commands to keep from getting email every 15 minutes if the list ends
> with `at now + 15 minutes'.  See the man page for `at' for more
> details.  I hope this helps.

The at program is intended more for scheduling jops to run one time.
While it could be run recursively, or something, cron is far more suited
to repetitive tasks. Run "man 5 crontab" for the syntax of crontab
files. Only running 'man crontab" gives you the syntax of the crontab
command which is different.

-- 
Unix is a user friendly operating system. It just picks its friends more
carefully than others.
Thomas Stivers	e-mail: stivers_t@tomass.dyndns.org	gpg: 45CBBABD

Re: cron

[Joseph C. Lininger]

What distribution are you using? Syntax varies from version to version of cron.

-- 
Joseph C. Lininger
jbahm@pcdesk.net

On Sat, 14 Jun 2003, Alex Snow wrote:

> Hi All.
> Does anyone know the syntax of the crontab file? I cant seem to find it.
> what I'm aiming to do is run a job every 15 mins or so but I cant seem to
> find the syntax and what all the fields are.
>
> --
> A message from the system administrator: "I've upped my priority, now up yours!"
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>

Re: cron

[Alex Snow]

slack 9.0

--
A message from the system administrator: "I've upped my priority, now up yours!"
On Mon, 16 Jun 2003, Joseph C. Lininger wrote:

> What distribution are you using? Syntax varies from version to version of cron.
>
> --
> Joseph C. Lininger
> jbahm@pcdesk.net
>
> On Sat, 14 Jun 2003, Alex Snow wrote:
>
> > Hi All.
> > Does anyone know the syntax of the crontab file? I cant seem to find it.
> > what I'm aiming to do is run a job every 15 mins or so but I cant seem to
> > find the syntax and what all the fields are.
> >
> > --
> > A message from the system administrator: "I've upped my priority, now up yours!"
> >
> > _______________________________________________
> > Speakup mailing list
> > Speakup@braille.uwo.ca
> > http://speech.braille.uwo.ca/mailman/listinfo/speakup
> >
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>

Re: cron

[Luke Davis]

Try man crontab

Actually, that will get you crontab(1).  What you probably want, is
crontab(5), so of course you would do:

man 5 crontab

Regards,

Luke


On Mon, 16 Jun 2003, Joseph C. Lininger wrote:

> What distribution are you using? Syntax varies from version to version of cron.
>
>

Re: cron

[Joseph C. Lininger]

Alex,
This is what I'm running as well. I'll give you a quick run down on how the crontab file works in this version of cron. You can also look this up in the manual by looking at the man page for crond. Don't look for crontab, as this will only give you the crontab program's page. There is no man page in section 5 for crontab for this version.

First, to edit crontab you will need to issue this command:

crontab -e

Make sure you set the VISUAL (notice that it's all caps) environment variable to the path to the text editor you want to use. This is the editor crontab will spawn.

The format of this file consists of several fields. basically, the line looks like this:

<minute> <hour> <day> <month> <days of the week> <command>

For any of these fields, you may use an absolute number, a list seperated by commas, or a * to indicate all values. Also, you can use a skip factor to have cron skip running the job at certin times. I'll show that in the examples below. For the <days of the week> field, you should use 0 for sunday through 6 for saturday. You'll want to direct the output of the command you run to /dev/null or some log file or you'll end up getting the results emailed to you.

Ok, now a couple of examples.

# run a command at 4:30 AM every day
30 4 * * * somecommand
# run a command at 2:30 in the afternoon on the first of the month
30 14 1 * * somecommand
# run a command at midnight every monday and tuesday
0 0 * * 1,2 somecommand
# illistrates the skip factor--run a command every 15 minutes
*/15 * * * * somecommand

Ok, if you have any more questions, let me know.
-- 
Joseph C. Lininger
jbahm@pcdesk.net

On Mon, 16 Jun 2003, Alex Snow wrote:

> slack 9.0
>
> --
> A message from the system administrator: "I've upped my priority, now up yours!"
> On Mon, 16 Jun 2003, Joseph C. Lininger wrote:
>
> > What distribution are you using? Syntax varies from version to version of cron.
> >
> > --
> > Joseph C. Lininger
> > jbahm@pcdesk.net
> >
> > On Sat, 14 Jun 2003, Alex Snow wrote:
> >
> > > Hi All.
> > > Does anyone know the syntax of the crontab file? I cant seem to find it.
> > > what I'm aiming to do is run a job every 15 mins or so but I cant seem to
> > > find the syntax and what all the fields are.
> > >
> > > --
> > > A message from the system administrator: "I've upped my priority, now up yours!"
> > >
> > > _______________________________________________
> > > Speakup mailing list
> > > Speakup@braille.uwo.ca
> > > http://speech.braille.uwo.ca/mailman/listinfo/speakup
> > >
> >
> > _______________________________________________
> > Speakup mailing list
> > Speakup@braille.uwo.ca
> > http://speech.braille.uwo.ca/mailman/listinfo/speakup
> >
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>

Re: cron

[Luke Davis]

Interesting.  Does the end of your contrab(1) manual page, give you a "see
also", to another crontab page?


On Tue, 17 Jun 2003, Joseph C. Lininger wrote:

> Alex,
> This is what I'm running as well. I'll give you a quick run down on how the crontab file works in this version of cron. You can also look this up in the manual by looking at the man page for crond. Don't look for crontab, as this will only give you the crontab program's page. There is no man page in section 5 for crontab for this version.
>
> First, to edit crontab you will need to issue this command:
>
> crontab -e
>
> Make sure you set the VISUAL (notice that it's all caps) environment variable to the path to the text editor you want to use. This is the editor crontab will spawn.
>
> The format of this file consists of several fields. basically, the line looks like this:
>
> <minute> <hour> <day> <month> <days of the week> <command>
>
> For any of these fields, you may use an absolute number, a list seperated by commas, or a * to indicate all values. Also, you can use a skip factor to have cron skip running the job at certin times. I'll show that in the examples below. For the <days of the week> field, you should use 0 for sunday through 6 for saturday. You'll want to direct the output of the command you run to /dev/null or some log file or you'll end up getting the results emailed to you.
>
> Ok, now a couple of examples.
>
> # run a command at 4:30 AM every day
> 30 4 * * * somecommand
> # run a command at 2:30 in the afternoon on the first of the month
> 30 14 1 * * somecommand
> # run a command at midnight every monday and tuesday
> 0 0 * * 1,2 somecommand
> # illistrates the skip factor--run a command every 15 minutes
> */15 * * * * somecommand
>
> Ok, if you have any more questions, let me know.
>

Re: cron

[Alex Snow]

Hi.
thanks for the info!


--
A message from the system administrator: "I've upped my priority, now up yours!"
On Tue, 17 Jun 2003, Joseph C. Lininger wrote:

> Alex,
> This is what I'm running as well. I'll give you a quick run down on how the crontab file works in this version of cron. You can also look this up in the manual by looking at the man page for crond. Don't look for crontab, as this will only give you the crontab program's page. There is no man page in section 5 for crontab for this version.
>
> First, to edit crontab you will need to issue this command:
>
> crontab -e
>
> Make sure you set the VISUAL (notice that it's all caps) environment variable to the path to the text editor you want to use. This is the editor crontab will spawn.
>
> The format of this file consists of several fields. basically, the line looks like this:
>
> <minute> <hour> <day> <month> <days of the week> <command>
>
> For any of these fields, you may use an absolute number, a list seperated by commas, or a * to indicate all values. Also, you can use a skip factor to have cron skip running the job at certin times. I'll show that in the examples below. For the <days of the week> field, you should use 0 for sunday through 6 for saturday. You'll want to direct the output of the command you run to /dev/null or some log file or you'll end up getting the results emailed to you.
>
> Ok, now a couple of examples.
>
> # run a command at 4:30 AM every day
> 30 4 * * * somecommand
> # run a command at 2:30 in the afternoon on the first of the month
> 30 14 1 * * somecommand
> # run a command at midnight every monday and tuesday
> 0 0 * * 1,2 somecommand
> # illistrates the skip factor--run a command every 15 minutes
> */15 * * * * somecommand
>
> Ok, if you have any more questions, let me know.
> --
> Joseph C. Lininger
> jbahm@pcdesk.net
>
> On Mon, 16 Jun 2003, Alex Snow wrote:
>
> > slack 9.0
> >
> > --
> > A message from the system administrator: "I've upped my priority, now up yours!"
> > On Mon, 16 Jun 2003, Joseph C. Lininger wrote:
> >
> > > What distribution are you using? Syntax varies from version to version of cron.
> > >
> > > --
> > > Joseph C. Lininger
> > > jbahm@pcdesk.net
> > >
> > > On Sat, 14 Jun 2003, Alex Snow wrote:
> > >
> > > > Hi All.
> > > > Does anyone know the syntax of the crontab file? I cant seem to find it.
> > > > what I'm aiming to do is run a job every 15 mins or so but I cant seem to
> > > > find the syntax and what all the fields are.
> > > >
> > > > --
> > > > A message from the system administrator: "I've upped my priority, now up yours!"
> > > >
> > > > _______________________________________________
> > > > Speakup mailing list
> > > > Speakup@braille.uwo.ca
> > > > http://speech.braille.uwo.ca/mailman/listinfo/speakup
> > > >
> > >
> > > _______________________________________________
> > > Speakup mailing list
> > > Speakup@braille.uwo.ca
> > > http://speech.braille.uwo.ca/mailman/listinfo/speakup
> > >
> >
> > _______________________________________________
> > Speakup mailing list
> > Speakup@braille.uwo.ca
> > http://speech.braille.uwo.ca/mailman/listinfo/speakup
> >
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>

Re: cron

[Joseph C. Lininger]

Luke,
I made a mistake in my previous post. The man page for crontab (1) will show the format of the crontab file. Sorry about that guys.

-- 
Joseph C. Lininger
jbahm@pcdesk.net

On Tue, 17 Jun 2003, Luke Davis wrote:

> Interesting.  Does the end of your contrab(1) manual page, give you a "see
> also", to another crontab page?
>
>
> On Tue, 17 Jun 2003, Joseph C. Lininger wrote:
>
> > Alex,
> > This is what I'm running as well. I'll give you a quick run down on how the crontab file works in this version of cron. You can also look this up in the manual by looking at the man page for crond. Don't look for crontab, as this will only give you the crontab program's page. There is no man page in section 5 for crontab for this version.
> >
> > First, to edit crontab you will need to issue this command:
> >
> > crontab -e
> >
> > Make sure you set the VISUAL (notice that it's all caps) environment variable to the path to the text editor you want to use. This is the editor crontab will spawn.
> >
> > The format of this file consists of several fields. basically, the line looks like this:
> >
> > <minute> <hour> <day> <month> <days of the week> <command>
> >
> > For any of these fields, you may use an absolute number, a list seperated by commas, or a * to indicate all values. Also, you can use a skip factor to have cron skip running the job at certin times. I'll show that in the examples below. For the <days of the week> field, you should use 0 for sunday through 6 for saturday. You'll want to direct the output of the command you run to /dev/null or some log file or you'll end up getting the results emailed to you.
> >
> > Ok, now a couple of examples.
> >
> > # run a command at 4:30 AM every day
> > 30 4 * * * somecommand
> > # run a command at 2:30 in the afternoon on the first of the month
> > 30 14 1 * * somecommand
> > # run a command at midnight every monday and tuesday
> > 0 0 * * 1,2 somecommand
> > # illistrates the skip factor--run a command every 15 minutes
> > */15 * * * * somecommand
> >
> > Ok, if you have any more questions, let me know.
> >
>
> _______________________________________________
> Speakup mailing list
> Speakup@braille.uwo.ca
> http://speech.braille.uwo.ca/mailman/listinfo/speakup
>