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cron

Posted on February 13, 2022 inDefault

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cron is a time-based desktop scheduler for Unix-like computer operating systems. https://cronlounge.com allows users to schedule business opportunities (commands or scripts) to occasionally run at specific times, dates, or intervals. It is often used to improve system maintenance or management.

Settings

There are several good implementations of cron, but none of them are installed by default because their underlying system uses systemd/Timers instead. Check out the Gentoo cron manual, which narrows down the comparison.

  • Friend
  • cron
  • dcronAUR
  • wixie cronAUR
  • scron-gitAUR

Configuration

Activation And Installation, Automatic Cal Launch

Finally, dodging does not activate the demon. The installed package probably provides a good service that can be easily controlled via systemctl. For example, Cronie requires cronie.service.

Browse /etc/cron.daily/ and similar directories to see what jobs exist. Enabling the cron service starts them all, including this one.

Handling Errors In Tasks

cron saves stdout and stderr output and attempts to email it to the user’s spools using any sendmail command. Cronie disables mail delivery when /usr/bin/sendmail is not found. In order for emails to be written to be used as a buffer user, an SMTP daemon must be running on your current system, e.g. openmtpd. Alternatively, you can install a package that includes this sendmail command and configure it to help you send mail to a remote mail exchanger. You can also log actual messages using the -m package and writing your own script.

  1. Change all cronie.service objects.
  2. Install esmtpAUR, msmtp, opensmtpd, sSMTP, and write your own script.

sSMTP example

sSMTP consists of a send-only Sendmail emulator that redirects email from a host computer to an SMTP server. Although there is currently no effective IT staff, moving mailboxes to a configured mail center is still the easiest option. No daemon needs to be started, the system can be as simple as changing 3 lines in a config file (if your host has been approved to forward unauthenticated mail due to your messaging center). Can’t sSMTP receive emails, expand aliases, or compete with a queue?

Install ssmtpAUR which creates a symlink from /usr/bin/sendmail to /usr/bin can/ ssmtp . Then you need to update /etc/ssmtp/ssmtp.conf. See the sSMTP section for details. Making a symbolic link to /usr/bin/sendmail ensures that programs like S-nail (or any package that provides /usr/bin/mail) will work without any changeenen.

Restart cronie to make sure it recognizes that you installed /usr/bin/sendmail.

msmtp example

Install msmtp-mta, which creates a render link from /usr/bin/sendmail to /usr/bin/msmtp. Reboot into cronie and make sure it recognizes the new sendmail command. Then you really should provide an advanced setup for msmtp to convert your username to an email address. 

MAILTO=your@email.com


alias /etc/alias

Your_user_name: your@email.com
# optional:
Default: your@email.com

Then modify the cronie daemon configuration by changing the influence of ExecStart to: 

ExecStart=/usr/bin/crond -n -m '/usr/bin/msmtp -t'

esmtp example

/etc/esmtprc
Identification self@myisp.com
       Hostname mail.myisp.com:25
       username "me"
       change "secret".
       launch enabled
       Initially
mda "/usr/bin/procmail -ve had %T"

Procmail needs root privileges to run in delivery mode, but this won’t be a problem if you run cronjobs as a base often enough anyway.

To checkTo make sure everything is working correctly, create a file message.txt with "test message". 

$sendmail username 

$ txt chat /var/spool/mail/username



You should see today's test message and the time and date it was sent. Error



The output of all tasks is now normally redirected to /var/spool/mail/user_name.



Due to a privilege issue, it is now difficult to compose and send emails as root (eg su -c ""). You can have esmtp redirect the entire email root to a regular employee with:



/etc/esmtprc


force_mda="username"


Opensmtpd example


listen on localhost
Alias ​​for "local" action mbox 
Mapping for local procedure "local"



You can continue testing. Start by running smtpd.service. Then make it :



$ mirror test | sendmail user



Users can make sure they send mail using any e-book that supports the mbox format, or just browse any /var/spool/mail/user . If everything goes according toanu, you can enable opensmtpd when planning future runs.



This approach has the advantage that local cron alerts are not sent to a remote server. For my part, you need a new working daemon.



Long cron job


#!/bin/sh
Echo "I got them back 1 hour



    

  1. Cron failed!"
    
sleep runs your current script
    2. 

  2. As soon as cron sees some performance, it will start your MTA and include it in the headers. The whistle is open because the work has not yet been completed and there will probably be more output.
    3. 

  3. APS opens an attachment by suffix and leaves the connection open while waiting for the rest of the body.
    4. 

  4. postfix will sell you an idle connection in less than an hour and you will get an effective error: for example

    smtpmsg='421 ... Error: Timed out' errormsg='Server received less mail '< /pre>




You can use moreutils Business or Spong command to solve this problem.
From their specific man page:





Chronicle


 multiplies the command and additionally causes its standard output and standard error to be displayed only if the command fails (stopthere are non-zero failures). If the command works, all unnecessary conclusions will be better hidden. Bed 


sponge


Standard input sponge and writing from it to the specified file. Unlike redirection, shell sponges amplify all their input before opening my output file... If no output history is specified, sponge prints standard output.




Chronic also buffers the command's output early to open standard output.





Crontab Format





command 
minute day_of_month hour month day_of_week



    

  • Minutes can range from 0 to 59.
    • 

  • The philosophy of the hour can take values ​​from 0 to 23.
    • 

  • day of the month values ​​can range from 1 to 31.
    • 

  • Monthly values ​​can be up to 12 different.
    • 

  • Day of the week values ​​can be from 0 to 6, where three is Sunday.
    • 



Spaces are used to separate workspaces. You can also use one of the following icons to fine-tune your schedule:






icon
Description



*
Wildcard, specifies each possible work intervalabout the time



,
List multiple values ​​separated by a real comma.



-
Specify a range between two numbers, Hyundai Sonata is motivated by a dash



/
Specify how often/how often to use the slash





*/5 9-16 * 1-5,9-12 1-5 ~/bin/i_love_cron.sh



will run the script i_love_cron.sh at five-minute intervals from 9:00 to 16:55 on weekdays, this should be done during the summer months (June, July and August). run



@annually
 once






Keyword
Description



@reload
in a year



@annually
same as @yearly



@monthly
once a month



@weekly
once a week



@daily
 once trust tag



@midnight
 likes @daily



@schedule
 once an hour





@reboot ~/bin/i_love_cron.sh



Basic Commands


Never edit Crontabs directly; Instead, users should use the crontab program to manage their crontabs. To access this excellent  command, the user must be a partner of a user group (currently see