How to log cron jobs

Question

I want to know how I can see exactly what the cron jobs are doing on each execution  Where are the log files located  Or can I send the output to my email  I have set the email address to send the log when the cron job runs but I haven t received anything yet

User · Answer

Incase you re running some command with sudo  it won t allow it  Sudo needs a tty

User · Answer

cron already sends the standard output and standard error of every job it runs by mail to the owner of the cron job   You can use MAILTO recipient in the crontab file to have the emails sent to a different account   For this to work  you need to have mail working properly  Delivering to a local mailbox is usually not a problem  in fact  chances are ls -l   MAIL  will reveal that you have already been receiving some  but getting it off the box and out onto the internet requires the MTA  Postfix  Sendmail  what have you  to be properly configured to connect to the world   If there is no output  no email will be generated   A common arrangement is to redirect output to a file  in which case of course the cron daemon won t see the job return any output  A variant is to redirect standard output to a file  or write the script so it never prints anything - perhaps it stores results in a database instead  or performs maintenance tasks which simply don t output anything   and only receive an email if there is an error message   To redirect both output streams  the syntax is  42 17       script  gt  gt stdout log 2 gt  gt stderr log   Notice how we append  double  gt  gt   instead of overwrite  so that any previous job s output is not replaced by the next one s   As suggested in many answers here  you can have both output streams be sent to a single file  replace the second redirection with 2 gt  amp 1 to say  standard error should go wherever standard output is going    But I don t particularly endorse this practice  It mainly makes sense if you don t really expect anything on standard output  but may have overlooked something  perhaps coming from an external tool which is called from your script    cron jobs run in your home directory  so any relative file names should be relative to that  If you want to write outside of your home directory  you obviously need to separately make sure you have write access to that destination file   A common antipattern is to redirect everything to  dev null  and then ask Stack Overflow to help you figure out what went wrong when something is  not working  but we can t see the lost output  either    From within your script  make sure to keep regular output  actual results  ideally in machine-readable form  and diagnostics  usually formatted for a human reader  separate  In a shell script   echo   results     regular results go to stdout echo   0  something went wrong   gt  amp 2   Some platforms  and e g  GNU Awk  allow you to use the file name  dev stderr for error messages  but this is not properly portable  in Perl  warn and die print to standard error  in Python  write to sys stderr  or use logging  in Ruby  try  stderr puts  Notice also how error messages should include the name of the script which produced the diagnostic message

User · Answer

Here is my code             your script fullpath  gt  gt  your log path 2 gt  amp 1

User · Answer

myjob sh  gt  gt   var log myjob log 2 gt  amp 1   will log all output from the cron job to  var log myjob log  You might use mail to send emails  Most systems will send unhandled cron job output by email to root or the corresponding user

User · Answer

By default cron logs to  var log syslog so you can see cron related entries by using   grep CRON  var log syslog   https   askubuntu com questions 56683 where-is-the-cron-crontab-log

User · Answer

If you d still like to check your cron jobs you should provide a valid   email account when setting the Cron jobs in cPanel    When you specify a valid email you will receive the output of the cron job that is executed  Thus you will be able to check it and make sure everything has been executed correctly  Note that you will not receive an email if there is no output from the cron job command   Please bear in mind that you will receive an email for each of the executed cron jobs  This may flood your inbox in case your crons run too often

User · Answer

There are at least three different types of logging    The logging BEFORE the program is executed  which only logs IF the cronjob TRIED to execute the command  That one is located in  var log syslog  as already mentioned by  Matthew Lock  The logging of errors AFTER the program tried to execute  which can be sent to an email or to a file  as mentioned by  Spliffster  I prefer logging to a file  because with email THEN you have a NEW source of problems  and its checking if email sending and reception is working perfectly  Sometimes it is  sometimes it s not  For example  in a simple common desktop machine in which you are not interested in configuring an smtp  sometimes you will prefer logging to a file             COMMAND ABSOLUTE PATH  gt   ABSOLUTE PATH TO LOG 2 gt  amp 1    I would also consider checking the permissions of  ABSOLUTE PATH TO LOG  and run the command from that user s permissions  Just for verification  while you test whether it might be a potential source of problems   The logging of the program itself  with its own error-handling and logging for tracking purposes    There are some common sources of problems with cronjobs     The ABSOLUTE PATH of the binary to be executed  When you run it from your    shell  it might work  but the cron process seems to use another    environment  and hence it doesn t always find binaries if you don t    use the absolute path       The LIBRARIES used by a binary  It s more or less the same previous point  but make sure that  if simply putting the NAME of the command  is referring to exactly the binary which uses the very same library  or better  check if the binary you are referring with the absolute path is the very same you refer when you use the console directly  The binaries can be found using the locate command  for example    locate python   Be sure that the binary you will refer  is the very same the binary you are calling in your shell  or simply test again in your shell using the absolute path that you plan to put in the cronjob    Another common source of problems is the syntax in the cronjob  Remember that there are special characters you can use for lists  commas   to define ranges  dashes -   to define increment of ranges  slashes   etc  Take a look   http   www softpanorama org Utilities cron shtml

User · Answer

On Ubuntu you can enable a cron log file to contain just the CRON entries   Uncomment the line that mentions cron in   etc rsyslog d 50-default conf file      Default rules for rsyslog                             For more information see rsyslog conf 5  and  etc rsyslog conf      First some standard log files   Log by facility    auth authpriv                    var log auth log     auth authpriv none          - var log syslog  cron                             var log cron log   Save and close the file and then restart the rsyslog service   sudo systemctl restart rsyslog   You can now see cron log entries in its own file   sudo tail -f  var log cron log   Sample outputs   Jul 18 07 05 01 machine-host-name CRON 13638    root  CMD  command -v debian-sa1  gt   dev null  amp  amp  debian-sa1 1 1    However  you will not see more information about what scripts were actually run inside  etc cron daily or  etc cron hourly  unless those scripts direct output to the cron log  or perhaps to some other log file    If you want to verify if a crontab is running and not have to search for it in cron log or syslog  create a crontab that redirects output to a log file of your choice - something like     For more information see the manual pages of crontab 5  and cron 8      m h  dom mon dow   command 30 2     1  usr local sbin certbot-auto renew  gt  gt   var log le-renew log 2 gt  amp 1   Steps taken from  https   www cyberciti biz faq howto-create-cron-log-file-to-log-crontab-logs-in-ubuntu-linux

[logging] How to log cron jobs?

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