Sh: fork: retry: Resource temporarily unavailable

I have the following set up as a cron job as per Matomo documentation.
php xxx.xxx.ca/console core:archive --url=https://traffic.umintmed.ca/ > matomo_archive_log
For the last few days I intermittently get errors from this.

Sometimes the errors are just a single
sh: fork: retry: Resource temporarily unavailable
and sometimes there are two.

What do I do to fix this?

At least once there was a lot more info:

ERROR [2020-10-07 00:05:09] 17403  Error unserializing the following response from ?module=API&method=API.get&idSite=1&period=month&date=last2&format=php&trigger=archivephp: sh: fork: retry: Resource temporarily unavailable a:2:{s:7:"2020-09";a:64:{s:16:"nb_uniq_visitors";d:81;s:9:"nb_visits";d:82;s:8:"nb_users";i:0;s:10:"nb_actions";d:105;s:11:"max_actions";d:6;s:12:"bounce_count";d:71;s:16:"sum_visit_length";d:3002;s:13:"nb_visits_new";d:78;s:14:"nb_actions_new";d:98;s:20:"nb_uniq_visitors_new";d:78;s:12:"nb_users_new";i:0;s:15:"max_actions_new";d:6;s:15:"bounce_rate_new";s:3:"87%";s:24:"nb_actions_per_visit_new";d:1.3;s:20:"avg_time_on_site_new";d:33;s:19:"nb_visits_returning";d:4;s:20:"nb_actions_returning";d:7;s:26:"nb_uniq_visitors_returning";d:4;s:18:"nb_users_returning";i:0;s:21:"max_actions_returning";d:4;s:21:"bounce_rate_returning";s:3:"75%";s:30:"nb_actions_per_visit_returning";d:1.8;s:26:"avg_time_on_site_returning";d:116;s:35:"Referrers_visitorsFromSearchEngines";i:60;s
 :36:"Referrers_visitorsFromSocialNetworks";i:0;s:33:"Referrers_visitorsFromDirectEntry";i:4;s:30:"Referrers_visitorsFromWebsites";i:18;s:31:"Referrers_visitorsFromCampaigns";i:0;s:31:"Referrers_distinctSearchEngines";d:2;s:32:"Referrers_distinctSocialNetworks";i:0;s:26:"Referrers_distinctKeywords";d:2;s:26:"Referrers_distinctWebsites";d:3;s:30:"Referrers_distinctWebsitesUrls";d:11;s:27:"Referrers_distinctCampaigns";i:0;s:41:"Referrers_visitorsFromDirectEntry_percent";s:2:"4%";s:43:"Referrers_visitorsFromSearchEngines_percent";s:3:"56%";s:39:"Referrers_visitorsFromCampaigns_percent";s:2:"0%";s:44:"Referrers_visitorsFromSocialNetworks_percent";s:2:"0%";s:38:"Referrers_visitorsFromWebsites_percent";s:3:"17%";s:14:"nb_conversions";i:0;s:19:"nb_visits_converted";i:0;s:7:"revenue";i:0;s:15:"conversion_rate";s:2:"0%";s:24:"nb_conversions_new_visit";i:0;s:29:"nb_visits_converted_new_visit";i:0;s:17:"revenue_new_visit";i:0;s:25:"conversion_rate_new_visit";s:2:"0%";s:30:"nb_conversions_return
 ing_visit";i:0;s:35:"nb_visits_converted_returning_visit";i:0;s:23:"revenue_returning_visit";i:0;s:31:"conversion_rate_returning_visit";s:2:"0%";s:12:"nb_pageviews";d:104;s:17:"nb_uniq_pageviews";d:101;s:12:"nb_downloads";i:0;s:17:"nb_uniq_downloads";i:0;s:11:"nb_outlinks";i:0;s:16:"nb_uniq_outlinks";i:0;s:11:"nb_searches";d:1;s:11:"nb_keywords";d:1;s:28:"nb_hits_with_time_generation";d:97;s:19:"avg_time_generation";d:0.912;s:11:"bounce_rate";s:3:"87%";s:20:"nb_actions_per_visit";d:1.3;s:16:"avg_time_on_site";d:37;}s:7:"2020-10";a:64:{s:16:"nb_uniq_visitors";d:26;s:9:"nb_visits";d:26;s:8:"nb_users";i:0;s:10:"nb_actions";d:31;s:11:"max_actions";d:3;s:12:"bounce_count";d:22;s:16:"sum_visit_length";d:222;s:13:"nb_visits_new";d:25;s:14:"nb_actions_new";d:28;s:20:"nb_uniq_visitors_new";d:25;s:12:"nb_users_new";i:0;s:15:"max_actions_new";d:2;s:15:"bounce_rate_new";s:3:"88%";s:24:"nb_actions_per_visit_new";d:1.1;s:20:"avg_time_on_site_new";d:4;s:19:"nb_visits_returning";d:1;s:20:"nb_action
 s_returning";d:3;s:26:"nb_uniq_visitors_returning";d:1;s:18:"nb_users_returning";i:0;s:21:"max_actions_returning";d:3;s:21:"bounce_rate_returning";s:2:"0%";s:30:"nb_actions_per_visit_returning";d:3;s:26:"avg_time_on_site_returning";d:133;s:35:"Referrers_visitorsFromSearchEngines";i:12;s:36:"Referrers_visitorsFromSocialNetworks";i:0;s:33:"Referrers_visitorsFromDirectEntry";i:12;s:30:"Referrers_visitorsFromWebsites";i:2;s:31:"Referrers_visitorsFromCampaigns";i:0;s:31:"Referrers_distinctSearchEngines";d:2;s:32:"Referrers_distinctSocialNetworks";i:0;s:26:"Referrers_distinctKeywords";d:1;s:26:"Referrers_distinctWebsites";d:1;s:30:"Referrers_distinctWebsitesUrls";d:2;s:27:"Referrers_distinctCampaigns";i:0;s:41:"Referrers_visitorsFromDirectEntry_percent";s:3:"11%";s:43:"Referrers_visitorsFromSearchEngines_percent";s:3:"11%";s:39:"Referrers_visitorsFromCampaigns_percent";s:2:"0%";s:44:"Referrers_visitorsFromSocialNetworks_percent";s:2:"0%";s:38:"Referrers_visitorsFromWebsites_percent";s:2:"
 2%";s:14:"nb_conversions";i:0;s:19:"nb_visits_converted";i:0;s:7:"revenue";i:0;s:15:"conversion_rate";s:2:"0%";s:24:"nb_conversions_new_visit";i:0;s:29:"nb_visits_converted_new_visit";i:0;s:17:"revenue_new_visit";i:0;s:25:"conversion_rate_new_visit";s:2:"0%";s:30:"nb_conversions_returning_visit";i:0;s:35:"nb_visits_converted_returning_visit";i:0;s:23:"revenue_returning_visit";i:0;s:31:"conversion_rate_returning_visit";s:2:"0%";s:12:"nb_pageviews";d:31;s:17:"nb_uniq_pageviews";d:30;s:12:"nb_downloads";i:0;s:17:"nb_uniq_downloads";i:0;s:11:"nb_outlinks";i:0;s:16:"nb_uniq_outlinks";i:0;s:11:"nb_searches";i:0;s:11:"nb_keywords";i:0;s:28:"nb_hits_with_time_generation";d:30;s:19:"avg_time_generation";d:1.08;s:11:"bounce_rate";s:3:"85%";s:20:"nb_actions_per_visit";d:1.2;s:16:"avg_time_on_site";d:9;}}
ERROR [2020-10-07 00:05:30] 17403  Got invalid response from API request: ?module=API&method=API.get&idSite=4&period=month&date=last2&format=php&trigger=archivephp. The response was empty. This usually means a server error. A solution to this error is generally to increase the value of 'memory_limit' in your php.ini file.  For more information and the error message please check in your PHP CLI error log file. As this core:archive command triggers PHP processes over the CLI, you can find where PHP CLI logs are stored by running this command: php -i | grep error_log ERROR [2020-10-07 00:05:36] 17403  2 total errors during this script execution, please investigate and try and fix these errors.
ERROR [2020-10-07 00:05:36] 17403  Uncaught exception: /home/xxx/xxx.xxx.ca/core/CronArchive.php(606): 2 total errors during this script execution, please investigate and try and fix these errors.
2 total errors during this script execution, please investigate and try and fix these errors.
#0 /home/xxx/xxx.xxx.ca/core/CronArchive.php(599): Piwik\CronArchive->logFatalError('2 total errors ...')
#1 /home/xxx/xxx.xxx.ca/core/CronArchive.php(331): Piwik\CronArchive->end()
#2 /home/xxx/xxx.xxx.ca/core/Access.php(635): Piwik\CronArchive->Piwik\{closure}()
#3 /home/xxx/xxx.xxx.ca/core/CronArchive.php(335): Piwik\Access::doAsSuperUser(Object(Closure))
#4 /home/xxx/xxx.xxx.ca/plugins/CoreConsole/Commands/CoreArchiver.php(27): Piwik\CronArchive->main()
#5 /home/xxx/xxx.xxx.ca/vendor/symfony/console/Symfony/Component/Console/Command/Command.php(257): Piwik\Plugins\CoreConsole\Commands\CoreArchiver->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#6 /home/xxx/xxx.xxx.ca/vendor/symfony/console/Symfony/Component/Console/Application.php(874): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#7 /home/xxx/xxx.xxx.ca/vendor/symfony/console/Symfony/Component/Console/Application.php(195): Symfony\Component\Console\Application->doRunCommand(Object(Piwik\Plugins\CoreConsole\Commands\CoreArchiver), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#8 [internal function]: Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#9 /home/xxx/xxx.xxx.ca/core/Console.php(140): call_user_func(Array, Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#10 /home/xxx/xxx.xxx.ca/core/Access.php(644): Piwik\Console->Piwik\{closure}()
#11 /home/xxx/xxx.xxx.ca/core/Console.php(141): Piwik\Access::doAsSuperUser(Object(Closure))
#12 /home/xxx/xxx.xxx.ca/core/Console.php(93): Piwik\Console->doRunImpl(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#13 /home/xxx/xxx.xxx.ca/vendor/symfony/console/Symfony/Component/Console/Application.php(126): Piwik\Console->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#14 /home/xxx/xxx.xxx.ca/console(32): Symfony\Component\Console\Application->run()
#15 {main}


                                                                                                 
  [Exception]                                                                                    
  2 total errors during this script execution, please investigate and try and fix these errors.  
                                                                                                 


core:archive [--url="..."] [--force-all-websites] [--force-all-periods[="..."]] [--force-timeout-for-periods[="..."]] [--skip-idsites[="..."]] [--skip-all-segments] [--force-idsites[="..."]] [--skip-segments-today] [--force-periods[="..."]] [--force-date-last-n="..."] [--force-date-range[="..."]] [--force-idsegments="..."] [--concurrent-requests-per-website[="..."]] [--concurrent-archivers[="..."]] [--disable-scheduled-tasks] [--accept-invalid-ssl-certificate] [--php-cli-options[="..."]]

Hi,

According to

this might happen for example if your user has limits set via ulimit and you are exceeding them. Maybe you have reached the set limit of processes per users and the archiving tried spawning additional ones.