{"id":19985,"date":"2014-01-28T12:30:50","date_gmt":"2014-01-28T10:30:50","guid":{"rendered":"https:\/\/mamchenkov.net\/wordpress\/?p=19985"},"modified":"2014-01-28T12:31:05","modified_gmt":"2014-01-28T10:31:05","slug":"3-things-to-remember-when-writing-cron-jobs","status":"publish","type":"post","link":"https:\/\/mamchenkov.net\/wordpress\/2014\/01\/28\/3-things-to-remember-when-writing-cron-jobs\/","title":{"rendered":"3 things to remember when writing cron jobs"},"content":{"rendered":"\n

Here is a reminder to myself with three things to remember when writing cron jobs. \u00a0Surprisingly, even after doing it fairly frequently for years and years, I still get caught by one of these once in a while.<\/p>\n

    \n
  1. User<\/strong>. \u00a0Just because the script is working fine under your user, it doesn’t mean it will work well from crontab. \u00a0Cron jobs are often executed under a different user account. \u00a0 Check, don’t assume. \u00a0And be noisy about permissions and other possibly related issues.<\/li>\n
  2. Environment<\/strong>. \u00a0This is slightly related to the previous point. \u00a0But just because something works fine from the command line, doesn’t mean it will run smoothly as a cron task. \u00a0Anything that requires particular environment variables, user input, or being executed in a specific directory should be double checked.<\/li>\n
  3. Duration<\/strong>. \u00a0Cron executes tasks on schedule. \u00a0It doesn’t really care if the previous instances finished running. \u00a0So, either make sure the script can run several instances simultaneously, or using a locking mechanism, to make sure two instances don’t step on each other’s toes.<\/li>\n<\/ol>\n\n","protected":false},"excerpt":{"rendered":"\n

    Here is a reminder to myself with three things to remember when writing cron jobs. \u00a0Surprisingly, even after doing it fairly frequently for years and years, I still get caught by one of these once in a while. User. \u00a0Just because the script is working fine under your user, it doesn’t mean it will work … Continue reading 3 things to remember when writing cron jobs<\/span><\/a><\/p>\n\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"_links_to":"","_links_to_target":""},"categories":[1,6,18,133,62],"tags":[],"keyring_services":[],"class_list":["post-19985","post","type-post","status-publish","format-standard","hentry","category-general","category-linux","category-programming","category-sysadmin","category-technology"],"aioseo_notices":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack-related-posts":[{"id":18479,"url":"https:\/\/mamchenkov.net\/wordpress\/2013\/07\/08\/there-is-nothing-like-a-cron-job-that-runs-every-m\/","url_meta":{"origin":19985,"position":0},"title":"There is nothing like a cron job that runs every m…","author":"Leonid Mamchenkov","date":"July 8, 2013","format":"status","excerpt":"There is nothing like a cron job that runs every minute, inserts a few thousand lines into the DB and then ... breaks in the middle of the night. \u00a0Inbox is fun.","rel":"","context":"In "All"","block_context":{"text":"All","link":"https:\/\/mamchenkov.net\/wordpress\/category\/general\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":26708,"url":"https:\/\/mamchenkov.net\/wordpress\/2016\/09\/28\/rundeck-job-scheduler-and-runbook-automation\/","url_meta":{"origin":19985,"position":1},"title":"Rundeck – Job Scheduler and Runbook Automation","author":"Leonid Mamchenkov","date":"September 28, 2016","format":false,"excerpt":"Rundeck is yet another one of those services that I want to get my hands on but haven't yet got the time to. \u00a0The simplest way to describe it is: cron on steroids. Rundeck allows one to define the commands and then allow for execution on those commands manually, periodically\u2026","rel":"","context":"In "All"","block_context":{"text":"All","link":"https:\/\/mamchenkov.net\/wordpress\/category\/general\/"},"img":{"alt_text":"Rundeck-EditJob","src":"https:\/\/i0.wp.com\/mamchenkov.net\/wordpress\/wp-content\/uploads\/2016\/09\/Rundeck-EditJob-500x344.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":22255,"url":"https:\/\/mamchenkov.net\/wordpress\/2014\/07\/24\/validating-website-html-css-and-links-from-the-command-line\/","url_meta":{"origin":19985,"position":2},"title":"Validating website HTML, CSS, and links from the command line","author":"Leonid Mamchenkov","date":"July 24, 2014","format":false,"excerpt":"When working on a long running projects, it's easy to lose track of HTML and CSS standard compliance. \u00a0Also, link rot is a common occurrence. \u00a0Gladly, there are command line tools that can be executed on a regular basis (think weekly or monthly cron jobs), that would check the site\u2026","rel":"","context":"In "All"","block_context":{"text":"All","link":"https:\/\/mamchenkov.net\/wordpress\/category\/general\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":28453,"url":"https:\/\/mamchenkov.net\/wordpress\/2018\/03\/26\/systemdaemon-simple-base-for-system-daemons-in-php\/","url_meta":{"origin":19985,"position":3},"title":"SystemDaemon – Simple base for system daemons in PHP","author":"Leonid Mamchenkov","date":"March 26, 2018","format":false,"excerpt":"SystemDaemon is a library that helps with writing system daemons and services in PHP.\u00a0 PHP is not my personal favorite language for such tasks, but there is often a need, despite the preference.\u00a0 Some examples are: scheduled tasks (cron jobs) that need to execute more often than once per minute\u2026","rel":"","context":"In "All"","block_context":{"text":"All","link":"https:\/\/mamchenkov.net\/wordpress\/category\/general\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":124,"url":"https:\/\/mamchenkov.net\/wordpress\/2003\/01\/21\/random-bits-13\/","url_meta":{"origin":19985,"position":4},"title":"Random bits","author":"Leonid Mamchenkov","date":"January 21, 2003","format":false,"excerpt":"Amanda configuration fooling around, miscelaneous bits are still restoring after the sytem crash, some DocBook, some cron, some LDAP, some whatever.","rel":"","context":"In "All"","block_context":{"text":"All","link":"https:\/\/mamchenkov.net\/wordpress\/category\/general\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":8021,"url":"https:\/\/mamchenkov.net\/wordpress\/2004\/10\/08\/domain-name-expiration-reminder\/","url_meta":{"origin":19985,"position":5},"title":"Domain name expiration reminder","author":"Leonid Mamchenkov","date":"October 8, 2004","format":false,"excerpt":"A very useful script was posted to PerlMonks today. It can be used from cron or command line to send a reminder about expiring domain name. Domains can be put into file and notification intervals can be set up for each separately. Great stuff!","rel":"","context":"In "All"","block_context":{"text":"All","link":"https:\/\/mamchenkov.net\/wordpress\/category\/general\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_sharing_enabled":true,"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/posts\/19985","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/comments?post=19985"}],"version-history":[{"count":0,"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/posts\/19985\/revisions"}],"wp:attachment":[{"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/media?parent=19985"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/categories?post=19985"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/tags?post=19985"},{"taxonomy":"keyring_services","embeddable":true,"href":"https:\/\/mamchenkov.net\/wordpress\/wp-json\/wp\/v2\/keyring_services?post=19985"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}