{"id":2076,"date":"2017-08-02T12:41:36","date_gmt":"2017-08-02T16:41:36","guid":{"rendered":"https:\/\/www.pair.com\/support\/kb\/?p=2076"},"modified":"2020-02-26T12:36:03","modified_gmt":"2020-02-26T17:36:03","slug":"what-is-a-503-error","status":"publish","type":"ht_kb","link":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/","title":{"rendered":"What is a 503 Error?"},"content":{"rendered":"

A 503 error message is generated on the server side to tell the user that the service is unavailable. <\/span><\/p>\n

<\/a><\/p>\n

Common Error Messages<\/h3>\n
HTTP Server Error 503<\/span><\/pre>\n
503 Error<\/span><\/pre>\n
HTTP 503<\/span><\/pre>\n
Http\/1.1 Service Unavailable<\/span><\/pre>\n
503 Service Unavailable<\/span><\/pre>\n
Service is unavailable<\/span><\/pre>\n
Service Unavailable - DNS Failure<\/span><\/pre>\n
503 errors can occur if a site is taken down for maintenance or if there is a server-side problem. A server-side problem doesn\u2019t necessarily mean your server itself. It could be that the server has too many processes running or it\u2019s trying to run inefficient programming.<\/span><\/p>\n
<\/a><\/p>\n
Here are some common causes:<\/h3>\n
<\/a><\/p>\n
Inefficient Programming<\/h4>\n
A 503 is often due to inefficient programming. Inefficient code can slow down your server and eventually cause 503 error. <\/span><\/p>\n
To fix the immediate problem, begin turning programs on your server off and on, one by one. If you are on a Dedicated or VPS server, you may also be able to restart Apache. See our\u00a0<\/span>How to Restart Apache<\/span><\/a> article for more information. <\/span><\/p>\n    \t\t
\r\n    \t\t\t    \t\t\t    \t\t\t\t
\r\n    \t\t\t\t\tKeep in mind that any websites or services on your server will be unavailable while you are doing this.    \t\t\t\t<\/p>\r\n    \t\t\t    \t\t\t\r\n    \t\t<\/div>\r\n    \t\t\n
To fix the overall problem, you must go through your code and look for ways to make it more efficient.<\/span><\/p>\n
<\/a><\/p>\n
Zombie Processes<\/h4>\n
Sometimes processes aren\u2019t properly deleted after they finish running. These processes are known as \u201czombie\u201d processes. They slow down your website simply by existing. <\/span><\/p>\n
The reason why requires some understanding of what zombie processes actually are. <\/span><\/p>\n
When a process is done running, it leaves its process descriptor in the memory. This process descriptor signals to the process\u2019 parent that the child process has ceased to run. If all goes correctly, the parent process will gather the child\u2019s information and then completely remove it from memory. <\/span><\/p>\n
Sometimes, though, the parent program isn\u2019t programmed correctly and never gathers the child process\u2019\u00a0information. Without the child\u2019s information, the child will not be completely removed. This is how a zombie process is made. One or two zombie processes are fine, but the problems usually start when they begin to pile up.<\/span><\/p>\n
While zombie processes don\u2019t use up any system resource, they do keep their process ID (PID). On Linux servers, there is a limited number of PIDs. Usually, when a process is completely removed, its PID becomes available for a new process to use. \u00a0<\/span><\/p>\n
The more zombie processes a server has, the fewer PIDs there are for legitimate processes. If a server runs out of PIDs due to an overabundance of zombie processes, it may generate a 503 error. <\/span><\/p>\n
Check out <\/span>HowToGeek\u2019s explanation<\/span><\/a> for more details about zombie processes on a Linux machine. <\/span><\/p>\n
To see if you have zombie processes bogging down your server, complete the following steps:<\/span><\/p>\n
    \n
  1. Open a terminal (Mac) or command prompt (Windows) window<\/span><\/li>\n
  2. Type: <\/span>ssh username@web-server.com\u00a0<\/span>and press the <\/span>Enter<\/b> key<\/span>\n
      \n
    1. username.pairserver.com<\/span> is the usual format of a Pair Network's web server. If you\u2019re not sure what your web server is, log into your <\/span>Account Control Center<\/span><\/a>. Under\u00a0Account Summary<\/strong><\/span>, you will see your Web Server<\/strong> name.<\/span><\/li>\n<\/ol>\n<\/li>\n
    2.  \u00a0Enter your password and press the <\/span>Enter <\/b>key<\/span><\/li>\n
    3. Type: <\/span>ps axo pid=,stat= | awk '$2~\/^Z\/ { print }'\u00a0<\/span><\/li>\n
    4. Press\u00a0Enter<\/strong><\/li>\n<\/ol>\n
      This will display the PID and status of any zombie processes existing on your server.<\/span>\u00a0<\/span><\/p>\n
      \"\"<\/a><\/p>\n
      How to Fix<\/h5>\n
      Once you\u2019ve found your zombie processes, you need to get rid of them to solve the problem. <\/span><\/p>\n
      The first step to ridding yourself of zombie processes is finding the parents. You can do this by inputting the following into your shell: <\/span><\/p>\n
      pstree -s -p zombie_PID<\/span><\/pre>\n
      Replace zombie_PID<\/span> with the PID of the zombie child. This will show the parent of the PID you put in. Keep in mind that this also shows the parents of the parent, but the parent you are looking for is will be directly next to the zombie child.<\/span><\/p>\n
      For example: <\/span><\/p>\n
      init(1)---httpd(27117)---<\/span>httpd(19531)<\/strong>---php5.cgi(19646)<\/span><\/pre>\n
      The <\/span>httpd<\/span> next to <\/span>php5.cgi<\/span> would be the parent you are looking for. <\/span><\/p>\n
      If you find that many of your zombie processes have the same parent, then that program most likely has a bug that is keeping it from correctly closing its child processes. <\/span><\/p>\n
      Once you have the PID of the parent, you have two options: <\/span><\/p>\n
      You can try to send a manual command to the parent process to gather the child process\u2019 information. <\/span><\/p>\n
      Do this by : <\/span><\/p>\n
      kill -s SIGCHLD parent_PID<\/span><\/pre>\n
      Replace parent_PID<\/span> with the PID of the parent.<\/span><\/p>\n
      However, this will not succeed if there is an error in the parent\u2019s programming. If this is the case, you need to close the parent process. Don\u2019t worry, you can re-open it when you finish. <\/span><\/p>\n
      Closing the parent process will send all the child process\u2019 to the <\/span>init<\/b>, the first process started when Linux starts up. <\/span>init<\/b> regularly performs checks for zombie processes and will wipe the zombie processes the next time it performs a check.<\/span><\/p>\n
      Close the parent by:<\/span><\/p>\n
      kill parent_PID<\/span><\/pre>\n
      This command asks the process to terminate. If the process has trouble shutting down, you can force the process to close by using:<\/span><\/p>\n
      Kill -KILL parent_PID<\/span><\/pre>\n
      Now, the problem may be fixed momentarily, but if you suspect the parent process has a bug that keeps it from properly closing its children processes, you may want to take steps to fix it. <\/span><\/p>\n
      If the coding is your\u2019s, you can look through it and see if anything is keeping the parent process from gathering and cleaning its zombie children. <\/span><\/p>\n
      If the code is not yours, you should report the bug to the code\u2019s owner. <\/span><\/p>\n","protected":false},"excerpt":{"rendered":"
      A 503 error message is generated on the server side to tell the user that the service is unavailable. Common Error Messages HTTP Server Error 503 503 Error HTTP 503 Http\/1.1 Service Unavailable 503 Service Unavailable Service is unavailable Service Unavailable – DNS Failure 503 errors can occur if a…<\/p>\n","protected":false},"author":11,"comment_status":"closed","ping_status":"open","template":"","format":"standard","meta":[],"ht-kb-category":[24],"ht-kb-tag":[],"yoast_head":"\nWhat is a 503 Error? - Knowledge Base - Pair Networks<\/title>\n<meta name=\"description\" content=\"A 503 error message is generated on the server side to tell the user that the service is unavailable. Learn about potential fixes here.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What is a 503 Error? - Knowledge Base - Pair Networks\" \/>\n<meta property=\"og:description\" content=\"A 503 error message is generated on the server side to tell the user that the service is unavailable. Learn about potential fixes here.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/\" \/>\n<meta property=\"og:site_name\" content=\"Knowledge Base - Pair Networks\" \/>\n<meta property=\"article:publisher\" content=\"https:\/\/www.facebook.com\/pairnetworks\/\" \/>\n<meta property=\"article:modified_time\" content=\"2020-02-26T17:36:03+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.pair.com\/support\/kb\/wp-content\/uploads\/2017\/08\/PID-copy.png\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:site\" content=\"@pairNetworks\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"5 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/\",\"url\":\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/\",\"name\":\"What is a 503 Error? - Knowledge Base - Pair Networks\",\"isPartOf\":{\"@id\":\"https:\/\/www.pair.com\/support\/kb\/#website\"},\"datePublished\":\"2017-08-02T16:41:36+00:00\",\"dateModified\":\"2020-02-26T17:36:03+00:00\",\"description\":\"A 503 error message is generated on the server side to tell the user that the service is unavailable. Learn about potential fixes here.\",\"breadcrumb\":{\"@id\":\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/\"]}]},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/www.pair.com\/support\/kb\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"What is a 503 Error?\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.pair.com\/support\/kb\/#website\",\"url\":\"https:\/\/www.pair.com\/support\/kb\/\",\"name\":\"Knowledge Base - Pair Networks\",\"description\":\"\",\"publisher\":{\"@id\":\"https:\/\/www.pair.com\/support\/kb\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/www.pair.com\/support\/kb\/?s={search_term_string}\"},\"query-input\":\"required name=search_term_string\"}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\/\/www.pair.com\/support\/kb\/#organization\",\"name\":\"Pair Networks\",\"url\":\"https:\/\/www.pair.com\/support\/kb\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.pair.com\/support\/kb\/#\/schema\/logo\/image\/\",\"url\":\"https:\/\/www.pair.com\/support\/kb\/wp-content\/uploads\/2022\/02\/Gb_TUkUE_400x400.jpeg\",\"contentUrl\":\"https:\/\/www.pair.com\/support\/kb\/wp-content\/uploads\/2022\/02\/Gb_TUkUE_400x400.jpeg\",\"width\":360,\"height\":360,\"caption\":\"Pair Networks\"},\"image\":{\"@id\":\"https:\/\/www.pair.com\/support\/kb\/#\/schema\/logo\/image\/\"},\"sameAs\":[\"https:\/\/www.facebook.com\/pairnetworks\/\",\"https:\/\/twitter.com\/pairNetworks\",\"https:\/\/www.instagram.com\/pairnetworks\/\",\"https:\/\/www.linkedin.com\/company\/2269676\/\",\"https:\/\/www.pinterest.com\/pairnetworksinc\/pins\/\",\"https:\/\/www.youtube.com\/user\/pairnetworks\"]}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"What is a 503 Error? - Knowledge Base - Pair Networks","description":"A 503 error message is generated on the server side to tell the user that the service is unavailable. Learn about potential fixes here.","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/","og_locale":"en_US","og_type":"article","og_title":"What is a 503 Error? - Knowledge Base - Pair Networks","og_description":"A 503 error message is generated on the server side to tell the user that the service is unavailable. Learn about potential fixes here.","og_url":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/","og_site_name":"Knowledge Base - Pair Networks","article_publisher":"https:\/\/www.facebook.com\/pairnetworks\/","article_modified_time":"2020-02-26T17:36:03+00:00","og_image":[{"url":"https:\/\/www.pair.com\/support\/kb\/wp-content\/uploads\/2017\/08\/PID-copy.png"}],"twitter_card":"summary_large_image","twitter_site":"@pairNetworks","twitter_misc":{"Est. reading time":"5 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/","url":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/","name":"What is a 503 Error? - Knowledge Base - Pair Networks","isPartOf":{"@id":"https:\/\/www.pair.com\/support\/kb\/#website"},"datePublished":"2017-08-02T16:41:36+00:00","dateModified":"2020-02-26T17:36:03+00:00","description":"A 503 error message is generated on the server side to tell the user that the service is unavailable. Learn about potential fixes here.","breadcrumb":{"@id":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/"]}]},{"@type":"BreadcrumbList","@id":"https:\/\/www.pair.com\/support\/kb\/what-is-a-503-error\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.pair.com\/support\/kb\/"},{"@type":"ListItem","position":2,"name":"What is a 503 Error?"}]},{"@type":"WebSite","@id":"https:\/\/www.pair.com\/support\/kb\/#website","url":"https:\/\/www.pair.com\/support\/kb\/","name":"Knowledge Base - Pair Networks","description":"","publisher":{"@id":"https:\/\/www.pair.com\/support\/kb\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.pair.com\/support\/kb\/?s={search_term_string}"},"query-input":"required name=search_term_string"}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/www.pair.com\/support\/kb\/#organization","name":"Pair Networks","url":"https:\/\/www.pair.com\/support\/kb\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.pair.com\/support\/kb\/#\/schema\/logo\/image\/","url":"https:\/\/www.pair.com\/support\/kb\/wp-content\/uploads\/2022\/02\/Gb_TUkUE_400x400.jpeg","contentUrl":"https:\/\/www.pair.com\/support\/kb\/wp-content\/uploads\/2022\/02\/Gb_TUkUE_400x400.jpeg","width":360,"height":360,"caption":"Pair Networks"},"image":{"@id":"https:\/\/www.pair.com\/support\/kb\/#\/schema\/logo\/image\/"},"sameAs":["https:\/\/www.facebook.com\/pairnetworks\/","https:\/\/twitter.com\/pairNetworks","https:\/\/www.instagram.com\/pairnetworks\/","https:\/\/www.linkedin.com\/company\/2269676\/","https:\/\/www.pinterest.com\/pairnetworksinc\/pins\/","https:\/\/www.youtube.com\/user\/pairnetworks"]}]}},"_links":{"self":[{"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/ht-kb\/2076"}],"collection":[{"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/ht-kb"}],"about":[{"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/types\/ht_kb"}],"author":[{"embeddable":true,"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/users\/11"}],"replies":[{"embeddable":true,"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/comments?post=2076"}],"version-history":[{"count":18,"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/ht-kb\/2076\/revisions"}],"predecessor-version":[{"id":7454,"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/ht-kb\/2076\/revisions\/7454"}],"wp:attachment":[{"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/media?parent=2076"}],"wp:term":[{"taxonomy":"ht_kb_category","embeddable":true,"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/ht-kb-category?post=2076"},{"taxonomy":"ht_kb_tag","embeddable":true,"href":"https:\/\/www.pair.com\/support\/kb\/wp-json\/wp\/v2\/ht-kb-tag?post=2076"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}