How to Resolve 503 Error in Linux

The 503 service unavailable error may be caused by a connectivity problem between the Linux servers hosting your application. Using the instructions in this knowledge base article is one of the simplest methods to resolve the 503 service temporarily unavailable problem.

Step 1
First you have to check if the website is a node.js/python hosted website. If yes, then go for node.js/python solutions :

Nodejs :

Cpanel >>  node.js >> open the application >> switch  to  the source path from terminal >> run the application : npm start / node app.js runserver &  (main file  may be  app.js, test.js,depends)

If the  error  occurs  for : port is already in  use  then :
netstat -nap | grep :port no.
lsof -p 21069

where 21069 = pid

kill -9 21069

Restart the  application and again run the application.

Check whether the website  is  proxy based or not,in that order check the proxy.

Python :

Cpanel >> node.js >> launch the application >> navigate from the terminal to the source directory >> execute the application: Runserver: python3 manage.py or python manage.py &

Follow the  steps as above as for  node.js

Step 2  

You need to check the resources of the account. If they are high, you need to optimize the resources of the account.

Step 3
Check if there is load on the server. If yes, reduce the server load.

Step 4  
Turn on the debug mode for the website (if it is a WordPress site, change the debug value from false to true in wp-config; if it is a different site, turn on the debug logs using the php ini editor in cPanel). The precise problem will be shown on the website.)

Step 5
Here is the error that you will get on the screen.

“Error :

You will get a memory exhaust error message.

*Allowed memory size of 41943040 bytes exhausted (tried to allocate 32768 bytes) in /home/mumbai/public_html/wp-content/plugins/userswp/vendor/ayecode/wp-super-duper/wp-super-duper.php on line 3060:

To resolve such errors, Increase the values in the multi PHP INI editor.”

Step 6  
If error is related to plugin/theme, then scan the security measures from wp-toolkit, and then you must know that there is error for  the respective plugin , theme ,
Ask the web hosts tech team to disable the plugin, with no changes in the theme.

Step 7  
Check applying different suitable PHP versions to the site (On priority: 5.6, 7.3, 8.0 and above).
That is how you can resolve 503 error on Linux operating systems compatible servers.