Troubleshooting

Fix Python SSL: CERTIFICATE_VERIFY_FAILED Error

You’re making an HTTP request in Python and suddenly: s s l . S S L C e r t V e r i f i c a t i o n E r r o r : [ S S L : C E R T I F I C A T E _ V E R I F Y _ F A I L E D ] c e r t i f i c a t e v e r i f y f a i l e d : u n a b l e t o g e t l o c a l i s s u e r c e r t i f i c a t e Or with requests: ...

Why Your Cron Job Isn't Running (And How to Fix It)

You added a cron job. It works when you run it manually. But cron just… doesn’t run it. No errors, no output, nothing. This is one of the most frustrating debugging experiences in Linux. Here’s a systematic checklist to find out what’s actually wrong. 1. Check If Cron Is Running First, make sure the cron daemon is actually running: 1 2 3 4 5 6 7 # systemd systems systemctl status cron # or systemctl status crond # Older init systems service cron status If it’s not running, start it: ...

Fix 'Address Already in Use' Error (EADDRINUSE) — Find and Kill the Process

You try to start your server and get hit with: E r r o r : l i s t e n E A D D R I N U S E : a d d r e s s a l r e a d y i n u s e : : : 3 0 0 0 Or the Python equivalent: ...

Fix: Python imaplib search() Returns Empty Results

You’re using Python’s imaplib to search emails, but mail.search() keeps returning empty results even though you know matching emails exist. Here’s why it happens and how to fix it. The Problem 1 2 3 4 5 6 7 8 9 import imaplib mail = imaplib.IMAP4_SSL('imap.gmail.com') mail.login('user@gmail.com', 'app-password') mail.select('INBOX') # This returns nothing! status, messages = mail.search(None, 'FROM "john@example.com" SUBJECT "invoice"') print(messages) # [b''] You’ve verified the emails exist. You can see them in Gmail. But search() returns an empty byte string. ...

Fix: Docker Container Can't Resolve DNS (And Why It Happens)

Your container builds fine, starts fine, then fails with Could not resolve host or Temporary failure in name resolution. Here’s how to fix it. Quick Diagnosis First, confirm it’s actually DNS and not a network issue: 1 2 3 4 5 6 7 8 # Get a shell in the container docker exec -it <container_name> sh # Test DNS specifically nslookup google.com # or cat /etc/resolv.conf ping 8.8.8.8 # If this works but nslookup fails, it's DNS If ping 8.8.8.8 works but nslookup google.com fails, you have a DNS problem. If both fail, it’s a broader network issue. ...