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"Address already in use": find who is using port 80 (or any port)
Fix "bind() failed (98: Address already in use)": find the process holding the port with ss or lsof, then stop it, move it, or change your port.
Beginner · 4 min read
Docker "exited with code 137": OOM kill or a stop that took too long
Exit code 137 means the container was killed with SIGKILL. Find out if it ran out of memory or ignored docker stop, and fix each case.
Intermediate · 5 min read
Kubernetes CrashLoopBackOff: 7 causes and how to find yours
CrashLoopBackOff means the container keeps exiting. Read the exit code and the previous logs, then fix the crash, OOM kill, probe or command.
Intermediate · 5 min read
MySQL ERROR 1045 (28000): Access denied for user — find which part is wrong
Fix MySQL "ERROR 1045 Access denied for user": check the user@host account, the password, socket vs TCP, option files, and Docker init passwords.
Beginner · 5 min read
Nginx "502 Bad Gateway": find the cause in the error log
Fix nginx 502 Bad Gateway: read error.log, then fix the backend that is down, the wrong address or socket, the crashing app, or SELinux on RHEL.
Intermediate · 5 min read
No space left on device: find what is filling your Linux disk
Fix "No space left on device" on Linux: find the biggest directories and files, free space safely, and handle the cases where df says there is space.
Beginner · 4 min read
"Permission denied" when running a script: 5 causes and fixes
Fix "bash: ./script.sh: Permission denied" and "bad interpreter" on Linux: execute bits, noexec mounts, directory permissions, Windows line endings and shebangs.
Beginner · 4 min read
PostgreSQL "duplicate key value violates unique constraint": causes and fixes
Fix "duplicate key value violates unique constraint" in PostgreSQL: tell a real duplicate from a sequence that is out of sync, and fix both safely.
Intermediate · 4 min read
PostgreSQL "permission denied for table": causes and fixes
Fix "ERROR: permission denied for table" in PostgreSQL: check what a role can do, grant the right privileges, and fix the schema, sequence and future-table cases.
Intermediate · 4 min read
SSH "Permission denied (publickey)": how to find the real cause
Fix SSH "Permission denied (publickey)": read the server log, fix ~/.ssh permissions, check the key and sshd_config, and handle SELinux on RHEL.
Intermediate · 3 min read