strace — Trace System Calls and Signals

strace traces system calls and signals made by a process. It is useful when a program fails but the error message does not explain what happened.

Trace a command

strace ls /tmp

Attach to a running process

strace -p 1234

Save output to a file

strace -o trace.log command

Common things to look for are missing files, permission errors, failed network calls and repeated retries.