Linux error 'Text file busy' (ETXTBSY), e.g. 'cp: cannot create regular file ...: Text file busy' when replacing a running binary, or 'bash: ./script: Text file busy' / 'fork/exec ...: text file busy' when running a file just written. How do I fix it?

Cause: the kernel won't let a program file be opened for writing while it is being executed, and won't execute a file that some process still has open for writing. So you get ETXTBSY ('Text file busy') in two common cases: (1) overwriting a binary in place while it's running (cp new-binary over a running service, deploy scripts, updating a tool that's in use), and (2) running a file right after writing it while a write handle is still open (a script that writes then executes a file without closing it, a parallel build step, or a forked child that inherited the open file descriptor, which is a known issue in Go and other multi-threaded programs). How to check: lsof /path/to/file or fuser -v /path/to/file shows which processes have it open. Fix: 1. To update a running program, don't write into the existing file. Write the new version to a temporary file in the same directory, then rename it over the old one: cp new-binary /usr/local/bin/.tool.new && mv /usr/local/bin/.tool.new /usr/local/bin/tool. rename() replaces the directory entry atomically; running processes keep using the old file until they restart. Then restart the service. 2. For a file you just created, make sure every write handle is closed before executing it (close the file in your code, or finish the redirect/heredoc before running it). In tests or builds, avoid running a file while another step is still writing it. 3. If a stray process holds the file open, find it with lsof/fuser and stop or restart it. 4. In programs that create and then run executables while other threads fork, open the file with close-on-exec (O_CLOEXEC, which most language runtimes do by default), and retry briefly or write the file before starting other threads. Don't kill unknown processes blindly; check what holds the file first. Verify: the copy or command succeeds, and lsof shows the expected process using the new file after restart. Sources: https://man7.org/linux/man-pages/man2/open.2.html https://man7.org/linux/man-pages/man2/execve.2.html https://man7.org/linux/man-pages/man2/rename.2.html