# A gotcha with fcntl file locking

Today I ran into an issue with [fcntl(2)](http://linux.die.net/man/2/fcntl) file locking[^1] on Linux. A little research confirmed my fear:

From ["On the Brokenness of File Locking"](https://0pointer.de/blog/projects/locking.html) by Lennart Poettering:

> The worst part however is that POSIX locks are automatically released if a process calls `close()` on *any* (!) of its open file descriptors for that file.

The whole post is well worth a read.

[^1]: Which is what OpenJDK uses for [FileChannel#lock](http://docs.oracle.com/javase/8/docs/api/java/nio/channels/FileChannel.html#lock--).

## Page metadata

URL: <https://dbohdan.com/fcntl.md>

Published 2015-09-26, updated 2021-08-21.

Tags:

- JVM
- Linux
- old blog
- programming
- Unix

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