Re^2: Best practices for modifying a file in place: q's about opening files, file locking, and using the rename function

in reply to Re: Best practices for modifying a file in place: q's about opening files, file locking, and using the rename function
in thread Best practices for modifying a file in place: q's about opening files, file locking, and using the rename function

As a side-note, it is rename() that does not work across file systems. The "mv" command itself actually acts as a wrapper when the source / destination are on different file systems.

Depending on the UNIX implementation, there are some considerations that may arise when moving a file across filesystems:

1) The source file is copied to the target filesystem and then deleted. It is roughly equivalent to "rm -f DEST && cp -PRp SRC DEST && rm -rf SRC".
2) mv must explicitly copy modification/access time, ownership and mode.
3) on some Unix systems, setuid/setgid permissions are not preserved.
4) ACLs may or may not be replicated.

Hence the Cookbook warning on rename() across file systems. The "mv" command actually does work across filesystems on modern UNIX systems, since it is a requirement of IEEE Std 1003.1-2001.

Regards,
Niel

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