[tpm] Renaming a file with multiple scripts having opened filehandles on it

[Madison Kelly]

Uri Guttman wrote:
>>>>>> "LREQ" == Liam R E Quin <liam at holoweb.net> writes:
> 
>   LREQ> On Fri, 2009-10-02 at 20:44 -0400, Madison Kelly wrote:
>   >> [...]  I noticed that if a second program/thread 
>   >> had an open file handle on the log file being 'rename'ed, it would 
>   >> follow the log file to the new name. This makes sense, now that I think 
>   >> of it (I am guessing it tracks the inode?).
> 
> 
>   LREQ> This is platform specific, but yes, on Unix-like systems, if you
>   LREQ> rename a file, something writing to that file will continue to write
>   LREQ> to it under the new name.  On a Unix (and Linux) file system,
>   LREQ> the directory entries (e.g. for "/etc/group" I mean the "group"
>   LREQ> entry in the "/etc" directory) just point to where the data is
>   LREQ> stored - this is why when you use "ln group fizz", there are
>   LREQ> now two names for the same data, and if you remove either one,
>   LREQ> the other remains behind.  This is different from symbolic links,
>   LREQ> ln -s, of course.
> 
>   >> 
>   >> What I want to do though is have some way for other threads recognize 
>   >> that the file name has changed.
> 
>   LREQ> You'd have to notify them, e.g. with a shared variable or a signal of
>   LREQ> some sort.
> 
> this is also why the best loggers use a server to do the logging and the
> programs send log message to it. then you only have one program opening
> and writing to the log files and you can manage/rotate them
> cleanly. having multiple processes logging to the same file is a poor
> design. one other way around it besides a shared variable or such is to
> mark the log dir with a flag file. this can be checked each time a
> process wants to write to the log file. it will slow things down but
> allow for the current design to work with log rotation.
> 
> uri
> 

Thank you both. I think I might try setting up a DBus-based server that 
does nothing more that listen for messages and triggers 
cycle'ing/truncating/whatever.

Madi