Re: delete and redirection

[James Youngman]

On Mon, Aug 4, 2008 at 2:34 PM, Fabien Carmagnac <address@hidden> wrote:
> Hello,
>
> I have a problem when I remove a file which is a redirection of the std 
> output of a process:
>
> I launch a process and redirect output to file:
> address@hidden ./myprocess &> mylog.log


This is somewhat dangerous.   The stdout output of that program will
be buffered and the stderr output will not.   It is quite possible
that you will see out-of-order results in that "log" file while
normally one would want to use a log file as an unambiguous record of
past events.

> Then (after a few days/weeks), I remove the mylog.log file, hoping the system 
> will create a new fresh one.

Somebody else already addressed the misconception here.
[snip]


> After a few days, df gives 100% disk used but kdirstat (a gui tool to watch 
> size of each folder recursivly), says 20%used.

Yes, the log file has no name any more but it has not yet been
deleted, since a process is holding it open.

>
> Then, if I reboot, df says 20%used also.
>
> So my question is : is there a way to rotate/remove/resize logs without:
>  - reboot computer

Obviously.   Many Unix programs do this.  One typically designs such
programs to manage their own log file.  A well-designed long-running
program will also do other things to prepare for robust longevity, for
example
 - disassociating itself from its controlling terminal
 - changing directory in order to avoid blocking the unmounting of filesystems

Long-running programs are often designed to reopen their logfile when
they receive SIGHUP.   See for example the documentation for the
logrotate tool to get some understanding of this.

>  - stop process flishing in it

Sorry, didn't understand this.


> The computer is used as a very critical node in our organisation (quick 
> trading 24/24).

In that case you should probably use more than one computer.  Being
physical objects, they can fail.    But then I have no way of knowing
if the cost of an outage in your environment would justify the use of
a second computer, so feel free not to take my advice.

James.