File system bafflement

[Robert Heller]

At Tue, 2 Sep 2014 18:42:27 +0100 "Ubuntu user technical support,  not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> On Tue, 2 Sep 2014 13:22:00 -0400
> Robert Heller wrote:
> 
> > All it takes is an open file that has been unlinked (ala rm). So long as
> > the file is open, the space is in use (and df will include that space as
> > used), but if there is no directory entry (eg the file *name* has been
> > removed [unlinked]), du won't see the space as used. This often happens
> > when syslogd's log file(s) are deleted *without* sending syslogd a HUP
> > signal.
> 
> So is rebooting a solution to this sort of problem?

Yes.  Less drasticly, sending SIGHUP to syslogd will also work (assuming it is 
specificly syslogd that is hanging onto the open file).  Basically, doing the 
needful thing to whatever process is hanging onto the unlinked file, whether 
that means sending it a signal to close its open files and re-open new ones 
(which is what SIGHUP tells syslogd to do), or simply killing off whatever 
wedged process that is doing this.  syslogd is just a common deamon that 
causes this, esp. when a novice sys admin sees his disk space vanishing and 
decides to something like 'bzip2 /var/log/syslog' and then wonders why his 
disk space usage just got *worse* and du ceases to be helpful or accurate 
(when compared to df).

> 
> - Richard.

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