> > Well, it doesn't disappear so much as having its permissions altered,
quoted text
> > but I'm certain you are aware of that.
>
> The device also turned into a regular file. Maybe the content of the
> null file gives a hint of what went wrong. Which files were you
> copying and to which directory? scp -v might help to see what is going on.

I replied to this post, though only to Otto directly and not to the
list - my fault, sorry! So I exchanged a few private emails with Otto,
and thanks to Otto's really powerful magic we have a solution for my
problem. :-)

The cause for the disappearing /dev/null is not SCP or SFTP but mysql
on the command line. The bug is described here:
http://bugs.mysql.com/bug.php?id=16803 and at the bottom of that
thread it seems that they say it's fixed since version 5.0.22, but
that's obviously not true. I'm running MySQL 5.0.33 (from
snapshots/packages/i386/) and the bug is still there.

I had "MYSQL_HISTFILE=/dev/null" in my .profile file because I didn't
want to have a file with my mysql history. That works fine as long as
you *don't* start mysql as the system user "root". You can start it as
normal user with "mysql -u root -p" to log into MySQL as the MySQL
user "root" and still everything's working fine.

But if you start mysql as sytem user "root" with "mysql -p" or "mysql
-u root -p", /dev/null will become a normal file with your latest
mysql history inside (or nothing inside if you didn't type any mysql
commands except "quit"), *after* you left the mysql shell with "quit".

So the solution is: Don't start mysql on the command line as system
user "root" or let mysql keep it's history whereever it wants (no
"MYSQL_HISTFILE=/dev/null" in .profile).

It seems that I always played with mysql while transfering a few
files, so I thought it would be a SFTP or SCP issue, but thanks to
Otto we know what is really happening. :-)

And while testing with mysql Darren's tip to test for changes on
/dev/null with a cronjob was very useful: The cronjob found the
changes at once. :-)

You can avoid the problems easily like described above, but maybe it's
even possible that someone fixes MySQL now or maybe adds a warning to
the mysql man page.

Again thank you very much, Otto and all the others on this great list!
I'll keep reading here every day. :-)

Tas.