Re: Detecting deamons running

["Luciano Moreira - igLnx" <lucianolnx@ig.com.br>]

EXPLAINING BETTER:

Today we'are writing the PID to a file, and when it is used (later), is
necessary to test de PID with "kill(pid, 0);", but still existing a problem:

When the deamon is droped down with SIGKILL, and the others programs or my
users stay a long time without consulting the deamon's PID, the OS could
raise a new process with the same PID (currently free), that is saved in the
deamon's PID file.

How can this problem be fixed ?  (how is it fixed today ?)

(Somebody suggest us to use shared memory (or SOCKET) mated with another
deamon, that whould be the "PID Server", instead using PID file - We think
that it's bad and so complex, and still can give us a "infinite problem" if
we need to control the new mated deamon)

Luciano Moreira

----- Original Message -----
From: "Glynn Clements" <glynn.clements@virgin.net>
To: <linux-c-programming@vger.kernel.org>
Sent: Friday, March 28, 2003 6:30 PM
Subject: Re: Detecting deamons running


>
> Andrés Roldán wrote:
>
> > > I have a application that run like a deamon, which write in a file its
PID,
> > > that is used to stop it later by others programs. But, I ve noted that
my
> > > users send signal 9 to stop deamons, and my application cannot remove
its
> > > PID file, because it cannot handle singal 9, keeping its PID file at
HD
> > > (FileSystem).
> > >
> > > Can someone sugest me a way to know the deamon's PID, without write it
to a
> > > file ?
> > > OR
> > > How can I do to know if my deamon is running and get its PID ?
> >
> > $ pidof process
> >
> > will return the PID or the PIDs of the specified process. If it returns
> > nothing, there is not such a process running.
>
> pidof will return all PIDs which match a given name, which isn't
> necessarily the same thing as determining the PIDs of specific
> processes.
>
> E.g. if you want to find the PID of the sendmail daemon, you have to
> read /var/run/sendmail.pid; "pidof sendmail" won't make any
> distinction between the daemon and other processes with the name
> "sendmail" (which may not even be running the same "sendmail"
> program).
>
> BTW, root should never use "killall", for similar reasons.
>
> The correct solution is to use a PID file. If a user issues SIGKILL,
> then tough; there are limits to how far you should go toward
> preventing users from shooting themselves in the foot.
>
> Note that the same problem exists for most other inter-process
> communication mechansims, such as FIFOs, Unix domain sockets or SysV
> IPC entities.
>
> --
> Glynn Clements <glynn.clements@virgin.net>
> -
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>


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