[syslog-ng] syslog-ng deadlock if /dev/console locks?

[Sandor Geller]

Hi,

On Wed, Jan 26, 2011 at 5:10 PM, Paul Krizak <paul.krizak at amd.com> wrote:
> Interesting.  We are definitely not seeing the 10 sec timeout protection --
> it flat-out hangs.  But we are using a file destination for the console
> device.  We used to use a pipe() destination back in the syslog-ng-2.x days,
> but when I tried that in 3.x it complained loudly about it, and suggested
> using file() instead.  We never had this problem in syslog-ng-2.x.  Could it
> be that pipe() is actually the better/more correct way to write to the
> console?

Under the hood the file() and pipe() drivers were more or less the
same. The issue is that only the source side sets the timeout, the
destination doesn't so when a log arrives on a source other than
file() or program() then timeout never gets set. One notable
difference between file() and pipe() is that for files syslog-ng
assumes that the file is always writeable (which is true at least on
linux) while for pipes syslog-ng checks with poll() first so when the
4k page used for the pipe is full then syslog-ng won't try to write to
the pipe effectively avoiding being blocked.

> Here's the relevant snippets from our configuration:
>
> source s_local {
>    # standard Linux log source (this is the default place for the syslog()
>    # function to send logs to)
>    unix-stream("/dev/log");
> }

it's somewhat better to use unix-dgram() for /dev/log

> source s_kernel {
>    # messages from the kernel
>    file("/proc/kmsg" program_override("kernel"));
> };
>
> log {
>    # /var/log/syslog-ng.log
>    source(s_self);
>    destination(d_self);
> };
>
> filter f_console {
>    # Stuff that goes to the console
>    ( facility(local1) and priority(info) ) or
>    ( priority(emerg) );
> };
>
> destination d_console {
>    file("/dev/console");
> };
>
> log {
>    # Console
>    source(s_local);
>    source(s_kernel);
>    source(s_self);
>    filter(f_console);
>    destination(d_console);
> };

and here you connect a stream source (/dev/log) with /dev/console

Regards,

Sandor