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Posted to modperl@perl.apache.org by David Booth <da...@dbooth.org> on 2012/01/03 18:48:43 UTC
How to run shell command from response handler? (Apache2 child
segmentation fault)
I am trying to run a shell command from a mod_perl2 response handler.
It works properly for some number of HTTP requests, but sometimes it
fails (somewhat randomly) and I see in my Apache2 error log that one of
the Apache2 child processes has died with a segmentation fault.
For example, /var/log/apache2/error.log shows:
[Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit signal Segmentation fault (11)
Is this normal? How does one normally run a shell command from a
response handler? I do not want to return the command's output to the
client.
Here is a trivial example response handler that exhibits this behavior:
sub handler
{
my $r = shift || die;
my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
system("date >> $f");
$r->internal_redirect("/date.txt");
return Apache2::Const::OK;
}
Can anyone provide any guidance? Does this work for you?
Note that you may not notice the problem if you don't carefully watch
the Apache2 error log (e.g., with "tail -f /var/log/apache2/error.log"),
because Apache2 automatically spawns new children processes as needed,
and client (such as Firefox or wget, though not curl) seem to
automatically re-try the request when it fails, thus giving the illusion
of succeeding.
P.S. I have posted about this on perlmonks, but thus far have not found
a solution:
http://www.perlmonks.org/?node_id=945947
--
David Booth, Ph.D.
http://dbooth.org/
Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Re: [SOLVED] Re: How to run shell command from response handler?
(Apache2 child segmentation fault)
Posted by David Booth <da...@dbooth.org>.
Hi Jon,
My code actually needed to run other shell commands. I just used the
`date` function as a simple example to demonstrate the problem.
David
On Sat, 2012-01-07 at 02:44 -0700, Jon wrote:
> Hello All,
>
>
> Ok, maybe I'm missing the whole point of this thread, but why is this
> solution better than using the built-in perl `date` function?
>
>
> Personally, I think using the system 'date' function provides too many
> variables [read: problems] when attempting cross-platform continuity.
>
>
>
> Maybe I have misunderstood the whole point of this thread, but it
> seems to me that everyone is over-engineering the problem... (i've
> only been a Perl programmer for like three years, so I still have
> ton's to learn... hopefully I can learn from this if I'm way off
> base)
>
>
> Thanks,
> Jon A
>
> On Tue, Jan 3, 2012 at 8:38 PM, David Booth <da...@dbooth.org> wrote:
> Thanks for the suggestion. I tried it with prefork and the
> problem
> still occurred. HOWEVER, I then decided to remove all modules
> down to a
> minimal example, and discovered that the mere inclusion of the
> following
> module:
>
> use Test::MockObject;
>
> was causing the segmentation fault after several successful
> requests,
> even though no functions whatsoever were called. Since this
> appears to
> be a bug in Test::MockObject, I reported the bug here:
> https://rt.cpan.org/Public/Bug/Display.html?id=73723
>
> The bug report shows the exact minimal handler code that I
> used to
> reproduce the bug.
>
> Best wishes,
> David
>
>
> On Tue, 2012-01-03 at 17:26 -0500, Daniel Risacher wrote:
> > I think I've been bitten by this too, years ago.
> >
> > I *think* I solved it by switching to mpm_prefork, which was
> > unsatisfying, but adequate for my needs.
> >
> > On Tue, Jan 3, 2012 at 5:21 PM, David Booth
> <da...@dbooth.org> wrote:
> > > I tried redirecting stderr to /dev/null and it did not
> help:
> > > system("date >> $f 2> /dev/null");
> > >
> > > I am using the worker processing model. Does it work for
> you (or anyone
> > > else) without causing periodic child process segmentation
> faults?
> > >
> > >
> > > On Tue, 2012-01-03 at 16:29 -0500, Daniel Risacher wrote:
> > >> It's been a while since I looked at doing this, but IIRC
> it's fairly
> > >> dependent on the processing model that Apache is using.
> Are you
> > >> mpm_prefork, or mpm_worker?
> > >>
> > >> Also, I found it was important to redirect stderr
> to /dev/null:
> > >>
> > >> sub play {
> > >> system "/usr/bin/xmms -t 2> /dev/null";
> > >> }
> > >>
> > >>
> > >> On Tue, Jan 3, 2012 at 12:48 PM, David Booth
> <da...@dbooth.org> wrote:
> > >> > I am trying to run a shell command from a mod_perl2
> response handler.
> > >> > It works properly for some number of HTTP requests, but
> sometimes it
> > >> > fails (somewhat randomly) and I see in my Apache2 error
> log that one of
> > >> > the Apache2 child processes has died with a
> segmentation fault.
> > >> > For example, /var/log/apache2/error.log shows:
> > >> >
> > >> > [Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit
> signal Segmentation fault (11)
> > >> >
> > >> > Is this normal? How does one normally run a shell
> command from a
> > >> > response handler? I do not want to return the
> command's output to the
> > >> > client.
> > >> >
> > >> > Here is a trivial example response handler that
> exhibits this behavior:
> > >> >
> > >> > sub handler
> > >> > {
> > >> > my $r = shift || die;
> > >> > my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
> > >> > system("date >> $f");
> > >> > $r->internal_redirect("/date.txt");
> > >> > return Apache2::Const::OK;
> > >> > }
> > >> >
> > >> > Can anyone provide any guidance? Does this work for
> you?
> > >> >
> > >> > Note that you may not notice the problem if you don't
> carefully watch
> > >> > the Apache2 error log (e.g., with "tail
> -f /var/log/apache2/error.log"),
> > >> > because Apache2 automatically spawns new children
> processes as needed,
> > >> > and client (such as Firefox or wget, though not curl)
> seem to
> > >> > automatically re-try the request when it fails, thus
> giving the illusion
> > >> > of succeeding.
> > >> >
> > >> > P.S. I have posted about this on perlmonks, but thus
> far have not found
> > >> > a solution:
> > >> > http://www.perlmonks.org/?node_id=945947
> > >> >
> > >> >
> > >> > --
> > >> > David Booth, Ph.D.
> > >> > http://dbooth.org/
> > >> >
> > >> > Opinions expressed herein are those of the author and
> do not necessarily
> > >> > reflect those of his employer.
> > >> >
> > >>
> > >>
> > >
> > > --
> > > David Booth, Ph.D.
> > > http://dbooth.org/
> > >
> > > Opinions expressed herein are those of the author and do
> not necessarily
> > > reflect those of his employer.
> > >
> >
> >
>
> --
> David Booth, Ph.D.
> http://dbooth.org/
>
> Opinions expressed herein are those of the author and do not
> necessarily
> reflect those of his employer.
>
>
>
>
>
>
> --
> Best Regards,
> Jonathan David
>
>
> Please excuse any brevity or typos as this e-mail is most likely sent
> from a mobile device.
>
>
--
David Booth, Ph.D.
http://dbooth.org/
Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Re: [SOLVED] Re: How to run shell command from response handler?
(Apache2 child segmentation fault)
Posted by Jon <th...@gmail.com>.
Hello All,
Ok, maybe I'm missing the whole point of this thread, but why is this
solution better than using the built-in perl `date` function?
Personally, I think using the system 'date' function provides too many
variables [read: problems] when attempting cross-platform continuity.
Maybe I have misunderstood the whole point of this thread, but it seems to
me that everyone is over-engineering the problem... (i've only been a Perl
programmer for like three years, so I still have ton's to learn...
hopefully I can learn from this if I'm way off base)
Thanks,
Jon A
On Tue, Jan 3, 2012 at 8:38 PM, David Booth <da...@dbooth.org> wrote:
> Thanks for the suggestion. I tried it with prefork and the problem
> still occurred. HOWEVER, I then decided to remove all modules down to a
> minimal example, and discovered that the mere inclusion of the following
> module:
>
> use Test::MockObject;
>
> was causing the segmentation fault after several successful requests,
> even though no functions whatsoever were called. Since this appears to
> be a bug in Test::MockObject, I reported the bug here:
> https://rt.cpan.org/Public/Bug/Display.html?id=73723
>
> The bug report shows the exact minimal handler code that I used to
> reproduce the bug.
>
> Best wishes,
> David
>
>
> On Tue, 2012-01-03 at 17:26 -0500, Daniel Risacher wrote:
> > I think I've been bitten by this too, years ago.
> >
> > I *think* I solved it by switching to mpm_prefork, which was
> > unsatisfying, but adequate for my needs.
> >
> > On Tue, Jan 3, 2012 at 5:21 PM, David Booth <da...@dbooth.org> wrote:
> > > I tried redirecting stderr to /dev/null and it did not help:
> > > system("date >> $f 2> /dev/null");
> > >
> > > I am using the worker processing model. Does it work for you (or
> anyone
> > > else) without causing periodic child process segmentation faults?
> > >
> > >
> > > On Tue, 2012-01-03 at 16:29 -0500, Daniel Risacher wrote:
> > >> It's been a while since I looked at doing this, but IIRC it's fairly
> > >> dependent on the processing model that Apache is using. Are you
> > >> mpm_prefork, or mpm_worker?
> > >>
> > >> Also, I found it was important to redirect stderr to /dev/null:
> > >>
> > >> sub play {
> > >> system "/usr/bin/xmms -t 2> /dev/null";
> > >> }
> > >>
> > >>
> > >> On Tue, Jan 3, 2012 at 12:48 PM, David Booth <da...@dbooth.org>
> wrote:
> > >> > I am trying to run a shell command from a mod_perl2 response
> handler.
> > >> > It works properly for some number of HTTP requests, but sometimes it
> > >> > fails (somewhat randomly) and I see in my Apache2 error log that
> one of
> > >> > the Apache2 child processes has died with a segmentation fault.
> > >> > For example, /var/log/apache2/error.log shows:
> > >> >
> > >> > [Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit signal
> Segmentation fault (11)
> > >> >
> > >> > Is this normal? How does one normally run a shell command from a
> > >> > response handler? I do not want to return the command's output to
> the
> > >> > client.
> > >> >
> > >> > Here is a trivial example response handler that exhibits this
> behavior:
> > >> >
> > >> > sub handler
> > >> > {
> > >> > my $r = shift || die;
> > >> > my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
> > >> > system("date >> $f");
> > >> > $r->internal_redirect("/date.txt");
> > >> > return Apache2::Const::OK;
> > >> > }
> > >> >
> > >> > Can anyone provide any guidance? Does this work for you?
> > >> >
> > >> > Note that you may not notice the problem if you don't carefully
> watch
> > >> > the Apache2 error log (e.g., with "tail -f
> /var/log/apache2/error.log"),
> > >> > because Apache2 automatically spawns new children processes as
> needed,
> > >> > and client (such as Firefox or wget, though not curl) seem to
> > >> > automatically re-try the request when it fails, thus giving the
> illusion
> > >> > of succeeding.
> > >> >
> > >> > P.S. I have posted about this on perlmonks, but thus far have not
> found
> > >> > a solution:
> > >> > http://www.perlmonks.org/?node_id=945947
> > >> >
> > >> >
> > >> > --
> > >> > David Booth, Ph.D.
> > >> > http://dbooth.org/
> > >> >
> > >> > Opinions expressed herein are those of the author and do not
> necessarily
> > >> > reflect those of his employer.
> > >> >
> > >>
> > >>
> > >
> > > --
> > > David Booth, Ph.D.
> > > http://dbooth.org/
> > >
> > > Opinions expressed herein are those of the author and do not
> necessarily
> > > reflect those of his employer.
> > >
> >
> >
>
> --
> David Booth, Ph.D.
> http://dbooth.org/
>
> Opinions expressed herein are those of the author and do not necessarily
> reflect those of his employer.
>
>
--
Best Regards,
Jonathan David
Please excuse any brevity or typos as this e-mail is most likely sent from
a mobile device.
[SOLVED] Re: How to run shell command from response handler?
(Apache2 child segmentation fault)
Posted by David Booth <da...@dbooth.org>.
Thanks for the suggestion. I tried it with prefork and the problem
still occurred. HOWEVER, I then decided to remove all modules down to a
minimal example, and discovered that the mere inclusion of the following
module:
use Test::MockObject;
was causing the segmentation fault after several successful requests,
even though no functions whatsoever were called. Since this appears to
be a bug in Test::MockObject, I reported the bug here:
https://rt.cpan.org/Public/Bug/Display.html?id=73723
The bug report shows the exact minimal handler code that I used to
reproduce the bug.
Best wishes,
David
On Tue, 2012-01-03 at 17:26 -0500, Daniel Risacher wrote:
> I think I've been bitten by this too, years ago.
>
> I *think* I solved it by switching to mpm_prefork, which was
> unsatisfying, but adequate for my needs.
>
> On Tue, Jan 3, 2012 at 5:21 PM, David Booth <da...@dbooth.org> wrote:
> > I tried redirecting stderr to /dev/null and it did not help:
> > system("date >> $f 2> /dev/null");
> >
> > I am using the worker processing model. Does it work for you (or anyone
> > else) without causing periodic child process segmentation faults?
> >
> >
> > On Tue, 2012-01-03 at 16:29 -0500, Daniel Risacher wrote:
> >> It's been a while since I looked at doing this, but IIRC it's fairly
> >> dependent on the processing model that Apache is using. Are you
> >> mpm_prefork, or mpm_worker?
> >>
> >> Also, I found it was important to redirect stderr to /dev/null:
> >>
> >> sub play {
> >> system "/usr/bin/xmms -t 2> /dev/null";
> >> }
> >>
> >>
> >> On Tue, Jan 3, 2012 at 12:48 PM, David Booth <da...@dbooth.org> wrote:
> >> > I am trying to run a shell command from a mod_perl2 response handler.
> >> > It works properly for some number of HTTP requests, but sometimes it
> >> > fails (somewhat randomly) and I see in my Apache2 error log that one of
> >> > the Apache2 child processes has died with a segmentation fault.
> >> > For example, /var/log/apache2/error.log shows:
> >> >
> >> > [Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit signal Segmentation fault (11)
> >> >
> >> > Is this normal? How does one normally run a shell command from a
> >> > response handler? I do not want to return the command's output to the
> >> > client.
> >> >
> >> > Here is a trivial example response handler that exhibits this behavior:
> >> >
> >> > sub handler
> >> > {
> >> > my $r = shift || die;
> >> > my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
> >> > system("date >> $f");
> >> > $r->internal_redirect("/date.txt");
> >> > return Apache2::Const::OK;
> >> > }
> >> >
> >> > Can anyone provide any guidance? Does this work for you?
> >> >
> >> > Note that you may not notice the problem if you don't carefully watch
> >> > the Apache2 error log (e.g., with "tail -f /var/log/apache2/error.log"),
> >> > because Apache2 automatically spawns new children processes as needed,
> >> > and client (such as Firefox or wget, though not curl) seem to
> >> > automatically re-try the request when it fails, thus giving the illusion
> >> > of succeeding.
> >> >
> >> > P.S. I have posted about this on perlmonks, but thus far have not found
> >> > a solution:
> >> > http://www.perlmonks.org/?node_id=945947
> >> >
> >> >
> >> > --
> >> > David Booth, Ph.D.
> >> > http://dbooth.org/
> >> >
> >> > Opinions expressed herein are those of the author and do not necessarily
> >> > reflect those of his employer.
> >> >
> >>
> >>
> >
> > --
> > David Booth, Ph.D.
> > http://dbooth.org/
> >
> > Opinions expressed herein are those of the author and do not necessarily
> > reflect those of his employer.
> >
>
>
--
David Booth, Ph.D.
http://dbooth.org/
Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Re: How to run shell command from response handler? (Apache2 child
segmentation fault)
Posted by Daniel Risacher <ma...@alum.mit.edu>.
I think I've been bitten by this too, years ago.
I *think* I solved it by switching to mpm_prefork, which was
unsatisfying, but adequate for my needs.
On Tue, Jan 3, 2012 at 5:21 PM, David Booth <da...@dbooth.org> wrote:
> I tried redirecting stderr to /dev/null and it did not help:
> system("date >> $f 2> /dev/null");
>
> I am using the worker processing model. Does it work for you (or anyone
> else) without causing periodic child process segmentation faults?
>
>
> On Tue, 2012-01-03 at 16:29 -0500, Daniel Risacher wrote:
>> It's been a while since I looked at doing this, but IIRC it's fairly
>> dependent on the processing model that Apache is using. Are you
>> mpm_prefork, or mpm_worker?
>>
>> Also, I found it was important to redirect stderr to /dev/null:
>>
>> sub play {
>> system "/usr/bin/xmms -t 2> /dev/null";
>> }
>>
>>
>> On Tue, Jan 3, 2012 at 12:48 PM, David Booth <da...@dbooth.org> wrote:
>> > I am trying to run a shell command from a mod_perl2 response handler.
>> > It works properly for some number of HTTP requests, but sometimes it
>> > fails (somewhat randomly) and I see in my Apache2 error log that one of
>> > the Apache2 child processes has died with a segmentation fault.
>> > For example, /var/log/apache2/error.log shows:
>> >
>> > [Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit signal Segmentation fault (11)
>> >
>> > Is this normal? How does one normally run a shell command from a
>> > response handler? I do not want to return the command's output to the
>> > client.
>> >
>> > Here is a trivial example response handler that exhibits this behavior:
>> >
>> > sub handler
>> > {
>> > my $r = shift || die;
>> > my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
>> > system("date >> $f");
>> > $r->internal_redirect("/date.txt");
>> > return Apache2::Const::OK;
>> > }
>> >
>> > Can anyone provide any guidance? Does this work for you?
>> >
>> > Note that you may not notice the problem if you don't carefully watch
>> > the Apache2 error log (e.g., with "tail -f /var/log/apache2/error.log"),
>> > because Apache2 automatically spawns new children processes as needed,
>> > and client (such as Firefox or wget, though not curl) seem to
>> > automatically re-try the request when it fails, thus giving the illusion
>> > of succeeding.
>> >
>> > P.S. I have posted about this on perlmonks, but thus far have not found
>> > a solution:
>> > http://www.perlmonks.org/?node_id=945947
>> >
>> >
>> > --
>> > David Booth, Ph.D.
>> > http://dbooth.org/
>> >
>> > Opinions expressed herein are those of the author and do not necessarily
>> > reflect those of his employer.
>> >
>>
>>
>
> --
> David Booth, Ph.D.
> http://dbooth.org/
>
> Opinions expressed herein are those of the author and do not necessarily
> reflect those of his employer.
>
Re: How to run shell command from response handler? (Apache2 child
segmentation fault)
Posted by David Booth <da...@dbooth.org>.
I tried redirecting stderr to /dev/null and it did not help:
system("date >> $f 2> /dev/null");
I am using the worker processing model. Does it work for you (or anyone
else) without causing periodic child process segmentation faults?
On Tue, 2012-01-03 at 16:29 -0500, Daniel Risacher wrote:
> It's been a while since I looked at doing this, but IIRC it's fairly
> dependent on the processing model that Apache is using. Are you
> mpm_prefork, or mpm_worker?
>
> Also, I found it was important to redirect stderr to /dev/null:
>
> sub play {
> system "/usr/bin/xmms -t 2> /dev/null";
> }
>
>
> On Tue, Jan 3, 2012 at 12:48 PM, David Booth <da...@dbooth.org> wrote:
> > I am trying to run a shell command from a mod_perl2 response handler.
> > It works properly for some number of HTTP requests, but sometimes it
> > fails (somewhat randomly) and I see in my Apache2 error log that one of
> > the Apache2 child processes has died with a segmentation fault.
> > For example, /var/log/apache2/error.log shows:
> >
> > [Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit signal Segmentation fault (11)
> >
> > Is this normal? How does one normally run a shell command from a
> > response handler? I do not want to return the command's output to the
> > client.
> >
> > Here is a trivial example response handler that exhibits this behavior:
> >
> > sub handler
> > {
> > my $r = shift || die;
> > my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
> > system("date >> $f");
> > $r->internal_redirect("/date.txt");
> > return Apache2::Const::OK;
> > }
> >
> > Can anyone provide any guidance? Does this work for you?
> >
> > Note that you may not notice the problem if you don't carefully watch
> > the Apache2 error log (e.g., with "tail -f /var/log/apache2/error.log"),
> > because Apache2 automatically spawns new children processes as needed,
> > and client (such as Firefox or wget, though not curl) seem to
> > automatically re-try the request when it fails, thus giving the illusion
> > of succeeding.
> >
> > P.S. I have posted about this on perlmonks, but thus far have not found
> > a solution:
> > http://www.perlmonks.org/?node_id=945947
> >
> >
> > --
> > David Booth, Ph.D.
> > http://dbooth.org/
> >
> > Opinions expressed herein are those of the author and do not necessarily
> > reflect those of his employer.
> >
>
>
--
David Booth, Ph.D.
http://dbooth.org/
Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Re: How to run shell command from response handler? (Apache2 child
segmentation fault)
Posted by Daniel Risacher <ma...@alum.mit.edu>.
It's been a while since I looked at doing this, but IIRC it's fairly
dependent on the processing model that Apache is using. Are you
mpm_prefork, or mpm_worker?
Also, I found it was important to redirect stderr to /dev/null:
sub play {
system "/usr/bin/xmms -t 2> /dev/null";
}
On Tue, Jan 3, 2012 at 12:48 PM, David Booth <da...@dbooth.org> wrote:
> I am trying to run a shell command from a mod_perl2 response handler.
> It works properly for some number of HTTP requests, but sometimes it
> fails (somewhat randomly) and I see in my Apache2 error log that one of
> the Apache2 child processes has died with a segmentation fault.
> For example, /var/log/apache2/error.log shows:
>
> [Tue Jan 03 12:16:10 2012] [notice] child pid 3538 exit signal Segmentation fault (11)
>
> Is this normal? How does one normally run a shell command from a
> response handler? I do not want to return the command's output to the
> client.
>
> Here is a trivial example response handler that exhibits this behavior:
>
> sub handler
> {
> my $r = shift || die;
> my $f = $ENV{DOCUMENT_ROOT} . "/date.txt";
> system("date >> $f");
> $r->internal_redirect("/date.txt");
> return Apache2::Const::OK;
> }
>
> Can anyone provide any guidance? Does this work for you?
>
> Note that you may not notice the problem if you don't carefully watch
> the Apache2 error log (e.g., with "tail -f /var/log/apache2/error.log"),
> because Apache2 automatically spawns new children processes as needed,
> and client (such as Firefox or wget, though not curl) seem to
> automatically re-try the request when it fails, thus giving the illusion
> of succeeding.
>
> P.S. I have posted about this on perlmonks, but thus far have not found
> a solution:
> http://www.perlmonks.org/?node_id=945947
>
>
> --
> David Booth, Ph.D.
> http://dbooth.org/
>
> Opinions expressed herein are those of the author and do not necessarily
> reflect those of his employer.
>