[erlang-questions] Lots of questions about error_logger

[Sergey A.]

Hello.

In the first place, sorry for several different questions placed in
one letter. I know it's something wearily to answer a list of
questions.

I tried using error_logger as a tool for handling error reports and
I've came across some oddities:

#1. Is there a way to set SASL options (I'm about sasl_error_logger,
errlog_type etc) from the Erlang code at runtime without using a
.config file + the "-config" argument? I just want to give an end user
only one config file to edit and use values from that to setup SASL.

#2. The following is from the "Programming Erlang":

--[Beginning of quote]-------------------------------------------------
The next configuration file lists error reports in the shell, and a copy of
everything reported in the shell is also made to a file:

%% single text file - minimal tty
[{sasl, [
%% All reports go to this file
{sasl_error_logger, {file, "/home/joe/error_logs/THELOG" }}
]}]."
--[End of quote]-------------------------------------------------

I replaced the path to just "THELOG" and then run the shell:

--[Beginning of erl session]-------------------------------------------------
erl -boot start_sasl -config elog2.config

Erlang (BEAM) emulator version 5.6.3 [source] [smp:2]
[async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.6.3 (abort with ^G)
1> error_logger:error_msg("foobar~n").
ok

=ERROR REPORT==== 10-Oct-2008::03:19:38 ===
foobar
2> error_logger:error_report("foobar\n").

=ERROR REPORT==== 10-Oct-2008::03:21:05 ===
foobar

ok
3>
User switch command
--> q
--[End of erl session]-------------------------------------------------

But after all, THELOG doesn't contain any string related to my
foobar-errors! Just only progress reports! Why does this happen?

#3. If I decide to use rotating of logs, those logs will be written in
binary format. What are the benefits of using binary format for
storing logs? Is there possibility to force Erlang to use plain text
files instead of binary ones?

#4. What is the "index" file for?

#5. Quote from Programming Erlang:
--[Beginning of quote]-------------------------------------------------
In a production environment, we are really interested only in errors and
not progress or information reports, so we tell the error logger to report
only errors. Without this setting, the system might get swamped with
information and progress reports.
Download elog4.config
%% rotating log and errors
[{sasl, [
%% minimise shell error logging
{sasl_error_logger, false},
%% only report errors
{errlog_type, error},
%% define the parameters of the rotating log
%% the log file directory
{error_logger_mf_dir,"/home/joe/error_logs" },
%% # bytes per logfile
{error_logger_mf_maxbytes,10485760}, % 10 MB
%% maximum number of
{error_logger_mf_maxfiles, 10}
]}].
--[End of quote]-------------------------------------------------

But using this config I see some progress reports:

3> rb:list().
No Type Process Date Time
== ==== ======= ==== ====
6 progress <0.30.0> 2008-10-10 03:39:59
5 progress <0.30.0> 2008-10-10 03:39:59
4 progress <0.30.0> 2008-10-10 03:39:59
3 progress <0.30.0> 2008-10-10 03:39:59
2 progress <0.23.0> 2008-10-10 03:39:59
1 error <0.24.0> 2008-10-10 03:40:20
ok

What is wrong?

--
Sergey.

P.S. Sorry for the possible English mistakes in my letter =)
_______________________________________________
erlang-questions mailing list
erlang-q...@erlang.org
http://www.erlang.org/mailman/listinfo/erlang-questions

[Edwin Fine]

On Fri, Oct 10, 2008 at 11:09 AM, Sergey A. <n39...@gmail.com> wrote:

Hello.

In the first place, sorry for several different questions placed in
one letter. I know it's something wearily to answer a list of
questions.

I tried using error_logger as a tool for handling error reports and
I've came across some oddities:

#1. Is there a way to set SASL options (I'm about sasl_error_logger,
errlog_type etc) from the Erlang code at runtime without using a
.config file + the "-config" argument?

Possibly, but I don't know how.

I just want to give an end user
only one config file to edit and use values from that to setup SASL.

 

You can put the sasl config along with other application configs. You can pass application environment variables in this way to your own apps. This usually goes into a file named sys.config, which is expected (or at least standard) if you use Erlang release management (see http://www.erlang.org/doc/man/systools.html).

[
    {sasl,
        [
            {sasl_error_logger, {file, "/data/shg/log_base/shg.sasl_log"}}
        ]},


    {myapp1,
        [
            {myappvar1, "value1"},
            {myappvar2,  value2}
        ]
    }
].   %% <-- dot and whitespace

Remember to have a dot and whitespace at end of file as shown above.

The standard error log handler in SASL only logs supervisor reports, crashes and progress reports. Take a look at http://www.erlang.org/doc/apps/sasl/index.html, from which the following was extracted:

Error Logger Event Handlers

The following error logger event handlers are defined in the SASL application.

sasl_report_tty_h

Formats and writes supervisor reports, crash reports and progress reports to stdio.

sasl_report_file_h

Formats and writes supervisor reports, crash report and progress report to a single file.

error_logger_mf_h

This error logger writes all events sent to the error logger to disk. It installs the log_mf_h event handler in the error_logger process.

You need to configure the error_logger_mf_h to get what you have logged, for example:
 
[
    {
        sasl, [
            % All supervisor, crash, and progress reports go to this file
            {sasl_error_logger, {file, "/tmp/error_logs/sasl_log" }},
            % And to these files, too
            {error_logger_mf_dir, "/tmp/error_logs"},
            {error_logger_mf_maxbytes, 10000000},
            {error_logger_mf_maxfiles, 10}
        ]
    }
].

#3. If I decide to use rotating of logs, those logs will be written in
binary format. What are the benefits of using binary format for
storing logs?

The binary format files are very fast to write and more compact than ASCII logs. However, they are much less convenient to browse. I think many people use ASCII logs, but you have to be careful and not flood your system with logs.
 

Is there possibility to force Erlang to use plain text
files instead of binary ones?

Yes, but you have to provide your own error logger callback module. Fortunately, there is at least one I know of that is publicly available, in Jungerl. You'll need to get these:
http://jungerl.cvs.sourceforge.net/viewvc/jungerl/jungerl/lib/msc/src/disk_log_h.erl?revision=1.2&view=markup
http://jungerl.cvs.sourceforge.net/viewvc/jungerl/jungerl/lib/msc/src/logger.erl?revision=1.2&view=markup
The files contain documentation on how to install and use these. I've used them for quite a while with no problems.
 

#4. What is the "index" file for?

I dunno. I think it's for the wrap logs, to ell the logger which number to use next. So if you are running 10 logs, they start off at 1. Once they get to 10, they start at 1 again. I think the index file contains the next index. Let's find out.

1> file:read_file("index").
{ok,<<2>>}
2>

Yes, looks like it's just a binary integer that has the next wrap index.
 

When you put in {sasl_error_logger, false}, the {errlog_type, error} is ignored because it pertains only to the sasl_error_logger file. If {sasl_error_logger, {file, "foo.bar"}} was specified, then {errlog_type, error} would mean, "Put only errors into foo.bar". It has no control over what goes into the error_logger_mf binary files.

It appears (AFAIK) that SASL will always log progress reports and crash reports to the binary file(s) controlled by error_logger_mf, if they are configured, but because you specified {sasl_error_logger, false} they are not being duplicated into a separate SASL ASCII log  file, e.g. "foo.bar". Hope this makes sense.

P.S. Sorry for the possible English mistakes in my letter =)

Your English is pretty good, actually.

Hope this helps.
Edwin

[Ulf Wiger (TN/EAB)]

Sergey A. skrev:

> Hello.
>
> In the first place, sorry for several different questions placed in
> one letter. I know it's something wearily to answer a list of
> questions.
>
> I tried using error_logger as a tool for handling error reports and
> I've came across some oddities:
>
> #1. Is there a way to set SASL options (I'm about sasl_error_logger,
> errlog_type etc) from the Erlang code at runtime without using a
> .config file + the "-config" argument? I just want to give an end user
> only one config file to edit and use values from that to setup SASL.

I guess application:set_env(App, Par, Val) is what you're after?

However, the function comes with a big fat warning:

"Use this function only if you know what you are doing, that is, on your
own applications. It is very application and configuration parameter
dependent when and how often the value is read by the application, and
careless use of this function may put the application in a weird,
inconsistent, and malfunctioning state."

(http://www.erlang.org/doc/apps/kernel/application.html)

Especially with things like the error logger, the value is expected
to be present from the beginning, and the warning is particularly
relevant.

If you don't want to mess with a config file, you can add the
parameters to the command line, using -App Par Val constructs.
Remember to escape special characters and omit spaces if you
want to declare complex terms this way. It's easy with simple
values, like

erl -sasl error_logger_mf_maxbytes 100000

BR,
Ulf W

[Sergey A.]

Hello.

Edwin Fine, Ulf Wiger, thanks for your detailed answers! They were
very-very helpful to me!

Trying all your suggestions in practice took some time, but now I know
what to do with logging and what to read in the following.

--
Sergey