Erlang -- SASL Error Logging

System Architecture Support Libraries (SASL)

User's Guide

Version 3.2.1

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### Chapters

- Introduction
  - Top of chapter
  - Scope
  - Prerequisites
- SASL Error Logging
  - Top of chapter
  - SASL reports
  - Multi-File Error Report Logging
  - Report Browser

# 2 SASL Error Logging

Note

The SASL error logging concept described in this section is deprecated since Erlang/OTP 21.0, when the new logging API was introduced.

The new default behaviour is that the SASL application no longer affects which log events that are logged. Supervisor reports and crash reports are logged via the default logger handler which is setup by Kernel. Progress reports are by default not logged, but can be enabled by setting the primary log level to info, for example by using the Kernel configuration parameter logger_level.

The old SASL error logging behaviour can be re-enabled by setting the Kernel configuration parameter logger_sasl_compatible to true.

The mechanism for multi-file error report logging as described in this section is also kept for backwards compatibility. However, the new logging API also introduces logger_disk_log_h(3), which is a logger handler that can print to multiple files using disk_log(3).

### 2.1 SASL reports

The SASL application introduces three types of reports:

- Supervisor report
- Progress report
- Crash report

When the SASL application is started, it adds a Logger handler that formats and writes these reports, as specified in the configuration parameters for SASL.

#### Supervisor Report

A supervisor report is issued when a supervised child terminates unexpectedly. A supervisor report contains the following items:

Supervisor

  Name of the reporting supervisor.

Context

  Indicates in which phase the child terminated from the supervisor's point of view. This can be start_error, child_terminated, or shutdown_error.

Reason

  Termination reason.

Offender

  Start specification for the child.

#### Progress Report

A progress report is issued when a supervisor starts or restarts a child. A progress report contains the following items:

Supervisor

  Name of the reporting supervisor.

Started

  Start specification for the successfully started child.

#### Crash Report

Processes started with functions proc_lib:spawn or proc_lib:spawn_link are wrapped within a catch. A crash report is issued when such a process terminates with an unexpected reason, which is any reason other than normal, shutdown, or {shutdown,Term}. Processes using behaviors gen_server, gen_fsm or gen_statem are examples of such processes. A crash report contains the following items:

Crasher

  Information about the crashing process, such as initial function call, exit reason, and message queue.

Neighbours

  Information about processes that are linked to the crashing process and do not trap exits. These processes are the neighbours that terminate because of this process crash. The information gathered is the same as the information for Crasher, described in the previous item.

#### Example

The following example shows the reports generated when a process crashes. The example process is a permanent process supervised by the test_sup supervisor. A division by zero is executed and the error is first reported by the faulty process. A crash report is generated, as the process was started using function proc_lib:spawn/3. The supervisor generates a supervisor report showing the crashed process. A progress report is generated when the process is finally restarted.

            =ERROR REPORT==== 27-May-1996::13:38:56 ===
            <0.63.0>: Divide by zero !

            =CRASH REPORT==== 27-May-1996::13:38:56 ===
            crasher:
            pid: <0.63.0>
            registered_name: []
            error_info: {badarith,{test,s,[]}}
            initial_call: {test,s,[]}
            ancestors: [test_sup,<0.46.0>]
            messages: []
            links: [<0.47.0>]
            dictionary: []
            trap_exit: false
            status: running
            heap_size: 128
            stack_size: 128
            reductions: 348
            neighbours:

            =SUPERVISOR REPORT==== 27-May-1996::13:38:56 ===
            Supervisor: {local,test_sup}
            Context:    child_terminated
            Reason:     {badarith,{test,s,[]}}
            Offender:   [{pid,<0.63.0>},
            {name,test},
            {mfa,{test,t,[]}},
            {restart_type,permanent},
            {shutdown,200},
            {child_type,worker}]

            =PROGRESS REPORT==== 27-May-1996::13:38:56 ===
            Supervisor: {local,test_sup}
            Started:  [{pid,<0.64.0>},
            {name,test},
            {mfa,{test,t,[]}},
            {restart_type,permanent},
            {shutdown,200},
            {child_type,worker}]

### 2.2 Multi-File Error Report Logging

Multi-file error report logging is used to store error messages received by error_logger. The error messages are stored in several files and each file is smaller than a specified number of kilobytes. No more than a specified number of files exist at the same time. The logging is very fast, as each error message is written as a binary term.

For more details, see the sasl(6) application in the Reference Manual.

### 2.3 Report Browser

The report browser is used to browse and format error reports written by the error logger handler log_mf_h defined in STDLIB.

The log_mf_h handler writes all reports to a report logging directory, which is specified when configuring the SASL application.

If the report browser is used offline, the reports can be copied to another directory specified when starting the browser. If no such directory is specified, the browser reads reports from the SASL error_logger_mf_dir.

#### Starting Report Browser

Start the rb_server with function rb:start([Options]) as shown in the following example:

            5> rb:start([{max, 20}]).
            rb: reading report...done.
            rb: reading report...done.
            rb: reading report...done.
            rb: reading report...done.
            {ok,<0.199.0>}

#### Online Help

Enter command rb:help() to access the report browser online help system.

#### List Reports in Server

Use function rb:list() to list all loaded reports:

            4> rb:list().
            No                Type          Process       Date     Time
            ==                ====          =======       ====     ====
            20            progress         <0.17.0> 1996-10-16 16:14:54
            19            progress         <0.14.0> 1996-10-16 16:14:55
            18               error         <0.15.0> 1996-10-16 16:15:02
            17            progress         <0.14.0> 1996-10-16 16:15:06
            16            progress         <0.38.0> 1996-10-16 16:15:12
            15            progress         <0.17.0> 1996-10-16 16:16:14
            14            progress         <0.17.0> 1996-10-16 16:16:14
            13            progress         <0.17.0> 1996-10-16 16:16:14
            12            progress         <0.14.0> 1996-10-16 16:16:14
            11               error         <0.17.0> 1996-10-16 16:16:21
            10               error         <0.17.0> 1996-10-16 16:16:21
            9        crash_report  release_handler 1996-10-16 16:16:21
            8   supervisor_report         <0.17.0> 1996-10-16 16:16:21
            7            progress         <0.17.0> 1996-10-16 16:16:21
            6            progress         <0.17.0> 1996-10-16 16:16:36
            5            progress         <0.17.0> 1996-10-16 16:16:36
            4            progress         <0.17.0> 1996-10-16 16:16:36
            3            progress         <0.14.0> 1996-10-16 16:16:36
            2               error         <0.15.0> 1996-10-16 16:17:04
            1            progress         <0.14.0> 1996-10-16 16:17:09
            ok

#### Show Reports

Use function rb:show(Number) to show details of a specific report:

    7> rb:show(4).

    PROGRESS REPORT  <0.20.0>                                   1996-10-16 16:16:36
    ===============================================================================
    supervisor                                                     {local,sasl_sup}
    started
    [{pid,<0.24.0>},
    {name,release_handler},
    {mfa,{release_handler,start_link,[]}},
    {restart_type,permanent},
    {shutdown,2000},
    {child_type,worker}]

    ok
    8> rb:show(9).

    CRASH REPORT  <0.24.0>                                      1996-10-16 16:16:21
    ===============================================================================
    Crashing process
    pid                                                                 <0.24.0>
    registered_name                                              release_handler
    error_info                             {undef,{release_handler,mbj_func,[]}}
    initial_call
    {gen,init_it,
    [gen_server,
    <0.20.0>,
    <0.20.0>,
    {erlang,register},
    release_handler,
    release_handler,
    [],
    []]}
    ancestors                                                [sasl_sup,<0.18.0>]
    messages                                                                  []
    links                                                    [<0.23.0>,<0.20.0>]
    dictionary                                                                []
    trap_exit                                                              false
    status                                                               running
    heap_size                                                                610
    stack_size                                                               142
    reductions                                                                54

    ok

#### Search Reports

All reports containing a common pattern can be shown. Suppose a process crashes because it tries to call a non-existing function release_handler:mbj_func/1. The reports can then be shown as follows:

    12> rb:grep("mbj_func").
    Found match in report number 11

    ERROR REPORT  <0.24.0>                                      1996-10-16 16:16:21
    ===============================================================================

    ** undefined function: release_handler:mbj_func[] **
    Found match in report number 10

    ERROR REPORT  <0.24.0>                                      1996-10-16 16:16:21
    ===============================================================================

    ** Generic server release_handler terminating
    ** Last message in was {unpack_release,hej}
    ** When Server state == {state,[],
    "/home/dup/otp2/otp_beam_sunos5_p1g_7",
    [{release,
    "OTP  APN 181 01",
    "P1G",
    undefined,
    [],
    permanent}],
    undefined}
    ** Reason for termination ==
    ** {undef,{release_handler,mbj_func,[]}}
    Found match in report number 9

    CRASH REPORT  <0.24.0>                                      1996-10-16 16:16:21
    ===============================================================================
    Crashing process
    pid                                                                 <0.24.0>
    registered_name                                              release_handler
    error_info                             {undef,{release_handler,mbj_func,[]}}
    initial_call
    {gen,init_it,
    [gen_server,
    <0.20.0>,
    <0.20.0>,
    {erlang,register},
    release_handler,
    release_handler,
    [],
    []]}
    ancestors                                                [sasl_sup,<0.18.0>]
    messages                                                                  []
    links                                                    [<0.23.0>,<0.20.0>]
    dictionary                                                                []
    trap_exit                                                              false
    status                                                               running
    heap_size                                                                610
    stack_size                                                               142
    reductions                                                                54

    Found match in report number 8

    SUPERVISOR REPORT  <0.20.0>                                 1996-10-16 16:16:21
    ===============================================================================
    Reporting supervisor                                           {local,sasl_sup}

    Child process
    errorContext                                                child_terminated
    reason                                 {undef,{release_handler,mbj_func,[]}}
    pid                                                                 <0.24.0>
    name                                                         release_handler
    start_function                               {release_handler,start_link,[]}
    restart_type                                                       permanent
    shutdown                                                                2000
    child_type                                                            worker

    ok

#### Stop Server

Use function rb:stop() to stop the rb_server:

    13> rb:stop().
    ok