error_log

(PHP 4, PHP 5, PHP 7, PHP 8)

error_log — 定義されたエラー処理ルーチンにエラーメッセージを送信する

説明

error_log(
    string $message,
    int $message_type = 0,
    ?string $destination = null,
    ?string $additional_headers = null
): bool

エラーメッセージを Web サーバーのエラーログあるいはファイルに送ります。

パラメータ

message

ログに記録されるエラーメッセージ。

message_type

メッセージをどこに送るのかを指定します。以下の中から指定できます。

**error_log()** ログタイプ
0	`message` は PHP のシステムロガーに送られ、設定ディレクティブ error_log の値に応じて、オペレーティングシステムのシステムログ機構を使って保存されるか、ファイルに保存されるかが決まります。これがデフォルトのオプションです。
1	`message` は、`destination` パラメータで指定されたアドレスに、電子メールにより送られます。このメッセージタイプの場合にのみ、 4 番目のパラメータである `additional_headers` が使われます。
2	このオプションは存在しません。
3	`message` は `destination` で指定されたファイルに追加されます。明示的に指定しない限り、`message` の最後には改行文字は追加されません。
4	`message` は、直接 SAPI のログ出力ハンドラに送信されます。

destination

メッセージの送信先。その設定は、上で説明している message_type パラメータの値によります。

additional_headers

追加のヘッダ。message_type パラメータが 1 に設定される場合に利用されます。このメッセージタイプは、mail() と同様に内部関数を利用します。

戻り値

成功した場合に true を、失敗した場合に false を返します。 message_type が0の場合、エラーがロギング出来たかそうでないかに関わらず、この関数は常に true を返します。

変更履歴

バージョン	説明
8.0.0	`destination` と `additional_headers` は、nullable になりました。

例

例1 error_log() の例

<?php
// データベースに接続できない場合、
// サーバーログを通してエラーを通知する。
if (!Ora_Logon($username, $password)) {
    error_log("オラクルのデータベースが使用できません!", 0);
}

// FOO に失敗したら、管理者に email で通知する
if (!($foo = allocate_new_foo())) {
    error_log("大変です。FOO に失敗しました!", 1,
               "operator@example.com");
}

// これ以外の error_log() のコール方法：
error_log("大変だ!", 3, "/var/tmp/my-errors.log");
?>

注意

警告

error_log() はバイナリセーフではありません。 message に null 文字があれば、そこで切り詰められます。

ヒント

message に null 文字を含めてはいけません。 message の送り先はファイルやメール、そして syslog などになることもあります。 base64_encode() や rawurlencode()、addslashes() などの関数で適切に変換してから error_log() に渡す必要があります。

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User Contributed Notes 19 notes

down

193

kevindougans at gmail dot com ¶

14 years ago

Advice to novices: This function works great along with "tail" which is a unix command to watch a log file live. There are versions of Tail for Windows too, like Tail for Win32 or Kiwi Log Viewer.

Using both error_log() and tail to view the php_error.log you can debug code without having to worry so much about printing debug messages to the screen and who they might be seen by.

Further Note: This works even better when you have two monitors setup. One for your browser and IDE and the other for viewing the log files update live as you go.

down

Sion ¶

6 years ago

DO NOT try to output TOO LARGE texts in the error_log();

if you try to output massive amounts of texts it will either cut of the text at about 8ooo characters (for reasonable massive strings, < 32 K characters) or (for insanely massive strings, about 1.6 million characters) totally crash without even throwing an error or anything (I even put it in a try/catch without getting any result from the catch).

I had this problem when I tried to debug a response from a wp_remote_get(); all of my error_log() worked as they should, except for ONE of them... (-_-)
After about a day of debugging I finally found out why & that's why I type this.

Apparently the response contained a body with over 1.6 million chars (or bytes? (whatever strlen() returns)).

If you have a string of unknown length, use this:
$start_index = 0;
$end_index = 8000;
error_log( substr( $output_text , $start_index , $end_index ) );

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roychri at php dot net ¶

14 years ago

There is a limit on the maximum length that you can pass as the $message.

The default seem to be 1024 but can be changed by adjusting the value of the runtime configuration value of 'log_errors_max_len'.

More details here:
http://www.php.net/manual/en/errorfunc.configuration.php

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frank at booksku dot com ¶

18 years ago

Beware!  If multiple scripts share the same log file, but run as different users, whichever script logs an error first owns the file, and calls to error_log() run as a different user will fail *silently*!

Nothing more frustrating than trying to figure out why all your error_log calls aren't actually writing, than to find it was due to a *silent* permission denied error!

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i dot buttinoni at intandtel dot com ¶

16 years ago

Be carefull. Unexpected PHP dies when 2GByte of file log reached (on systems having upper file size limit). 
A work aorund is rotate logs :)

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php at kennel17 dot NOSPAM dot co dot uk ¶

19 years ago

It appears that the system log = stderr if you are running PHP from the command line, and that often stderr = stdout.  This means that if you are using a custom error to both display the error and log it to syslog, then a command-line user will see the same error reported twice.

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Matthew Swift ¶

5 years ago

Relative paths are accepted as the destination of message_type 3, but beware that the root directory is determined by the context of the call to error_log(), which can change, so that one instance of error_log () in your code can lead to the creation of multiple log files in different locations.

In a WordPress context, the root directory will be the site's root in many cases, but it will be /wp-admin/ for AJAX calls, and a plugin's directory in other cases. If you want all your output to go to one file, use an absolute path.

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Anonymous ¶

21 years ago

when using error_log to send email, not all elements of an extra_headers string are handled the same way.  "From: " and "Reply-To: " header values will replace the default header values. "Subject: " header values won't: they are *added* to the mail header but don't replace the default, leading to mail messages with two Subject fields.

<?php

error_log("sometext", 1, "zigzag@my.domain", 
  "Subject: Foo\nFrom: Rizzlas@my.domain\n");

?>

---------------%<-----------------------
To: zigzag@my.domain
Envelope-to: zigzag@my.domain
Date: Fri, 28 Mar 2003 13:29:02 -0500
From: Rizzlas@my.domain
Subject: PHP error_log message
Subject: Foo
Delivery-date: Fri, 28 Mar 2003 13:29:03 -0500

sometext
---------------%<---------------------

quoth the docs: "This message type uses the same internal function as mail() does."  

mail() will also fail to set a Subject field based on extra_header data - instead it takes a seperate argument to specify a "Subject: " string.

php v.4.2.3, SunOS 5.8

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russ at russtanner dot com ¶

4 years ago

You can easily filter messages sent to error_log() using "tail" and "grep" on *nix systems. This makes monitoring debug messages easy to see during development.

Be sure to "tag" your error message with a unique string so you can filter it using "grep":

In your code:

error_log("DevSys1 - FirstName: $FirstName - LastName: $Lastname");

On your command line:

tail -f /var/log/httpd/error_log | grep DevSys1

In this example, we pipe apache log output to grep (STDIN) which filters it for you only showing messages that contain "DevSys1".

The "-f" option means "follow" which streams all new log entries to your terminal or to any piped command that follows, in this case "grep".

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SJL ¶

16 years ago

"It appears that the system log = stderr if you are running PHP from the command line"

Actually, it seems that PHP logs to stderr if it can't write to the log file. Command line PHP falls back to stderr because the log file is (usually) only writable by the webserver.

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paul dot chubb at abs dot gov dot au ¶

16 years ago

When logging to apache on windows, both error_log and also trigger_error result in an apache status of error on the front of the message. This is bad if all you want to do is log information. However you can simply log to stderr however you will have to do all message assembly:

LogToApache($Message) {
        $stderr = fopen('php://stderr', 'w'); 
        fwrite($stderr,$Message); 
        fclose($stderr); 
}

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p dot lhonorey at nospam-laposte dot net ¶

18 years ago

Hi !

Another trick to post "HTML" mail body. Just add "Content-Type: text/html; charset=ISO-8859-1" into extra_header string. Of course you can set charset according to your country or Env or content.

EG: Error_log("<html><h2>stuff</h2></html>",1,"eat@joe.com","subject  :lunch\nContent-Type: text/html; charset=ISO-8859-1");

Enjoy !

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franz at fholzinger dot com ¶

19 years ago

In the case of missing your entries in the error_log file:
When you use error_log in a script that does not produce any output, which means that you cannot see anything during the execution of the script, and when you wonder why there are no error_log entries produced in your error_log file, the reasons can be:
- you did not configure error_log output in php.ini
- the script has a syntax error and did therefore not execute

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stepheneliotdewey at GmailDotCom ¶

17 years ago

Note that since typical email is unencrypted, sending data about your errors over email using this function could be considered a security risk. How much of a risk it is depends on how much and what type of information you are sending, but the mere act of sending an email when something happens (even if it cannot be read) could itself imply to a sophisticated hacker observing your site over time that they have managed to cause an error.

Of course, security through obscurity is the weakest kind of security, as most open source supporters will agree. This is just something that you should keep in mind. 

And of course, whatever you do, make sure that such emails don't contain sensitive user data.

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eguvenc at gmail dot com ¶

16 years ago

<?php

//Multiline error log class

// ersin güvenç 2008 eguvenc@gmail.com

//For break use "\n" instead '\n'



Class log {

  //

  const USER_ERROR_DIR = '/home/site/error_log/Site_User_errors.log';

  const GENERAL_ERROR_DIR = '/home/site/error_log/Site_General_errors.log';



  /*

   User Errors...

  */

    public function user($msg,$username)

    {

    $date = date('d.m.Y h:i:s');

    $log = $msg."   |  Date:  ".$date."  |  User:  ".$username."\n";

    error_log($log, 3, self::USER_ERROR_DIR);

    }

    /*

   General Errors...

  */

    public function general($msg)

    {

    $date = date('d.m.Y h:i:s');

    $log = $msg."   |  Date:  ".$date."\n";

    error_log($msg."   |  Tarih:  ".$date, 3, self::GENERAL_ERROR_DIR);

    }



}



$log = new log();

$log->user($msg,$username); //use for user errors

//$log->general($msg); //use for general errors

?>

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-1

daniel dot fukuda at gmail dot com ¶

15 years ago

If you have a problem with log file permission *silently*
it's best to leave error_log directive unset so errors will be written in your Apache log file for current VirtualHost.

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-4

Robert Chapin ¶

6 years ago

When error_log() unexpectedly uses stdout, you should check if the php.ini value for error_log is empty in your CLI environment.  Something as simple as this might restore expected behavior:

<?php ini_set('error_log', 'error_log'); ?>

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-4

ccb2357 at gmail dot com ¶

1 year ago

// Pretty function to log info
<?php
function logger($log, $clear = true){
  file_put_contents('/path/log/logger.log', (is_object($log) || is_array($log) || is_resource($log) ? json_encode($log, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE) : $log), (!$clear) ? FILE_APPEND : 0);
}

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-4

Anonymous ¶

4 years ago

Depending on the error, you may also want to add an error 500 header, and a message for the user:

$message =  'Description of the error.';
error_log($message);
header($_SERVER['SERVER_PROTOCOL'] . ' 500 Internal Server Error', true, 500);
exit($message);

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