How to configure Nginx access and error logs

Nginx is an open source, high-performance HTTP and reverse proxy server responsible for handling the load of some of the largest sites on the Internet. One of the most common tasks you'll perform when managing an NGINX web server is checking log files.

Knowing how to configure and read logs is very useful when troubleshooting server or application issues because they provide detailed debugging information.

Nginx uses two types of logs to record its events: access logs and error logs. Access logging records information about client requests, and error logging records information about server and application problems.

Configuring Nginx access log

Nginx will generate a new record in the access log every time a customer request is processed. Each event record contains a timestamp and contains various information about the client and the requested resource. Access logs can show the visitor's location, the pages visited by the visitor, etc. The

log_format directive allows you to define the format for logging. The access_log directive enables and sets the location and format of log files.

access_log The most basic syntax of the command is as follows:

access_log log_file log_format;

where log_file is the full path of the log file, log_format is The format used for log files. Access logs can be enabled in the context of a http , server or location directive.

By default, the http directive in the Nginx main configuration file configures the global access log format.

http {
  ...
  access_log  /var/log/nginx/access.log;
  ...
}

/etc/nginx/nginx.conf

For better maintainability, it is recommended to set up a separate access log file for each server. The access_log directive set in the server directive will overwrite the access_log set in the http directive.

http {
  ...
  access_log  /var/log/nginx/access.log;
  ...
  server {
    server_name domain.com
    access_log  /var/log/nginx/domain.access.log;
    ...
  }
}

/etc/nginx/conf.d/domain.com.conf

If no log format is specified, Nginx will use the predefined combined combination format as follows:

log_format combined '$remote_addr - $remote_user [$time_local] '
                    '"$request" $status $body_bytes_sent '
                    '"$http_referer" "$http_user_agent"';

To change the logging format, override the default setting or define a new setting. For example, define a new logging format named main which will extend the combined format by adding the value of the X-Forwarded-For header, in # Add the following definition directive to ##http or server:

log_format  custom  '$remote_addr - $remote_user [$time_local] "$request" '
                    '$status $body_bytes_sent "$http_referer" '
                    '"$http_user_agent" "$http_x_forwarded_for"';

To use the new log format, specify its name after the log file, as follows:

access_log  /var/log/nginx/access.log custom;

Although access logs provide very useful information. But it takes up disk space and may affect server performance. If your server is low on resources and your site is busy, you may want to disable access logs. To do this, set the value of the

access_log directive to off . Theoretically you will not have this situation, Nginx will automatically delete the previous log files:

access_log off;

Configuration error log

Nginx writes application and general server error messages to the error log file . If you encounter an error in your web application, the error log is the first place you start to troubleshoot the problem. The

error_log directive enables and sets the location and severity level of the error log. It takes the following format and can be set in the http , server or location context:

error_log log_file log_level

log_level Parameters Set logging level. The following are the levels listed from lowest to highest severity:

debug
info
notice
warn
error
crit
alert
emerg

Each log level includes higher levels. For example, if you set the log level to

warn , Nginx will also log error , crit , alert and emerg information. When the log_level parameter is not specified, the default is error. By default, the error_log directive is defined in the context of the http directive within the main nginx.conf file:

http {
  ...
  error_log  /var/log/nginx/error.log;
  ...
}

/etc/nginx/nginx.conf with access logs Likewise, it is recommended to set up a separate error log file for each server, which will override higher level settings such as http directive context. For example, to set the error log for domain.com to

warn , you would use:

http {
  ...
  error_log  /var/log/nginx/error.log;
  ...

  server {
    server_name domain.com
    error_log  /var/log/nginx/domain.error.log warn;
    ...
  }
}

Whenever you modify the configuration file, you must reload the Nginx service for the changes to take effect.

Location of Log Files

In most Linux distributions, such as Ubuntu, CentOS and Debian. By default, access and error logs are located in the

/var/log/nginx directory.

Read and understand Nginx log files

You can use

cat , less , grep , cut , awk and other commands open and parse nginx log files. The following is the record of the access log file using the default Nginx log format:

192.168.33.1 - - [15/Oct/2019:19:41:46 +0000] "GET / HTTP/1" 200 396 "-" "Mozilla/0 (X11; Linux x86_64) AppleWebKit/536 (KHTML, like Gecko) Chrome/38120 Safari/536"

让我们细分Nginx日志文件记录的每个字段意味着什么：

• $remote_addr – 192.168.33.1 -发出请求的客户端的IP地址。

• $remote_user  – - -HTTP身份验证用户。未设置用户名时，此字段显示 - 。

• [$time_local] – [15/Oct/2019:19:41:46 +0000]

本地服务器时间。

• "$request"  – "GET / HTTP/1.1" -请求类型，路径和协议。

• $status  – 200 -服务器响应代码。

• $body_bytes_sent  – 396 -服务器响应的大小（以字节为单位）。

• "$http_referer"  – "-" -引荐网址。

• "$http_user_agent"  – Mozilla/5.0 ... -客户端的用户代理（网络浏览器）。

使用 tail 命令实时观看日志文件记录： tail -f access.log

The above is the detailed content of How to configure Nginx access and error logs. For more information, please follow other related articles on the PHP Chinese website!