How to enable NGINX access log?
In general, the access log can be enabled with access_log directive either in http or in server section. The first argument log_file is mandatory whereas the second argument log_format is optional. If you don’t specify any format then logs will be written in default combined format.
access_log log_file log_format;
The access log is enabled by default in the http context of core NGINX configuration file. That means access log of all the virtual host will be recorded in the same file.
http {
...
...
access_log /var/log/nginx/access.log;
...
...
}
It is always better to segregate the access logs of all the virtual hosts by recording them in a separate file. To do that, you need to override the access_log directive that is defined in the http section with another access_log directive in the server context.
`http {
...
...
access_log /var/log/nginx/access.log;
server {
listen 80;
server_name domain1.com
access_log /var/log/nginx/domain1.access.log;
...
...
}
}
`
Reload NGINX to apply the new settings. To view the access logs for the domain domain1.com in the file /var/log/nginx/domain1.access.log, use the following tail command in the terminal.
# tail -f /var/log/nginx/domain1.access.log
Apply Custom Format in Access Log
The default log format used to record an event in the access log is combined log format. You can override the default behavior by creating your own custom log format and then specify the name of the custom format in the access_log directive. The following example defines a custom log format by extending the predefined combined format with the value of gzip compression ratio of the response. The format is then applied by indicating the log format with the access_log directive.
`http {
log_format custom '$remote_addr - $remote_user [$time_local] '
'"$request" $status $body_bytes_sent '
'"$http_referer" "$http_user_agent" "$gzip_ratio"';
server {
gzip on;
...
access_log /var/log/nginx/domain1.access.log custom;
...
}
}
`
Once you have applied above log format in your environment, reload NGINX. Now tail the access log to find the gzip ratio at the end of the log event.
# tail -f /var/log/nginx/domain1.access.log
47.29.201.179 - - [28/Feb/2019:13:17:10 +0000] "GET /?p=1 HTTP/2.0" 200 5316 "https://domain1.com/?p=1" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36" "2.75"
How to enable NGINX error log?
The error_log directive sets up error logging to file or stderr, or syslog by specifying minimal severity level of error messages to be logged. The syntax of error_log directive is:
error_log log_file log_level;
The first argument log_file defines the path of the log file and the second argument log_level defines the severity level of the log event to be recorded. If you don’t specify the log_level then by default, only log events with a severity level of error are recorded. For example, the following example sets the severity level of error messages to be logged to crit. Further, the error_log directive in the http context implies that the error log for all the virtual host will be available in a single file.
http {
...
error_log /var/log/nginx/error_log crit;
...
}
It is also possible to record error logs for all the virtual host separately by overriding the error_log directive in the server context. The following example exactly does that by overriding error_log directive in the server context.
http {
...
...
error_log /var/log/nginx/error_log;
server {
listen 80;
server_name domain1.com;
error_log /var/log/nginx/domain1.error_log warn;
...
}
server {
listen 80;
server_name domain2.com;
error_log /var/log/nginx/domain2.error_log debug;
...
}
}
All the examples described above records the log events to a file. You can also configure the error_log directive for sending the log events to a syslog server. The following error_log directive sends the error logs to syslog server with an IP address of 192.168.10.11 in debug format.
error_log syslog:server=192.168.10.11 debug;
In some situation, you might want to disable the error log. To do that, set the log file name to /dev/null.
error_log /dev/null;
Nginx Error Log Severity Levels
There are many types of log levels that are associated with a log event and with a different priority. All the log levels are listed below. In the following log levels, debug has top priority and includes the rest of the levels too. For example, if you specify error as a log level, then it will also capture log events those are labeled as crit, alert and emergency.
emerg: Emergency messages when your system may be unstable.
alert: Alert messages of serious issues.
crit: Critical issues that need to be taken care of immediately.
error: An error has occured. Something went wrong while processing a page.
warn: A warning messages that you should look into it.
notice: A simple log notice that you can ignore.
info: Just an information messages that you might want to know.
debug: Debugging information used to pinpoint the location of error.
