A debugging log (original) (raw)

To enable a debugging log, nginx needs to be configured to support debugging during the build:

./configure --with-debug ...

Then the debug level should be set with theerror_log directive:

error_log /path/to/log debug;

To verify that nginx is configured to support debugging, run the nginx -V command:

configure arguments: --with-debug ...

Pre-built Linux packages provide out-of-the-box support for debugging log with the nginx-debug binary (1.9.8) which can be run using commands

service nginx stop service nginx-debug start

and then set the debug level. The nginx binary version for Windows is always built with the debugging log support, so only setting the debug level will suffice.

Note that redefining the log without also specifying thedebuglevel will disable the debugging log. In the example below, redefining the log on theserverlevel disables the debugging log for this server:

error_log /path/to/log debug;

http { server { error_log /path/to/log; ...

To avoid this, either the line redefining the log should be commented out, or the debug level specification should also be added:

error_log /path/to/log debug;

http { server { error_log /path/to/log debug; ...

Debugging log for selected clients

It is also possible to enable the debugging log forselected client addresses only:

error_log /path/to/log;

events { debug_connection 192.168.1.1; debug_connection 192.168.10.0/24; }

Logging to a cyclic memory buffer

The debugging log can be written to a cyclic memory buffer:

error_log memory:32m debug;

Logging to the memory buffer on the debug level does not have significant impact on performance even under high load. In this case, the log can be extracted using a gdb script like the following one:

set $log = ngx_cycle->log

while $log->writer != ngx_log_memory_writer set log=log = log=log->next end

set buf=(ngxlogmemorybuft∗)buf = (ngx_log_memory_buf_t *) buf=(ngxl​ogm​emoryb​uft​∗)log->wdata dump binary memory debug_log.txt buf−>startbuf->start buf−>startbuf->end

Or using an lldb script as follows:

expr ngx_log_t *$log = ngx_cycle->log expr while ($log->writer != ngx_log_memory_writer) { log=log = log=log->next; } expr ngx_log_memory_buf_t *$buf = (ngx_log_memory_buf_t *) $log->wdata memory read --force --outfile debug_log.txt --binary buf−>startbuf->start buf−>startbuf->end