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=encoding utf-8
=head1 Name
debugging_log - A debugging log
=head1
To enable a debugging log, nginx needs to be configured to support
debugging during the build:
./configure --with-debug ...
Then the C<debug> level should be set with the
L<ngx_core_module> directive:
error_log /path/to/log debug;
To verify that nginx is configured to support debugging,
run the C<nginx -V> command:
configure arguments: --with-debug ...
Pre-built L<Linux|linux_packages> packages
provide out-of-the-box support for debugging log with
the C<nginx-debug> binary (1.9.8)
which can be run using commands
service nginx stop
service nginx-debug start
and then set the C<debug> level.
The nginx binary version for Windows is always built with the debugging log
support, so only setting the C<debug> level will suffice.
Note that redefining the log without also specifying the
C<debug>
level will disable the debugging log.
In the example below, redefining the log on the
L<ngx_http_core_module>
level 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 C<debug> level specification should
also be added:
error_log /path/to/log debug;
http {
server {
error_log /path/to/log debug;
...
=head1 Debugging log for selected clients
It is also possible to enable the debugging log for
L<selected
client addresses|ngx_core_module> only:
error_log /path/to/log;
events {
debug_connection 192.168.1.1;
debug_connection 192.168.10.0/24;
}
=head1 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 C<debug> level
does not have significant impact on performance even under high load.
In this case, the log can be extracted using
a C<gdb> script like the following one:
set $log = ngx_cycle->log
while $log->writer != ngx_log_memory_writer
set $log = $log->next
end
set $buf = (ngx_log_memory_buf_t *) $log->wdata
dump binary memory debug_log.txt $buf->start $buf->end
Or using an C<lldb> script as follows:
expr ngx_log_t *$log = ngx_cycle->log
expr while ($log->writer != ngx_log_memory_writer) { $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->start $buf->end
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