A debugging log
Debugging log for selected clients Logging to a cyclic memory buffer |
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 the
error_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 the
debug
level will disable the debugging log.
In the example below, redefining the log on the
server
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 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 for selected 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->next end set $buf = (ngx_log_memory_buf_t *) $log->wdata dump binary memory debug_log.txt $buf->start $buf->end
Or using an lldb
script as follows:
expr ngx_log_t *$log = ngx_cycle->log expr while ($log->writer != ngx_log_memory_writer) { $log = $log->next; } expr ngx_log_memory_buf_t *$buf = (ngx_log_memory_buf_t *) $log->wdata memory read --force --outfile debug_log.txt --binary $buf->start $buf->end