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Server Debugging

Server event messages can arise from different sources and be controlled by different configuration options. The following table summarizes sshd command-line options and server configuration keywords that affect logging; and describes where to find the output.



Output Location


Debug a single client connection

-d debug_level


Use 1, 2, 3, or 99. (Values 4-98 are accepted, but are equivalent to 3.) With this option, sshd terminates after the first client connection closes.

This option is independent of the setting for LogLevel.

Enable persistent debugging

-D debug_level


A debug file is created using the following file name format: debugYYMMDD_HHMMSS, where YY=year, MM=month, DD=day, HH=hour, MM=minutes, and SS=seconds.

This option is independent of the setting for LogLevel.

Suppress debug messages


N/A — affects syslog output only

This option overrides LogLevel.

View server startup messages



Output to stderr includes errors and warnings found while parsing sshd2_config.