Generates and logs the specified message to the Syslog-ng utility. This command works by performing variable expansion on the message as defined for the HTTP profile Header Insert setting.
The log command can produce large amounts of output. Use with care in production environments, especially where disk space is limited.
The syslog facility is limited to logging 1024 bytes per request. Longer strings will be truncated.
The High Speed Logging feature offers the ability to send TCP or UDP syslog messages from an iRule with very low CPU or memory overhead. Consider using HSL instead of the default log command for remote logging.


log <message>
log [-noname] <facility>.[<level>] <message>
log [-noname] <remote_ip>[:<remote_port>] <facility>.[<level>] <message>

log <message>

  • Logs the specified message to the syslog-ng utility. Log entries are written to the local system log (/var/log/ltm). (See Note below about supression.)

log [-noname] <facility>.[<level>] <message>

  • Logs the specified message to the syslog-ng utility at the specified facility & log level. The iRule name (and event) prefixing the message text may optionally suppressed by including the -noname option.

log [-noname] <remote_ip>[:<remote_port>] <facility>.[<level>] <message>

  • (LTM only) Logs the specified message directly to the specified IP address (and optional alternate port when specified) via UDP. Facility and/or level are required. The iRule name prefixing the message text may optionally suppressed by including the -noname option. <remote_ip> must be a TMM-routed address. If you must route specific messages to a remote address via the management interface, you must log locally. syslog-ng is able to route messages via both TMM and management interfaces using the standard syntax. You can define an appropriate filter and remote log destination in LTM’s syslog-ng service.

Note: There is a significant behavioral difference when the optional . is specified. When iRule logs messages without the facility and/or level, they are rate-limited as a class and subsequently logged messages within the rate-limit period may be suppressed even though they are textually different. However, when the and/or are specified, the log messages are not rate-limited (though syslog-ng will still perform suppression of repeated duplicates).


Log to the local facility with no duplicate message suppression:
log local0. "Found $isCard $type CC# $card_number"

Log in the default message format to a remote syslog server on the default port:
   log local0.info "Client Connected, IP: [IP::client_addr]"