A clause can contain any number of actions and variable manipulations. If a clause is left empty, the default action is taken. The default action is to trace the enabled probe identifier (EPID) to the principal buffer. The EPID identifies a particular enabling of a particular probe with a particular predicate and actions. From the EPID, DTrace consumers can determine the probe that induced the action. Indeed, whenever any data is traced, it must be accompanied by the EPID to enable the consumer to make sense of the data. Therefore, the default action is to trace the EPID and nothing else.

Using the default action allows for simple use of dtrace ( 1M ) . For example, the following example command enables all probes in the TS timeshare scheduling module with the default action:

# dtrace -m TS

The preceding command might produce output similar to the following example:

# dtrace -m TS
dtrace: description 'TS' matched 80 probes
CPU     ID                    FUNCTION:NAME
  0  12077                 ts_trapret:entry 
  0  12078                ts_trapret:return 
  0  12069                   ts_sleep:entry 
  0  12070                  ts_sleep:return 
  0  12033                  ts_setrun:entry 
  0  12034                 ts_setrun:return 
  0  12081                  ts_wakeup:entry 
  0  12082                 ts_wakeup:return 
  0  12069                   ts_sleep:entry 
  0  12070                  ts_sleep:return 
  0  12033                  ts_setrun:entry 
  0  12034                 ts_setrun:return 
  0  12069                   ts_sleep:entry 
  0  12070                  ts_sleep:return 
  0  12033                  ts_setrun:entry 
  0  12034                 ts_setrun:return 
  0  12069                   ts_sleep:entry 
  0  12070                  ts_sleep:return 
  0  12023                  ts_update:entry 
  0  12079             ts_update_list:entry 
  0  12080            ts_update_list:return 
  0  12079             ts_update_list:entry 
...