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man pages section 1M: System Administration Commands

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Updated: July 2017



strace - print STREAMS trace messages


strace [mid sid level]...


strace without arguments writes all STREAMS event trace messages from all drivers and modules to its standard output. These messages are obtained from the STREAMS log driver (see log(7D)). If arguments are provided, they must be in triplets of the form mid, sid, level, where mid is a STREAMS module ID number, sid is a sub-ID number, and level is a tracing priority level. Each triplet indicates that tracing messages are to be received from the given module/driver, sub-ID (usually indicating minor device), and priority level equal to, or less than the given level. The token all may be used for any member to indicate no restriction for that attribute.

The format of each trace message output is:

<seq> <time> <ticks> <level> <flags> < mid> <sid> <text>


trace sequence number


time of message in hh:mm:ss


time of message in machine ticks since boot


tracing priority level


E : message is also in the error log F : indicates a fatal error N : mail was sent to the system administrator (hardcoded as root)


module ID number of source


sub-ID number of source


formatted text of the trace message

Once initiated, strace will continue to execute until terminated by the user.


Example 1 A sample output of the strace command:

The following example outputs all trace messages from the module or driver whose module ID is 41:

strace  41 all all

The following example outputs those trace messages from driver or module ID 41 with sub-IDs 0, 1, or 2:

strace  41 0 1  41 1 1  41 2 0

Messages from sub-IDs 0 and 1 must have a tracing level less than or equal to 1. Those from sub-ID 2 must have a tracing level of 0.


See attributes(5) for descriptions of the following attributes:


See Also

attributes(5), log(7D)

STREAMS Programming Guide


  • There is no restriction to the number of strace processes opening the STREAMS log driver at a time.

  • The log-driver records the list of the triplets specified in the command invocation, and compares each potential trace message against this list to decide if it should be formatted and sent up to the strace process. Hence, long lists of triplets will have a greater impact on overall STREAMS performance. Running strace will have the most impact on the timing of the modules and drivers generating the trace messages that are sent to the strace process. If trace messages are generated faster than the strace process can handle them, some of the messages will be lost. This last case can be determined by examining the sequence numbers on the trace messages output.