Command Section
KTRACE(1)               FreeBSD General Commands Manual              KTRACE(1)

     ktrace - enable kernel process tracing

     ktrace [-aCcdi] [-f trfile] [-g pgrp | -p pid] [-t trstr]
     ktrace [-adi] [-f trfile] [-t trstr] command

     The ktrace utility enables kernel trace logging for the specified
     processes.  Kernel trace data is logged to the file ktrace.out.  The
     kernel operations that are traced include system calls, namei
     translations, signal processing, and I/O.

     Once tracing is enabled on a process, trace data will be logged until
     either the process exits or the trace point is cleared.  A traced process
     can generate enormous amounts of log data quickly; It is strongly
     suggested that users memorize how to disable tracing before attempting to
     trace a process.  The following command is sufficient to disable tracing
     on all user-owned processes, and, if executed by root, all processes:

           $ ktrace -C

     The trace file is not human readable; use kdump(1) to decode it.

     The utility may be used only with a kernel that has been built with the
     ``KTRACE'' option in the kernel configuration file.

     The options are:

     -a      Append to the trace file instead of recreating it.

     -C      Disable tracing on all user-owned processes, and, if executed by
             root, all processes in the system.

     -c      Clear the specified trace points associated with the given file
             or processes.

     -d      Descendants; perform the operation for all current children of
             the designated processes.

     -f trfile
             Log trace records to trfile instead of ktrace.out.

     -g pgid
             Enable (disable) tracing on all processes in the process group
             (only one -g flag is permitted).

     -i      Inherit; pass the trace flags to all future children of the
             designated processes.

     -p pid  Enable (disable) tracing on the indicated process id (only one -p
             flag is permitted).

     -t trstr
             Specify the list of trace points to enable or disable, one per
             letter.  If an explicit list is not specified, the default set of
             trace points is used.

             The following trace points are supported:

             c     trace system calls
             f     trace page faults
             i     trace I/O
             n     trace namei translations
             p     trace capability check failures
             s     trace signal processing
             t     trace various structures
             u     userland traces
             w     context switches
             y     trace sysctl(3) requests
             +     trace the default set of trace points - c, i, n, p, s, t,
                   u, y

             Execute command with the specified trace flags.

     The -p, -g, and command options are mutually exclusive.

     # trace all kernel operations of process id 34
           $ ktrace -p 34

     # trace all kernel operations of processes in process group 15 and # pass
     the trace flags to all current and future children
           $ ktrace -idg 15

     # disable all tracing of process 65
           $ ktrace -cp 65

     # disable tracing signals on process 70 and all current children
           $ ktrace -t s -cdp 70

     # enable tracing of I/O on process 67
           $ ktrace -ti -p 67

     # run the command "w", tracing only system calls
           $ ktrace -tc w

     # disable all tracing to the file "tracedata"
           $ ktrace -c -f tracedata

     # disable tracing of all user-owned processes
           $ ktrace -C

     kdump(1), ktrace(2)

     The ktrace command appeared in 4.4BSD.

     Only works if trfile is a regular file.

FreeBSD 11.1-RELEASE-p4         March 31, 2016         FreeBSD 11.1-RELEASE-p4
Command Section