Manual browser: ktruss(1)

KTRACE(1) General Commands Manual KTRACE(1)


ktrace, ktrussenable kernel process tracing


ktrace [-aCcdins] [-f trfile] [-g pgrp] [-p pid] [-t trstr]

ktrace [-adis] [-f trfile] [-t trstr] command

ktruss [-aCcdilnRT] [-e emulation] [-f infile] [-g pgrp] [-m maxdata] [-o outfile] [-p pid] [-t trstr]

ktruss [-adinRT] [-e emulation] [-m maxdata] [-o outfile] [-t trstr] [-v vers] command


ktrace 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.

ktruss is functionally the same as ktrace except that trace output is printed on standard output or to the file specified with the -o option. ktruss is useful to see the kernel operations interleaved with the program output.

The options are as follows:

Append to the trace file instead of truncating it.
Disable tracing on all user owned processes, and, if executed by root, all processes in the system.
Clear the trace points associated with the specified file or processes.
Descendants; perform the operation for all current children of the designated processes.
-f trfile
Log trace records to trfile instead of ktrace.out.
-f infile
Read the trace records from infile and print them in a human readable format to standard out.
-g pgid
Enable (disable) tracing on all processes in the process group (only one -g flag is permitted).
Inherit; pass the trace flags to all future children of the designated processes.
Poll the trace file for new data and print it to standard out. Only for use together with the -f option.
-m maxdata
Print at most maxdata bytes of data. This is used for pointer type arguments, e.g., strings. The data will be escaped in C-style unless -x is specified when it will be output in hex and ascii.
Stop tracing if attempts to write to the trace file would block. This option always affects ktruss and only affects ktrace when writing to stdout. If this flag is not set, then the traced program will block until it can write more data to the trace file descriptor.
-o outfile
Log trace records to outfile. Without this option ktruss will print its output in a human readable format to standard out.
-p pid
Enable (disable) tracing on the indicated process id (only one -p flag is permitted).
Write to the trace file with synchronized I/O.
Display relative time stamps to output.
Same as the -R option, but use absolute timestamps instead.
-t trstr
The string argument represents the kernel trace points, one per letter. The following table equates the letters with the tracepoints:

trace all tracepoints
trace exec arguments
trace system calls
trace emulation changes
trace open file descriptors after exec
trace I/O
trace namei translations
trace MIB access (sysctl)
trace signal processing
trace user data
trace exec environment
trace context switches
trace the default set of trace points (c, e, i, n, s, u)
do not trace following trace points
-e emulation
If an emulation of a process is unknown, interpret system call maps assuming the named emulation instead of default "netbsd".
Execute command with the specified trace flags.
-v version
Determines the version of the file generated. Version 0 is the compatible ktrace format, and version 1 is the new format with lwp IDs and nanosecond (instead of microsecond) timestamps.

The -p, -g, and command options are mutually exclusive. The -R and -T options are also 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 processes owned by the user

$ ktrace -C

# run the command "w", displaying to standard output

$ ktruss w

# trace process 42 and log the records to "ktruss.out"

$ ktruss -p 42 -o ktruss.out

# poll ktruss.out for available records and print them

$ ktruss -lf ktruss.out


kdump(1), ktrace(2)


The ktrace command appears in 4.4BSD.
January 8, 2015 NetBSD 7.0