KTRACE(1) BSD General Commands Manual KTRACE(1)
ktrace, ktruss -- enable 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]
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:
-a Append to the trace file instead of truncating it.
-C Disable tracing on all user owned processes, and, if executed by root, all processes
in the system.
-c Clear the trace points associated with the specified file or processes.
-d Descendants; perform the operation for all current children of the designated pro-
Log trace records to trfile instead of ktrace.out.
Read the trace records from infile and print them in a human readable format to
Enable (disable) tracing on all processes in the process group (only one -g flag is
-i Inherit; pass the trace flags to all future children of the designated processes.
-l Poll the trace file for new data and print it to standard out. Only for use
together with the -f option.
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.
-n 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
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 permit-
-s Write to the trace file with synchronized I/O.
-R Display relative time stamps to output.
-T Same as the -R option, but use absolute timestamps instead.
The string argument represents the kernel trace points, one per letter. The follow-
ing table equates the letters with the tracepoints:
A trace all tracepoints
a trace exec arguments
c trace system calls
e trace emulation changes
f trace open file descriptors after exec
i trace I/O
n trace namei translations
S trace MIB access (sysctl)
s trace signal processing
u trace user data
v trace exec environment
w trace context switches
+ trace the default set of trace points (c, e, i, l, m, n, s, u)
- do not trace following trace points
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.
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
The -p, -g, and command options are mutually exclusive. The -R and -T options are also
# 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
The ktrace command appears in 4.4BSD.
BSD June 1, 2011 BSD