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.Dd November 1, 2024
.Dt KTRACE 1
.Os
.Sh NAME
.Nm ktrace
.Nd enable kernel process tracing
.Sh SYNOPSIS
.Nm
.Op Fl aCcdi
.Op Fl f Ar trfile
.Op Fl g Ar pgrp | Fl p Ar pid
.Op Fl t Ar trstr
.Nm
.Op Fl adi
.Op Fl f Ar trfile
.Op Fl t Ar trstr
.Ar command
.Sh DESCRIPTION
The
.Nm
utility enables kernel trace logging for the specified processes.
Kernel trace data is logged to the file
.Pa ktrace.out .
The kernel operations that are traced include system calls
.Pq see Xr intro 2 ,
file system path lookups
.Pq Xr namei 9 ,
signal processing
.Pq Xr sigaction 2 ,
and
.Tn I/O .
.Pp
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:
.Pp
.Dl \&$ ktrace -C
.Pp
The trace file is not human readable; use
.Xr kdump 1
to decode it.
.Pp
The utility may be used only with a kernel that has been built with the
.Dq KTRACE
option in the kernel configuration file.
.Pp
The options are:
.Bl -tag -width indent
.It Fl a
Append to the trace file instead of recreating it.
.It Fl C
Disable tracing on all user-owned processes, and, if executed by root, all
processes in the system.
.It Fl c
Clear the specified trace points associated with the given file or processes.
.It Fl d
Descendants; perform the operation for all current children of the
designated processes.
See also the
.Fl i
option.
.It Fl f Ar trfile
Log trace records to
.Ar trfile
instead of
.Pa ktrace.out .
.It Fl g Ar pgid
Enable (disable) tracing on all processes in the process group (only one
.Fl g
flag is permitted).
.It Fl i
Inherit; pass the trace flags to all future children of the designated
processes.
See also the
.Fl d
option.
.It Fl p Ar pid
Enable (disable) tracing on the indicated process id (only one
.Fl p
flag is permitted).
.It Fl t Ar 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.
.Pp
The following trace points are supported:
.Pp
.Bl -tag -width flag -compact
.It Cm c
trace system calls
.It Cm f
trace page faults
.It Cm i
trace
.Tn I/O
.It Cm n
trace
.Xr namei 9
translations
.It Cm p
trace capability check failures
.It Cm s
trace signal processing
.It Cm t
trace various structures
.It Cm u
userland traces generated by
.Xr utrace 2
.It Cm w
context switches
.It Cm y
trace
.Xr sysctl 3
requests
.It Cm a
trace
.Xr execve 2
arguments
.It Cm e
trace
.Xr execve 2
environment variables
.It Cm +
trace the default set of trace points -
.Cm c , i , n , s , t , u , y
.El
.It Ar command
Execute
.Ar command
with the specified trace flags.
.El
.Pp
The
.Fl p ,
.Fl g ,
and
.Ar command
options are mutually exclusive.
.Sh CAPABILITY VIOLATION TRACING
When the
.Cm p
trace point is specified,
.Nm
will record
.Xr capsicum 4
capability mode violations made by the traced process.
Violations will be logged regardless of whether the process has actually
entered capability mode.
.Pp
For developers that are interested in Capsicumizing their programs, the
.Cm c , n , p
trace points can help quickly identify any system calls and path lookups that
are triggering violations.
.Sh EXAMPLES
Run "make", then trace it and any child processes:
.Dl $ ktrace -i make
.Pp
Trace all kernel operations of process id 34:
.Dl $ ktrace -p 34
.Pp
Trace all kernel operations of processes in process group 15 and
pass the trace flags to all current and future children:
.Dl $ ktrace -idg 15
.Pp
Disable all tracing of process 65:
.Dl $ ktrace -cp 65
.Pp
Disable tracing signals on process 70 and all current children:
.Dl $ ktrace -t s -cdp 70
.Pp
Enable tracing of
.Tn I/O
on process 67:
.Dl $ ktrace -ti -p 67
.Pp
Disable all tracing to the file "tracedata":
.Dl $ ktrace -c -f tracedata
.Pp
Disable tracing of all user-owned processes:
.Dl $ ktrace -C
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr kdump 1 ,
.Xr truss 1 ,
.Xr intro 2 ,
.Xr ktrace 2 ,
.Xr sigaction 2 ,
.Xr utrace 2 ,
.Xr capsicum 4 ,
.Xr namei 9
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.4 .
.Sh BUGS
Only works if
.Ar trfile
is a regular file.