7e6cabd06e
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
205 lines
6.2 KiB
Groff
205 lines
6.2 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)ktrace.2 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.Dd March 31, 2016
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.Dt KTRACE 2
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.Os
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.Sh NAME
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.Nm ktrace
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.Nd process tracing
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/time.h
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.In sys/uio.h
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.In sys/ktrace.h
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.Ft int
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.Fn ktrace "const char *tracefile" "int ops" "int trpoints" "int pid"
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.Sh DESCRIPTION
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The
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.Fn ktrace
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system call enables or disables tracing of one or more processes.
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Users may only trace their own processes.
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Only the super-user can trace setuid or setgid programs.
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.Pp
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The
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.Fa tracefile
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argument
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gives the pathname of the file to be used for tracing.
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The file must exist and be a regular file writable by the calling process.
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All trace records are always appended to the file,
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so the file must be truncated to zero length to discard
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previous trace data.
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If tracing points are being disabled (see KTROP_CLEAR below),
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.Fa tracefile
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may be NULL.
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.Pp
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The
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.Fa ops
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argument specifies the requested ktrace operation.
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The defined operations are:
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.Bl -column KTRFLAG_DESCENDXXX -offset indent
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.It KTROP_SET Ta "Enable trace points specified in"
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.Fa trpoints .
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.It KTROP_CLEAR Ta "Disable trace points specified in"
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.Fa trpoints .
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.It KTROP_CLEARFILE Ta "Stop all tracing."
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.It KTRFLAG_DESCEND Ta "The tracing change should apply to the"
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specified process and all its current children.
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.El
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.Pp
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The
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.Fa trpoints
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argument specifies the trace points of interest.
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The defined trace points are:
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.Bl -column KTRFAC_PROCCTORXXX -offset indent
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.It KTRFAC_SYSCALL Ta "Trace system calls."
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.It KTRFAC_SYSRET Ta "Trace return values from system calls."
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.It KTRFAC_NAMEI Ta "Trace name lookup operations."
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.It KTRFAC_GENIO Ta "Trace all I/O (note that this option can"
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generate much output).
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.It KTRFAC_PSIG Ta "Trace posted signals."
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.It KTRFAC_CSW Ta "Trace context switch points."
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.It KTRFAC_USER Ta "Trace application-specific events."
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.It KTRFAC_STRUCT Ta "Trace certain data structures."
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.It KTRFAC_SYSCTL Ta "Trace sysctls."
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.It KTRFAC_PROCCTOR Ta "Trace process construction."
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.It KTRFAC_PROCDTOR Ta "Trace process destruction."
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.It KTRFAC_CAPFAIL Ta "Trace capability failures."
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.It KTRFAC_FAULT Ta "Trace page faults."
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.It KTRFAC_FAULTEND Ta "Trace the end of page faults."
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.It KTRFAC_INHERIT Ta "Inherit tracing to future children."
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.El
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.Pp
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Each tracing event outputs a record composed of a generic header
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followed by a trace point specific structure.
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The generic header is:
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.Bd -literal
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struct ktr_header {
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int ktr_len; /* length of buf */
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short ktr_type; /* trace record type */
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pid_t ktr_pid; /* process id */
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char ktr_comm[MAXCOMLEN+1]; /* command name */
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struct timeval ktr_time; /* timestamp */
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intptr_t ktr_tid; /* was ktr_buffer */
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};
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.Ed
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.Pp
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The
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.Va ktr_len
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field specifies the length of the
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.Va ktr_type
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data that follows this header.
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The
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.Va ktr_pid
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and
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.Va ktr_comm
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fields specify the process and command generating the record.
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The
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.Va ktr_time
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field gives the time (with microsecond resolution)
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that the record was generated.
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The
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.Va ktr_tid
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field holds a thread id.
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.Pp
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The generic header is followed by
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.Va ktr_len
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bytes of a
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.Va ktr_type
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record.
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The type specific records are defined in the
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.In sys/ktrace.h
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include file.
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.Sh SYSCTL TUNABLES
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The following
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.Xr sysctl 8
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tunables influence the behaviour of
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.Fn ktrace :
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.Bl -tag -width indent
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.It Va kern.ktrace.geniosize
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bounds the amount of data a traced I/O request will log
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to the trace file.
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.It Va kern.ktrace.request_pool
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bounds the number of trace events being logged at a time.
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.El
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.Pp
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Sysctl tunables that control process debuggability (as determined by
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.Xr p_candebug 9 )
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also affect the operation of
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.Fn ktrace .
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.Sh RETURN VALUES
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.Rv -std ktrace
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.Sh ERRORS
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The
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.Fn ktrace
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er ENOTDIR
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A component of the path prefix is not a directory.
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded 255 characters,
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or an entire path name exceeded 1023 characters.
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.It Bq Er ENOENT
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The named tracefile does not exist.
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.It Bq Er EACCES
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Search permission is denied for a component of the path prefix.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating the pathname.
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.It Bq Er EIO
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An I/O error occurred while reading from or writing to the file system.
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.It Bq Er ENOSYS
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The kernel was not compiled with
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.Nm
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support.
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.El
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.Pp
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A thread may be unable to log one or more tracing events due to a
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temporary shortage of resources.
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This condition is remembered by the kernel, and the next tracing request
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that succeeds will have the flag
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.Li KTR_DROP
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set in its
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.Va ktr_type
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field.
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.Sh SEE ALSO
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.Xr kdump 1 ,
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.Xr ktrace 1 ,
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.Xr utrace 2 ,
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.Xr sysctl 8 ,
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.Xr p_candebug 9
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.Sh HISTORY
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The
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.Fn ktrace
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system call first appeared in
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.Bx 4.4 .
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