208 lines
6.3 KiB
Groff
208 lines
6.3 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 November 2, 2022
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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_STRUCT_ARRAY Ta "Trace arrays of certain data structures."
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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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long ktr_tid; /* thread id */
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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 EINTEGRITY
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Corrupted data was detected while reading from 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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