usr.bin/kdump/kdump.1

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.Dd July 16, 2022
.Dt KDUMP 1
.Os
.Sh NAME
.Nm kdump
.Nd display kernel trace data
.Sh SYNOPSIS
.Nm
.Op Fl dEnlHRSsTA
.Op Fl f Ar trfile
.Op Fl m Ar maxdata
.Op Fl p Ar pid
.Op Fl t Ar trstr
.Sh DESCRIPTION
The
.Nm
command displays the kernel trace files produced with
.Xr ktrace 1
in human readable format.
By default, the file
.Pa ktrace.out
in the current directory is displayed.
.Pp
The options are as follows:
.Bl -tag -width Fl
.It Fl A
Display the ABI of the traced process.
.It Fl c
Display the CPU number with each trace entry.
.It Fl d
Display all numbers in decimal.
.It Fl E
Display elapsed timestamps (time since beginning of trace).
.It Fl f Ar trfile
Display the specified file instead of
.Pa ktrace.out .
.It Fl H
List the thread ID (tid) of the thread with each trace record, if available.
If no thread ID is available, 0 will be printed.
.It Fl l
Loop reading the trace file, once the end-of-file is reached, waiting for
more data.
.It Fl m Ar maxdata
Display at most
.Ar maxdata
bytes when decoding
.Tn I/O .
.It Fl n
Suppress ad hoc translations.
Normally
.Nm
tries to decode many system calls into a more human readable format.
For example,
.Xr ioctl 2
values are replaced with the macro name and
.Va errno
values are replaced with the
.Xr strerror 3
string.
Suppressing this feature yields a more consistent output format and is
easily amenable to further processing.
.It Fl p Ar pid
Display only trace events that correspond to the process or thread
.Ar pid .
This may be useful when there are multiple processes or threads recorded in the
same trace file.
.It Fl R
Display relative timestamps (time since previous entry).
.It Fl r
When decoding STRU records, display structure members such as UIDs,
GIDs, dates etc. symbolically instead of numerically.
.It Fl S
Display system call numbers.
.It Fl s
Suppress display of I/O data.
.It Fl T
Display absolute timestamps for each entry (seconds since epoch).
.It Fl t Ar trstr
See the
.Fl t
option of
.Xr ktrace 1 .
.El
.Pp
The output format of
.Nm
is line oriented with several fields.
The example below shows a section of a kdump generated by the following
commands:
.Bd -literal -offset indent
?> ktrace echo "ktrace"

?> kdump

 85045 echo     CALL  writev(0x1,0x804b030,0x2)
 85045 echo     GIO   fd 1 wrote 7 bytes
       "ktrace
       "
 85045 echo     RET   writev 7
.Ed
.Pp
The first field is the PID of the process being traced.
The second field is the name of the program being traced.
The third field is the operation that the kernel performed
on behalf of the process.
If thread IDs are being printed, then an additional thread ID column will be
added to the output between the PID field and program name field.
.Pp
In the first line above, the kernel executes the
.Xr writev 2
system call on behalf of the process so this is a
.Li CALL
operation.
The fourth field shows the system call that was executed,
including its arguments.
The
.Xr writev 2
system call takes a file descriptor, in this case 1, or standard
output, then a pointer to the iovector to write, and the number of
iovectors that are to be written.
In the second line we see the operation was
.Li GIO ,
for general I/O, and that file descriptor 1 had
seven bytes written to it.
This is followed by the seven bytes that were written, the string
.Qq Li ktrace
with a carriage return and line feed.
The last line is the
.Li RET
operation, showing a return from the kernel, what system call we are
returning from, and the return value that the process received.
Seven bytes were written by the
.Xr writev 2
system call, so 7 is the return value.
.Pp
The possible operations are:
.Bl -column -offset indent ".Li CALL" ".No data from user process"
.It Sy Name Ta Sy Operation Ta Sy Fourth field
.It Li CALL Ta enter syscall Ta syscall name and arguments
.It Li RET Ta return from syscall Ta syscall name and return value
.It Li NAMI Ta file name lookup Ta path to file
.It Li GIO Ta general I/O Ta fd, read/write, number of bytes
.It Li PSIG Ta signal Ta signal name, handler, mask, code
.It Li CSW Ta context switch Ta stop/resume user/kernel wmesg
.It Li USER Ta data from user process Ta the data
.It Li STRU Ta various syscalls Ta structure
.It Li SCTL Ta Xr sysctl 3 requests Ta MIB name
.It Li PFLT Ta enter page fault Ta fault address and type
.It Li PRET Ta return from page fault Ta fault result
.El
.Sh SEE ALSO
.Xr ktrace 1
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.4 .