KDUMP(1) BSD General Commands Manual KDUMP(1)NAMEkdump — display kernel trace data
SYNOPSISkdump [-dEnlHRsT] [-f trfile] [-m maxdata] [-p pid] [-t trstr]
The kdump command displays the kernel trace files produced with ktrace(1)
in human readable format. By default, the file ktrace.out in the current
directory is displayed.
The options are as follows:
-d Display all numbers in decimal.
-E Display elapsed timestamps (time since beginning of trace).
-f trfile Display the specified file instead of ktrace.out.
-H List the thread ID (tid) of the thread with each trace
record, if available. If no thread ID is available, 0 will
-l Loop reading the trace file, once the end-of-file is reached,
waiting for more data.
-m maxdata Display at most maxdata bytes when decoding I/O.
-n Suppress ad hoc translations. Normally kdump tries to decode
many system calls into a more human readable format. For
example, ioctl(2) values are replaced with the macro name and
errno values are replaced with the strerror(3) string. Sup‐
pressing this feature yields a more consistent output format
and is easily amenable to further processing.
-p pid Display only trace events that correspond to the process pid.
This may be useful when there are multiple processes recorded
in the same trace file.
-R Display relative timestamps (time since previous entry).
-r When decoding STRU records, display structure members such as
UIDs, GIDs, dates etc. symbolically instead of numerically.
-s Suppress display of I/O data.
-T Display absolute timestamps for each entry (seconds since
-t trstr See the -t option of ktrace(1).
The output format of kdump is line oriented with several fields. The
example below shows a section of a kdump generated by the following com‐
?> ktrace echo "ktrace"
85045 echo CALL writev(0x1,0x804b030,0x2)
85045 echo GIO fd 1 wrote 7 bytes
85045 echo RET writev 7
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 opera‐
tion 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.
In the first line above, the kernel executes the writev(2) system call on
behalf of the process so this is a CALL operation. The fourth field
shows the system call that was executed, including its arguments. The
writev(2) system call takes a file descriptor, in this case 1, or stan‐
dard 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 opera‐
tion was 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 "ktrace" with a carriage return and line feed. The last line
is the 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 writev(2) system call, so 7 is the return
The possible operations are:
Name Operation Fourth field
CALL enter syscall syscall name and arguments
RET return from syscall syscall name and return value
NAMI file name lookup path to file
GIO general I/O fd, read/write, number of bytes
PSIG signal signal name, handler, mask, code
CSW context switch stop/resume user/kernel
USER data from user process the data
STRU various syscalls structure
SCTL sysctl(3) requests MIB name
The kdump command appeared in 4.4BSD.
BSD February 23, 2008 BSD