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Man Pages

Manual Reference Pages  -  KDUMP (1)


kdump - display kernel trace data


See Also


kdump [-dEnlHRSsTA] [-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 be printed.
-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. Suppressing 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 or thread pid. This may be useful when there are multiple processes or threads 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 Display system call numbers.
-s Suppress display of I/O data.
-T Display absolute timestamps for each entry (seconds since epoch).
-A Display description of the ABI of traced process.
-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 commands:

?> 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

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.

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 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 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 value.

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 wmesg
USER      data from user process      the data
STRU      various syscalls      structure
SCTL      sysctl 3 requests      MIB name
PFLT      enter page fault      fault address and type
PRET      return from page fault      fault result




The kdump command appeared in BSD 4.4 .
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