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kdump - display kernel trace data


See Also


kdump [-dEnlRT] [-f trfile] [-m maxdata] [-p pid] [-t [cnisuw]]


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.
-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 pid. This may be useful when there are multiple processes recorded in the same trace file.
-R Display relative timestamps (time since previous entry).
-T Display absolute timestamps for each entry (seconds since epoch).
-t cnisuw
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 echoCALL writev(0x1,0x804b030,0x2)
85045 echoGIO fd 1 wrote 7 bytes
85045 echoRET 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.

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
GENIO general I/O fd, read/write, number of bytes
SIG signal signal name, handler, mask, code
CSW context switch stop/resume user/kernel
USER data from user process the data




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