Linux Configure Netconsole To Log Messages Over UDP Network

Posted on in Categories CentOS, Debian Linux, File system, FreeBSD, Gentoo Linux, GNU/Open source, Hardware, kernel, Linux, Linux distribution, Linux Log Management, Security, Sys admin, Tips, Troubleshooting, Ubuntu Linux last updated July 2, 2008

Linux netconsole kernel module allows dmesg output to be transmitted via the syslogd network. It is kernel-level network logging over udp allowing debugging of problem where disk logging fails and serial consoles are impractical. This is a step-by-step mini howto about netconsole configuration under Red Hat, CentOS, Fedora and Debian Linux.

ktrace – FreeBSD / Mac OS X Process Tracing and Reporting Tool

Posted on in Categories FreeBSD, Howto, Monitoring, OpenBSD, OS X, programming, Sys admin, Troubleshooting last updated April 16, 2008

Under Linux you can use strace or valgrind tool for reporting and finding a bug. However, under *BSD / Mac OS X you need to use ktrace as replacement for strace tool.

kreace runs on the following platforms:
=> FreeBSD
=> OpenBSD
=> Mac OS X
=> NetBSD

The ktrace utility enables kernel trace logging for the specified processes. Kernel trace data is logged to the file ktrace.out. The kernel operations that are traced include system calls, namei translations, sig nal processing, and I/O. Once tracing is enabled on a process, trace data will be logged until either the process exits or the trace point is cleared. A traced process can generate enormous amounts of log data quickly; It is strongly suggested that users memorize how to disable tracing before attempting to trace a process.

To trace all kernel operations for process id # 2546, enter:
$ ktrace -p 2546
To disable all tracing of process # 2546, enter:
$ ktrace -cp 2546
To disable tracing on all user-owned processes, and, if executed by root, all processes in the system:
# ktrace -C
Attach to process id # 123 and log trace records to myapp.dbg.log instead of ktrace.out.
$ ktrace -p 123 -f myapp.dbg.log
To enable tracing of I/O on process # 123
$ ktrace -ti -p 123
The -t option is very useful to trace various kernel trace points, one per letter. The following table equates the letters with the trace points:

  • c : trace system calls
  • n : trace namei translations
  • i : trace I/O
  • s : trace signal processing
  • u : userland traces
  • w : context switches
  • + : trace the default set of trace points – c, n, i, s, u

Run the command called myapp and track only system calls, enter:
$ ktrace -tc ./myapp
Please note that the output of ktrace is not as informative as strace, but it does help to solve many problems.

truss: trace system calls

FreeBSD has another tool called truss. It traces the system calls called by the specified process or program. Output is to the specified output file, or standard error by default.
Attach to an already-running process # 123, enter
$ truss -p 123
Follow the system calls used myapp
$ truss ./myapp -d /tmp -f 120
Same as above, but put the output into a file called /tmp/myapp.dbg
$ truss -o /tmp/truss.out ./myapp -d /tmp -f 120

strace under FreeBSD

You can install strace under FreeBSD and other *BSD like oses.

Further readings:

  • ktrace man page
  • truss man page