DTRACE GETTING STARTED

Quick-start guide

FreeBSD 9-CURRENT (or later)

1. Compile KDTRACE_HOOKS and DDB_CTF into your kernel. On AMD64 you'll also need KDTRACE_FRAME and enable gdb(1) debug symbols.

   options KDTRACE_HOOKS        # all architectures - enable general DTrace hooks 

   options DDB_CTF              # all architectures - kernel ELF linker loads CTF data  

   options KDTRACE_FRAME        # amd64 - ensure frames are compiled in  

   makeoptions DEBUG="-g"       # amd64? - build kernel with gdb(1) debug symbols  

   makeoptions WITH_CTF=1

   Note: WITH_CTF=1 has to be defined in the kernel config file. It will not be picked up from make.conf or src.conf for the kernel build.
2. Recompile and install your kernel; then reboot:

   make buildkernel KERNCONF=DTRACE  

   make installkernel KERNCONF=DTRACE shutdown -r NOW

3. Load some or all DTrace kernel modules:

   kldload dtraceall

4. Confirm that you have piles of available DTrace hooks:

   dtrace -l | head

   You'll need to su to root in order to use DTrace, which may be fixed once we add a more comprehensive fine-grained privilege policy.
5. For userland DTrace support add the following to your make.conf: (optional)

   STRIP= CFLAGS+=-fno-omit-frame-pointer

   This allows stack traces to work and display even more information.
6. Rebuild and install world with 'WITH_CTF=1' in either make.conf (if you also want to have it for ports) or src.conf: (optional)

   make buildworld shutdown -r NOW boot -s 

   make installworld reboot

FreeBSD 8-STABLE (or earlier)

1. Compile KDTRACE_HOOKS and DDB_CTF into your kernel. On AMD64 you'll also need KDTRACE_FRAME and enable gdb(1) debug symbols.

   options KDTRACE_HOOKS      # all architectures - enable general DTrace hooks  

   options DDB_CTF            # all architectures - kernel ELF linker loads CTF data  

   options KDTRACE_FRAME      # amd64 - ensure frames are compiled in  

   makeoptions DEBUG="-g"     # amd64? - build kernel with gdb(1) debug symbols

   Note: WITH_CTF=1 has to be specified on the command line. It will not be picked up from either make.conf, src.conf or inside the kernel config file for the kernel build.
2. Recompile and install your kernel; then reboot:

   make buildkernel WITH_CTF=1 KERNCONF=DTRACE 

   make installkernel KERNCONF=DTRACE shutdown -r NOW

3. Load some or all DTrace kernel modules:

   kldload dtraceall

4. Confirm that you have piles of available DTrace hooks:

   dtrace -l | head

   You'll need to su to root in order to use DTrace, which may be fixed once we add a more comprehensive fine-grained privilege policy.
5. For userland DTrace support add the following to your make.conf: (optional)

   STRIP= CFLAGS+=-fno-omit-frame-pointer

   This allows stack traces to work and display even more information.
6. Rebuild and install world: (optional)

   make WITH_CTF=1 buildworld shutdown -r NOW boot -s 

   make installworld

   
   
   
   
   
   
   
   
   
   
   
   

   Using DTrace

   Before making use of DTrace functionality, the DTrace device must exist. To load the device, issue the following command:

   # kldload dtraceall 

   DTrace support should now be available. To view all probes the administrator may now execute the following command:

   # dtrace -l | more

   Probes

    • Data is generated from instrumentation points called “probes”. • DTrace provides thousands of probes.

    • Probe examples: Probe Name                Description syscall::read:entry     A read() syscall began proc:::exec-success     A process created successfully io:::start              An I/O was issued (disk/vol/NFS) io:::done               An I/O completed

    Probe Names • Probe names are a four-tuple,

    Provider:Module:Function:Name

    syscall::exece:return

    > Provider : A library of related probes.
   > Module :The module the function belongs to,either a kernel module or user segment. > Function : The function name that contains the probe.
   > Name : The name of the probe.