DDB(8) FreeBSD System Manager's Manual DDB(8)


ddbconfigure DDB kernel debugger properties


ddb capture [ -M -core][ -N -system] print

ddb capture [ -M -core][ -N -system] status

ddb script scriptname

ddb script scriptname= script

ddb scripts

ddb unscript scriptname

ddb pathname


The ddb utility configures certain aspects of the ddb(4) kernel debugger from user space that are not configured at compile-time or easily via sysctl(8) MIB entries.

To ease configuration, commands can be put in a file which is processed using ddb as shown in the last synopsis line. An absolute pathname must be used. The file will be read line by line and applied as arguments to the ddb utility. Whitespace at the beginning of lines will be ignored as will lines where the first non-whitespace character is ‘ #’.


The ddb utility can be used to extract the contents of the ddb(4) output capture buffer of the current live kernel, or from the crash dump of a kernel on disk. The following debugger commands are available from the command line:
capture [ -M core][ -N system] print
Print the current contents of the ddb(4) output capture buffer.
capture [ -M core][ -N system] status
Print the current status of the ddb(4) output capture buffer.


The ddb utility can be used to configure aspects of ddb(4) scripting from user space; scripting support is described in more detail in ddb(4). Each of the debugger commands is available from the command line:
script scriptname
Print the script named scriptname.
script scriptname= script
Define a script named scriptname. As many scripts contain characters interpreted in special ways by the shell, it is advisable to enclose script in quotes.
List currently defined scripts.
unscript scriptname
Delete the script named scriptname.


The ddb utility exits 0 on success, and >0 if an error occurs.


The following example defines a script that will execute when the kernel debugger is entered as a result of a break signal:

ddb script kdb.enter.break="show pcpu; bt"

The following example will delete the script:

ddb unscript kdb.enter.break

For further examples, see the ddb(4) and textdump(4) manual pages.


The ddb utility first appeared in FreeBSD 7.1.


Robert N M Watson


Ideally, ddb would not exist, as all pertinent aspects of ddb(4) could be configured directly via sysctl(8).
December 24, 2008 FreeBSD