DDB(8)

💅 DDB(8) — the ddb girlie's guide to poking the kernel debugger ✨

ok so real talk: ddb is a lil system management utility (the man page calls it a "System Manager's Manual" situation) that lets u tweak certain aspects of the ddb(4) kernel debugger from user space 💖 — specifically the stuff that isn't set at compile-time and isn't easy to do through sysctl(8) MIB entries. no cap, it's the missing piece 🫶

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🌸 SYNOPSIS 🌸

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

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✨ DESCRIPTION ✨

okay so ddb configures certain aspects of the ddb(4) kernel debugger from user space — the ones that are not configured at compile-time, and not easily configured via sysctl(8) MIB entries. iconic behavior honestly 👑

And to make ur life easier 🎀 commands can be put in a file, and that file gets processed using ddb — that's the last line of the synopsis up there, ddb pathname. An absolute pathname must be used, ok? don't be out here with relative paths bestie 😭

The file gets read line by line and applied as arguments to the ddb utility. Whitespace at the beginning of lines is ignored 🙈 — and so are lines where the first non-whitespace character is # (comments, we love her 💅).

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🦋 OUTPUT CAPTURE 🦋

The ddb utility can be used to extract the contents of the ddb(4) output capture buffer — either 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 🌈

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🎀 SCRIPTING 🎀

The ddb utility can also be used to configure aspects of ddb(4) scripting from user space — and the scripting support is described in more detail over in ddb(4) iykyk 📖. 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. And listen 👀: since so many scripts contain characters that the shell interprets in special ways, it is advisable to enclose script in quotes — fr fr, save urself the pain 💀
• scripts — list currently defined scripts 📋
• unscript scriptname — delete the script named scriptname 💔

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💜 EXIT STATUS 💜

The ddb utility exits 0 on success, and >0 if an error occurs. that's it, that's the vibe check 🌸

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⭐ EXAMPLES ⭐

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 🫶

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🌈 SEE ALSO 🌈

ddb(4), mac_ddb(4), textdump(4), sysctl(8) 👑

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🎀 HISTORY 🎀

The ddb utility first appeared in FreeBSD 7.1 ⏳ — a whole era.

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💖 AUTHORS 💖

Robert N M Watson 🫶

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💀 BUGS 💀

ngl, ideally ddb would not exist at all, because all pertinent aspects of ddb(4) could be configured directly via sysctl(8) 🙈. that's the actual documented take, and honestly? she said what she said.

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and that's the whole page bestie!! this lil Debian build is dated December 24, 2008 and the manual is DDB(8) — go forth and debug, mwah 💋✨