man/man4/textdump.4

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.Dd October 18, 2019
.Dt TEXTDUMP 4
.Os
.Sh NAME
.Nm textdump
.Nd textdump kernel dumping facility
.Sh SYNOPSIS
.Cd options DDB
.Cd options KDB
.Pp
.Cd options TEXTDUMP_PREFERRED
.Cd options TEXTDUMP_VERBOSE
.Sh DESCRIPTION
The
.Nm
facility allows the capture of kernel debugging information to disk in a
human-readable rather than the machine-readable form normally used with
kernel memory dumps and minidumps.
This representation, while less complete in that it does not capture full
kernel state, can provide debugging information in a more compact, portable,
and persistent form than a traditional dump.
By combining
.Nm
with other
.Xr ddb 4
facilities, such as scripting and output capture, detailed bug information
can be captured in a fully automated manner.
.Sh FORMAT
.Nm
data is stored in a dump partition in the same style as a regular memory
dump, and will be automatically extracted by
.Xr savecore 8
if present on boot.
.Pp
.Nm
files are stored in the
.Xr tar 5
format, and consist of one or more text files, each storing a particular type
of debugging output.
The following parts may be present:
.Bl -tag -width version.txt
.It Pa ddb.txt
Captured
.Xr ddb 4
output, if the capture facility has been used.
May be disabled by clearing the
.Va debug.ddb.textdump.do_ddb
sysctl.
.It Pa config.txt
Kernel configuration, if
.Cd options INCLUDE_CONFIG_FILE
has been compiled into the kernel.
May be disabled by clearing the
.Va debug.ddb.textdump.do_config
sysctl.
.It Pa msgbuf.txt
Kernel message buffer, including recent console output if the capture
facility has been used.
May be disabled by clearing the
.Va debug.ddb.textdump.do_msgbuf
sysctl.
.It Pa panic.txt
Kernel panic string, if the kernel panicked before the dump was generated.
May be disabled by clearing the
.Va debug.ddb.textdump.do_panic
sysctl.
.It Pa version.txt
Kernel version string.
My be disabled by clearing the
.Va debug.ddb.textdump.do_version
sysctl.
.El
.Pp
Kernel textdumps may be extracted using
.Xr tar 1 .
.Sh CONFIGURATION
The
.Nm
facility is enabled as part of the kernel debugger using
.Cd options KDB
and
.Cd options DDB .
By default, kernel dumps generated on panic or via explicit requests for a
dump will be regular memory dumps; however, by using the
.Ic textdump set
command in
.Xr ddb 4 ,
or by setting the
.Va debug.ddb.textdump.pending
sysctl to 1 using
.Xr sysctl 8 ,
it is possible to request that the next dump be a textdump.
One may also directly trigger a textdump in
.Xr ddb 4
by running the command
.Ic textdump dump .
.Pp
If at the
.Xr ddb 4
command line, the commands
.Ic textdump set ,
.Ic textdump status ,
and
.Ic textdump unset
may be used to set, query, and clear the textdump pending flag.
.Pp
As with regular kernel dumps, a dump partition must be automatically or
manually configured using
.Xr dumpon 8 .
.Pp
Additional kernel
.Xr config 8
options:
.Bl -tag -width TEXTDUMP_PREFERRED
.It Cd TEXTDUMP_PREFERRED
sets textdumps to be the default manner of doing dumps.
This means there will be no need to
.Xr sysctl 8
or use the
.Ic textdump set
.Xr ddb 8
commands.
.It Cd TEXTDUMP_VERBOSE
will have the textdump facility be more verbose about each file it is emitting
as well as other diagnostics useful to debug the textdump facility itself.
.El
.Sh EXAMPLES
In the following example, the script
.Va kdb.enter.panic
will run when the kernel debugger is entered as a result of a panic, enable
output capture, dump several useful pieces of debugging information, and then
invoke panic in order to force a kernel dump to be written out followed by a
reboot:
.Bd -literal -offset indent
script kdb.enter.panic=textdump set; capture on; show allpcpu; bt;
  ps; alltrace; show alllocks; textdump dump; reset
.Ed
.Pp
In the following example, the script
.Va kdb.enter.witness
will run when the kernel debugger is entered as a result of a witness
violation, printing lock-related information for the user:
.Bd -literal -offset indent
script kdb.enter.witness=show locks
.Ed
.Pp
These scripts may also be configured using the
.Xr ddb 8
utility.
.Sh SEE ALSO
.Xr tar 1 ,
.Xr ddb 4 ,
.Xr tar 5 ,
.Xr ddb 8 ,
.Xr dumpon 8 ,
.Xr savecore 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
facility first appeared in
.Fx 7.1 .
.Sh AUTHORS
The
.Nm
facility was created by
.An Robert N. M. Watson .