examine[/AISabcdghilmorsuxz...] [addr][,count]
x[/AISabcdghilmorsuxz...] [addr][,count]
Display the addressed locations according to the formats in the modifier. Multiple modifier
formats display multiple locations. If no format is specified, the last format specified for
this command is used.
The format characters are:
b look at by bytes (8 bits)
h look at by half words (16 bits)
l look at by long words (32 bits)
g look at by quad words (64 bits)
a print the location being displayed
A print the location with a line number if possible
x display in unsigned hex
z display in signed hex
o display in unsigned octal
d display in signed decimal
u display in unsigned decimal
r display in current radix, signed
c display low 8 bits as a character. Non-printing characters are displayed as an octal
escape code (e.g., ‘\000’).
s display the null-terminated string at the location. Non-printing characters are
displayed as octal escapes.
m display in unsigned hex with character dump at the end of each line. The location is
also displayed in hex at the beginning of each line.
i display as an instruction
I display as an instruction with possible alternate formats depending on the machine. On
i386, this selects the alternate format for the instruction decoding (16 bits in a 32-bit
code segment and vice versa).
S display a symbol name for the pointer stored at the address
xf Examine forward: execute an examine command with the last specified parameters to it except that
the next address displayed by it is used as the start address.
xb Examine backward: execute an examine command with the last specified parameters to it except that
the last start address subtracted by the size displayed by it is used as the start address.
print[/acdoruxz]
p[/acdoruxz]
Print addrs according to the modifier character (as described above for examine). Valid formats
are: a, x, z, o, d, u, r, and c. If no modifier is specified, the last one specified to it is
used. The argument addr can be a string, in which case it is printed as it is. For example:
print/x "eax = " $eax "\necx = " $ecx "\n"
will print like:
eax = xxxxxx
ecx = yyyyyy
write[/bhl] addrexpr1 [expr2...]
w[/bhl] addrexpr1 [expr2...]
Write the expressions specified after addr on the command line at succeeding locations starting
with addr. The write unit size can be specified in the modifier with a letter b (byte), h (half
word) or l (long word) respectively. If omitted, long word is assumed.
Warning: since there is no delimiter between expressions, strange things may happen. It is best
to enclose each expression in parentheses.
set$variable [=] expr
Set the named variable or register with the value of expr. Valid variable names are described
below.
break[/u] [addr][,count]
b[/u] [addr][,count]
Set a break point at addr. If count is supplied, the continue command will not stop at this
break point on the first count - 1 times that it is hit. If the break point is set, a break
point number is printed with ‘#’. This number can be used in deleting the break point or adding
conditions to it.
If the u modifier is specified, this command sets a break point in user address space. Without
the u option, the address is considered to be in the kernel space, and a wrong space address is
rejected with an error message. This modifier can be used only if it is supported by machine
dependent routines.
Warning: If a user text is shadowed by a normal user space debugger, user space break points may
not work correctly. Setting a break point at the low-level code paths may also cause strange
behavior.
delete [addr]
d [addr]
delete#numberd#number
Delete the specified break point. The break point can be specified by a break point number with
‘#’, or by using the same addr specified in the original break command, or by omitting addr to
get the default address of dot.
watch [addr][,size]
Set a watchpoint for a region. Execution stops when an attempt to modify the region occurs. The
size argument defaults to 4. If you specify a wrong space address, the request is rejected with
an error message.
Warning: Attempts to watch wired kernel memory may cause unrecoverable error in some systems such
as i386. Watchpoints on user addresses work best.
hwatch [addr][,size]
Set a hardware watchpoint for a region if supported by the architecture. Execution stops when an
attempt to modify the region occurs. The size argument defaults to 4.
Warning: The hardware debug facilities do not have a concept of separate address spaces like the
watch command does. Use hwatch for setting watchpoints on kernel address locations only, and
avoid its use on user mode address spaces.
dhwatch [addr][,size]
Delete specified hardware watchpoint.
step[/p][,count]
s[/p][,count]
Single step count times. If the p modifier is specified, print each instruction at each step.
Otherwise, only print the last instruction.
Warning: depending on machine type, it may not be possible to single-step through some low-level
code paths or user space code. On machines with software-emulated single-stepping (e.g., pmax),
stepping through code executed by interrupt handlers will probably do the wrong thing.
continue[/c]
c[/c] Continue execution until a breakpoint or watchpoint. If the c modifier is specified, count
instructions while executing. Some machines (e.g., pmax) also count loads and stores.
Warning: when counting, the debugger is really silently single-stepping. This means that single-
stepping on low-level code may cause strange behavior.
until[/p]
Stop at the next call or return instruction. If the p modifier is specified, print the call
nesting depth and the cumulative instruction count at each call or return. Otherwise, only print
when the matching return is hit.
next[/p]
match[/p]
Stop at the matching return instruction. If the p modifier is specified, print the call nesting
depth and the cumulative instruction count at each call or return. Otherwise, only print when
the matching return is hit.
trace[/u] [pid | tid][,count]
t[/u] [pid | tid][,count]
where[/u] [pid | tid][,count]
bt[/u] [pid | tid][,count]
Stack trace. The u option traces user space; if omitted, trace only traces kernel space. The
optional argument count is the number of frames to be traced. If count is omitted, all frames
are printed.
Warning: User space stack trace is valid only if the machine dependent code supports it.
search[/bhl] addrvalue [mask][,count]
Search memory for value. The optional count argument limits the search.
findstackaddr
Prints the thread address for a thread kernel-mode stack of which contains the specified address.
If the thread is not found, search the thread stack cache and prints the cached stack address.
Otherwise, prints nothing.
showallprocs[/a]
ps[/a] Display all process information. The process information may not be shown if it is not supported
in the machine, or the bottom of the stack of the target process is not in the main memory at
that time. The a modifier will print command line arguments for each process.
showalltracealltrace
Show a stack trace for every thread in the system.
showallttys
Show all TTY's within the system. Output is similar to pstat(8), but also includes the address
of the TTY structure.
showallvnets
Show the same output as "show vnet" does, but lists all virtualized network stacks within the
system.
showallchains
Show the same information like "show lockchain" does, but for every thread in the system.
showalllocks
Show all locks that are currently held. This command is only available if witness(4) is included
in the kernel.
showallpcpu
The same as "show pcpu", but for every CPU present in the system.
showallrman
Show information related with resource management, including interrupt request lines, DMA request
lines, I/O ports, I/O memory addresses, and Resource IDs.
showapic
Dump data about APIC IDT vector mappings.
showbreaks
Show breakpoints set with the "break" command.
showbioaddr
Show information about the bio structure structbio present at addr. See the sys/bio.h header
file and g_bio(9) for more details on the exact meaning of the structure fields.
showbufferaddr
Show information about the buf structure structbuf present at addr. See the sys/buf.h header
file for more details on the exact meaning of the structure fields.
showcalloutaddr
Show information about the callout structure structcallout present at addr.
showcbstat
Show brief information about the TTY subsystem.
showcdev
Without argument, show the list of all created cdev's, consisting of devfs node name and struct
cdev address. When address of cdev is supplied, show some internal devfs state of the cdev.
showconifhk
Lists hooks currently waiting for completion in run_interrupt_driven_config_hooks().
showcpusets
Print numbered root and assigned CPU affinity sets. See cpuset(2) for more details.
showcyrixreg
Show registers specific to the Cyrix processor.
showdevmap
Prints the contents of the static device mapping table. Currently only available on the ARM
architecture.
showdomainaddr
Print protocol domain structure structdomain at address addr. See the sys/domain.h header file
for more details on the exact meaning of the structure fields.
showffs [addr]
Show brief information about ffs mount at the address addr, if argument is given. Otherwise,
provides the summary about each ffs mount.
showfileaddr
Show information about the file structure structfile present at address addr.
showfiles
Show information about every file structure in the system.
showfreepages
Show the number of physical pages in each of the free lists.
showgeom [addr]
If the addr argument is not given, displays the entire GEOM topology. If addr is given, displays
details about the given GEOM object (class, geom, provider or consumer).
showidt
Show IDT layout. The first column specifies the IDT vector. The second one is the name of the
interrupt/trap handler. Those functions are machine dependent.
showigi_listaddr
Show information about the IGMP structure structigmp_ifsoftc present at addr.
showinodedeps [addr]
Show brief information about each inodedep structure. If addr is given, only inodedeps belonging
to the fs located at the supplied address are shown.
showinpcbaddr
Show information on IP Control Block structin_pcb present at addr.
showintr
Dump information about interrupt handlers.
showintrcnt
Dump the interrupt statistics.
showirqs
Show interrupt lines and their respective kernel threads.
showjails
Show the list of jail(8) instances. In addition to what jls(8) shows, also list kernel internal
details.
showlapic
Show information from the local APIC registers for this CPU.
showlockaddr
Show lock structure. The output format is as follows:
class:
Class of the lock. Possible types include mutex(9), rmlock(9), rwlock(9), sx(9).
name: Name of the lock.
flags:
Flags passed to the lock initialization function. flags values are lock class specific.
state:
Current state of a lock. state values are lock class specific.
owner:
Lock owner.
showlockchainaddr
Show all threads a particular thread at address addr is waiting on based on non-spin locks.
showlockedbufs
Show the same information as "show buf", but for every locked structbuf object.
showlockedvnods
List all locked vnodes in the system.
showlocks
Prints all locks that are currently acquired. This command is only available if witness(4) is
included in the kernel.
showlocktreeshowmalloc
Prints malloc(9) memory allocator statistics. The output format is as follows:
Type Specifies a type of memory. It is the same as a description string used while
defining the given memory type with MALLOC_DECLARE(9).
InUse Number of memory allocations of the given type, for which free(9) has not been
called yet.
MemUse Total memory consumed by the given allocation type.
Requests Number of memory allocation requests for the given memory type.
The same information can be gathered in userspace with “vmstat-m”.
showmap[/f] addr
Prints the VM map at addr. If the f modifier is specified the complete map is printed.
showmsgbuf
Print the system's message buffer. It is the same output as in the “dmesg” case. It is useful
if you got a kernel panic, attached a serial cable to the machine and want to get the boot
messages from before the system hang.
showmount
Displays short info about all currently mounted file systems.
showmountaddr
Displays details about the given mount point.
showobject[/f] addr
Prints the VM object at addr. If the f option is specified the complete object is printed.
showpanic
Print the panic message if set.
showpage
Show statistics on VM pages.
showpageq
Show statistics on VM page queues.
showpciregs
Print PCI bus registers. The same information can be gathered in userspace by running “pciconf-lv”.
showpcpu
Print current processor state. The output format is as follows:
cpuid Processor identifier.
curthread Thread pointer, process identifier and the name of the process.
curpcb Control block pointer.
fpcurthread FPU thread pointer.
idlethread Idle thread pointer.
APICID CPU identifier coming from APIC.
currentldt LDT pointer.
spinlocksheld Names of spin locks held.
showpgrpdump
Dump process groups present within the system.
showproc [addr]
If no [addr] is specified, print information about the current process. Otherwise, show
information about the process at address addr.
showprocvm
Show process virtual memory layout.
showprotoswaddr
Print protocol switch structure structprotosw at address addr.
showregisters[/u]
Display the register set. If the u modifier is specified, it displays user registers instead of
kernel registers or the currently saved one.
Warning: The support of the u modifier depends on the machine. If not supported, incorrect
information will be displayed.
showrmanaddr
Show resource manager object structrman at address addr. Addresses of particular pointers can
be gathered with "show allrman" command.
showrtc
Show real time clock value. Useful for long debugging sessions.
showsleepchain
Deprecated. Now an alias for showlockchain.
showsleepqshowsleepqueue
Both commands provide the same functionality. They show sleepqueue structsleepqueue structure.
Sleepqueues are used within the FreeBSD kernel to implement sleepable synchronization primitives
(thread holding a lock might sleep or be context switched), which at the time of writing are:
condvar(9), sx(9) and standard msleep(9) interface.
showsockbufaddrshowsocketaddr
Those commands print structsockbuf and structsocket objects placed at addr. Output consists of
all values present in structures mentioned. For exact interpretation and more details, visit
sys/socket.h header file.
showsysregs
Show system registers (e.g., cr0-4 on i386.) Not present on some platforms.
showtcpcbaddr
Print TCP control block structtcpcb lying at address addr. For exact interpretation of output,
visit netinet/tcp.h header file.
showthread [addr]
If no addr is specified, show detailed information about current thread. Otherwise, information
about thread at addr is printed.
showthreads
Show all threads within the system. Output format is as follows:
Firstcolumn Thread identifier (TID)
Secondcolumn Thread structure address
Thirdcolumn Backtrace.
showttyaddr
Display the contents of a TTY structure in a readable form.
showturnstileaddr
Show turnstile structturnstile structure at address addr. Turnstiles are structures used within
the FreeBSD kernel to implement synchronization primitives which, while holding a specific type
of lock, cannot sleep or context switch to another thread. Currently, those are: mutex(9),
rwlock(9), rmlock(9).
showuma
Show UMA allocator statistics. Output consists five columns:
Zone Name of the UMA zone. The same string that was passed to uma_zcreate(9) as a
first argument.
Size Size of a given memory object (slab).
Used Number of slabs being currently used.
Free Number of free slabs within the UMA zone.
Requests Number of allocations requests to the given zone.
The very same information might be gathered in the userspace with the help of “vmstat-z”.
showunpcbaddr
Shows UNIX domain socket private control block structunpcb present at the address addr.
showvmochk
Prints, whether the internal VM objects are in a map somewhere and none have zero ref counts.
showvmopag
This is supposed to show physical addresses consumed by a VM object. Currently, it is not
possible to use this command when witness(4) is compiled in the kernel.
showvnetaddr
Prints virtualized network stack structvnet structure present at the address addr.
showvnode [addr]
Prints vnode structvnode structure lying at [addr]. For the exact interpretation of the output,
look at the sys/vnode.h header file.
showvnodebufsaddr
Shows clean/dirty buffer lists of the vnode located at addr.
showvpathaddr
Walk the namecache to lookup the pathname of the vnode located at addr.
showwatches
Displays all watchpoints. Shows watchpoints set with "watch" command.
showwitness
Shows information about lock acquisition coming from the witness(4) subsystem.
gdb Toggles between remote GDB and DDB mode. In remote GDB mode, another machine is required that
runs gdb(1) using the remote debug feature, with a connection to the serial console port on the
target machine. Currently only available on the i386 architecture.
halt Halt the system.
killsigpid
Send signal sig to process pid. The signal is acted on upon returning from the debugger. This
command can be used to kill a process causing resource contention in the case of a hung system.
See signal(3) for a list of signals. Note that the arguments are reversed relative to kill(2).
reboot [seconds]
reset [seconds]
Hard reset the system. If the optional argument seconds is given, the debugger will wait for
this long, at most a week, before rebooting.
help Print a short summary of the available commands and command abbreviations.
captureoncaptureoffcaptureresetcapturestatusddb supports a basic output capture facility, which can be used to retrieve the results of
debugging commands from userspace using sysctl(3). captureon enables output capture; captureoff disables capture. capturereset will clear the capture buffer and disable capture. capturestatus will report current buffer use, buffer size, and disposition of output capture.
Userspace processes may inspect and manage ddb capture state using sysctl(8):
debug.ddb.capture.bufsize may be used to query or set the current capture buffer size.
debug.ddb.capture.maxbufsize may be used to query the compile-time limit on the capture buffer
size.
debug.ddb.capture.bytes may be used to query the number of bytes of output currently in the
capture buffer.
debug.ddb.capture.data returns the contents of the buffer as a string to an appropriately
privileged process.
This facility is particularly useful in concert with the scripting and textdump(4) facilities,
allowing scripted debugging output to be captured and committed to disk as part of a textdump for
later analysis. The contents of the capture buffer may also be inspected in a kernel core dump
using kgdb(1).
runscriptscriptsunscript
Run, define, list, and delete scripts. See the “SCRIPTING” section for more information on the
scripting facility.
textdumpdumptextdumpsettextdumpstatustextdumpunset
Use the textdumpdump command to immediately perform a textdump. More information may be found
in textdump(4). The textdumpset command may be used to force the next kernel core dump to be a
textdump rather than a traditional memory dump or minidump. textdumpstatus reports whether a
textdump has been scheduled. textdumpunset cancels a request to perform a textdump as the next
kernel core dump.
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