vmzcore(7)vmzcore(7)NAMEvmzcore - compressed memory core dump interface
DESCRIPTION
The vmzcore character special device file provides access to in-memory
compressed kernel core dumps. During the boot sequence, savecore uses
this device to recover an existing dump. (See the savecore(8) reference
page for more information.)
An application can determine whether a dump exists by opening and
attempting to read a single byte from vmzcore; if no data is available,
no dump exists. If a dump exists, the dump header can be read from
byte offset 1024 (2 * DEV_BSIZE); upon reading the header, an applica‐
tion may treat vmzcore like a traditional swap device dump. A dump
remains in memory until either an application writes to vmzcore or the
memory system is powered down or reset.
By default, the system attempts a memory dump only after failing the
initial disk dump. The dump_to_memory system attribute changes this
behavior. If set to `1', the system attempts to save core dumps to
memory then attempts to save them to disk if the memory dump fails. If
set to `-1', core dumps never are written to memory. The default value
is `0'. (See sys_attrs_generic(5) for more information on system
attributes.)
This interface also supports a variation of memory dumps called "exempt
memory dumps". A contiguous chunk of exempt memory is first reserved
at boot time using the Contiguous Memory Allocator. (See syscon‐
figdb(8).) A portion or all of this memory may then be handed to the
kernel dump subsystem, which will use it in the event of a memory core
dump. The system attribute dump_exmem_addr identifies the start of the
dumpable region (either as a virtual or physical address). The
dump_exmem_size system attribute specifies the number of bytes avail‐
able. By default, exempt memory is not included in the core dump; this
can be changed by setting the system attribute dump_exmem_include to
`1'.
RESTRICTIONS
Regarding the exempt memory system attributes, dump_exmem_addr must be
page aligned and dump_exmem_size a multiple of the machine word size (8
bytes). When combined, this range of pages must be of type M_EXEMPT.
If any of these conditions are not met, the system displays an error
message and no exempt memory dump will be generated.
Memory dumps must be compressed. If the compressed_dump system
attribute is not set, the system automatically will enable compression
before attempting to write the dump.
FILES
/dev/vmzcore
SEE ALSO
Commands: dxkerneltuner(8), savecore(8), sysconfig(8), sysconfigdb(8)
Files: sys_attrs_generic(5)mem(7), kmem(7)
Kernel Debugging, System Administration
vmzcore(7)
