dumpsys - Copies a snapshot of memory to a dump file
/sbin/dumpsys [-fisuz] [-r num] directory
Perform a full core dump -- the default is a partial dump.
Ignore filesystem space limit warning -- copy the dump
even if there is insufficient filesystem space to save it.
Only the portion of the dump that fits in the space available
is copied. Set the expected dump compression ratio,
defaulting to 0.5. A lower number means a better compression
ratio is expected. Print the expected size of a full
and partial dump file -- no dump is taken. Produce a noncompressed
dump. Disable contiguous zero suppression.
The dumpsys command allows you to save a snapshot of the
system memory to a dump file. There are times when system
memory requires analysis but it may not be possible to
halt the system and take a normal crash dump. Many problems
can be resolved by taking a snapshot of the system
memory while the system is running. The dumpsys command
performs this function after it determines that there is
enough file system space to save a core dump (see the following
for information about minfree).
Note that the system is running while dumpsys takes a
snapshot of memory. This means that memory may be changing
as it is copied. As a result, analysis of the resulting
dump may show inconsistencies such as incomplete
linked lists and partially zeroed pages. These are features
caused by the transitory state of memory, caused by
the working system. For this reason, some system problems
cannot be detected by dumpsys and you must halt the system
to take a normal crash dump.
The dumpsys command writes information in directory. By
default, directory is /var/adm/crash.
The dump contains the contents of a portion of physical
memory (or all of physical memory in the case of a full
core dump) at the time of the command execution. The
dumpsys command saves this information in the file vmzcore.n,
or vmcore.n if compression is supressed. The command
also copies the kernel executable image, usually
/vmunix, to the vmunix.n file. You can then analyze the
vmzcore.n and vmunix.n files (See the Kernel Debugging
manual for information about analyzing core dump files.)
The variable n indicates the number of the core file. For
the first file, dumpsys creates the files vmunix.0 and
vmcore.0. It then creates a file named directory/bounds
and initializes the file with the value 1. For each succeeding
dump, the dumpsys command uses the value in the
directory/bounds file and then increments that value.
By default dumpsys produces specially compressed dump
files. The compression scheme used is not as powerful as
compress or gzip but has the unusual feature that any byte
in the file can be extracted without decompressing more
than about 40K (typically less), even if the dump is very
large. Tools such as dbx, ladebug, and kdbx, are able to
read the compressed core files. The expand_dump utility
is provided to convert compressed dumps into non-compressed
dumps if you want to use an analysis tool that
does not understand the compressed format.
A traditional non-compressed dump can be generated using
the -u switch. In this case the dump file will be named
vmcore.n instead of vmzcore.n.
It is possible that you may run dumpsys on a kernel that
is not recent enough to support compressed dumps. If this
happens, dumpsys will display a warning that the kernel is
too old, but will then produce a non-compressed dump. The
message is suppressed if -u is used. Conversely, if you
try to use older versions of dumpsys with a newer kernel a
non-compressed dump is created without a message. The
older dumpsys version will not recognize the -u or -r
options.
The text file directory/minfree specifies the minimum number
of kilobytes that must be left on the filesystem containing
directory after dumpsys copies the dump. By
default, this file does not exist, indicating that the
minimum is set to zero. To specify a minimum, create the
file and store the number of kilobytes you want reserved
in it.You can override the minimum check of directory/minfree
using the -i option.
The -s option displays the approximate number of disk
blocks that full and partial dumps will require. The
exact size can not be determined ahead of time for many
reasons, such as: By default, dumpsys optimizes disk space
requirements by suppressing the writing of contiguous
zeroes. System use of dynamic memory (malloc/free)
changes while the system is in use. If the dump is to be
compressed, the ratio by which it will be compressed is
not known.
The -z option disables contiguous zero suppression. A
considerable amount of memory consists of contiguous
zeros, that do not need to be written to disk. The dumpsys
command optimizes disk space by default, but optimization
of disk space causes longer execution times. If
you specify the -z option, the run time can be 25% faster,
although you will require more disk space. Note that if
the dump is to be compressed, zero supression is not usedm
therefore the -z option is meaningless.
With the exception of the -s option, execution of dumpsys
requires root (superuser) access rights.
Success -- dump taken General error -- dump failed Insufficient
file system space -- dump failed
Specifies the number of the next dump Specifies the minimum
number of kilobytes to be left after dump files are
written
Commands: dbx(1), expand_dump(8), savecore(8)
System Administration
dumpsys(8)
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