dumpsys(8)dumpsys(8)NAMEdumpsys - 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 insuf‐
ficient filesystem space to save it. Only the portion of the dump that
fits in the space available is copied. Set the expected dump compres‐
sion ratio, defaulting to 0.5. A lower number means a better compres‐
sion ratio is expected. Print the expected size of a full and partial
dump file -- no dump is taken. Produce a non-compressed 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 mem‐
ory. 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, direc‐
tory 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 vmu‐
nix.n file. You can then analyze the vmzcore.n and vmunix.n files (See
the Kernel Debugging manual for information about analyzing core dump
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 com‐
pression 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 analy‐
sis 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 dis‐
play 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 kilo‐
bytes that must be left on the filesystem containing directory after
dumpsys copies the dump. By default, this file does not exist, indicat‐
ing 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 com‐
pressed, zero supression is not usedm therefore the -z option is mean‐
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)