HP-UX System Administrator's Guide: Overview HP-UX 11i v3 (B3921-90011, September 2010)

• In the kernel
• During system initialization when the initialization script for crashconf runs (and reads
entries from the /etc/fstab file)
• During run time, by an operator or administrator manually running the /sbin/crashconf
command
Preparing for a System Crash
The dump process exists so that you have a way of capturing what your system was doing at
the time of a crash. This is not for recovery purposes; processes cannot resume where they left
off following a system crash. Rather, this is for analysis purposes in order to help you determine
why the system crashed and hopefully prevent it from happening again.
If you want to be able to capture the memory image of your system when a crash occurs (for
later analysis), you need to define in advance the location(s) where HP-UX will put that image
at the time of the crash. This location can be on local disk devices or logical volumes.
Wherever you decide that HP-UX should put the dump, it is important to have enough space at
the dump location (see “How Much Dump Space You Need” (page 79)). If you do not have
enough space, not every page selected to be dumped will be saved and you might not capture
the part of memory that contains the instruction or data that caused the crash.
If necessary, you can define more than one dump device so that if the first one fills up, the next
one is used to continue the dumping process until the dump is complete or no more defined
space is available. Beginning with HP-UX 11i version 3 you can even configure multiple dump
devices to be written to in parallel (rather than one after the other), significantly cutting down
dump times.
How Much Dump Space You Need
To guarantee that you have enough dump space, define a dump area that is at least as big as
your computer’s physical memory, plus one megabyte. If you are doing a selective dump (which
is the default dump mode in most cases), much less dump space will actually be needed. Full
dumps require dump space equal to the size of your computer’s memory plus a little extra for
header information.
In HP-UX Release 11i compressed dumps are enabled by default, however, dump compression
will only occur if conditions in the crash environment are favorable. Do not plan your dump
storage space based on potential compression; allow enough space for an uncompressed full or
selective dump. For more information on compressed dumps, see “Compressed Dumps”
(page 81).
Dump Configuration Decisions
As computers continue to grow in speed and processing power, they also tend to grow in physical
memory size. Where once a system with 256MB of memory was considered to be a huge system,
today it is barely adequate for most tasks. Some of today’s HP-UX systems can have terabytes
of memory. This is important to consider because the larger the size of your computer’s physical
memory the longer it will take to dump its contents following a system crash (and the more disk
space the dump will consume).
Usually, when your system crashes it is important to get it back up and running as fast as possible.
If your computer has a very large amount of memory, the time it takes to dump that memory to
disk might be unacceptably long when you are trying to get the system back up quickly. And,
if you happen to already know why the computer crashed (for example, if somebody accidently
disconnected the wrong cable), there’s little or no need for a dump anyway.
Start-up and Shutdown 79