IBM AIX Continuous Availability Features - IBM Redbooks

are valid when applied in a serial manner. The customer will manage Concurrent AIX
Updates using the emgr command.
Installation requires specification of new options specific to Concurrent AIX Updates.
Installation of a concurrent update will always perform an in-memory update. However, the
customer can chose to additionally perform an on-disk update. Executable modules are
provided for this purpose. The patch is then unpacked on the customer’s system, and verified
to be of correct version for the system. After verification, it is loaded into a reserved place
within the kernel’s allocated memory. The system loader, via new functionality, links
concurrent update objects with the in-memory image of the operating system. Linkage
performs symbol resolution and relocation of the patchset.
Defective functions that are to be patched have their first instruction saved aside and then
subsequently replaced with a branch. The branch serves to redirect calls to a defective
function to the corrected (patched) version of that function. To maintain system coherency,
instruction replacements are collectively performed under special operation of the system.
After patching is successfully completed, the system is fully operational with corrected code,
and no reboot is required. To remove a Concurrent AIX Update from the system, the
saved-aside instructions are simply restored. Again, no reboot is required.
This method is suitable to the majority of kernel and kernel extension code, including interrupt
handlers, locking code, and possibly even the concurrent update mechanism itself.
2.3.16 Core file control
A core file is created in the current directory when various errors occur. Errors such as
memory-address violations, illegal instructions, bus errors, and user-generated quit signals,
commonly cause this core dump. The core file that is created contains a memory image of the
terminated process. If the faulty process is multi-threaded and the current core size ulimit is
less than what is required to dump the data section, then only the faulting thread stack area is
dumped from the data section.
Two new commands, lscore and chcore, have been introduced to check the settings for the
corefile creation and change them, respectively. SMIT support has also been added; the
fastpath is smitty corepath.
For AIX 5.3, the chcore command can change core file creation parameters, as shown:
chcore [ -R registry ] [ -c {on|off|default} ] [ -p {on|off|default} ] [ -l {path|
default] [ -n {on|off|default} ] [ username | -d ]
-c {on|off|default} Setting for core compression.
-d Changes the default setting for the system.
-l path Directory path for stored corefiles.
-n {on|off|default} Setting for core naming.
-p {on|off|default} Setting for core location.
-R registry Specifies the loadable I&A module.
New features have been added to control core files that will avoid key file systems being filled
up by core files generated by faulty programs. AIX allows users to compress the core file and
specify its name and destination directory.
The chcore command, as shown in Example 2-7, can be used to control core file parameters.
Example 2-7 Core file settings
lpar15root:/root#chcore -c on -p on -l /coredumps
lpar15root:/root#lscore
Chapter 2. AIX continuous availability features 35