You can create non-disruptive kernel dumps on a running Linux® system with the zgetdump tool.
Before you begin
- A Linux kernel image that was compiled with the common code kernel configuration option CONFIG_STRICT_DEVMEM=n.
- The dump directory needs enough free space (memory
size + 10 MB) to hold the system memory.
- Ensure that during the dump process no memory hotplug or CPU hotplug
is performed.
- If applicable, stop the cpuplugd service by issuing the command:
service
cpuplugd stop.
Procedure
- Optional: Use the -i option to print information for the currently running Linux image:
# zgetdump -i /dev/mem
General dump info:
Dump format........: devmem
Dump method........: live
UTS node name......: mylnxsys
UTS kernel release.: 6.6.0
UTS kernel version.: #5 SMP Wed Oct 25 13:47:57 UTC 2023
System arch........: s390x (64 bit)
Dump memory range..: 512 MB
Memory map:
0000000000000000 - 000000001fffffff (512 MB)
-
Create a dump from a live system by specifying /dev/mem as
input dump and redirecting the output to a dump file. Run the dump
process with a high priority.
# nice -n -20 zgetdump /dev/mem > dump.elf
- Optional: Print information for the live-system
dump.
Use the -i option to print information
for live-system dumps that are generated by zgetdump:
# zgetdump -i dump.elf
General dump info:
Dump format........: elf
Version............: 1
Dump method........: live
UTS node name......: mylnxsys
UTS kernel release.: 6.6.0
UTS kernel version.: #5 SMP Wed Oct 25 13:47:57 UTC 2023
System arch........: s390x (64 bit)
Dump memory range..: 512 MB
Memory map:
0000000000000000 - 000000001fffffff (512 MB)
The
value "live" in the Dump method field indicates
that this is a dump from a live system.
Example
# nice -n -20 zgetdump /dev/mem > dump.elf
Format Info:
Source: devmem
Target: elf
Copying dump:
00000000 / 00000512 MB
00000110 / 00000512 MB
...
00000512 / 00000512 MB
Success: Dump has been copied
What to do next
After you create a dump from a live system, you can work
with crash, see Opening a live-system dump with the crash tool.