System information

kexec and kdump 217
RIP: 00007fa958991f60 RSP: 00007fff61330390 RFLAGS: 00010246
RAX: 0000000000000001 RBX: ffffffff8020bfbb RCX: 0000000000000001
RDX: 0000000000000002 RSI: 00007fa959284000 RDI: 0000000000000001
RBP: 0000000000000002 R8: 00007fa9592516f0 R9: 00007fa958c209c0
R10: 00007fa958c209c0 R11: 0000000000000246 R12: 00007fa958c1f780
R13: 00007fa959284000 R14: 0000000000000002 R15: 00000000595569d0
ORIG_RAX: 0000000000000001 CS: 0033 SS: 002b
crash>
Now it is clear what happened: The internal echo command of Bash shell sent a
character to /proc/sysrq-trigger. After the corresponding handler recognized
this character, it invoked the crash_kexec() function. This function called pan-
ic() and kdump saved a dump.
In addition to the basic GDB commands and the extended version of bt, the crash
utility defines many other commands related to the structure of the Linux kernel.
These commands understand the internal data structures of the Linux kernel and
present their contents in a human readable format. For example, you can list the tasks
running at the moment of the crash with ps. With sym, you can list all the kernel
symbols with the corresponding addresses, or inquire an individual symbol for its
value. With files, you can display all the open file descriptors of a process. With
kmem, you can display details about the kernel memory usage. With vm, you can in-
spect the virtual memory of a process, even at the level of individual page mappings.
The list of useful commands is very long and many of these accept a wide range of
options.
The commands that we mentioned reflect the functionality of the common Linux
commands, such as ps and lsof. If you would like to find out the exact sequence of
events with the debugger, you need to know how to use GDB and to have strong de-
bugging skills. Both of these are out of the scope of this document. In addition, you
need to understand the Linux kernel. Several useful reference information sources are
given at the end of this document.
18.8 Advanced kdump
Configuration
The configuration for kdump is stored in /etc/sysconfig/kdump. You can al-
so use YaST to configure it. kdump configuration options are available under System
> Kernel Kdump in YaST Control Center. The following kdump options may be useful
for you: