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8b4a503d | 1 | ================================== |
7d4c738c | 2 | The s390 SCSI dump tool (zfcpdump) |
8b4a503d | 3 | ================================== |
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4 | |
5 | System z machines (z900 or higher) provide hardware support for creating system | |
6 | dumps on SCSI disks. The dump process is initiated by booting a dump tool, which | |
7 | has to create a dump of the current (probably crashed) Linux image. In order to | |
8 | not overwrite memory of the crashed Linux with data of the dump tool, the | |
7d4c738c | 9 | hardware saves some memory plus the register sets of the boot CPU before the |
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10 | dump tool is loaded. There exists an SCLP hardware interface to obtain the saved |
11 | memory afterwards. Currently 32 MB are saved. | |
12 | ||
13 | This zfcpdump implementation consists of a Linux dump kernel together with | |
7d4c738c | 14 | a user space dump tool, which are loaded together into the saved memory region |
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15 | below 32 MB. zfcpdump is installed on a SCSI disk using zipl (as contained in |
16 | the s390-tools package) to make the device bootable. The operator of a Linux | |
17 | system can then trigger a SCSI dump by booting the SCSI disk, where zfcpdump | |
18 | resides on. | |
19 | ||
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20 | The user space dump tool accesses the memory of the crashed system by means |
21 | of the /proc/vmcore interface. This interface exports the crashed system's | |
22 | memory and registers in ELF core dump format. To access the memory which has | |
23 | been saved by the hardware SCLP requests will be created at the time the data | |
24 | is needed by /proc/vmcore. The tail part of the crashed systems memory which | |
25 | has not been stashed by hardware can just be copied from real memory. | |
26 | ||
27 | To build a dump enabled kernel the kernel config option CONFIG_CRASH_DUMP | |
28 | has to be set. | |
411ed322 | 29 | |
7d4c738c | 30 | To get a valid zfcpdump kernel configuration use "make zfcpdump_defconfig". |
411ed322 | 31 | |
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32 | The s390 zipl tool looks for the zfcpdump kernel and optional initrd/initramfs |
33 | under the following locations: | |
411ed322 | 34 | |
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35 | * kernel: <zfcpdump directory>/zfcpdump.image |
36 | * ramdisk: <zfcpdump directory>/zfcpdump.rd | |
411ed322 | 37 | |
7d4c738c | 38 | The zfcpdump directory is defined in the s390-tools package. |
411ed322 | 39 | |
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40 | The user space application of zfcpdump can reside in an intitramfs or an |
41 | initrd. It can also be included in a built-in kernel initramfs. The application | |
42 | reads from /proc/vmcore or zcore/mem and writes the system dump to a SCSI disk. | |
411ed322 | 43 | |
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44 | The s390-tools package version 1.24.0 and above builds an external zfcpdump |
45 | initramfs with a user space application that writes the dump to a SCSI | |
46 | partition. | |
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47 | |
48 | For more information on how to use zfcpdump refer to the s390 'Using the Dump | |
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49 | Tools' book, which is available from IBM Knowledge Center: |
50 | https://www.ibm.com/support/knowledgecenter/linuxonibm/liaaf/lnz_r_dt.html |