--- name: "kdump-tools" section: "5" platform: "linux" package: "kdump-tools" version: "1:1.10.7" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/kdump-tools" --- # kdump-tools(5) configuration file for the kdump-tools init script ## NAME kdump-tools.conf - configuration file for the kdump-tools init script ## SYNOPSIS - **/etc/default/kdump-tools** ## DESCRIPTION **kdump-tools** manages the kdump feature of the Linux kernel. The */etc/default/kdump-tools* file contains local configuration settings of kdump. This file is sourced into a shell script, so it's format should be consistent with shell scripting. ## OPTIONS - **USE\_KDUMP** Controls whether or not **kdump-tools** will take any action. If not set or 0, the **kdump-tools** init script will not run. - **KDUMP\_KERNEL** A full pathname to a kdump kernel (the kernel that is kexec'd at crash time in a reserved memory area, exposing the old kernel's memory for dumping). If not set, **kdump-config** will use the boot kernel as the kdump kernel if it is relocatable; otherwise you must set **KDUMP\_KERNEL** in order for **kdump-tools** to work. - **KDUMP\_INITRD** A full pathname to the kdump initrd (if used). If *KDUMP\_KERNEL* is set and *KDUMP\_INITRD* is not set, a warning message will be printed, and an initrd will not be used. - **KDUMP\_COREDIR** Full path to a directory where the vmcore will be saved. Date stamped subdirectories are created each time a vmcore file is processed. If not set, */var/crash* will be used. - **KDUMP\_FAIL\_CMD** This variable specifies a command to run if the vmcore save fails. If not set, no special action is taken. - **KDUMP\_DUMP\_DMESG** This variable controls if the dmesg buffer is dumped. If not set or set to 1, the dmesg buffer is dumped. If set to 0, the dmesg buffer is not dumped. - **KDUMP\_NUM\_DUMPS** This variable specifies how many dump files should be kept on the local machine. If not set or set to 0, no special action is taken. If set to \>1 and there are too many dump files on the machine, older dumps are removed. The cleanup action is only taken after a successful dump. This variable is ignored if remote dumping is enabled. - **MAKEDUMP\_ARGS** Extra arguments passed to [**makedumpfile**(8)](/makedumpfile/8.md). If not set, “*-c -d 31*” will be used. This tells makedumpfile to use compression, and reduce the corefile to in-use kernel pages only. See [**makedumpfile**(8)](/makedumpfile/8.md) for details. - **KDUMP\_KEXEC\_ARGS** Additional arguments to the kexec command used to load the kdump kernel. - **KDUMP\_CMDLINE** Normally, the current kernel commandline is obtained from */proc/cmdline*. Set this variable to override */proc/cmdline*. - **KDUMP\_CMDLINE\_APPEND** Additional arguments to append to the command line for the kdump kernel. If not set, “*reset\_devices systemd.unit=kdump-tools-dump.service nr\_cpus=1 irqpoll usbcore.nousb*” will be used. - **SSH** username and hostname of the remote server that will receive the dump and dmesg files. *username@hostname* format must be used. - **SSH\_KEY** Full path of the ssh private key to be used to login to the remote server. Use “*kdump-config propagate*” to send the public key to the remote server. If not set, the default */root/.ssh/kdump\_id\_rsa* will be used - **HOSTTAG** Select if hostname of IP address will be used as a prefix to the timestamped directory when sending files to the remote server. If not set, “*ip*” will be used. - **NFS** Hostname and mount point of the NFS server configured to receive the crash dump. The syntax must be HOSTNAME:MOUNTPOINT (e.g. *remote:/var/crash* ) ## USAGE **kdump-tools** is as automated as can be at this point but there are some prerequisites to using it. Additionally, some manual configuration is still required. By default, kernel dumps are stored locally on the system. **kdump-tools** can be configured to store the kernel dumps on a remote server accessible through the network. ### Manual Configuration - 1\. **USE\_KDUMP** is set to 0 by default. To enable **kdump-tools**, edit the */etc/default/kdump-tools* configuration file and set **USE\_KDUMP=1**. - 2\. **Kernel Command line parameters** - the kernel must be booted with a *crashkernel*= command line parameter. Some example crashkernel parameters: ``` ia64: crashkernel=384M x86: crashkernel=128M x86_64: crashkernel=256M ``` Some users may also want to add *nmi\_watchdog=1* on certain systems. The nmi watchdog will cause the kernel to panic (and kdump) if a system hang is detected. The kernel command line parameter is generally set in one of these files: */etc/default/grub*, */boot/grub/menu.lst*, */etc/elilo.conf*, or */etc/lilo.conf*. If the command line parameter is changed, a reboot is required in order for it to take effect. - 3\. **Architectural considerations** - A) **x86 && PAE && memory \> 4 Gigabytes** - use *KDUMP\_KEXEC\_ARGS="--elf64-core-headers"* - B) **x86 and x86\_64** - Some systems can take advantage of the nmi watchdog. Add *nmi\_watchdog=1* to the boot commandline to turn on the watchdog. The nmi interrupt will call panic if activated. - C) **ia64** - Some systems may need *KDUMP\_KEXEC\_ARGS="--noio"*. Use this if the system hangs after a panic, but before the kdump kernel begins to boot. ### Networked kernel dump Configuration - 1\. Either use **SSH** or **NFS** to choose which protocol to use to remotely access the target server. - 2 For **SSH** *username@hostname* needs to be provided along with an appropriate **SSH\_KEY** definition or use “*kdump-config propagate*” to propagate a new default ssh key. - 3 For **NFS** the remote server name must be provided along with the directory where files are to be copied. ### Prerequisites - 1\. **Boot Kernel Configuration** - The boot kernel must be configured with *CONFIG\_KEXEC=y* and, if it is also to be used as the kdump kernel, *CONFIG\_CRASHDUMP=y*. For ia64, only makedumpfile level 1 will work if the memory model selected is *CONFIG\_DISCONTIG*. *CONFIG\_SPARSEMEM* is recommended instead. - 2\. **Kdump Kernel Configuration** - The kdump kernel must be relocated or relocatable. ia64 is relocatable by default, but x86, x86\_64, and powerpc must be built with *CONFIG\_RELOCATABLE=y*. Other architectures may require a predermined start location via *CONFIG\_PHYSICAL\_START*. If the boot kernel is relocatable, **kdump-tools** will automatically use that kernel. Otherwise, a relocatable or relocated kernel will need to be provided. The kdump kernel can be specified in the */etc/default/kdump-tools* file. Set the **KDUMP\_KERNEL** variable and if necessary the **KDUMP\_INITRD** variable to point to the provided kernel and its initrd. The kdump kernel must be configured with: **CONFIG\_CRASH\_DUMP=y** ## SYSCTLS Currently kdump-tools automatically sets the kernel sysctl for panic on oops, in order to collect a dump in this case. If the users want more panic triggers, like panic on OOM, or when a NMI is detected, it's recommended that they edit the sysctl configuration files (/etc/sysctl.conf or files on /etc/sysctl.d) in order to do so, and/or apply the sysctl settings with sysctl tool. ### Sysctl handling \*during a kdump\* kdump-tools allows users to configure sysctls overrides on kdump environment; this is specially useful to prevent sysctls from the regular boot to mess with the resource-impaired kdump environment. The mechanism is restricted to kdump boot and will not affect regular boots. In order to add overrides, user should edit the file */etc/kdump/sysctl.conf.* By default, hugepages overrides are set and is highly recommended to keep them in the file, to prevent kdump out-of-memory conditions. ## EXAMPLES Use this option on x86 systems with PAE and more than 4 gig of memory: KDUMP\_KEXEC\_ARGS="--elf64-core-headers" This option starts a shell if **kdump-tools** cannot save the vmcore file: KDUMP\_FAIL\_CMD="/bin/bash; reboot -f" ## FILES - */etc/init.d/kdump-tools* an init script to automatically load a kdump kernel, or save a vmcore and reboot. - */etc/default/kdump-tools* the **kdump-tools** configuration file - */etc/kdump/sysctl.conf* kdump-tools sysctl override file - */var/crash/kernel\_link* a link to the current debug kernel - */var/crash/kexec\_cmd* the last kexec\_cmd executed by **kdump-config** ## DIAGNOSTICS See [**kdump-config**(8)](/kdump-config/8.md) for explanations of various error messages. ## SEE ALSO */usr/share/doc/kdump-tools/README*\ */usr/share/doc/kdump-tools/README.Debian*\ [**kdump-config**(8)](/kdump-config/8.md), [**kexec**(8)](/kexec/8.md), [**sysctl**(8)](/sysctl/8.md), [**makedumpfile**(8)](/makedumpfile/8.md), [**crash**(8)](/crash/8.md), [**gdb**(1)](/gdb/1.md), ## AUTHOR Terry Loftin \