On Mon, May 25, 2009 at 08:16:14PM +0200, Leopold Palomo Avellaneda wrote: > > first of all sorry because the mails is off topic: it's not about the amd64 > port of debian. But, I have a problem with a kernel, and maybe some of the > clever minds here could help me, because nobody in my LUG have solved it. > > In one of my servers, running lenny, with a stock xen kernel, the box crashes > aleatory. There's an open bug [1] > > My question is how can I obtain the information from a console when the > kernel > crash? Because there's nothing on the kern.log, syslog.
The best way is to use a serial console. Hook up a null-modem serial cable from the problem box to a working box. Run minicom on the working box, turn on logging in minicom, boot the problem box and wait for the crash. Here's my /boot/grub/menu.lst that shows how to set it up. Grub will start with something like "press a key to continue" so that it knows whether you're at the serial console or the main (VGA) console, and thend presents the usual menu. # menu.lst - See: grub(8), info grub, update-grub(8) # grub-install(8), grub-floppy(8), # grub-md5-crypt, /usr/share/doc/grub # and /usr/share/doc/grub-legacy-doc/. #### set up for both regular console and serial terminal on mgmt port #### don't automatically boot any entry #### require a password to edit configs #### require a password to boot any entry #### have separate entries for use with serial console or regular console #### #### mgmt port is /dev/ttyS1 serial --unit=1 --speed=38400 --word=8 --parity=no --stop=1 terminal serial console ## default num # Set the default entry to the entry number NUM. Numbering starts from 0, and # the entry number 0 is the default if the command is not used. # # You can specify 'saved' instead of a number. In this case, the default entry # is the entry saved with the command 'savedefault'. # WARNING: If you are using dmraid do not change this entry to 'saved' or your # array will desync and will not let you boot your system. default 0 <snip> ### BEGIN AUTOMAGIC KERNELS LIST ## lines between the AUTOMAGIC KERNELS LIST markers will be modified ## by the debian update-grub script except for the default options below ## DO NOT UNCOMMENT THEM, Just edit them to your needs ## ## Start Default Options ## ## default kernel options ## default kernel options for automagic boot options ## If you want special options for specific kernels use kopt_x_y_z ## where x.y.z is kernel version. Minor versions can be omitted. ## e.g. kopt=root=/dev/hda1 ro ## kopt_2_6_8=root=/dev/hdc1 ro ## kopt_2_6_8_2_686=root=/dev/hdc2 ro # kopt=root=LABEL=root ro ## default grub root device ## e.g. groot=(hd0,0) # groot=(hd0,0) ## should update-grub create alternative automagic boot options ## e.g. alternative=true ## alternative=false # alternative=true ## should update-grub lock alternative automagic boot options ## e.g. lockalternative=true ## lockalternative=false # lockalternative=false ## additional options to use with the default boot option, but not with the ## alternatives ## e.g. defoptions=vga=791 resume=/dev/hda5 # defoptions= ## should update-grub lock old automagic boot options ## e.g. lockold=false ## lockold=true # lockold=false ## Xen hypervisor options to use with the default Xen boot option # xenhopt= ## Xen Linux kernel options to use with the default Xen boot option # xenkopt=console=tty0 ## altoption boot targets option ## multiple altoptions lines are allowed ## e.g. altoptions=(extra menu suffix) extra boot options ## altoptions=(single-user) single # altoptions=(serial console) console=tty0 console=ttyS1,38400n8 # altoptions=(single-user mode) single # altoptions=(single-user serial console) console=tty0 console=ttyS1,38400n8 single ## controls how many kernels should be put into the menu.lst ## only counts the first occurence of a kernel, not the ## alternative kernel options ## e.g. howmany=all ## howmany=7 # howmany=all ## should update-grub create memtest86 boot option ## e.g. memtest86=true ## memtest86=false # memtest86=true ## should update-grub adjust the value of the default booted system ## can be true or false # updatedefaultentry=false ## should update-grub add savedefault to the default options ## can be true or false # savedefault=false ## ## End Default Options ## title Debian GNU/Linux, kernel 2.6.26-2-686 root (hd0,0) kernel /boot/vmlinuz-2.6.26-2-686 root=LABEL=root ro initrd /boot/initrd.img-2.6.26-2-686 title Debian GNU/Linux, kernel 2.6.26-2-686 (serial console) root (hd0,0) kernel /boot/vmlinuz-2.6.26-2-686 root=LABEL=root ro console=tty0 console=ttyS1,38400n8 initrd /boot/initrd.img-2.6.26-2-686 title Debian GNU/Linux, kernel 2.6.26-2-686 (single-user mode) root (hd0,0) kernel /boot/vmlinuz-2.6.26-2-686 root=LABEL=root ro single initrd /boot/initrd.img-2.6.26-2-686 title Debian GNU/Linux, kernel 2.6.26-2-686 (single-user serial console) root (hd0,0) kernel /boot/vmlinuz-2.6.26-2-686 root=LABEL=root ro console=tty0 console=ttyS1,38400n8 single initrd /boot/initrd.img-2.6.26-2-686 <snip> Here's the end of my /etc/inittab to allow a login on the serial console: ## note S0 will be or is modem, on Port A ## S3 is Port B. S3:23:respawn:/sbin/getty -L -w ttyS3 38400 vt100 ## S1 is management port S1:23:respawn:/sbin/getty -L -w ttyS1 38400 vt100 I hope this helps. Doug. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
