Sunday, August 30, 2015

Automating the 3270 part of a Debian System z install

If you try to install Debian on System z within z/VM you might be annoyed at the various prompts it shows before it lets you access the network console via SSH. We can do better. From within CMS copy the default EXEC and default PARMFILE:


Now edit DEBAUTO EXEC A and replace the DEBIAN in 'PUNCH PARMFILE DEBIAN * (NOHEADER' with DEBAUTO. This will load the alternate kernel parameters file into the card reader, while still loading the original kernel and initrd files.

Replace PARMFILE DEBAUTO A's content with this (note the 80 character column limit):

ro locale=C                                                              
s390-netdevice/choose_networktype=qeth s390-netdevice/qeth/layer2=true   
netcfg/get_ipaddress=<IPADDR> netcfg/get_netmask=       
netcfg/get_gateway=<GW> netcfg/get_nameservers=<FIRST-DNS>    
netcfg/confirm_static=true netcfg/get_hostname=debian                    

Replace <IPADDR>, <GW>, and <FIRST-DNS> to suit your local network config. You might also need to change the netmask, which I left in for clarity about the format. Adjust the device address of your OSA network card. If it's in layer 3 mode (very likely) you should set layer2=false. Note that mixed case matters, hence you will want to SET CASE MIXED in xedit.

Then there are the two URLs that need to be changed. The authorized_keys_url file contains your SSH public key and is fetched unencrypted and unauthenticated, so be careful what networks you traverse with your request (HTTPS is not supported by debian-installer in Debian).

preseed/url is needed for installation parameters that do not fit the parameters file - there is an upper character limit that's about two lines longer than my example. This is why this example only contains the bare minimum for the network part, everything else goes into this preseeding file. It file can optionally be protected with a MD5 checksum in preseed/url/checksum.

Both URLs need to be very short. I thought that there was a way to specify a line continuation, but in my tests I was unable to produce one. Hence it needs to fit on one line, including the key. You might want to use an IPv4 as the hostname.

To skip the initial boilerplate prompts and to skip straight to the user and disk setup you can use this as preseed.cfg:

d-i debian-installer/locale string en_US
d-i debian-installer/country string US
d-i debian-installer/language string en
d-i time/zone US/Eastern
d-i mirror/country manual
d-i mirror/http/mirror string
d-i mirror/http/directory string /debian
d-i mirror/http/proxy string

I'm relatively certain that the DASD disk setup part cannot be automated yet. But the other bits of the installation should be preseedable just like on non-mainframe hardware.

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