11. Various hints

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This chapter has various hints which may not always be explained in great detail.

To generate a md5 hash for the password use this echo "yoursecrectpassword" | mkpasswd -Hmd5 -s
When using HTTP access to a Debian mirror, the local /var partition on all install clients must be big enough to keep the downloaded Debian packages. Do not try with less than 250 Mbytes unless you know why. You can limit the number of packages installed at a time with the variable $MAXPACKAGES.
You can remove the red logo on the install client by simply calling reset once. If will also not appear if you create a file using this command on the install server:

touch /srv/fai/nfsroot/live/filesystem.dir/.nocolorlogo

You can shorten some scripts by using one single fcopy command fcopy -r /.
If you rebuild the nfsroot, you will create a new ssh host key inside the nfsroot. Then logging in to an install client may fail, because the host key changes. You can use this:

$ ssh -o StrictHostKeyChecking=no root@installclient

You can also delete the host entry on your install client in your ~/.ssh/known_hosts file by unsing the ssh-keygen -R command.
In the tasks chboot and savelog, a connection using secure shell is opened to the FAI server (see [isavelog]). To ensure that this works non-interactively, a proper entry in NFSROOT/root/.ssh/known_hosts must be created. When using fai-setup, this is done automatically, but it may require manual editing in case the name of your FAI server was not determined correctly. If you stumble over ssh connections that require typing "yes" to accept the host key during installation, please check the contents of your NFSROOT/root/.ssh/known_hosts file
You can calculate the IP subnet address by using the nice tool ipcalc. Following example gives you the notation for a class C network (16) when the server netork interface has the IP address 123.45.6.123

$ ipcalc -nb 123.45.6.123 16|grep Network:

You can merge two directories which contain configuration information, if one is a global one, and the other a local one. We use it to merge the templates from the FAI package, and our local configuration, which contains encrypted passwords and other information that should not be readable by others. If you remove a file in your local configuration, do not forget to remove this file also in the configuration space, otherwise it will still be used.
After calling set-disk-info, a list of all local hard disks is stored in $disklist and $device_size contains a list of disk devices and their sizes.
Use fai-divert -a if a postinst script calls a configuration program, e.g. the postinst script for package apache calls apacheconfig, which needs manual input. You can fake the configuration program so the installation can be fully automatic. But don't forget to use fai-divert -R to remove all faked scripts.
During the installation you can execute commands inside the newly installed system in a chroot environment by using chroot /target or just $ROOTCMD followed by the command you want to call; for example $ROOTCMD dpkg -l shows the packages installed on the new system.
If your computer can't boot from the network card, you do not always need to boot from floppy. Add the class FAI_BOOTPART and FAI will automatically create a lilo or grub entry for booting the FAI bootfloppy from this partition. So you can start the re-installation without a boot floppy. This will also make the test phase shorter, since booting from hard disk is much faster than booting from floppy. You can also set a password for this boot menu.
How can I define classes on the kernel command line?
Read the man page of fai-class(8)
How to use a custom kernel inside the nfsroot?
Build your customized kernel by building a kernel package using make-kpkg(8) and use the option —initrd. Copy this Debian package to a local repository and add it to /etc/fai/sources.list. Add the name of your package to /etc/fai/NFSROOT. Then rebuild the nfsroot.
On http://www.layer-acht.org/fai you will find an example how to fully automatically install a system using the Debian Installer (d-i) in conjunction with FAI's softupdate (see [softupdate]).