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Editing: README.TEMPLATING
IMPORTANT NOTE: As of Feb. 11, 2002 (and indeed, for quite some time before that), the /etc/rc.diskless{1,2} scripts support a slightly different diskless boot process than the one documented in the rest of this file (which is 3 years old). I am not deleting the information below because it contains some useful background information on diskless operation, but for the actual details you should look at /etc/rc.diskless1, /etc/rc.diskless2, and the /usr/share/examples/diskless/clone_root script which can be useful to set up clients and server for diskless boot. --- $FreeBSD$ --- ------------------------------------------------------------------------ TEMPLATING machine configurations Matthew Dillon dillon@backplane.com This document describes a general mechanism by which you can template / and /usr. That is, to keep a 'master template' of / and /usr on a separate machine which is then used to update the rest of your machines. Generally speaking, you can't simply mirror /. You might be able to get away with mirroring /usr. There are two main problems involved with templating: (1) Avoiding overwriting run-time generated files By default, the system maintains a number of files in the root partition. For example, sendmail will dbm /etc/aliases into /etc/aliases.db. vipw or chpass or other password related routines will regenerate the password dbm's /etc/spwd.db, /etc/pwd.db, and passwd. /etc/namedb/s might contain generated secondaries. And so forth. The templating mechanism must avoid copying over such files. (2) Customizing machines. Customizing machines is actually considerably simpler. You create a configuration hierarchy and convert the configuration files that have to be customized into softlinks that run through a special softlink in the configuration directory. This will work for every configuration file except possibly /etc/master.passwd For example, /etc/resolv.conf would be turned into a softlink to /conf/ME/resolv.conf, and /conf/ME itself would be a softlink to /conf/<HOSTNAME>. The actual resolv.conf configuration file would reside in /conf/<HOSTNAME>. If you have a lot of hosts, some configuration files may be commonly classified. For example, all your shell machines might have the same /etc/resolv.conf. The solution is to make /conf/<HOSTNAME>/resolv.conf a softlink to a common directory, say /conf/HT.SHELL/resolv.conf. It may sound a little messy, but this sort of categorization actually makes the sysadmins job much, much easier. The /conf/ directory hierarchy is stored on the template and distributed to all the machines along with the rest of the root partition. This type of customization is taken from my direct experience instituting such a system at BEST. At the time, BEST had over 45 machines managed from a single template. RUN-TIME GENERATED OR MODIFIED FILES IN / or /USR /etc/aliases.db /etc/master.passwd /etc/spwd.db /etc/pwd.db /etc/passwd /etc/namedb/s /root/.history /root/.ssh/identity /root/.ssh/identity.pub /root/.ssh/random_seed /root/.ssh/known_hosts /conf/ME /kernel* ( note 2 ) /dev ( note 3 ) /var ( note 4 ) /home ( note 4 ) /lost+found /usr/lost+found /usr/home ( note 4 ) /usr/crash ( note 5 ) /usr/obj ( note 5 ) /usr/ports ( note 5 ) /usr/src ( note 5 ) /usr/local/crack ( note 5 ) /usr/local/lib/X11/xdm/xdm-errors ( note 6 ) /usr/local/lib/X11/xdm/xdm-pid ( note 6 ) /usr/local/etc/ssh_host_key ( note 6 ) /usr/local/etc/ssh_host_key.pub ( note 6 ) /usr/local/etc/ssh_random_seed ( note 6 ) /conf/ME ( note 7 ) note 2: You typically want to update kernels manually and *NOT* template them as a safety measure. This also allows you to run different kernels on different machines or. note 3: /dev must be updated manually. Some devices, such as tty's and pty's, use the access and/or modify time and/or user/group operationally and regenerating the devices on the fly would be bad. note 4: /var and /home are usually separately mounted partitions and thus would not fall under the template, but as a safety measure the template copier refuse to copy directories named 'home'. note 5: These are directories that are as often created directly on /usr as they are separately-mounted partitions. You typically do not want to template such directories. note 6: Note that you can solve the problem of xdm and sshd creating files in /usr. With xdm, edit /usr/local/lib/xdm/xdm-config and change the errorLogFile and pidFile config lines. With sshd, add 'HostKey' and 'RandomSeed' directives to specify /var/db for the location of the host key and run-time sshd random seed: HostKey /var/db/ssh_host_key RandomSeed /var/db/ssh_random_seed note 7: In this example, /conf/ME is the machine customizer and must be pointed to the /conf/<full-host-name>/ directory, which is different for each machine. Thus, the /conf/ME softlink should never be overwritten by the templating copy. TYPICAL CUSTOMIZED CONFIGURATION SOFTLINKS The following files typically need to be turned into softlinks to /conf/ME/<filename>: /etc/ccd.conf -> /conf/ME/ccd.conf /etc/ipfw.conf ... /etc/fstab /etc/motd /etc/resolv.conf /etc/aliases /etc/sendmail.cw /etc/organization /etc/named.conf /etc/rc.conf.local /etc/printcap /etc/inetd.conf /etc/login.conf /etc/gettytab /etc/ntp.conf /etc/exports /root/.k5login -> /conf/ME/root/.k5login And, of course, /conf/ME is usually a softlink to the appropriate /conf/<full-host-name>/. Depending on your system configuration, there may be other files not listed above that you have to worry about. In many cases, /conf/ME/filename is itself a softlink to "../HT.xxxx/filename", where HT.xxxx is something like HT.STD ... this added complexity actually makes it easier to manage multiple classifications of machines. DELETION OF FILES Any file found on the template destination that does not exist in the source and is not listed as an exception by the source should be deleted. However, deletion can be dangerous and cpdup will ask for confirmation by default. Once you know you aren't going to blow things up, you can turn this feature off and update your systems automatically from cron. By formalizing the delete operation, you can be 100% sure that it is possible to recreate / and /usr on any machine with only the original template and a backup of the ( relatively few ) explicitly-excepted files. The most common mistake a sysop makes is to make a change to a file in / or /usr on a target machine instead of the template machine. If the target machine is updated once a night from cron, the sysop quickly learns not to do this ( because his changes get overwritten overnight ). With a manual update, these sorts of mistakes can propagate for weeks or months before they are caught. TEMPLATE COPYING AND SAFETY THE CPDUP PROGRAM The 'cpdup' program is a program which efficiently duplicates a directory tree. The program copies source to destination, duplicating devices, softlinks, hardlinks, files, modification times, uid, gid, flags, perms, and so forth. The program incorporates several major features: * The program refuses, absolutely, to cross partition boundaries. i.e. if you were copying the template /usr from an NFS mount to your /usr, and you had a mount point called /usr/home, the template copying program would *NOT* descend into /usr/home on the destination. This is a safety. * The program accesses a file called .cpignore in each directory it descends into on the source to obtain a list of exceptions for that directory -- that is, files not to copy or mess with. This is a templating function. * The program refuses to delete a directory on the destination being replaced by a softlink or file on the source. This is a safety mechanism * The program is capable of maintaining MD5 check cache files and doing an MD5 check between source and destination during the scan. * The program is capable of deleting files/directories on the destination that do not exist on the source, but asks for confirmation by default. This is a templating and a safety mechanism. * The program uses a copy-to-tmp-and-rename methodology allowing it to be used to update live filesystems. This is a templating mechanism. * The program, by default, tries to determine if a copy is required by checking modify times, file size, perms, and other stat elements. If the elements match, it does not bother to copy ( unless an MD5 check is being made, in which case it must read the destination file ). You typically run cpdup on the target machine. The target machine temporarily mounts the template machine's / and /usr via NFS, read-only, and runs cpdup to update / and /usr. If you use this methodology note that THERE ARE SECURITY CONSIDERATIONS! See 'SECURITY CONSIDERATIONS WITH NFS' below. Whatever script you use that does the NFS mounts should ensure that the mount succeeded before continuing with the cpdup. You should create .cpignore files in the appropriate directories on the template machine's / and /usr partitions so as not to overwrite active files on the target. The most critical .cpignore files should be protected with 'chflags schg .cpignore'. Specifically, the ones in / and /etc, but possibly others as well. For example, the .cpignore hierarchy for protect /root is: # /root/.cpignore contains .history # /root/.ssh/.cpignore contains random_seed known_hosts authorized_keys identity identity.pub WHEN INITIALLY CONVERTING A TARGET MACHINE TO USE TEMPLATING, ALWAYS MAKE A FULL BACKUP OF THE TARGET MACHINE FIRST! You may accidentally delete files on the target during the conversion due to forgetting to enter items into appropriate .cpignore files on the source. SECURITY CONSIDERATIONS WITH NFS ROOT EXPORT FROM TEMPLATE MACHINE SECURITY CONSIDERATIONS WITH NFS USR EXPORT FROM TEMPLATE MACHINE There are some serious security considerations that must be taken into account when exporting / and /usr on the template machine. * only export read-only * the password file ( aka vipw ) may not contain any crypted passwords at all. You MUST use ssh or kerberos to access the template machine. You can get away with giving only root a crypted password, but only if you disallow network root logins and only allow direct root logins on the console. * The machine's private ssh_host_key usually resides in /usr/local/etc. You must move this key to /var/db. You can softlink link so no modification of sshd_config is required. * The machine's private ~root/.ssh/identity file is also exposed by the NFS export, you should move this file to /var/db as well and put a softlink in ~root/.ssh. * DON'T EXPORT /var ! Either that, or don't put the private keys in /var/db ... put them somewhere else. * You may want to redirect the location of the random_seed file, which can be done by editing ~root/.ssh/sshd_config and /usr/local/etc/sshd_config so it is not exposed either. -Matt Matthew Dillon dillon@backplane.com
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