[info-afs] AFS
Russ Allbery
rra@stanford.edu
Tue, 05 Dec 2006 22:16:59 -0800
sura <suranjith_e@yahoo.com> writes:
> what is
> afs/group1@EXAMPLE.COM
> i didn't create anything like above.
That would be the service principal for AFS, which you need to create so
that people can authenticate to AFS. That has to be done before you can
start setting up file permissions and the like.
There isn't good documentation out there right now for how to set up AFS
in a modern manner using K5 authentication. Here are the instructions
from the Debian package, which may help. Unless you're using Debian,
you'll have to adjust for some Debianisms, but they're probably a better
starting point.
Setting up a Debian OpenAFS Server
Introduction
This document describes how to set up an OpenAFS server using the Debian
packages. If you are not already familiar with the basic concepts of
OpenAFS, you should review the documentation at:
<http://www.openafs.org/doc/index.htm>
particularly the AFS Administrator's Guide. This documentation is
somewhat out of date (it doesn't talk about how to use a Kerberos v5 KDC
instead of the AFS kaserver, for example), but it's a good introduction
to the basic concepts and servers you will need to run.
The Debian OpenAFS packages follow the FHS and therefore use different
paths than the standard AFS documentation or the paths that experienced
AFS administrators may be used to. In the first column below are the
traditional paths, and in the second column, the Debian paths:
/usr/afs/etc /etc/openafs/server
/usr/afs/local /etc/openafs/server-local
/usr/afs/db /var/lib/openafs/db
/usr/afs/logs /var/log/openafs
/usr/afs/bin /usr/lib/openafs
/usr/vice/etc /etc/openafs
The AFS kaserver (a Kerberos v4 KDC) is not packaged for Debian. Any
new OpenAFS installation should use Kerberos v5 for authentication in
conjunction with either the tools packaged in the openafs-krb5 package
or the Heimdal KDC. When setting up a new cell, you should therefore
not set up a kaserver as described in the AFS Administrator's Guide, and
you will need to follow a slightly different method of setting the cell
key.
Creating a New Cell
For documentation on adding a server to an existing cell, see below.
These instructions assume that you are using MIT Kerberos and the
openafs-krb5 package. If you are using Heimdal instead, some of the
steps will be slightly different (Heimdal can write the AFS KeyFile
directly, for example, so you don't have to use asetkey). The
afs-newcell and afs-rootvol scripts are the same, however.
/usr/share/doc/openafs-dbserver/configuration-transcript.txt.gz has a
transcript of the results of these directions, which you may want to
follow along with as you do this.
1. If you do not already have a Kerberos KDC (Key Distribution Center,
the daemon that handles Kerberos authentication) configured, do so.
You can run the KDC on the same system as your OpenAFS db server,
although if you plan on using Kerberos for other things, you may
eventually want to use separate systems. If you do not have a
Kerberos realm set up already, you can do so in Debian with:
apt-get install krb5-admin-server
krb5_newrealm
This will install a KDC and kadmind server (the server that handles
password changes and account creations) on the local system. Please
be aware that the security of everything that uses Kerberos for
authentication, including AFS, depends on the security of the KDC.
The name of your Kerberos realm should, for various reasons, be in
all uppercase and be a domain name that you control, although
neither is technically required.
Right now, for the aklog from openafs-krb5 to work, you need to
enable krb4 support (either full or nopreauth) and run krb524d.
Eventually this will no longer be necessary.
2. It is traditional (and recommended) in AFS (and for Kerberos) to
give administrators two separate Kerberos principals, one regular
principal to use for regular purposes and a separate admin principal
to use for privileged actions. This is similar to the distinction
between a regular user and the root user in Unix, except that
everyone can have their own separate root identity. Kerberos
recommends username/admin as the admin principal for username, and
this will work for AFS as well.
If you have not already created such an admin principal for yourself
in your Kerberos realm, do so now (using kadmin.local on your KDC,
unless you have a local method that you prefer). Also create a
regular (non-admin) principal for yourself if you have not already;
this is the identity that you'll use for regular operations, like
storing files or reading mail. To do this with kadmin.local, run
that program and then run the commands:
addprinc username/admin
addprinc username
at the kadmin prompt. You'll be prompted for passwords for both
accounts.
If the KDC is not on the same system that the OpenAFS db server will
be on, you will also need to give your admin principal the rights to
download the afs keytab in /etc/krb5kdc/kadm5.acl by adding a lines
like:
username/admin@REALM *
where REALM is your Kerberos realm and username/admin is the admin
principal that you created. That line gives you full admin access
to the Kerberos v5 realm. You can be more restrictive if you want;
see the kadmind man page for the syntax.
3. Install the OpenAFS db server package on an appropriate system with:
apt-get install openafs-dbserver openafs-krb5
The openafs-krb5 package will be used to create the AFS KeyFile.
As part of this installation, you will need to configure
openafs-client with the cell you are creating as the local cell name
and the server on which you're working as the db server. This name
is technically arbitrary but should, for various reasons, be a valid
domain name that you control; unlike Kerberos realms, it should be
in all lowercase. Enter the name of the local system when prompted
for the names of your OpenAFS db servers. Don't start the client;
that will happen below. For right now, say that you don't want it
to start at boot. You can change that later with dpkg-reconfigure
openafs-client.
If you have already installed openafs-client and configured it for
some other cell, you do need to configure it to point to your new
cell for these instructions to work. Stop the AFS client on the
system with /etc/init.d/openafs-client stop and then run:
dpkg-reconfigure openafs-client
pointing it to the new cell you're about to create instead.
Remember, your cell name should be in lowercase. If you have had to
do this several times, double-check /etc/openafs/CellServDB when
you're done and make sure that there is only one entry for your new
cell at the top of that file and that it lists the correct IP
address for your new db server.
In order to complete the AFS installation, you will also need a
working AFS client installed on that system, which means that you
need to install an OpenAFS kernel module. Please see:
/usr/share/doc/openafs-client/README.modules
for information on how to do that.
4. Create an AFS principal in Kerberos. This is the AFS service
principal, used by clients to authenticate to AFS and for AFS
servers to authenticate to each other. It *must* be a DES key; AFS
does not support any other encryption type. Run kadmin.local on
your KDC and then, at the kadmin.local prompt, run:
addprinc -randkey -e des-cbc-crc:v4 afs
If your Kerberos realm name does not match your AFS cell name (if,
for instance, you have one Kerberos realm with multiple AFS cells),
use "afs/cell.name" as the name of the principal above instead of
just "afs", where cell.name is the name of your new AFS cell.
5. On the db server, download this key into a keytab. If this is the
same system as the KDC, you can use kadmin.local again. If not, you
should use kadmin (make sure that krb5-user is installed), and you
may need to pass -p username/admin to kadmin to tell it what
principal to authenticate as. Whichever way you get into kadmin,
run:
ktadd -k /tmp/afs.keytab -e des-cbc-crc:v4 afs
(or afs/cell.name if you used that instead). In the message that
results, note the kvno number reported, since you'll need it later
(it will normally be 3).
Don't forget the -e des-cbc-crc:v4 to force the afs key to be DES.
You can verify this with:
getprinc afs
and checking to be sure that the only key listed is a DES key. If
there are multiple keys listed, delprinc the afs principal, delete
the /tmp/afs.keytab file, and then start over with addprinc, making
sure not to forget the -e option.
6. Create the AFS KeyFile with:
asetkey add <kvno> /tmp/afs.keytab afs
(or afs/cell.name if you used that instead). <kvno> should be
replaced by the kvno number reported by kadmin. This tells AFS the
Kerberos key that it should use, making it match the key in the
Kerberos KDC.
7. If the name of your Kerberos realm does not match the name of your
AFS cell, tell AFS what Kerberos realm to use with:
echo REALM > /etc/openafs/server/krb.conf
where REALM is the name of your Kerberos realm. If your AFS cell
and Kerberos realm have the same name, this is unnecessary.
8. Create some space to use for AFS volumes. You can set up a separate
AFS file server on a different system from the Kerberos KDC and AFS
db server, and for a larger cell you will want to do so, but when
getting started you can make the db server a file server as well.
For a production cell, you will want to create a separate partition
devoted to AFS and mount it as /vicepa (and may want to make
multiple partitions mounted as /vicepb, /vicepc, etc.), but for
testing purposes, you can use the commands below to create a
zero-filled file, create a file system in it, and then mount it:
dd if=/dev/zero of=/var/lib/openafs/vicepa bs=1024k count=32
mke2fs /var/lib/openafs/vicepa
mkdir /vicepa
mount -oloop /var/lib/openafs/vicepa /vicepa
mke2fs will ask you if you're sure you want to create a file system
on a non-block device; say yes.
9. Run afs-newcell. This will prompt you to be sure that the above
steps have been complete and will ask you for the Kerberos principal
to use for AFS administrative access. You should use the
username/admin principal discussed above. afs-newcell sets up the
initial protection database (which stores users and groups),
configures the AFS database and file server daemons, and creates the
root volume for AFS clients.
At the completion of this step, you should see bosserver and several
other AFS server processes running, and you should be able to see
the status of those processes with:
bos status localhost -local
bosserver is a master server that starts and monitors all the
individual AFS servers, and bos is the program used to send it
commands.
Now, you should be able to run:
kinit username/admin@REALM
aklog cell.name -k REALM
where username/admin is the admin principal discussed above, REALM
is the name of your Kerberos realm, and cell.name is the name of
your AFS cell. This will obtain Kerberos tickets and AFS tokens in
your Kerberos realm and new AFS cell. You should be able to see
your AFS tokens by running:
tokens
Finally, you should be able to see the status of the AFS server
processes with:
bos status <hostname>
where <hostname> is the hostname of the local system, once you've
done the above. This tests authenticated bos access as your admin
principal (rather than using the local KeyFile to authenticate).
10. Run afs-rootvol. This creates the basic AFS volume structure for
your new cell, including the top-level volume, the mount point for
your cell in the AFS root volume, and the mount points for all known
public cells. It will prompt you to be sure that the above steps
are complete and then will ask you what file server and partition to
create the volume on. If you were following the above instructions,
use the local hostname and "a" as the partition (without the
quotes), which will use /vicepa.
After this command completes, you should be able to /bin/ls /afs and
see your local cell (and, if you aren't using dynroot, mount points
for several other cells). Note that if you're not using fakestat,
run /bin/ls rather than just ls to be sure that ls isn't aliased to
ls -F, ls --color, or some other option that would stat each file in
/afs, since this would require contacting lots of foreign cells and
could take a very long time.
You should now be able to cd to /afs/cell.name where cell.name is
the AFS cell name that you used. Currently, there isn't anything in
your cell except two volumes, user and service, created by
afs-rootvol. To make modifications, cd to /afs/.cell.name (note the
leading period) and make changes there. To make those changes show
up at /afs/cell.name, run vos release root.cell. For more details
on what you can do now, see the AFS Administrator's Reference.
11. While this is optional, you probably want to add AFSDB records to
DNS for your new AFS cell. These special DNS records let AFS
clients find the db servers for your cell without requiring local
configuration. To do this, create a DNS record like:
<cell>. 3600 IN AFSDB 1 <server>.
where <cell> is the name of your AFS cell and <server> is the name
of your db server. Note the trailing periods to prevent the DNS
server from appending the origin. You can, of course, choose what
you prefer for the lifetime. The 1 is not a priority; it's a
special indicator saying that this record is for an AFS database
server.
If you have multiple db servers (see below for adding new ones), you
should create multiple records of this type, one per db server.
Congratulations! You now have an AFS cell. If any of the above steps
failed, please check the steps carefully and make sure that you've done
them all in order. If that doesn't reveal the cause of the problem,
please feel free to submit a bug report with reportbug. Include as many
details as possible on exactly what you typed and exactly what you saw
as a result, particularly any error messages.
Adding Additional Servers
If you decide one server is not enough, or if you're adding a server to
an existing cell, here is roughly what you should do:
1. Copy securely (using scp, encrypted Kerberos rcp, or some other
secure method) all of /etc/openafs/server to the new server.
2. Install the openafs-fileserver package on the new server.
3. If the machine is to be a file server, create an fs instance using
bos create:
bos create <host> fs fs -cmd /usr/lib/openafs/fileserver \
-cmd /usr/lib/openafs/volserver \
-cmd /usr/lib/openafs/salvager -localauth
For a file server, this is all you have to do. The above uses the
default fileserver options, however, which are not particularly
well-tuned for modern systems. afs-newcell uses the following
parameters from Harald Barth:
-p 23 -busyat 600 -rxpck 400 -s 1200 -l 1200 -cb 65535
-b 240 -vc 1200
If you want to add any additional fileserver options, enclose
/usr/lib/openafs/fileserver and the following options in double
quotes when giving the bos create command.
4. For database servers, also install openafs-dbserver and then use bos
addhost to add the new server to /etc/openafs/server/CellServDB:
bos addhost <server> <new-server>
for each db server <server> in your cell (including the new one).
Then, restart the ptserver and vlserver instances on each of your
existing servers with:
bos restart <server> ptserver
bos restart <server> vlserver
It's best to wait a few seconds after doing this for each server
before doing the next server so that voting finishes and you never
lose a quorum.
Only after ptserver and vlserver have been restarted on each of your
existing servers, create ptserver and vlserver instances on the new
server:
bos create <host> ptserver simple /usr/lib/openafs/ptserver \
-localauth
bos create <host> vlserver simple /usr/lib/openafs/vlserver \
-localauth
The existing servers should then propagate the database to the new
server. If you are using buserver, you will need to do the same
thing for it as with ptserver and vlserver.
Note that you do not need to run a file server on a db server if you
don't want to (and larger sites probably will not want to), but you
always need to have the openafs-fileserver package installed on db
servers. It contains the bosserver binary and some of the shared
infrastructure.
5. If you added a new db server, configure your clients to use it. If
you are using AFSDB records in DNS, you can just add a new record
(see point 10 in the instructions for creating a new cell).
Otherwise, clients will need to have the new server IP address added
to their /etc/openafs/CellServDB file (or /usr/vice/etc/CellServDB
for non-Debian clients using the standard AFS paths), and the client
will have to be restarted before it will know about the new db
server.
The standard rule of thumb is that all of your database servers and file
servers should ideally be running the same version of OpenAFS. However,
in practice OpenAFS is fairly good at backward compatibility and you can
generally mix and match different versions. Be careful, though, to
ensure that all of your database servers are built the same when it
comes to options like --enable-supergroups (enabled in the Debian
packages).
Upgrades
Currently, during an upgrade of the openafs-fileserver package, all
services will be stopped and restarted. If openafs-dbserver is upgraded
without upgrading openafs-fileserver, those server binaries will not be
stopped and restarted; that restart will have to be done by hand.
It is possible that future versions of this package will install for
example /usr/lib/openafs/fileserver.package instead of
/usr/lib/openafs/fileserver and then create links to the actual binaries
in postinst. Upgrades would then not replace the old binaries, but
instead a script will be provided to roll the links forward to the new
versions. The intent is that people could install the new package on
all their servers and then quickly move the links before restarting the
bosserver. This has not yet been implemented.
--
Russ Allbery (rra@stanford.edu) <http://www.eyrie.org/~eagle/>