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Subject: AFS distributed filesystem FAQ Newsgroups: alt.filesystems.afs,alt.answers,news.answers From: mpb@mailserver.aixssc.uk.ibm.com (Paul Blackburn) Date: 29 Apr 1994 21:56:56 GMT Archive-name: afs-faq Version: 1.77 Last-modified: 1108 GMT Friday 29th April 1994 AFS frequently asked questions ______________________________________________________________________________ This posting contains answers to frequently asked questions about AFS. Your comments and contributions are welcome (email: mpb@acm.org) Most newsreaders can skip from topic to topic with control-G. ______________________________________________________________________________ Subject: Table of contents: 0 Preamble 0.01 Purpose and audience 0.02 Acknowledgements 0.03 Disclaimer 0.04 Release Notes 0.05 Quote 1 General 1.01 What is AFS? 1.02 Who supplies AFS? 1.03 What is /afs? 1.04 What is an AFS cell? 1.05 What are the benefits of using AFS? 1.05.a Cache Manager 1.05.b Location independence 1.05.c Scalability 1.05.d Improved security 1.05.e Single systems image (SSI) 1.05.f Replicated AFS volumes 1.05.g Improved robustness to server crash 1.05.h "Easy to use" networking 1.05.i Communications protocol 1.05.j Improved system management capability 1.06 Which systems is AFS available for? 1.07 What does "ls /afs" display in the Internet AFS filetree? 1.08 Why does AFS use Kerberos authentication? 2 Using AFS 2.01 What are the differences between AFS and a unix filesystem? 2.02 What is an AFS protection group? 2.03 What are the AFS defined protection groups? 2.04 What is an AFS access control list (ACL)? 2.05 What are the AFS access rights? 2.06 What is pagsh? 2.07 Why use a PAG? 2.08 How can I tell if I have a PAG? 2.09 Can I still run cron jobs with AFS? 2.10 How much disk space does a 1 byte file occupy in AFS? 2.11 Is it possible to specify a user who is external to the current AFS cell on an ACL? 2.12 Are there any problems printing files in /afs? 3 AFS administration 3.01 Is there a version of xdm available with AFS authentication? 3.02 Is there a version of xlock available with AFS authentication? 3.03 How does AFS compare with NFS? 3.04 Given that AFS data is location independent, how does an AFS client determine which server houses the data its user is attempting to access? 3.05 Which protocols does AFS use? 3.06 Are setuid programs executable across AFS cell boundaries? 3.07 How does AFS maintain consistency on read-write files? 3.08 How can I run daemons with tokens that do not expire? 3.09 Can I check my user's passwords for security purposes? 3.10 Is there a way to automatically balance disk usage across fileservers? 3.11 Can I shutdown an AFS fileserver without affecting users? 3.12 How can I set up mail delivery to users with $HOMEs in AFS? 3.13 Should I replicate a ReadOnly volume on the same partition and server as the ReadWrite volume? 3.14 Should I start AFS before NFS in /etc/inittab? 3.15 Will AFS run on a multi-homed fileserver? 3.16 Can I replicate my user's home directory AFS volumes? 3.17 Which TCP/IP ports and protocols do I need to enable in order to operate AFS through my Internet firewall? 3.18 What is the Andrew Benchmark? 3.19 Is there a version of HP VUE login with AFS authentication? 4 Getting more information 4.01 Is there an anonymous FTP site with AFS information? 4.02 Which USENET newsgroups discuss AFS? 4.03 Where can I get training in AFS? 5 About the AFS faq 5.01 How can I get a copy of the AFS faq? 5.02 How can I get my question (and answer) into the AFS faq? 5.03 How can I access the AFS faq via the World Wide Web? 6 Bibliography ______________________________________________________________________________ Subject: 0 Preamble Subject: 0.01 Purpose and audience The aim of this compilation is to provide information about AFS including: + A brief introduction + Answers to some often asked questions + Pointers to further information Definitive and detailed information on AFS is provided in Transarc's AFS manuals ([23], [24], [25]). The intended audience ranges from people who know little of the subject and want to know more to those who have experience with AFS and wish to share useful information by contributing to the faq. Subject: 0.02 Acknowledgements The information presented here has been gleaned from many sources. Some material has been directly contributed by people listed below. I would like to thank the following for contributing: Pierette VanRyzin (Transarc) Lyle Seaman (Transarc) Joseph Jackson (Transarc) Dan Lovinger (Carnegie Mellon University) Lucien Van Elsen (IBM) Jim Rees (University of Michigan) Derrick J. Brashear (Carnegie Mellon University) Hans-Werner Paulsen (MPI fuer Astrophysik, Garching) Thanks also to indirect contributors: Ken Paquette (IBM) Lance Pickup (IBM) Lisa Chavez (IBM) Dawn E. Johnson (Transarc) Subject: 0.03 Disclaimer I make no representation about the suitability of this information for any purpose. While every effort is made to keep the information in this document accurate and current, it is provided "as is" with no warranty expressed or implied. Subject: 0.04 Release Notes This faq compilation contains material used with permission of Transarc Corporation. Permission to copy is given provided any copyright notices and acknowledgements are retained. Column 1 is used to indicate changes from the last issue: N = new item U = updated item Subject: 0.05 Quote "'Tis true; there's magic in the web of it;" Othello, Act 3 Scene 4 --William Shakespeare (1564-1616) ______________________________________________________________________________ Subject: 1 General Subject: 1.01 What is AFS? AFS is a distributed filesystem that enables co-operating hosts (clients and servers) to efficiently share filesystem resources across both local area and wide area networks. AFS is marketed, maintained, and extended by Transarc Corporation. AFS is based on a distributed file system originally developed at the Information Technology Center at Carnegie-Mellon University that was called the "Andrew File System". "Andrew" was the name of the research project at CMU - honouring the founders of the University. Once Transarc was formed and AFS became a product, the "Andrew" was dropped to indicate that AFS had gone beyond the Andrew research project and had become a supported, product quality filesystem. However, there were a number of existing cells that rooted their filesystem as /afs. At the time, changing the root of the filesystem was a non-trivial undertaking. So, to save the early AFS sites from having to rename their filesystem, AFS remained as the name and filesystem root. Subject: 1.02 Who supplies AFS? Transarc Corporation phone: +1 (412) 338-4400 The Gulf Tower 707 Grant Street fax: +1 (412) 338-4404 Pittsburgh PA 15219 email: information@transarc.com United States of America afs-sales@transarc.com Subject: 1.03 What is /afs? The root of the AFS filetree is /afs. If you execute "ls /afs" you will see directories that correspond to AFS cells (see below). These cells may be local (on same LAN) or remote (eg halfway around the world). With AFS you can access all the filesystem space under /afs with commands you already use (eg: cd, cp, rm, and so on) provided you have been granted permission (see AFS ACL below). Subject: 1.04 What is an AFS cell? An AFS cell is a collection of servers grouped together administratively and presenting a single, cohesive filesystem. Typically, an AFS cell is a set of hosts that use the same Internet domain name. Normally, a variation of the domain name is used as the AFS cell name. Users log into AFS client workstations which request information and files from the cell's servers on behalf of the users. Subject: 1.05 What are the benefits of using AFS? The main strengths of AFS are its: + caching facility + security features + simplicity of addressing + scalability + communications protocol Here are some of the advantages of using AFS in more detail: Subject: 1.05.a Cache Manager AFS client machines run a Cache Manager process. The Cache Manager maintains information about the identities of the users logged into the machine, finds and requests data on their behalf, and keeps chunks of retrieved files on local disk. The effect of this is that as soon as a remote file is accessed a chunk of that file gets copied to local disk and so subsequent accesses (warm reads) are almost as fast as to local disk and considerably faster than a cold read (across the network). Local caching also significantly reduces the amount of network traffic, improving performance when a cold read is necessary. Subject: 1.05.b Location independence Unlike NFS, which makes use of /etc/filesystems (on a client) to map (mount) between a local directory name and a remote filesystem, AFS does its mapping (filename to location) at the server. This has the tremendous advantage of making the served filespace location independent. Location independence means that a user does not need to know which fileserver holds the file, the user only needs to know the pathname of a file. Of course, the user does need to know the name of the AFS cell to which the file belongs. Use of the AFS cellname as the second part of the pathname (eg: /afs/$AFSCELL/somefile) is helpful to distinguish between file namespaces of the local and non-local AFS cells. To understand why such location independence is useful, consider having 20 clients and two servers. Let's say you had to move a filesystem "/home" from server a to server b. Using NFS, you would have to change the /etc/filesystems file on 20 clients and take "/home" off-line while you moved it between servers. With AFS, you simply move the AFS volume(s) which constitute "/home" between the servers. You do this "on-line" while users are actively using files in "/home" with no disruption to their work. (Actually, the AFS equivalent of "/home" would be /afs/$AFSCELL/home where $AFSCELL is the AFS cellname.) Subject: 1.05.c Scalability With location independence comes scalability. An architectural goal of the AFS designers was client/server ratios of 200:1 which has been successfully exceeded at some sites. Transarc do not recommend customers use the 200:1 ratio. A more cautious value of 50:1 is expected to be practical in most cases. It is certainly possible to work with a ratio somewhere between these two values. Exactly what value depends on many factors including: number of AFS files, size of AFS files, rate at which changes are made, rate at which file are being accessed, speed of servers processor, I/O rates, and network bandwidth. AFS cells can range from the small (1 server/client) to the massive (with tens of servers and thousands of clients). Cells can be dynamic: it is simple to add new fileservers or clients and grow the computing resources to meet new user requirements. Subject: 1.05.d Improved security Firstly, AFS makes use of Kerberos to authenticate users. This improves security for several reasons: + passwords do not pass across the network in plaintext + encrypted passwords no longer need to be visible You don't have to use NIS, aka yellow pages, to distribute /etc/passwd - thus "ypcat passwd" can be eliminated. If you do choose to use NIS, you can replace the password field with "X" so the encrypted password is not visible. (These issues are discussed in detail in [25]). + AFS uses mutual authentication - both the service provider and service requester prove their identities Secondly, AFS uses access control lists (ACLs) to enable users to restrict access to their own directories. Subject: 1.05.e Single systems image (SSI) Establishing the same view of filestore from each client and server in a network of systems (that comprise an AFS cell) is an order of magnitude simpler with AFS than it is with, say, NFS. This is useful to do because it enables users to move from workstation to workstation and still have the same view of filestore. It also simplifies part of the systems management workload. In addition, because AFS works well over wide area networks the SSI is also accessible remotely. As an example, consider a company with two widespread divisions (and two AFS cells): ny.acme.com and sf.acme.com. Mr Fudd, based in the New York office, is visiting the San Francisco office. Mr. Fudd can then use any AFS client workstation in the San Francisco office that he can log into (a unprivileged guest account would suffice). He could authenticate himself to the ny.acme.com cell and securely access his New York filespace. For example: The following shows a guest in the sf.acme.com AFS cell: {1} obtaining a PAG with pagsh command (see 2.06) {2} use the klog command to authenticate into the ny.acme.com AFS cell {3} making a HOME away from home {4} invoking a homely .profile guest@toontown.sf.acme.com $ /usr/afsws/etc/pagsh # {1} $ /usr/afsws/bin/klog -cell ny.acme.com -principal elmer # {2} Password: $ HOME=/afs/ny.acme.com/user/elmer; export HOME # {3} $ cd $ . .profile # {4} you have new mail guest@toontown $ It is not necessary for the San Francisco sys admin to give Mr. Fudd an AFS account in the sf.acme.com cell. Mr. Fudd only needs to be able to log into an AFS client that is: 1) on the same network as his cell and 2) his ny.acme.com cell is mounted in the sf.acme.com cell (as would certainly be the case in a company with two cells). Subject: 1.05.f Replicated AFS volumes AFS files are stored in structures called Volumes. These volumes reside on the disks of the AFS file server machines. Volumes containing frequently accessed data can be read-only replicated on several servers. Cache managers (on users client workstations) will make use of replicate volumes to load balance. If accessing data from one replicate copy, and that copy becomes unavailable due to server or network problems, AFS will automatically start accessing the same data from a different replicate copy. An AFS client workstation will access the closest volume copy. By placing replicate volumes on servers closer to clients (eg on same physical LAN) access to those resources is improved and network traffic reduced. Subject: 1.05.g Improved robustness to server crash The Cache Manager maintains local copies of remotely accessed files. This is accomplished in the cache by breaking files into chunks of up to 64k (default chunk size). So, for a large file, there may be several chunks in the cache but a small file will occupy a single chunk (which will be only as big as is needed). A "working set" of files that have been accessed on the client is established locally in the client's cache (copied from fileserver(s)). If a fileserver crashes, the client's locally cached file copies are usable. Also, if the AFS configuration has included replicated read-only volumes then alternate fileservers can satisfy requests for files from those volumes. Subject: 1.05.h "Easy to use" networking Accessing remote file resources via the network becomes much simpler when using AFS. Users have much less to worry about: want to move a file from a remote site? Just copy it to a different part of /afs. Once you have wide-area AFS in place, you don't have to keep local copies of files. Let AFS fetch and cache those files when you need them. Subject: 1.05.i Communications protocol AFS communications protocol is optimized for Wide Area Networks. Retransmitting only the single bad packet in a batch of packets and allowing the number of unacknowledged packets to be higher (than in other protocols, see [4]). Subject: 1.05.j Improved system management capability Systems administrators are able to make configuration changes from any client in the AFS cell (it is not necessary to login to a fileserver). With AFS it is simple to effect changes without having to take systems off-line. Example: A department (with its own AFS cell) was relocated to another office. The cell had several fileservers and many clients. How could they move their systems without causing disruption? First, the network infrastructure was established to the new location. The AFS volumes on one fileserver were migrated to the other fileservers. The "freed up" fileserver was moved to the new office and connected to the network. A second fileserver was "freed up" by moving its AFS volumes across the network to the first fileserver at the new office. The second fileserver was then moved. This process was repeated until all the fileservers were moved. All this happened with users on client workstations continuing to use the cell's filespace. Unless a user saw a fileserver being physically moved (s)he would have no way to tell the change had taken place. Finally, the AFS clients were moved - this was noticed! Subject: 1.06 Which systems is AFS available for? AFS runs on systems from: HP, Next, DEC, IBM and SUN. Transarc customers have done ports to Crays, and the 3090, but all are based on some flavour of unix. Some customers have done work to make AFS data available to PCs and Macs, although they are using something similar to the AFS/NFS translator (a system that enables "NFS only" clients to NFS mount the AFS filetree /afs). The following list (current at time of writing) is for AFS version 3.3 (check with Transarc for the most up-to-date list). This information can also be found on grand.central.org: via AFS: /afs/grand.central.org/pub/afsps/doc/SUPPORTED_SYSTEMS.afs.* via FTP: grand.central.org:/pub/afsps/doc/SUPPORTED_SYSTEMS.afs.* System-name CPU and Operating System hp300_ux90 Hewlett Packard 9000 Series 300/400 running HP-UX 9.0 hp700_ux90 Hewlett Packard 9000 Series 700 running HP-UX 9.0 hp800_ux90 Hewlett Packard 9000 Series 800 running HP-UX 9.0 next_mach20 NeXT (68030 or 68040 systems) running NeXT OS Rel 2.0,2.1 next_mach30 NeXT (68030 or 68040 systems) running NeXT OS Rel 3.0 pmax_ul43 DECstation 2100, 3100 or 5000 (single processor) running Ultrix 4.3 rs_aix32 IBM RS/6000 running AIX 3.2, 3.2.1 and 3.2.2 rt_aix221 IBM RT/PC running AIX 2.2.1 rt_aos4 IBM-RT/PC running AOS Release 4 sgi_51 Silicon Graphics running IRIX 5.1 sun3_411 Sun 3 (68020 systems) running Sun OS 4.1.1 sun3x_411 Sun 3 (68030 systems) running Sun OS 4.1.1 sun4_411 Sun 4 (EXCEPT SparcStations) running Sun OS 4.1.1, 4.1.2 or 4.1.3 sun4_52 Sun 4 (EXCEPT SparcStations) running Solaris 2.2 sun4c_411 Sun SparcStations running Sun OS 4.1.1, 4.1.2 or 4.1.3 sun4c_52 Sun SparcStations running Solaris 2.2 sun4m_412 Sun SparcServer 600MP running Sun OS 4.1.2/Solaris 1.0, 4.1.3/Solaris 2.1 sun4m_52 Sun SparcServer 600MP running Solaris 2.2 vax_ul43 VAX systems running Ultrix 4.3 (single processor). There are also ports of AFS done by customers available from Transarc on an "as is" unsupported basis. More information on this can be found on grand.central.org: via AFS: /afs/grand.central.org/pub/afs-contrib/bin/README via FTP: grand.central.org:/pub/afs-contrib/bin/README These ports of AFS client code include: HP (Apollo) Domain OS - by Jim Rees at the University of Michigan. sun386i - by Derek Atkins and Chris Provenzano at MIT. Subject: 1.07 What does "ls /afs" display in the Internet AFS filetree? Essentially this displays the AFS cells that co-operate in the Internet AFS filetree. Note that the output of this will depend on the cell you do it from; a given cell may not have all the publicly advertised cells available, and it may have some cells that aren't advertised outside of the given site. The definitive source for this information is: /afs/transarc.com/service/etc/CellServDB.export I've included the list of cell names included in it below: uni-freiburg.de #Albert-Ludwigs-Universitat Freiburg anl.gov #Argonne National Laboratory bcc.ac.uk #Bloomsbury Computing Consortium bstars.com #Boeing Aerospace and Electronics/STARS bu.edu #Boston University cs.brown.edu #Brown University Department of Computer Science ciesin.org #CIESIN cards.com #Cards - Electronic Warfare Associates cmu.edu #Carnegie Mellon University andrew.cmu.edu #Carnegie Mellon University - Campus ce.cmu.edu #Carnegie Mellon University - Civil Eng. Dept. club.cc.cmu.edu #Carnegie Mellon University Computer Club cs.cmu.edu #Carnegie Mellon University - School of Comp. Sci. ece.cmu.edu #Carnegie Mellon University - Elec. Comp. Eng. Dept. me.cmu.edu #Carnegie Mellon University - Mechanical Engineering others.chalmers.se #Chalmers University of Technology - General users cs.cornell.edu #Cornell University Computer Science Department graphics.cornell.edu #Cornell University Program of Computer Graphics theory.cornell.edu #Cornell University Theory Center msc.cornell.edu #Cornell University Materials Science Center pegasus.cranfield.ac.uk #Cranfield Insitute of Technology grand.central.org #DARPA Central File Server at Transarc hrzone.th-darmstadt.de #TH-Darmstadt kiewit.dartmouth.edu #Dartmouth College, Kiewit northstar.dartmouth.edu #Dartmouth College, Project Northstar es.net #Energy Sciences Net cern.ch #European Laboratory for Particle Physics, Geneva fnal.gov #Fermi National Acclerator Laboratory jrc.flinders.edu.au #Flinders School of Info. Sci. and Tech. - Australia hepafs1.hep.net #FNAL HEPNET cell 1 pub.nsa.hp.com #HP Cupertino palo_alto.hpl.hp.com #HP Palo Alto ctp.se.ibm.com #IBM/4C, Chalmers, Sweden ibm.uk #IBM UK, AIX Systems Support Centre inel.gov #Idaho National Engineering Lab iastate.edu #Iowa State University ipp-garching.mpg.de #Institut fuer Plasmaphysik sfc.keio.ac.jp #Keio University, Japan cc.keio.ac.jp #Keio University, Fac. of Sci. & Tech. Computing Ctr lrz-muenchen.de #Leibniz-Rechenzentrum Muenchen Germany athena.mit.edu #MIT/Athena cell rel-eng.athena.mit.edu #MIT/Athena Release Engineering (primary sources) net.mit.edu #MIT/Network Group cell sipb.mit.edu #MIT/SIPB cell media-lab.mit.edu #MIT/Media Lab cell mtxinu.com #mt Xinu Incorporated nada.kth.se #Royal Institute of Technology, NADA nce_ctc #National Computational Env. - Cornell Theory Center nce #National Computing Environment - wide area cell nce_psc #National Computing Environment (Metacenter) nersc.gov #National Energy Research Supercomputer Center alw.nih.gov #National Institutes of Health test.alw.nih.gov #National Institutes of Health (test cell) cmf.nrl.navy.mil #Naval Research Lab ncat.edu #North Carolina Agricultural and Technical State U. nsf-centers.edu #NSF Supercomputing Centers ctd.ornl.gov #Computing and Telecommunications Div ORNL ri.osf.org #OSF Research Institute gr.osf.org #OSF Research Institute, Grenoble vfl.paramax.com #Paramax (Unisys) Paoli Research Center stars.reston.unisys.com #Paramax (Unisys) - Reston, Va. psc.edu #PSC (Pittsburgh Supercomputing Center) rwcp.or.jp #Real World Computer Partnership(rwcp) rhrk.uni-kl.de #Rechenzentrum University of Kaiserslautern rus.uni-stuttgart.de #Rechenzentrum University of Stuttgart ihf.uni-stuttgart.de #University of Stuttgart, Ins. fuer Hochfrequenz-Tec rpi.edu #Rensselaer Polytechnic Institute rose-hulman.edu #Rose-Hulman Institute of Technology dsg.stanford.edu #Stanford Univ. - Comp. Sci. - Distributed Systems ir.stanford.edu #Stanford University slac.stanford.edu #Stanford Linear Accelerator Center stars.com #STARS Technology Center - Ballston, Va. ssc.gov #Superconducting Supercollider Lab ethz.ch #Swiss Federal Inst. of Tech. - Zurich, Switzerland telos.com #Telos Systems Group - Chantilly, Va. titech.ac.jp #Tokyo Institute of Technology transarc.com #Transarc Corporation cs.arizona.edu #University of Arizona - Computer Science Dept. ece.ucdavis.edu #Univ California - Davis campus spc.uchicago.edu #University of Chicago - Social Sciences rrz.uni-koeln.de #University of Cologne - Reg Comp Center urz.uni-heidelberg.de #Universitaet Heidelberg uni-hohenheim.de #University of Hohenheim ncsa.uiuc.edu #University of Illinois wam.umd.edu #University of Maryland Network WAM Project umich.edu #University of Michigan - Campus sph.umich.edu #University of Michigan -- School of Public citi.umich.edu #University of Michigan - IFS Development dmsv.med.umich.edu #University of Michigan - DMSV lsa.umich.edu #University of Michigan - LSA College math.lsa.umich.edu #University of Michigan - Math Cell cs.unc.edu #University of North Carolina at Chapel Hill nd.edu #University of Notre Dame pitt.edu #University of Pittsburgh rus-cip.uni-stuttgart.de #RUS Cip-Pool,Rechenzentrum University of Stuttgart mathematik.uni-stuttgart.de #University of Stuttgart, Math Dept. isi.edu #University of Southern California/ISI cs.utah.edu #University of Utah Computer Science Dept cs.washington.edu #University of Washington Comp Sci Department cs.wisc.edu #University of Wisconsin-Madison, Computer S ucop.edu #University of California Office of the President This shows different and widespread organizations making use of the Internet AFS filetree. Note that it is also possible to use AFS "behind the firewall" within the confines of your organization's network - you don't have to participate in the Internet AFS filetree. Indeed, there are lots of benefits of using AFS on a local area network without using the WAN capabilities. Subject: 1.08 Why does AFS use Kerberos authentication? It improves security. Kerberos uses the idea of a trusted third party to prove identification. This is a bit like using a letter of introduction or quoting a referee who will vouch for you. When a user authenticates using the klog command (s)he is prompted for a password. If the password is accepted the Kerberos Authentication Server (KAS) provides the user with an encrypted token (containing a "ticket granting ticket"). From that point on, it is the encrypted token that is used to prove the user's identity. These tokens have a limited lifetime (typically a day) and are useless when expired. In AFS, it is possible to authenticate into multiple AFS cells. A summary of the current set of tokens held can be displayed by using the "tokens" command. For example: elmer@toontown $ tokens Tokens held by the Cache Manager: User's (AFS ID 9997) tokens for afs@ny.acme.com [Expires Sep 15 06:50] User's (AFS ID 5391) tokens for afs@sf.acme.com [Expires Sep 15 06:48] --End of list-- Kerberos improves security because a users's password need only be entered once (at klog time). AFS uses Kerberos to do complex mutual authentication which means that both the service requester and the service provider have to prove their identities before a service is granted. Transarc's implementation of Kerberos is slightly different from MIT Kerberos V4 but AFS can work with either version. For more detail on this and other Kerberos issues see the faq for Kerberos (posted to news.answers and comp.protocols.kerberos) [28]. (Also, see [15], [16], [26], [27]) Subject: 2 Using AFS Subject: 2.01 What are the differences between AFS and a unix filesystem? Essentially, from a user's point of view, there is little difference between AFS and local unix filestore. Nearly all the commands normally used to access local files can be used to access files in /afs. In the following set of sections, I have attempted to "target" each section to an appropriate type of user by including to the right of each section heading one of: User, Programmer, SysAdmin. Here is a summary of the differences: Authentication: [ User ] Before a user can access protected AFS files (s)he needs to become authenticated to AFS using the klog command (Kerberos login) to get a Kerberos "ticket granting ticket" (called a token from here on). Without a token, an unauthenticated user is given the AFS identity "system:anyuser" and as such is only able to access files in directories that have ACLs granting system:anyuser access. Many systems have the klog function built into the system login program. So a user would not even have to know they gain a token on logging in. If you use a system where you have to issue the klog command after login then you should run the pagsh command first (see below). AFS provides access control lists to give more precise control to users wishing to protect their files (see AFS ACL below). File permissions: [ User ] Unix mode bits for group and other are ignored. The mode bits for the file owner don't work the way they used to. Users should protect their AFS files with (directory) ACLs only. Just use mode bits to make a file executable. Data protection with AFS ACLs: [ User ] Some versions of unix (eg IBM's AIX version 3) allow ACLs on local files. In AFS, ACLs protect directories and used with AFS protection groups (see below) provide a finer granularity of protection than can be achieved with basic unix file permissions. (AFS ACLs are described in more detail below.) Protection groups: [ User ] Users can create and maintain their own protection groups in AFS - as opposed to unix where only sys admins can manage protection groups. Hard links: [ User ] In AFS, hard links (eg: ln old new) are only valid within a directory. This is because AFS ACLs protect directories (not individual files) and allowing hard links that span directories would subvert ACL protection. Symbolic links work in AFS because they reference a pathname and not an i-node directly. (Hard links reference an i-node directly.) Changing file protection by moving a file: [ User ] Moving a file to a different directory will change the protection of a file if the ACL on the new directory if different to the ACL on the original directory. chown and chgrp: [ User ] Only members of the AFS group "system:administrators" can use these commands on files in /afs. Save on close: [ Programmer ] AFS Cache Manager does not send file modifications to a file server until the close() or fsync() system call. write() system calls only update the local cache copy on the client. Note the difference in semantic of writing a file: local unix file: writes update the file "immediately" AFS file: local cached copy updated "immediately" but the server copy is only updated when the file is closed or fsync'ed. It is important to understand that most applications (eg: vi, emacs, frame, interleaf, wingz, etc) issue the close() system call when the user chooses/issues the "save" command in the application. Users are not required to exit the application to "save" their changes back to the server. byte-range file locking: [ Programmer ] AFS does not support byte-range locking within a file, although lockf() and fcntl() calls will return 0 (success). The first time a byte-range lock is attempted, AFS will display: "afs: byte-range lock/unlock ignored; make sure no one else else is running this program." whole file locking: [ Programmer ] AFS does support advisory locking an entire file with flock(). Processes on the same client workstation that attempt to lock a file obey the proper locking semantics. Processes on different AFS clients requesting a lock on the same file would get EWOULDBLOCK returned. character and block special files: [ SysAdmin ] AFS does not support character and block special files. The mknod command does not create either character or block special files in /afs. AFS version of fsck: [ SysAdmin ] On an AFS server, the partitions containing served files are NOT unix filesystems and standard fsck *must* not be used - use the AFS version instead. Subject: 2.02 What is an AFS protection group? A named list of users. Group names are used in AFS ACLs to identify lists of users with particular access permissions. In AFS, users can create and maintain their own protection groups. This is different to unix where only the system administrator can manage /etc/group. AFS groups are stored in the protection database on fileserver(s) and managed by using the "pts" command. An AFS group typically has the format: owner-id:group-name By default, only the owner of a group can change its members. It is possible to have both users and IP addresses as members of an AFS group. By using an IP address like this you can specify all the users from the host with that IP address. Subject: 2.03 What are the AFS defined protection groups? system:anyuser Everyone who has access to an AFS client in any cell that is on the same network as your cell. system:authuser Everyone who has access to an AFS client in any cell that is on the same network as your cell *and* has valid tokens for your cell (ie has been authenticated in your cell). system:administrators Users who have privileges to execute some but not all system administrator commands. Subject: 2.04 What is an AFS access control list (ACL)? There is an ACL for every directory in AFS. The ACL specifies protection at the directory level (not file level) by listing permissions of users and/or groups to a directory. There is a maximum of 20 entries on an ACL. For example: An AFS ACL is displayed by using the "fs" command as shown below: tweety@toontown $ fs listacl . Access list for . is Normal rights: fac:coords rlidwka system:anyuser rl This ACL shows that members of the AFS protection group "fac:coords" have full access rights to the current directory and "system:anyuser" has only read and lookup rights. The members of "fac:coords" can be determined by accessing the protection group database using the "pts" command as shown below: tweety@toontown $ pts membership fac:coords Members of fac:coords (id: -1577) are: sylvester roadrunner yosemite.sam Subject: 2.05 What are the AFS access rights? In AFS, there are seven access rights that may be set or not set: lookup l Permission to examine the ACL and traverse the directory (needed with most other access rights). Permission to look up filenames in a directory. read r View the contents of files in the directory insert i Add new files or sub-directories write w Modify file contents, use "chmod" delete d Remove file(s) in directory lock k Permission for programs to "flock" files in the directory administer a Ability to change the ACL There are short-hand forms: read rl read and lookup write rlidwk all rights except administer all rlidwka none removes all rights Subject: 2.06 What is pagsh? A command to get a new shell with a process authentication group (PAG). This is normally used if your system does not use the AFS version of login. It is used to get a PAG prior to running klog. The PAG uniquely identifies the user to the Cache Manager. Without a PAG the Cache Manager uses the unix UID to identify a user. Subject: 2.07 Why use a PAG? There are two reasons: a) Child processes inherit the PAG and the Kerberos token so they are AFS authenticated. b) For security: if you don't have a PAG then the Cache Manager identifies you by unix UID. Another user with root access to the client could su to you and therefore use your token. Subject: 2.08 How can I tell if I have a PAG? You can tell if you have a PAG by typing "groups". A PAG is indicated by the appearance of two integers in the list of groups. For example: sylvester@toontown $ groups 33536 32533 staff catz Subject: 2.09 Can I still run cron jobs with AFS? Yes, but remember that in order to fully access files in AFS you have to be AFS authenticated. If your cron job doesn't klog then it only gets system:anyuser access. The klog command has a "-pipe" option which will read a password from stdin. IF (yes, that's a big if :-) you are prepared to store your password in a local (non-AFS) file then you might use the following: a) create a script to get your AFS token: #!/bin/sh - # # NAME afsgt # PURPOSE Get AFS token by using password stored in a file. # Only need this to run cron jobs that need # authenticated AFS access usage() { echo "Usage: afsgt passwordfile" >&2 } if [ -z "${1}" ]; then echo "afsgt error: need name of password file" >&2 usage exit 1 fi /usr/afsws/bin/klog -pipe < ${1} b) Store your password in a local (non-AFS) file that only you have access to (perhaps: /home/$USER/.p). Make sure that this file is mode 600 and also be sure that you trust whoever has root access on this system and whoever has access to backup tapes! Also, don't forget to change this file if you change your AFS password. c) In your crontab file, run afsgt before whatever task you run. 0 6 * * * /usr/local/bin/afsgt /home/$USER/.p; $HOME/bin/6AMdaily Subject: 2.10 How much disk space does a 1 byte file occupy in AFS? One kilobyte. Other filesystems allocate different file block sizes. For example, IBM's AIX version 3 journaled file system (JFS) uses 4K blocks (exception: 2K for the 160MB disk drive). Such blocksize differences lead to variations on the amount of disk space required to store files. Copying a directory from AFS to AIX JFS would require more space in JFS because of the block fragmentation. Example: a) Create a one byte file in AFS and use "ls -s" to show how many kilobytes it occupies: ariel@atlantica $ echo z >/afs/dsea/tmp/one.byte.file ariel@atlantica $ ls -s /afs/dsea/tmp/one.byte.file 1 /afs/dsea/tmp/one.byte.file b) Create same file in local filesystem (AIX JFS): ariel@atlantica $ echo z >/tmp/one.byte.file ariel@atlantica $ ls -s /tmp/one.byte.file 4 /tmp/one.byte.file Subject: 2.11 Is it possible to specify a user who is external to the current AFS cell on an ACL? No. You cannot reference a particular user from another AFS cell. You can specify an IP address on the ACL; this means any and all users from the host with that IP address. Another solution to this problem is to give the external user an "authentication-only" account in your AFS cell. This means that (s)he can klog (but has no home directory) in your cell. Cross-realm authentication (where co-operating cells are able to specify remore users as "user@remote.cell" on an ACL) is an *unsupported* feature of AFS 3.3a. That means that Transarc doesn't promise to make it work for you, nor keep it running in future releases. Subject: 2.12 Are there any problems printing files in /afs? The issue of printing in AFS is almost always the same: what do you send to the printing daemon? Do you send it the bytes you want to print or do you just send the file name containing those bytes? If you send it a file name, you have to be sure that the printing daemon can read it. Most daemons run with no AFS tokens, so can't access directories unless they are open for system:anyuser read access. Often, printing commands (lpr, lp, enq) have an option that allows for both modes of operation, though the default behavior varies from system to system. If you're interested in making your daemons authenticate to AFS, check out the example scripts in AFS-Contrib: /afs/grand.central.org/pub/afs-contrib/tools/reauth-example Another common problem is setuid printing commands. For instance, the "enq" command runs as root, daemon, or some such user. If you aren't using the AFS login and simply issue "klog" to get tokens, those tokens are associated with your uid. When setuid programs run, they lose access to your token and often can't read the file name given as an argument. The solution in this case is to use "pagsh" before "klog" so that your tokens are transferred to subprocesses automatically by group membership. This works even if the uid changes, as for setuid programs. Subject: 3 AFS administration Subject: 3.01 Is there a version of xdm available with AFS authentication? Yes, grand.central.org:pub/afs-contrib/tools/xdm/* Subject: 3.02 Is there a version of xlock available with AFS authentication? Yes, grand.central.org:pub/afs-contrib/tools/xlock/* Subject: 3.03 How does AFS compare with NFS? AFS NFS File Access Common name space from Different file names from all workstations different workstations File Location Automatic tracking by Mountpoints to files set by Tracking file system processes administrators and users and databases Performance Client caching to reduce No local disk caching; network load; callbacks limited cache consistency to maintain cache consis- tency Andrew Benchmark Average time of 210 Average time of 280 (5 phases, 8 clients) seconds/client seconds/client Scaling capabilities Maintains performance in Best in small to mid-size small and very large installations installations Excellent performance on Best in local-area wide-area configuration configurations Security Kerberos mutual authen- Security based on tication unencrypted user ID's Access control lists on No access control lists directories for user and group access Availability Replicates read-mostly No replication data and AFS system information Backup Operation No system downtime with Standard UNIX backup system specially developed AFS Backup System Reconfiguration By volumes (groups of Per-file movement files) No user impact; files Users lose access to files remain accessible during and filenames change moves, and file names do (mountpoints need to be not change reset) System Management Most tasks performed from Frequently involves telnet any workstation to other workstations Autonomous Autonomous administrative File servers and clients Architecture units called cells, in addition to file servers and clients No trust required between No security distinctions cells between sites [ source: grand.central.org:pub/afsps/doc/afs-nfs.comparison ] Subject: 3.04 Given that AFS data is location independent, how does an AFS client determine which server houses the data its user is attempting to access? The Volume Location Database (VLDB) is stored on AFS Database Servers and is ideally replicated across 3 or more Database Server machines. Replication of the Database ensures high availability and load balances the requests for the data. The VLDB maintains information regarding the current physical location of all volume data (files and directories) in the cell, including the IP address of the FileServer, and the name of the disk partition the data is stored on. A list of a cell's Database Servers is stored on the local disk of each AFS Client machine as: /usr/vice/etc/CellServDB The Database Servers also house the Kerberos Authentication Database (encrypted user and server passwords), the Protection Database (user UID and protection group information) and the Backup Database (used by System Administrators to backup AFS file data to tape). Subject: 3.05 Which protocols does AFS use? AFS may be thought of as a collection of protocols and software processes, nested one on top of the other. The constant interaction between and within these levels makes AFS a very sophisticated software system. At the lowest level is the UDP protocol, which is part of TCP/IP. UDP is the connection to the actual network wire. The next protocol level is the remote procedure call (RPC). In general, RPCs allow the developer to build applications using the client/server model, hiding the underlying networking mechanisms. AFS uses Rx, an RPC protocol developed specifically for AFS during its development phase at Carnegie Mellon University. Above the RPC is a series of server processes and interfaces that all use Rx for communication between machines. Fileserver, volserver, upserver, upclient, and bosserver are server processes that export RPC interfaces to allow their user interface commands to request actions and get information. For example, a bos status <machine name> command will examine the bos server process on the indicated file server machine. Database servers use ubik, a replicated database mechanism which is implemented using RPC. Ubik guarantees that the copies of AFS databases of multiple server machines remain consistent. It provides an application programming interface (API) for database reads and writes, and uses RPCs to keep the database synchronized. The database server processes, vlserver, kaserver, and ptserver, reside above ubik. These processes export an RPC interface which allows user commands to control their operation. For instance, the pts command is used to communicate with the ptserver, while the command klog uses the kaserver's RPC interface. Some application programs are quite complex, and draw on RPC interfaces for communication with an assortment of processes. Scout utilizes the RPC interface to file server processes to display and monitor the status of file servers. The uss command interfaces with kaserver, ptserver, volserver and vlserver to create new user accounts. The Cache Manager also exports an RPC interface. This interface is used principally by file server machines to break callbacks. It can also be used to obtain Cache Manager status information. The program cmdebug shows the status of a Cache Manager using this interface. For additional information, Section 1.5 of the AFS System Administrator's Guide and the April 1990 Cache Update contain more information on ubik. Udebug information and short descriptions of all debugging tools were included in the January 1991 Cache Update. Future issues will discuss other debugging tools in more detail. [ source: grand.central.org:pub/cache.update/apr91 ] [ Copyright 1991 Transarc Corporation ] Subject: 3.06 Are setuid programs executable across AFS cell boundaries? By default, the setuid bit is ignored but the program may be run (without setuid privilege). It is possible to configure an AFS client to honour the setuid bit (see: "fs setcell". Use with care!). NB: making a program setuid (or setgid) in AFS does *not* mean that the program will get AFS permissions of a user or group. To become AFS authenticated, you have to klog. If you are not authenticated, AFS treats you as "system:anyuser". Subject: 3.07 How does AFS maintain consistency on read-write files? AFS uses a mechanism called "callback". Callback is a promise from the fileserver that the cache version of a file/directory is up-to-date. It is established by the fileserver with the caching of a file. When a file is modified the fileserver breaks the callback. When the user accesses the file again the Cache Manager fetches a new copy if the callback has been broken. The following paragraphs describe AFS callback mechanism in more detail: If I open() fileA and start reading, and you then open() fileA, write() a change ***and close() or fsync()*** the file to get your changes back to the server - at the time the server accepts and writes your changes to the appropriate location on the server disk, the server also breaks callbacks to all clients to which it issued a copy of fileA. So my client receives a message to break the callback on fileA, which it dutifully does. But my application (editor, spreadsheet, whatever I'm using to read fileA) is still running, and doesn't really care that the callback has been broken. When something causes the application to read() more of the file the read() system call executes AFS cache manager code via the VFS switch, which does check the callback and therefore gets new copies of the data. Of course, the application may not re-read data that it has already read, but that would also be the case if you were both using the same host. So, for both AFS and local files, I may not see your changes. Now if I exit the application and start it again, or if the application does another open() on the file, then I will see the changes you've made. This information tends to cause tremendous heartache and discontent - but unnecessarily so. People imagine rampant synchronization problems. In practice this rarely happens and in those rare instances, the data in question is typically not critical enough to cause real problems or crashing and burning of applications. Over the past 8 years we've found that the synchronization algorithm has been more than adequate in practice - but people still like to worry! The source of worry is that, if I make changes to a file from my workstation, your workstation is not guaranteed to be notified until I close or fsync the file, at which point AFS guarantees that your workstation will be notified. This is a significant departure from NFS, in which no guarantees are provided. Partially because of the worry factor and largely because of Posix, this will change in DFS. DFS synchronization semantics are identical to local file system synchronization. [ DFS is the Distributed File System which is part of the Distributed ] [ Computing Environment (DCE). ] Subject: 3.08 How can I run daemons with tokens that do not expire? It is not a good idea to run with tokens that do not expire because this would weaken one of the security features of Kerberos. A better approach is to re-authenticate just before the token expires. There are two examples of this that have been contributed to grand.central.org. The first is "reauth": via AFS: /afs/grand.central.org/pub/afs-contrib/tools/reauth* via FTP: grand.central.org:/pub/afs-contrib/tools/reauth* The second is "lat": via AFS: /afs/grand.central.org/pub/afs-contrib/pointers\ /UMich-lat-authenticated-batch-jobs via FTP: grand.central.org:/pub/afs-contrib/pointers\ /UMich-lat-authenticated-batch-jobs Subject: 3.09 Can I check my user's passwords for security purposes? Yes. Alec Muffett's Crack tool (at version 4.1f) has been converted to work on the Transarc kaserver database. This modified Crack (AFS Crack) is available via anonymous ftp from: export.acs.cmu.edu:/pub/crack.tar.Z and is known to work on: pmax_* sun4*_* hp700_* rs_aix* next_* It uses the file /usr/afs/db/kaserver.DB0, which is the database on the kaserver machine that contains the encrypted passwords. As a bonus, AFS Crack is usually two to three orders of magnitude faster than the standard Crack since there is no concept of salting in a Kerberos database. On a normal UNIX /etc/passwd file, each password can have been encrypted around 4096 (2^12) different saltings of the crypt(3) algorithm, so for a large number of users it is easy to see that a potentially large (up to 4095) number of seperate encryptions of each word checked has been avoided. Author & Contact: Dan Lovinger, del+@cmu.edu Note: AFS Crack does not work for MIT Kerberos Databases. The author is willing to give general guidance to someone interested in doing the (probably minimal) amount of work to port it to do MIT Kerberos. The author does not have access to a MIT Kerberos server to do this. Subject: 3.10 Is there a way to automatically balance disk usage across fileservers? Yes. There is a tool, balance, which does exactly this. It can be retrieved via anonymous ftp from: export.acs.cmu.edu:/pub/balance.tar.Z Actually, it is possible to write arbitrary balancing algorithms for this tool. The default set of "agents" provided for the current version of balance balance by usage, # of volumes, and activity per week, the latter currently requiring a source patch to the AFS volserver. Balance is highly configurable. Author: Dan Lovinger, del+@cmu.edu Subject: 3.11 Can I shutdown an AFS fileserver without affecting users? Yes, this is an example of the flexibility you have in managing AFS. Before attempting to shutdown an AFS fileserver you have to make some arrangements that any services that were being provided are moved to another AFS fileserver: 1) Move all AFS volumes to another fileserver. (Check you have the space!) This can be done "live" while users are actively using files in those volumes with no detrimental effects. 2) Make sure that critical services have been replicated on one (or more) other fileserver(s). Such services include: kaserver - Kerberos Authentication server vlserver - Volume Location server ptserver - Protection server buserver - Backup server It is simple to test this before the real shutdown by issuing: bos shutdown $server $service where: $server is the name of the server to be shutdown and $service is one (or all) of: kaserver vlserver ptserver buserver Other points to bear in mind: + "vos remove" any RO volumes on the server to be shutdown. Create corresponding RO volumes on the 2nd fileserver after moving the RW. There are two reasons for this: 1) An RO on the same partition ("cheap replica") requires less space than a full-copy RO. 2) Because AFS always accesses RO volumes in preference to RW, traffic will be directed to the RO and therefore quiesce the load on the fileserver to be shutdown. + If the system to be shutdown has the lowest IP address there may be a brief delay in authenticating because of timeout experienced before contacting a second kaserver. Subject: 3.12 How can I set up mail delivery to users with $HOMEs in AFS? There are many ways to do this. Here, only two methods are considered: Method 1: deliver into local filestore This is the simplest to implement. Set up your mail delivery to append mail to /var/spool/mail/$USER on one mailserver host. The mailserver is an AFS client so users draw their mail out of local filestore into their AFS $HOME (eg: inc). U Note that if you expect your (AFS unauthenticated) mail delivery program to be able to process .forward files in AFS $HOMEs then you need to add "system:anyuser rl" to each $HOMEs ACL. The advantages are: + Simple to implement and maintain. + No need to authenticate into AFS. The drawbacks are: - It doesn't scale very well. - Users have to login to the mailserver to access their new mail. - Probably less secure than having your mailbox in AFS. - System administrator has to manage space in /var/spool/mail. Method 2: deliver into AFS This takes a little more setting up than the first method. First, you must have your mail delivery daemon AFS authenticated (probably as "postman"). The reauth example on grand.central.org shows how a daemon can renew its token. You will also need to setup the daemon startup soon after boot time to klog (see the -pipe option). Second, you need to set up the ACLs so that "postman" has lookup rights down to the user's $HOME and "lik" on $HOME/Mail. Advantages: + Scales better than first method. + Delivers to user's $HOME in AFS giving location independence. + Probably more secure than first method. + User responsible for space used by mail. Disadvantages: - More complicated to set up. - Need to correctly set ACLs down to $HOME/Mail for every user. - Probably need to store postman's password in a file so that the mail delivery daemon can klog after boot time. This may be OK if the daemon runs on a relatively secure host. Subject: 3.13 Should I replicate a ReadOnly volume on the same partition and server as the ReadWrite volume? Yes, Absolutely! It improves the robustness of your served volumes. If ReadOnly volumes exist (note use of term *exist* rather than *are available*), Cache Managers will *never* utilize the ReadWrite version of the volume. The only way to access the RW volume is via the "dot" path (or by special mounting). This means if *all* RO copies are on dead servers, are offline, are behind a network partition, etc, then clients will not be able to get the data, even if the RW version of the volume is healthy, on a healthy server and in a healthy network. However, you are *very* strongly encouraged to keep one RO copy of a volume on the *same server and partition* as the RW. There are two reasons for this: 1) The RO that is on the same server and partition as the RW is a clone (just a copy of the header - not a full copy of each file). It therefore is very small, but provides access to the same set of files that all other (full copy) ReadOnly volume do. Transarc trainers refer to this as the "cheap replica". 2) To prevent the frustration that occurs when all your ROs are unavailable but a perfectly healthy RW was accessible but not used. If you keep a "cheap replica", then by definition, if the RW is available, one of the RO's is also available, and clients will utilize that site. Subject: 3.14 Should I start AFS before NFS in /etc/inittab? Yes, it is possible to run both AFS and NFS on the same system but you should start AFS first. In IBM's AIX 3.2, your /etc/inittab would contain: rcafs:2:wait:/etc/rc.afs > /dev/console 2>&1 # Start AFS daemons rcnfs:2:wait:/etc/rc.nfs > /dev/console 2>&1 # Start NFS daemons With AIX, you need to load NFS kernel extensions before the AFS KEs in /etc/rc.afs like this: #!/bin/sh - # example /etc/rc.afs for an AFS fileserver running AIX 3.2 # echo "Installing NFS kernel extensions (for AFS+NFS)" /etc/gfsinstall -a /usr/lib/drivers/nfs.ext echo "Installing AFS kernel extensions..." D=/usr/afs/bin/dkload ${D}/cfgexport -a ${D}/export.ext ${D}/cfgafs -a ${D}/afs.ext /usr/afs/bin/bosserver & Subject: 3.15 Will AFS run on a multi-homed fileserver? (multi-homed = host has more than one network interface.) Yes, it will. However, AFS was designed for hosts with a single IP address. There can be problems if you have one host name being resolved to several IP addresses. Transarc suggest designating unique hostnames for each network interface. For example, a host called "spot" has two tokenring and one ethernet interfaces: spot-tr0, spot-tr1, spot-en0. Then, select which interface will be used for AFS and use that hostname in the CellServDB file (eg: spot-tr0). You also have to remember to use the AFS interface name with any AFS commands that require a server name (eg: vos listvol spot-tr0). There is a more detailed discussion of this in the August 1993 issue of "Cache Update" (see: /afs/grand.central.org/pub/cache.update/aug93). The simplest way of dealing with this is to make your AFS fileservers single-homed (eg only use one network interface). Subject: 3.16 Can I replicate my user's home directory AFS volumes? No. Users with $HOMEs in /afs normally have an AFS ReadWrite volume mounted in their home directory. You can replicate a RW volume but only as a ReadOnly volume and there can only be one instance of a ReadWrite volume. In theory, you could have RO copies of a user's RW volume on a second server but in practice this won't work for the following reasons: a) AFS has built-in bias to always access the RO copy of a RW volume. So the user would have a ReadOnly $HOME which is not too useful! b) Even if a) was not true you would have to arrange frequent synchronisation of the RO copy with the RW volume (for example: "vos release user.fred; fs checkv") and this would have to be done for all such user volumes. c) Presumably, the idea of replicating is to recover the $HOME in the event of a server crash. Even if a) and b) were not problems consider what you might have to do to recover a $HOME: 1) Create a new RW volume for the user on the second server (perhaps named "user.fred.2"). 2) Now, where do you mount it? The existing mountpoint cannot be used because it already has the ReadOnly copy of the original volume mounted there. Let's choose: /afs/MyCell/user/fred.2 3) Copy data from the RO of the original into the new RW volume user.fred.2 4) Change the user's entry in the password file for the new $HOME: /afs/MyCell/user/fred.2 You would have to attempt steps 1 to 4 for every user who had their RW volume on the crashed server. By the time you had done all of this, the crashed server would probably have rebooted. The bottom line is: you cannot replicate $HOMEs across servers. Subject: 3.17 Which TCP/IP ports and protocols do I need to enable in order to operate AFS through my Internet firewall? Assuming you have already taken care of nameserving, you may wish to use an Internet timeserver for Network Time Protocol: ntp 123/tcp A list of NTP servers is available via anonymous FTP from: louie.udel.edu:/pub/ntp/doc/clock.txt For a "minimal" AFS service which does not allow inbound or outbound klog: fileserver 7000/udp cachemanager 7001/udp ptserver 7002/udp vlserver 7003/udp kaserver 7004/udp volserver 7005/udp reserved 7006/udp bosserver 7007/udp (Ports in the 7020-7029 range are used by the AFS backup system, and won't be needed by external clients performing simple file accesses.) Additionally, For "klog" to work through the firewall you need to allow inbound and outbound UDP on ports >1024 (probably 1024<port<2048 would suffice depending on the number of simultaneous klogs). Subject: 3.18 What is the Andrew Benchmark? "It is a script that operates on a collection of files constituting an application program. The operations are intended to represent typical actions of an average user. The input to the benchmark is a source tree of about 70 files. The files total about 200 KB in size. The benchmark consists of five distinct phases: I MakeDir - Construct a target subtree that is identical to the source subtree. II Copy - Copy every file from the source subtree to the target subtree. III ScanDir - Traverse the target subtree and examine the status of every file in it. IV ReadAll - Scan every byte of every file in the target subtree. V Make - Complete and link all files in the target subtree." [ source: ] [ grand.central.org:pub/afs-contrib/doc/benchmark/Andrew.Benchmark.ps ] [ /afs/grand.central.org/pub/afs-contrib/doc/benchmark/Andrew.Benchmark.ps ] Subject: 3.19 Is there a version of HP VUE login with AFS authentication? Yes, the availability of this is described in: /afs/transarc.com/public/afs-contrib/pointers/HP-VUElogin.txt Subject: 4 Getting more information Subject: 4.01 Is there an anonymous FTP site with AFS information? Yes, it is: grand.central.org [192.54.226.100]. A brief summary of contents: Directory Contents pub/cache-update AFS user group newsletters pub/afs-contrib Contributed tools and documents pub/afsps/doc release notes, SUPPORTED_SYSTEMS.afs.* pub/afsug AFS user group (see README for detail) darpa/doc/afs/specs/progint AFS programming interface docs grand.central.org also participates in the Internet AFS filetree. Subject: 4.02 Which USENET newsgroups discuss AFS? alt.filesystems.afs and occasionally in comp.unix.admin Subject: 4.03 Where can I get training in AFS? Transarc provide user and administrator courses. These can be provided at the customer site or at Transarc's offices. Transarc's education coordinator may be contacted by: telephone: +1 412 338 4363 email: education@transarc.com Subject: 5 About the AFS faq This compilation is dedicated to those who inspire through good humour, enthusiasm, wit and wisdom. Subject: 5.01 How can I get a copy of the AFS faq? There are several ways: The best way to access the AFS faq is via AFS so you see the latest version. If you take a copy via FTP or email your copy can only be a snapshot of this changing file. via AFS: /afs/grand.central.org/pub/afs-contrib/doc/faq/afs.faq /afs/ibm.uk/public/doc/afs.faq /afs/aixssc.uk.ibm.com/public/doc/afs.faq via FTP: grand.central.org:/pub/afs-contrib/doc/faq/afs.faq rtfm.mit.edu:/pub/usenet/news.answers/afs-faq ftp.aixssc.uk.ibm.com:/pub/src/afs.faq via World Wide Web: http://www.cis.ohio-state.edu/hypertext/faq/usenet/afs-faq/faq.html via email: mail -s afs.faq auto-send@mailserver.aixssc.uk.ibm.com </dev/null via USENET news: From time to time this faq will be posted to the USENET newsgroups: alt.filesystems.afs alt.answers news.answers If you have no luck with any of the above methods, send email to mpb@acm.org (Paul Blackburn) and I will be pleased to send you a copy of the AFS faq. Subject: 5.02 How can I get my question (and answer) into the AFS faq? Comments and contributions are welcome, please send to: mpb@acm.org I am looking for reviewers to help me check the material here, please let me know if you would like to help. Subject: 5.03 How can I access the AFS faq via the World Wide Web? To access the World Wide Web you either need your own browser or have telnet access to WWW servers. WWW browsers exist for most machines. Here's a list of some browsers; Name System/requirements Available from (among others) ==== =================== ============== Mosaic X windows, MS-Windows, Mac ftp.ncsa.uiuc.edu /Web lynx vt100 ftp.wustl.edu /packages/www/lynx From your own browser, OPEN or GO to the following document: http://www.cis.ohio-state.edu/hypertext/faq/usenet/afs-faq/faq.html It is much better to run your own browser but if this is not possible there are several WWW servers accessible via telnet: + telnet info.cern.ch then type: go http://www.cis.ohio-state.edu/hypertext/faq/usenet/afs-faq/faq.html + telnet www.njit.edu (login: www) then type: g http://www.cis.ohio-state.edu/hypertext/faq/usenet/afs-faq/faq.html + telnet ukanaix.cc.ukans.edu (login: www) needs vt100 then type: ghttp://www.cis.ohio-state.edu/hypertext/faq/usenet/afs-faq/faq.html Subject: 6 Bibliography If documentation is available via anonymous FTP it is indicated in square brackets like: [ athena-dist.mit.edu:pub/kerberos/doc/usenix.PS ] where: athena-dist.mit.edu is the anonymous FTP site and pub/kerberos/doc/usenix.PS is the filename Similarly, for those who have appropriate access, documents available via AFS are shown with the format: [ /afs/........ ] [1] John H Howard, Michael L Kazar, Sherri G Menees, David A Nichols, M Satyanarayanan, Robert N Sidebotham, Michael J West "Scale and Performance in a Distributed File System", ACM Transactions on Computer Systems, Vol. 6, No. 1, Feb 1988 pp 51-81. [2] Michael L Kazar, "Synchronisation and Caching Issues in the Andrew File System", USENIX Proceedings, Dallas, TX, Winter 1988 [3] Alfred Z Spector, Michael L Kazar, "Uniting File Systems", UNIX Review, March 1989 [4] Johna Till Johnson, "Distributed File System brings LAN Technology to WANs", Data Communications, November 1990, pp 66-67. [5] Michael Padovano, PADCOM Associates, "AFS widens your horizons in distributed computing", Systems Integration, March 1991 [6] Steve Lammert, "The AFS 3.0 Backup System", LISA IV Conference Proceedings, Colorado Springs, Colorado, October 1990. [7] Michael L Kazar, Bruce W Leverett, Owen T Anderson, Vasilis Apostolides, Beth A Bottos, Sailesh Chutani, Craig F Everhart, W Anthony Mason, Shu-Tsui Tu, Edward R Zayas, "DEcorum File System Architectural Overview", USENIX Conference Proceedings, Anaheim, Texas, Summer 1990. [8] "AFS Drives DCE Selection", Digital Desktop, Vol 1 No 6 Sept 1990. [9] James J Kistler, M Satyanarayanan, "Disconnected Operation in the Coda Filesystem", CMU School of Computer Science technical report, CMU-CS-91-166 26th July 1991. [10] Puneet Kumar. M Satyanarayanan, "Log-based Directory Resolution in the Coda File System", CMU School of Computer Science internal document, 2 July 1991. [11] Edward R Zayas, "Administrative Cells: Proposal for Cooperative Andrew File Systems", Information Technology Center internal document, Carnegie-Mellon University, 25th June 1987 [12] Ed Zayas, Craig Everhart, "Design and Specification of the Cellular Andrew Environment", Information Technology Center, Carnegie-Mellon University, CMU-ITC-070, 2 August 1988 [13] Kazar, Michael L, Information Technology Center, Carnegie-Mellon University, "Ubik - A library for Managing Ubiquitous Data", ITCID, Pittsburgh, PA, 1988 [14] Kazar, Michael L, Information Technology Center, Carnegie-Mellon University, "Quorum Completion", ITCID, Pittsburgh, PA, 1988 [15] SP Miller, BC Neuman, JI Schiller, JH Saltzer, "Kerberos Authentication and Authorization System", Project Athena technical Plan, Section E.2.1, MIT, December 1987. [ athena-dist.mit.edu:pub/kerberos/doc/techplan.PS ] [ athena-dist.mit.edu:pub/kerberos/doc/techplan.txt ] [ /afs/watson.ibm.com/projects/agora/papers/kerberos/techplan.PS ] [16] Bill Bryant, "Designing an Authentication System: a Dialogue in Four Scenes", Project Athena internal document, MIT, draft of 8th February 1988 [ athena-dist.mit.edu:pub/kerberos/doc/dialog.PS ] [ athena-dist.mit.edu:pub/kerberos/doc/dialog.mss ] [ /afs/watson.ibm.com/projects/agora/papers/kerberos/dialog.PS ] [17] Edward R Zayas, "AFS-3 Programmer's Reference: Architectural Overview", Transarc Corporation, FS-00-D160, September 1991 [ grand.central.org:darpa/doc/afs/specs/progint/archov/archov-doc.ps ] [ /afs/watson.ibm.com/projects/agora/papers/afs/archov-doc.ps ] [18] "AFS Programmer's Reference: Authentication Server Interface", Transarc Corporation, 12th April 1993 [ grand.central.org:darpa/doc/afs/specs/progint/arsv/asrv-ispec.ps ] [ /afs/watson.ibm.com/projects/agora/papers/afs/asrv-ispec.ps ] [19] Edward R Zayas, "AFS-3 Programmer's Reference: BOS Server Interface", Transarc Corporation, FS-00-D161, 28th August 1991 [ grand.central.org:darpa/doc/afs/specs/progint/bsrv/bsrv-spec.ps ] [ /afs/watson.ibm.com/projects/agora/papers/afs/bsrv-spec.ps ] [20] Edward R Zayas, "AFS-3 Programmer's Reference: File Server/Cache Manager Interface", Transarc Corporation, FS-00-D162, 20th August 1991 [ grand.central.org:darpa/doc/afs/specs/progint/fscm/fscm-ispec.ps ] [ /afs/watson.ibm.com/projects/agora/papers/afs/fscm-ispec.ps ] [21] Edward R Zayas, "AFS-3 Programmer's Reference: Specification for the Rx Remote Procedure Call Facility", Transarc Corporation, FS-00-D164, 28th August 1991 [ grand.central.org:darpa/doc/afs/specs/progint/rx/rx-spec.ps ] [ /afs/watson.ibm.com/projects/agora/papers/afs/rx-spec.ps ] [22] Edward R Zayas, "AFS-3 Programmer's Reference: Volume Server/Volume Location Server Interface", Transarc Corporation, FS-00-D165, 29th August 1991 [ grand.central.org:darpa/doc/afs/specs/progint/vvl/vvl-spec.ps ] [ /afs/watson.ibm.com/projects/agora/papers/afs/vvl-spec.ps ] [23] "AFS User Guide", Transarc Corporation, FS-D200-00.08.3 [24] "AFS Commands Reference Manual", Transarc Corporation, FS-D200-00.11.3 [25] "AFS Systems Administrators Guide", Transarc Corporation, FS-D200-00.10.3 [26] Steven M. Bellovin, Michael Merritt "Limitations of the Kerberos Authentication System", Computer Communications Review, October 1990, Vol 20 #5, pp. 119-132 [ research.att.com:/dist/internet_security/kerblimit.usenix.ps ] [ /afs/watson.ibm.com/projects/agora/papers/kerberos/limitations.PS ] [27] Jennifer G. Steiner, Clifford Neuman, Jeffrey I. Schiller "Kerberos: An Authentication Service for Open Network Systems" [ athena-dist.mit.edu:/pub/kerberos/doc/usenix.PS ] [ athena-dist.mit.edu:/pub/kerberos/doc/usenix.txt ] [28] Barry Jaspan "Kerberos Users' Frequently Asked Questions" [ rtfm.mit.edu:/pub/usenet/news.answers/kerberos-faq/user ] [29] P. Honeyman, L.B. Huston, M.T. Stolarchuk "Hijacking AFS" [ ftp.sage.usenix.org:/pub/usenix/winter92/hijacking-afs.ps.Z ] [30] R.N. Sidebotham "Rx: Extended Remote Procedure Call" Proceedings of the Nationwide File System Workshop Information Technology Center, Carnegie Mellon University, (August 1988) [31] R.N. Sidebotham "Volumes: The Andrew File System Data Structuring Primitive" Technical Report CMU-ITC-053, Information Technology Center, Carnegie Mellon University, (August 1986)