UNIX(cid:226) System Administration
`
`Frank G. Fiamingo
`
`fgf+@osu.edu
`
`University Technology Services
`The Ohio State University
`
`August 16, 1996
`
`Olympus et al. 1108
`
`

`
`ª 1996 Frank G. Fiamingo, University Technology Services, The Ohio State University, 406 Baker
`Systems, 1971 Neil Avenue, Columbus, OH 43210.
`
`All rights reserved. You may reproduce all or parts of this document for personal, non-commercial use,
`so long as you attribute the work to the author.
`
`UNIX was a registered trademark of UNIX System Laboratories, Inc., and now is registered to the
`X/Open Consortium. Sun, SunOS, Solaris, SPARC, NFS, NIS, NIS+, JumpStart, OpenWindows,
`Sunview and SunInstall are trademarks or registered trademarks of Sun Microsystems, Inc. Ultrix,
`Digital UNIX and DEC are trademarks of Digital Equipment Corporation. HP-UX is a trademark of
`Hewlett-Packard Co. IRIX is a trademark of Silicon Graphics, Inc. AIX is a trademark of International
`Business Machines, Inc. AT&T is a trademark of American Telephone and Telegraph, Inc. GNU is
`a trademark of the Free Software Foundation. X Window System is a trademark of Massachusetts
`Institute of Technology. Ethernet is a registered trademark of Xerox Corporation. Netscape is a
`copyright of Netscape Communications Crop. Mosaic is a copyright of the National Center for
`Supercomputing Applications at the University of Illinois, Urbana-Champaign. All other products
`mentioned are trademarks of their respective owners.
`
`This publication is provided “as is” without warranty of any kind. This publication may include
`technical inaccuracies or typographical errors.
`
`This publication is available via the Internet as:
`ftp://www-wks.acs.ohio-state.edu/sysadm_course/sysadm_book.ps
`
`and
`
`http://www-wks.acs.ohio-state.edu/sysadm_course/sysadm.html.
`
`Also available via the Internet is Introduction to Unix:
`ftp://www-wks.acs.ohio-state.edu/unix_course/unix_book.ps
`
`and
`
`http://www-wks.acs.ohio-state.edu/unix_course/unix.html.
`
`Acknowledgements: The author wishes to thank the following for helpful advice and discussions
`related to the material presented in this document: Harpal Chohan, Bob DeBula, Bob Manson, Steve
`Romig, and Bill Yang.
`
`2
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`© 1996 Frank Fiamingo
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`UNIX System Administration
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`

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`PART I
`1
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`2
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`3
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`4
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`5
`
`Table of Contents
`
`Introduction .......................................................9
`Overview ............................................................................11
`1.1 What is UNIX System Administration? ........................11
`1.2
`Daily Tasks of a System Administrator ........................11
`1.3
`Startup and Shutdown ....................................................11
`1.4
`Periodic Processes ...........................................................12
`1.5 Managing File Systems ...................................................12
`1.6
`Responsibilities to the users ...........................................12
`1.7
`Hardware responsibilities ..............................................12
`1.8
`Types of SunOS Systems ................................................12
`1.9
`Resources for System Administrators ...........................13
`1.10 UTS Software Support ...................................................15
`Disk Structure and Partitions ..........................................17
`2.1
`Disk Structure and Partitions ........................................17
`2.2
`Disk Partitions .................................................................19
`Devices ...............................................................................27
`3.1
`Logical Names .................................................................27
`3.2
`Disk Partitioning .............................................................28
`3.3
`Disk Label and Bootblock ..............................................31
`3.4
`Tapes ................................................................................32
`The UNIX File System ......................................................33
`4.1
`File Systems .....................................................................33
`4.2
`File System Types ............................................................35
`4.3
`Compatibility ...................................................................38
`4.4
`Names & contents of important UNIX directories ......40
`4.5
`File structure of standalone and server machines .......43
`4.6
`Disk Partitioning .............................................................43
`File System Management .................................................45
`5.1
`File System Management ...............................................45
`5.2
`Fsck ...................................................................................46
`5.3
`Disk Check Commands ..................................................47
`5.4
`Swapping and Paging .....................................................48
`5.5
`Adding swap space ..........................................................49
`5.6
`Setting up a Cache File System ......................................50
`5.7
`XFS (IRIX) ......................................................................52
`5.8
`File System Quotas ..........................................................52
`5.9 Miscellaneous useful commands ....................................53
`5.10 Log files ............................................................................54
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`UNIX System Administration
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`6
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`7
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`8
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`9
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`10
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`11
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`12
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`Startup and Shutdown .................................................... 55
`6.1
`Booting .............................................................................55
`6.2
`Run Levels (SunOS 5.X, IRIX 5.X) ...............................57
`6.3
`/etc/inittab (SunOS 5.X, IRIX 5.X, Digital UNIX) .......57
`6.4
`Sun PROM .......................................................................65
`6.5
`SGI Indy PROM .............................................................67
`6.6
`Diskless Workstations .....................................................67
`6.7
`Shutdown .........................................................................69
`6.8
`Crashes .............................................................................70
`Operating System Installation ........................................ 71
`7.1
`Suninstall .........................................................................71
`7.2
`SunOS 4.1.X .....................................................................71
`7.3
`SunOS 5.X ........................................................................74
`7.4
`Post Install Actions ........................................................84
`7.5
`Current Sun Patch List ..................................................86
`7.6
`IRIX 5.X ...........................................................................90
`Kernel Configuration ...................................................... 91
`8.1
`SunOS 4.1.X .....................................................................91
`8.2
`SunOS 5.X ........................................................................92
`8.3
`IRIX 5.X .........................................................................100
`8.4
`Digital UNIX ..................................................................101
`8.5
`Ultrix ..............................................................................101
`Adding Hardware .......................................................... 103
`9.1
`SunOS 4.1.X ...................................................................103
`9.2
`SunOS 5.X ......................................................................110
`9.3
`IRIX 5.X .........................................................................110
`Special Files .................................................................... 111
`10.1
`Special Files ...................................................................111
`10.2
`SunOS 4.X ......................................................................112
`10.3
`SunOS 5.X ......................................................................112
`10.4
`IRIX 5.X .........................................................................113
`10.5 Ultrix and Digital UNIX ...............................................114
`System Directories ......................................................... 115
`11.1
`System Directories ........................................................115
`11.2
`/ - root ............................................................................115
`11.3
`/etc - system and network configuration .....................118
`11.4
`/usr - system programs, libraries, etc. .........................120
`User accounts ................................................................. 123
`12.1 User accounts .................................................................123
`12.2 Admittance - login procedure ......................................126
`12.3
`Password Aging, SunOS 4.1.X .....................................126
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`© 1996 Frank Fiamingo
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`UNIX System Administration
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`13
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`14
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`15
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`16
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`Daily System Administration .........................................127
`13.1 User and Group Administration .................................127
`13.2 Communicating with system users ..............................129
`13.3 Running programs automatically, cron & at .............129
`Administration Tool & Solstice Adminsuite ................131
`14.1 Admintool ......................................................................131
`14.2
`Solstice Adminsuite .......................................................131
`14.3
`Services Managed ..........................................................132
`14.4 The Distributed System Administration Daemon ......140
`14.5
`Program Locations ........................................................140
`Package Administration .................................................141
`15.1
`Packages .........................................................................141
`15.2
`Packages Distributed with Solaris 2.5 .........................143
`15.3
`Swmtool ..........................................................................150
`15.4
`SunOS 4.X ......................................................................152
`15.5
`IRIX 5.X .........................................................................153
`15.6 Digital UNIX and Ultrix ...............................................154
`Backup Procedures .........................................................155
`16.1 Backup Procedures .......................................................155
`16.2 Backup strategies .........................................................155
`16.3 Backup and Restore Commands .................................156
`PART II Network Services ...........................................161
`17
`Service Access Facility ....................................................163
`17.1 Overview of Service Access ..........................................163
`17.2
`Service Access Facility Overview ................................164
`17.3
`Service Access Controller .............................................164
`17.4
`Port Monitors ................................................................165
`17.5
`Setting Up a Terminal ..................................................166
`17.6 Network Port Monitors ................................................168
`17.7 Terminal Control ..........................................................170
`17.8
`Summary ........................................................................172
`The Network ....................................................................173
`18.1 The Network ..................................................................173
`18.2 Hardware used in a network ........................................174
`18.3 Ethernet Frame .............................................................175
`18.4 Trouble shooting the Ethernet .....................................176
`18.5 Monitoring the network ...............................................177
`18.6 Difference between Ethernet and Internet Addresses 179
`Network Administration ................................................181
`19.1 Network Initialization ...................................................181
`19.2 Host Names and addresses ...........................................185
`19.3
`Services ...........................................................................187
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`18
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`19
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`UNIX System Administration
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`20
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`21
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`22
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`19.4 Network Programs ........................................................188
`19.5
`SunOS 5.X ......................................................................191
`19.6 Ultrix and Digital UNIX ...............................................193
`19.7 Miscellaneous Configuration Files ..............................194
`Distributed File System Administration ...................... 195
`20.1 Distributed File Systems ...............................................195
`20.2 NFS Protocol ..................................................................196
`20.3
`SunOS 4.1.X ...................................................................198
`20.4
`SunOS 5.X ......................................................................202
`20.5 DFS Command Summary ............................................205
`20.6
`IRIX 5.X, Ultrix and Digital UNIX .............................206
`20.7 NFS statistics .................................................................206
`Network Information Services (NIS and NIS+) .......... 209
`21.1 What is it and what does it do for you? ......................209
`21.2 NIS ..................................................................................209
`21.3 NIS+ ................................................................................211
`Adding Clients ................................................................ 219
`22.1 Clients .............................................................................219
`22.2
`Server configuration and software .............................219
`22.3
`Installing the client of a server, SunOS 4.1.X .............220
`22.4
`JumpStart ......................................................................221
`22.5 AutoClient ......................................................................221
`
`24
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`PART III Selected Topics ..............................................223
`23
`Usenet .............................................................................. 225
`23.1 Usenet .............................................................................225
`23.2 Reading news, rn/rrn/xrn/trn/nn .................................226
`23.3 Network news transfer protocol, nntp ........................226
`23.4 Disk space requirements ...............................................226
`23.5 Relevant UNIX newsgroups .........................................227
`Useful Utilities ................................................................ 229
`24.1
`Format online manual pages, catman .........................229
`24.2
`System process status, ps ..............................................230
`24.3
`Swap space and kernel inode usage, pstat ..................231
`24.4
`top ...................................................................................231
`24.5
`vmstat .............................................................................232
`24.6
`iostat ...............................................................................234
`24.7
`ProCtool .........................................................................236
`24.8
`System usage, uptime, users, who and w ....................239
`24.9
`File Compression, compress & gzip ............................240
`24.10 Shells, tcsh & bash ........................................................240
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`© 1996 Frank Fiamingo
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`UNIX System Administration
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`25
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`Print Service ....................................................................241
`25.1
`SunOS 4.1.X ...................................................................241
`25.2
`SunOS 5.X ......................................................................243
`25.3
`IRIX 5.X .........................................................................252
`25.4 Ultrix and Digital UNIX ...............................................252
`26 Mail ..................................................................................253
`26.1
`Send and receive electronic mail via SMTP, sendmail 253
`26.2 Network mail configuration file ...................................253
`26.3 The mail alias file ..........................................................254
`26.4
`Installation of sendmail ................................................255
`26.5
`Security ..........................................................................256
`26.6 Mail programs, mail, Mail, Columbia mm, elm, etc. .256
`27 World Wide Web ............................................................257
`27.1 WWW .............................................................................257
`27.2 URLs ...............................................................................257
`27.3 WWW Server ................................................................258
`27.4 WWW Browsers ............................................................258
`27.5
`Setting up your Server ..................................................258
`27.6 Home Page .....................................................................261
`System Security ...............................................................265
`28.1
`Security Concerns .........................................................265
`28.2 What needs to be Secured? ..........................................266
`28.3
`Security Programs ........................................................266
`28.4
`Security Response Teams .............................................267
`28.5 The password and group files ......................................267
`28.6
`File and Directory Permissions ....................................269
`28.7 EEPROM Security ........................................................269
`28.8
`Secure the console port .................................................270
`28.9
`Security Loopholes ........................................................271
`28.10 Additional Security Features in SunOS 5.X ...............273
`28.11 SRI Security Report ......................................................275
`28.12 CERT Security Advisories ...........................................276
`Secure Shell, SSH ............................................................277
`29.1
`Secure SHell ...................................................................277
`29.2
`SSH Programs ...............................................................279
`29.3 Control Files ..................................................................280
`29.4
`Setting up the Service ...................................................284
`29.5 Login Process .................................................................286
`29.6
`Installation .....................................................................287
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`UNIX System Administration
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`© 1996 Frank Fiamingo
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`PART IV Summary ........................................................291
`30
`Summary of SunOS/Solaris Differences ...................... 293
`30.1
`SunOS 4.1.X and 5.X Administrative Command Differences 293
`30.2
`SunOS 4.1.X and 5.X Administrative File Differences 296
`UTS UNIX Workstation Support ................................. 297
`31.1 UTS WORKSTATION SUPPORT TEAM ................297
`31.2
`Software .........................................................................298
`
`31
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`© 1996 Frank Fiamingo
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`UNIX System Administration
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`

`
`PART I
`
`Introduction
`
`Overview
`Disk Structure
`Devices
`File Systems
`Startup & Shutdown
`Installation
`Kernel Configuration
`Adding Hardware
`Special Files
`System Directories
`User Accounts
`Daily System Administration
`Administration Tool & Solstice AdminSuite
`Package Administration
`Backup Procedures
`
`UNIX System Administration
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`© 1996 Frank Fiamingo
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`

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`Introduction
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`10
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`© 1996 Frank Fiamingo
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`UNIX System Administration
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`

`
`CHAPTER 1
`
`Overview
`
`1.1 What is UNIX System Administration?
`
`Systems administration is the installation and maintenance of the UNIX computer system. The system
`administrator will need to maintain the software and hardware for the system. This includes hardware
`configuration, software installation, reconfiguration of the kernel, networking, and anything else that’s
`required to make the system work and keep it running in a satisfactory manner. To do this the system
`administrator can assume superuser, or root, privileges to perform many tasks not normally available
`to the average user of the system.
`
`1.2 Daily Tasks of a System Administrator
`
`1.2.1 Manage user logins
`You add accounts by assigning login id’s, groups, user id numbers, group id numbers, login
`directories, and set-up the users’ login environments. You also need to balance the needs of various
`users, e.g. with quotas on disk space or limits on simultaneous processes.
`
`1.2.2 Monitor system activity and security
`You need to monitor disk status, system processes, user process activity, system security, and system
`log files to make sure that your resources are available and that only valid users have access to them.
`
`1.2.3 Administer file systems, devices, and network services
`You need to manage disk space usage, tape and CDROM devices and network services to make sure
`that these resources are available.
`
`1.3 Startup and Shutdown
`
`Startup is when you boot the system from the PROM. This can be from cdrom, disk, or over the
`network (ethernet). The shutdown programs, shutdown/reboot/halt, allow you to close down the
`system in an orderly fashion.
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`© 1996 Frank Fiamingo
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`OverviewOverviewOverview
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`1.4 Periodic Processes
`
`Cron is the clock daemon. It executes periodic processes at pre-arranged times. You can use this to
`clean up old files, manage log files, backup the system to tape nightly, etc.
`
`1.5 Managing File Systems
`
`1.5.1 File System Backups
`Backup and restore procedures are need to insure data integrity against disk crashes, users accidently
`deleting files, for the removal of seldom used programs to free up disk space, etc. You can usually
`automate this task.
`
`1.5.2 Disk space quotas
`Quotas restrict users to a finite disk space and can be set individually. This insures that individual
`users don’t hog the available disk space.
`
`1.6 Responsibilities to the users
`
`You have the responsibility to provide access to disk space, CPU cycles, data integrity, operating
`system software updates, install necessary software, mail and network access, system security.
`
`1.7 Hardware responsibilities
`
`You are responsible for keeping the system running and maintaining it, adding new hardware, and
`making sure that everything is working properly.
`
`1.8 Types of SunOS Systems
`
`Standalone - system can function alone, independently of other systems.
`Server - a standalone machine that can serve others, e.g. with disk space via NFS; can boot diskless
`workstations; can serve different architectures.
`Dataless - has minimal disk space for systems programs and swap space only, shares file space via
`NFS mount of server disk space.
`Diskless - has no disk; requires server for boot (via network), swap, and all program and file space.
`AutoClient - similar to a diskless client except that it uses a local disk for caching. Requires a 100 MB
`local disk.
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`
`Resources for System AdministratorsResources for System AdministratorsResources for System Administrators
`
`1.9 Resources for System Administrators
`
`1.9.1 Network Resources
`Usenet newsgroups/Mailing lists - via Internet through SONNET (the Ohio State University network).
`WWW pages, you can start at the Workstation Groups home page: http://www-wks.acs.ohio-state.edu.
`SunWorld Online (formerly Advanced Systems formerly SunWorld) - now available via the World
`Wide Web at http://www.sun.com/sunworldonline/index.html.
`
`1.9.2 Periodicals
`Information Week - weekly publication for high-end business and technology users, Information
`Week, CMP Publications, Inc., 600 Community Drive, Manhasset, NY 11030.
`SunExpert - monthly publication for Sun users, Computer Publishing Group, 1330 Beacon St.
`Brookline, MA 02146-3202.
`UnixWorld - monthly publication, McGraw Hill, Inc., 1900 O’Farrell Street, San Mateo, CA 94403-
`1311.
`/AIXtra - bimonthly publication for AIX users, IBM Corp., Mail Stop 40-B3-04, One East Kirkwood
`Blvd., Roanoke, TX 76299-0015.
`RS/Magazine - monthly publication for RS/6000 users, Computer Publishing Group, 1330 Beacon St.
`Brookline, MA 02146-3202.
`DECProfessional - monthly publication for DEC users, Cardinal Business Media, Inc., 101 Witmer
`Rd., Horsham, PA 17601.
`SysAdmin - monthly publication, 1601 W. 23rd St., Suite 200, Lawrence, KS 66046-9950 (913-841-
`1631).
`
`1.9.3 Books
`
`1.9.3.1 Unix and the Internet
`A Student’s Guide to Unix, Harley Hahn (McGraw Hill, 1993, ISBN 0-07-025511-3).
`UNIX in a Nutshell for BSD 4.3, A Desktop Quick Reference (O’Reilly & Associates, Inc. 1990, 0-
`937175-20-x).
`UNIX in a Nutshell, A Desktop Quick Reference for System V & Solaris 2.0, Dan Gilly and the staff
`of O’Reilly & Associates, Inc. (O’Reilly & Associates, Inc. 1992, ISBN 1-56592-001-5)
`The C Programming Language, 2nd Ed., Brian Kernighan and Dennis Ritchie (Prentice Hall, 1988,
`ISBN 0-13-110362-8).
`Unix Shell Programming, Stephen Kochan and Patrick Wood (Hayden, 1990 ISBN 0-672-48448-X).
`Programming Perl, Larry Wall and Randal L. Schwartz (O’Reilly & Associates, 1991, ISBN 0-
`937175-64-1).
`The Whole Internet - User’s Guide & Catalog, 2nd Ed., Ed Krol (O’Reilly, 1994, ISBN 1-56592-063-
`5).
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`OverviewOverviewOverview
`
`Zen and the Art of the Internet, 3rd Ed., Brendan Kehoe (1994, ISBN 013-121492-6).
`UNIX Power Tools, Jerry Peek, Tim O’Reilly, and Mike Loukides (O’Reilly & Associates, 1993,
`ISBN 0-679-79073-X). (Includes a CDROM of useful software for various OSs.)
`
`1.9.3.2 System Administration
`UNIX System Administration Handbook, 2nd Ed., Evi Nemeth, Garth Snyder, Scott Seabass and
`Trent Hein (Prentice-Hall, 1995, ISBN 0-13-151051-722). (Includes a CD-ROM)
`Essential System Administration, 2nd Ed., Aeleen Frisch (O’Reilly, 1995, ISBN 1-56592-127-5).
`When You Can’t Find Your UNIX System Administrator, Linda Mui (O’Reilly & Associates, Inc.,
`1995, ISBN 1-56592-104-6).
`Solaris System Administrator’s Guide, Janice Winsor (Ziff-Davis, 1993, ISBN 1-56276-080-7).
`Solaris Advanced System Administrator’s Guide, Janice Winsor (Ziff-Davis, 1993, ISBN 1-56276-
`131-5).
`System Performance Tuning, Mike Loukides (O’Reilly & Associates, 1991, ISBN 0-937175-60-9).
`Sun Performance and Tuning, Adrian Cockroft (Prentice Hall, 1995, ISBN 0-13-149642-5).
`Unix System V Release 4 Administration, 2nd Ed., David Fiedler, Bruce Hunter, and Ben Smith
`(Hayden, 1991, ISBN 0-672-22810-6).
`Managing NFS and NIS, Hal Stern (O’Reilly & Associates, 1991, ISBN 0-937175-75-7).
`All About Administering NIS+, Rick Ramsey (SunSoft Press/Prentice Hall, 1992, ISBN 013-068800-
`2)
`DNS and BIND, Paul Albitz and Cricket Liu (O’Reilly & Associates, 1993, ISBN 1-56592-010-4).
`TCP/IP Network Administration, Craig Hunt (O’Reilly & Associates, 1992, ISBN 0-937175-82-X).
`sendmail, Bryan Costales with Eric Allman and Neil Rickert (O’Reilly & Associates, 1994, ISBN 1-
`56592-056-2).
`Panic! UNIX System Crash Dump Analysis, Chris Drake and Kimberley Brown (SunSoft Press,
`1995, ISBN 0-13-149386-8). (Includes a CD-ROM).
`
`1.9.3.3 Security
`UNIX System Security, Patrick Wood and Stephen G. Kochan (Hayden Books, 1985, ISBN 0-8104-
`6267).
`Practical UNIX & Internet Security, 2nd Ed., Simon Garfinkel and Gene Spafford (O’Reilly &
`Associates, 1996, ISBN 1-56592-148-8).
`Firewalls and Internet Security, W. R. Cheswick and S. M. Bellovin (Addison-Wesley, 1994).
`Building Internet Firewalls, D. Brent Chapman and Elizabeth D. Zwicky (O’Reilly & Associates, Inc.
`1995 ISBN 1-56592-124-0).
`Improving the Security of Your UNIX System, David A. Curry (SRI International), available via
`anonymous ftp from www-wks.acs.ohio-state.edu:/pub/security/security-doc.tar.
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`UTS Software SupportUTS Software SupportUTS Software Support
`
`1.10 UTS Software Support
`
`University Technology Services UNIX Workstation Support - Software support for SunOS/Solaris
`(Sun), Ultrix and Digital UNIX (formerly OSF/1) (DEC), and IRIX (SGI); Sun hardware support
`through group rate from Sun.
`
`1.10.1 Solaris
`The Sun operating system, SunOS, along with the OpenWindows graphical user interface (GUI) and
`the productivity tools, DeskSet, make up the complete Sun UNIX environment. The latest release is
`Solaris 2.5, which includes: SunOS 5.5, OW 3.5, and DeskSet 3.5. SunOS 5 is based on the System
`V version of UNIX. Solaris 2.4 runs on all SPARC hardware. Solaris 2.5 runs on all SPARC
`hardware except the Sun4 series (i.e. Sun 4/110, 4/280, etc.). Solaris 2.4 is still available for those
`who need it.
`
`The latest release of the BSD version of UNIX for the SPARC architecture is Solaris 1.1.2, which
`includes SunOS 4.1.4 and OW 3_414. Solaris 1.1.2 runs on all SPARC hardware except the Sun4u
`series (UltraSPARCs).
`
`Sun software is site licensed for all Ohio State University faculty, staff, and students, and can be
`borrowed from UTS Customer Services, 508 Baker Systems. All software is on CDROM.
`
`1.10.2 IRIX
`IRIX 5.3 is supported on all R3000 and R4000 hardware. IRIX 6.2 is support only on the R4000 and
`later hardware.
`
`Software licenses must be purchased at the University Bookstore. The Bookstore receipt, along with
`the serial number(s) of the machine(s), must be presented before the software can be loaned to you.
`
`SGI software is site licensed for all Ohio State University faculty, staff, and students, and can be
`borrowed from UTS Customer Services, 508 Baker Systems. All software is on CDROM.
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`UNIX System Administration
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`OverviewOverviewOverview
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`CHAPTER 2
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`Disk Structure and
`Partitions
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`Modern disk drives include a CPU and memory to control the disk operation. The drive can accept
`many simultaneous requests, sort them, and process them concurrently. This minimizes the amount
`of head movement required to find all the requested data. It stores the data for all these commands in
`its own memory and can pre-fetch data that it expects you to ask for next, when it’s not too busy with
`current requests.
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`2.1 Disk Structure and Partitions
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`2.1.1 Disk Structure
`A hard disk is physically composed of a series of flat, magnetically coated platters stacked on a spindle.
`The spindle turns while the heads move between the platters, in tandem, radially reading/writing data
`onto the platters.
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`FIGURE 2.1
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`Physical Disk Structure
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`Cylinder
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`Platter
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`Head
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`Spindle
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`Actuator
`Arm
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`Disk Structure and Partitions
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`FIGURE 2.2
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`Disk Platter
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`Sector
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`Track
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`2.1.2 Disk tracks, cylinders, and sectors
`A disk is divided into tracks, cylinders, and sectors. A track is that portion of a disk which passes
`under a single stationary head during a disk rotation, a ring 1 bit wide. A cylinder is comprised of the
`set of tracks described by all the heads (on separate platters) at a single seek position. Each cylinder
`is equidistant from the center of the disk. A track is divided into segments of sectors, which is the basic
`unit of storage.
`On Sun systems a sector is 512 bytes (1 disk block) of data, with header and trailer information. The
`latter make it possible for the controller to identify sectors, detect data errors, and perform error
`corrections when necessary. The actual layout of a disk sector will vary depending on the controller,
`but should look something like that shown in Fig. 2.3. There are two Preambles and a Postamble
`(whose sizes may vary due to rotational speed, etc., and are disk dependent). The Header field lets the
`controller know where the head is positioned, and the ECC field is for error correction.
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`FIGURE 2.3
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`Sector
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`Preamble 1 Header Sync Preamble 2 Sync Data Field ECC Postamble
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` 25 bytes 8 bytes 1 byte 25 bytes 1 byte 512 bytes 6 bytes 22 bytes
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`Disk Partitions
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`The number of sectors per track varies with the radius of the track on the platter. The outermost
`tracks is larger and can hold more sectors than the inner ones. These outer tracks also spin faster
`under the head than do the inner ones, because while the angular speed remains the same, the larger
`circumference results in more sectors spinn