Appendix C. Glossary

a (administer) Permission

The ACL permission that allows the possessor to change the entries on the ACL .

a Privacy Flag

The fourth privacy flag on a group, which enables the possessor to add members to it.

Access Control List (ACL)

A list associated with an AFS directory that specifies what actions a user or group can perform on the directory and the files in it. There are seven access permissions: a (administer), d (delete), i (insert), k (lock), l (lookup), r (read), and w (write).

ACL Entry

An entry on an ACL that pairs a user or group with specific access permissions.

Alias

An alternative name for an AFS command.

all ACL Shorthand

A shorthand notation used with the fs setacl command to represent all seven permissions.

Anonymous

The identity assigned to a user who does not have a valid token for the local cell.

Argument

The portion of a command that names an entity to be affected by the command. Arguments consist of two parts: a switch and one or more instances. Some AFS commands take one or more arguments.

Authenticate

To become recognized as a valid AFS user by providing the correct password. Authenticate by logging onto a machine that uses an AFS-modified login utility or by issuing the klog command. Only authenticated users can perform most AFS actions.

Byte, kilobyte

A unit of measure used to measure usage of space in a volume or on a partition. A kilobyte block is equal to 1024 bytes.

Cache Manager

A set of modifications to the operating system on a client machine which enables users on the machine to access files stored in AFS. The Cache Manager requests files from the File Server and stores (caches) a copy of each file on the client machine's local disk. Application programs then use the cached copy, which eliminates repeated network requests to file server machines.

Cached File

A copy of a file that the Cache Manager stores on a workstation's local disk.

Callback

A promise from the File Server to contact the Cache Manager if the centrally stored copy of the file changes while the Cache Manager has a cached copy. If the file is altered, the File Server breaks the callback. The next time an application program asks for data from the file, the Cache Manager notices the broken callback and retrieves an updated copy of the file from the File Server. Callbacks ensure the user is working with the most recent copy of a file.

Cell

An independently administered site running AFS, consisting of a collection of file server machines and client machines defined to belong to the cell. A machine can belong to only one cell at a time.

Client Machines

Computers that perform computations for users. Users normally work on a client machine, accessing files stored on a file server machine.

Client/Server Computing

A computing system in which two types of computers (client machines and server machines) perform different specialized functions.

Command

A string of characters indicating an action for an AFS server to perform. For a description of AFS command syntax, see Appendix B, AFS Command Syntax and Online Help.

Command Suite

A group of AFS commands with related functions. The command suite name is the first word in many AFS commands.

Complete Pathname

A full specification of a file's location in AFS, starting at the root of the filespace (by convention mounted at the /afs directory) and specifying all the directories the Cache Manager must pass through to access the file. The names of the directories are separated by slashes.

d (delete) Permission

The ACL permission that enables the possessor to remove elements from a directory.

Directory

A logical structure containing a collection of files and other directories.

Distributed File System

A file system that joins the file systems of individual machines. Files are stored on different machines in the network but are accessible from all machines.

File

A collection of information stored and retrieved as a unit.

File Server Machine

A type of machine that stores files and transfers them to client machines on request.

Flag

Part of a command that determines how the command executes, or the type of output it produces.

Foreign Cell

A cell other than the cell to which the client machine belongs. If the client machine is appropriately configured, users can access the AFS filespace in foreign cells as well as the local cell, and can authenticate in foreign cells in which they have AFS accounts.

Group

A defined list of users, which can be placed on a directory's ACL to extend a set of permissions to all of its members at once.

Group-owned Group

A group owned by another group. All members of the owning group can administer the owned group; the members of the owned group do not have administer permissions themselves.

Hierarchical File Structure

A method of storing data in directories that are organized in a tree structure.

Home Directory

A directory owned by a user and dedicated to storage of the user's personal files.

i (insert) Permission

The ACL permission that enables the possessor to add files or subdirectories to a directory.

Instance

The part of a command string that defines the entity to affect.

k (lock) Permission

See the k (lock) Permission entry. The ACL permission that enables programs to place advisory locks on a file.

Kilobyte

A unit of measure used to measure usage of space in a volume or on a partition. A kilobyte is equal to 1024 bytes. The term kilobyte block is sometimes used when referring to disk space.

l (lookup) Permission

The ACL permission that enables the possessor to list the contents of a directory and display its ACL.

Local Cell

The cell to which the user's account and client machine belong.

lock Permission

See the k (lock) Permission entry.

Login

The process of establishing a connection to a client machine's local file system as a specific user.

Logout

The process of ending a connection to the local file system.

m Privacy Flag

The third privacy flag on a group, which enables the possessor to list the members of a group or the groups to which a user belongs.

Mode Bits

A set of permissions that the UNIX file system associates with a file or directory to control access to it. They appear in the first field of the output from the ls -l command.

Mount Point

A special type of directory that associates a location in the AFS file space with a volume. It acts like a standard UNIX directory in that users can change directory to it and list its contents with the UNIX cd and ls commands.

Mutual Authentication

A procedure through which two parties prove their identities to one another. AFS server and client processes normally mutually authenticate as they establish a connection.

NFS/AFS Translator

A program that enables users on NFS client machines to access files in the AFS filespace.

none ACL Shorthand

A shorthand notation used with the fs setacl command to delete an entry from an ACL.

o Privacy Flag

The second privacy flag on a group, which enables the possessor to list groups owned by the user or group.

Operation Code

The second word in an AFS command that belongs to a suite. It indicates the command's function.

Owner of a Group

The person or group who can administer a group.

Parent Directory

The directory in which a directory or file resides.

Partition

A logical section of a disk in a computer.

Password

A unique, user-defined string of characters validating the user's system identity. The user must correctly enter the password in order to be authenticated.

Permission

A certain type of access granted on an ACL. Anyone who possesses the permission can perform the action.

Quota

The size limit of a volume, assigned by the system administrator and measured in kilobyte blocks.

r (read) Permission

The ACL permission that enables the possessor to examine the contents of a file.

r Privacy Flag

The fifth privacy flag on a group, which enables the possessor to remove members from it.

read ACL Shorthand

A shorthand notation used with the fs setacl command to represent the r and l permissions.

Relative Pathname

A pathname that does not begin at the root of the AFS or local filespace and so represents a file or directory's location with respect to the current working directory.

Remote Commands

Commands used to run programs on a remote machine without establishing a persistent connection to it.

s Privacy Flag

The first privacy flag on a group, which enables the possessor to list general information about it.

Self-owned Group

A group that owns itself, enabling all of its members to administer it.

Server

A program or machine that provides a specialized service to its clients, such as storing and transferring files or performing authentication.

Subdirectory

A directory that resides in another directory in the file system hierarchy.

Switch

The part of a command string defining the type of an argument. It is preceded by a hyphen.

Syntax Statement

A specification of the options available on a command and their ordering.

System Administrator

A user who is authorized to administer an AFS cell.

System Groups

Groups that AFS defines automatically to represent users who share certain characteristics. See the following three entries.

System:administrators group

A system group that includes users authorized to administer AFS.

System:anyuser group

A system group that includes everyone who can gain access the cell's AFS filespace. It includes unauthenticated users, who are assigned the identity anonymous.

System:authuser group

A system group that includes all users who currently have valid AFS tokens for the local cell.

Token

A collection of data that the AFS server processes accept as evidence that the possessor has successfully proved his or her identity to the cell's AFS authentication service. AFS assigns the identity anonymous to users who do not have a token.

UNIX Mode Bits

See the Mode Bits entry.

Username

A character string entered at login that uniquely identifies a person in the local cell.

Volume

A structure that AFS uses to group a set of files and directories into a single unit for administrative purposes. The contents of a volume reside on a single disk partition and must be mounted in the AFS filespace to be accessible.

w (write) Permission

The ACL permission that enables the possessor to modify the contents of a file.

write ACL Shorthand

A shorthand notation used with the fs setacl command to represent all permissions except the a permission.