Open System Utilities Semantics over XNFS

Introduction

Many of the interfaces described in the X/Open Commands and Utilities Specification (see reference XCU) are directly or indirectly concerned with accessing files stored on the system's file system. This appendix identifies those commands and utilities which may operate differently when used with XNFS.

The table "Utilities with no Semantic Differences" below lists the commands and utilities that show no semantic difference when invoked in an XNFS environment. That is, they behave the same as when running in a local file system environment.

Utilities with Semantic Differences lists the commands and utilities that may show semantic differences when invoked in an XNFS environment.

Semantic Difference Summary for File Access lists the potential differences that can affect those commands and utilities.

Common Semantic Differences lists the differences that are most common.

The following utilities and commands have no change over XNFS:

Common Semantic Differences

The following differences apply to almost all of the commands and utilities that may show semantic differences under an XNFS environment.

Execution of Remote Files

This applies to all of the utilities and commands. If local execution of a remote utility or command occurs (such as executing the remote image of cmp locally), then the following semantic difference applies:

• It is possible that the remote program may be incompatible for execution on a local machine. (See Local Execution of a Remote Program .)

Interruption of any XNFS Operation

All NFS operations involve issuing one or more requests from the client to the server. Therefore the following semantic difference applies to all NFS operations:

• As described in Server or Network-Induced Delays , a system call which refers to an NFS file or directory may take an arbitrary length of time to complete. However, it is possible for the user to interrupt such an operation if the "Intr=" MountedFileSystem attribute has been set to "True". (See Interruption of Function Calls .)

File Access

Every command or utility that opens and then accesses a remote file is subject to the following semantic differences:

• Access to a file located on a remote file system can be denied, even in the case that the file permissions do not themselves restrict access. (See UID Mapping by Server .)

• Access to a file on the server may be denied because the attributes in the client cache are more restrictive than the attributes on the server. (See Denial of Access .)

• Further access to an open file may be denied if the file is located on a remote file system and the file has either been deleted or the file attributes have changed. (See File Accessibility Changed after Open .)

• The deletion of a file on a server may not be immediately recorded on the clients due to directory caching. (See Directory Caching .)

• The creation of a file on a server may not be immediately noticeable to clients due to directory caching. (See Directory Caching .)

• During client/server operations, there may be delays of arbitrary duration. These delays can be the result of network traffic and server load or availability. (See Server or Network-Induced Delays and Interrupted Root File System Service .)

• Access protection mechanisms will not function as intended if the user ID databases are not consistently maintained over the network. (See User and Group ID Database Consistency .)

Remote file access could conceivably occur with every command or utility if its standard input or standard output is redirected to a remote file.

Utilities with Semantic Differences

The following is a list of those utilities and commands that have semantic differences:

Where the semantic difference described only applies to the XNFS Issue 3W Specification this is identified by shading of the appropriate text. Semantic differences which do not contain this code marking are applicable to both XNFS Issue 3 and XNFS Issue 3W Specifications.