The Network File System (NFS) client software enables client users to access file systems made available by an NFS server. These files and directories physically reside on the remote (server) host but appear to the client as if they were on the local system. For example, any files accessed by an OpenVMS client --- even a UNIX file --- appear to be OpenVMS files and have typical OpenVMS file names.

This chapter reviews key concepts and provides guidelines for configuring and administering the NFS client software on your OpenVMS system. For information about the NFS server, see Chapter 16.

17.1 Reviewing Key Concepts

Because the NFS software was originally developed on and used for UNIX machines, NFS implementations use UNIX-style file system conventions and characteristics. This means that the rules and conventions that apply to UNIX file types, file names, file ownership, and user identification also apply to NFS.

Because the DIGITAL TCP/IP Services NFS client runs on OpenVMS, the client must accommodate the differences between the two file systems, for example, by converting file names and mapping file ownership information. You must understand these differences to properly configure NFS and successfully mount file systems from an NFS server.

The following sections serve as a review only. If you are not familiar with these topics, see the DIGITAL TCP/IP Services for OpenVMS Concepts and Planning guide for a more detailed discussion of the NFS implementation available with DIGITAL TCP/IP Services for OpenVMS.

17.1.1 NFS Clients and Servers

NFS is a client/server environment that allows computers to share disk space and users to work with their files from multiple computers without copying them to the local system. Computers that make files available to remote users are NFS servers. Computers with local users accessing and creating remote files are NFS clients. A computer can be an NFS server, an NFS client, or both a server and a client.

Attaching a remote directory to the local file system is called mounting a directory. A directory cannot be mounted unless it is first exported by an NFS server. The NFS client identifies each file system by the name of its mount point on the server. The mount point is the name of the device or directory at the top of the file system hierarchy. An NFS device is always named DNFSn.

All files below the mount point are available to client users as if they resided on the local system. The NFS client requests file operations by contacting a remote NFS server. The server then performs the requested operation. The NFS client automatically converts all mounted directories and file structures, contents, and names to the format required by OpenVMS. For example, a UNIX file named

/usr/webster/.login

would appear to an OpenVMS client as

DNFS1:[USR.WEBSTER].LOGIN;1

For more information on how NFS converts file names, see Appendix D

17.1.2 Storing File Attributes

The OpenVMS operating system supports multiple file types and record formats. In contrast, NFS and UNIX systems support only byte-stream files, seen to the OpenVMS client as sequential STREAM_LF files.

This means the client must use special record handling to store and access non-STREAM_LF files. The OpenVMS NFS client accomplishes this with attribute description files (ADFs). These are special companion files the client uses to hold the attribute information that would otherwise be lost in the translation to STREAM_LF format. For example, a SET FILE/NOBACKUP command causes the client to create an ADF, because NFS has no concept of this OpenVMS attribute.

17.1.2.1 Using Default ADFs

The client provides default ADFs for files with the following extensions: .EXE, .HLB, .MLB, .OBJ, .OLB, .STB, and .TLB. (The client does not provide ADFs for files with the .TXT and .C extensions, because these are STREAM_LF.) The client maintains these ADFs on the server.

For example, SYS$SYSTEM:TCPIP$EXE.ADF is the default ADF for all .EXE type files. When you create .EXE files (or if they exist on the server), they are defined with the record attributes from the single default ADF file. The client refers only to the record attributes and file characteristics fields in the default ADF.

17.1.2.2 How the Client Uses ADFs

By default, the client uses ADFs if they exist on the server. The client updates existing ADFs or creates them as needed for new files. If you create a non-STREAM_LF OpenVMS file or a file with access control lists (ACLs) associated with it on the NFS server, the NFS client checks to see if a default ADF can be applied. If not, the client creates a companion ADF to hold the attributes.

The client hides these companion files from the user's view. If a user renames or deletes the orginal file, the client automatically renames or deletes the companion file. However, if a user renames or deletes a file on the server side, the user must also rename the companion file; otherwise file attributes are lost.

You can modify this behavior with the /NOADF qualifier to the MOUNT command. The /NOADF qualifier tells the client to handle all files as STREAM_LF unless a default ADF matches. This mode is only appropriate for read-only file systems because the client cannot adequately handle application-created files when /NOADF is operational.

17.1.2.3 Creating Customized Default ADFs

You can create customized default ADFs for special applications. To do so:

1. On the client, create a special application file that results in creating an ADF on the server. Suppose that application file is called TEST.GAF.
2. On the server, check the listing for the newly created file. For example:

   > ls -a . .. .$ADF$test.gaf;1 test.gaf

   
   Note the ADF (.$ADF$test.gaf;1) was created with the data file (TEST.GAF).

3. On the server, copy the ADF file to a newly created default ADF file on the client. For example:

   > cp .\$ADF\$test.gaf\;1 gaf.adf

   
   Note that the backslashes (\) are required to enter the UNIX system nonstandard "$" and ";" symbols.

4. On the client, copy the new default ADF file to the SYS$SYSTEM directory. For example:

   $ COPY GAF.ADF SYS$COMMON:[SYSEXE]TCPIP$GAF.ADF

5. Dismount all the NFS volumes and mount them again. This starts another NFS ancillary control process (ACP) so the newly copied default ADF file can take effect.

Both the NFS server and NFS client use the proxy database to authenticate users. The proxy database is a collection of entries used to register user identities. To access file systems on the remote server, local users must have valid accounts on the remote server system.

The proxy entries map each user's OpenVMS identity to a corresponding NFS identity on the server host. When a user initiates a file access request, NFS checks the proxy database before granting or denying access to the file.

The proxy database is an index file called TCPIP$PROXY.DAT. If you use the configuration procedure to configure NFS, this empty file is created for you. You populate this file by adding entries for each NFS user. See Section 17.2 for instructions on how to add entries to the proxy database.

17.1.4 How the Client Maps User Identities

Both OpenVMS and UNIX based systems use identification codes as a general method of resource protection and access control. Just as OpenVMS employs user names and UICs for identification, UNIX identifies users with a user name and a user identification (UID) and group identification (GID) pair. Both UIDs and GIDs are numbers to identify a user on a system.

The proxy database contains entries for each user wanting to access files on a server host. Each entry contains the user's local OpenVMS account name, the UID/GID pair that identifies the user's account on the server system, and the name of the server host. This file is loaded into dynamic memory when the NFS client starts. Whenever you modify the UID/GID to UIC mapping, you must restart the NFS client software by dismounting and remounting all the client devices. (Proxy mapping always occurs even when operating in OpenVMS-to-OpenVMS mode.)

The only permission required by the UNIX file system for deleting a file is write access to the last directory in the path specification.

You can print a file that is located on a DNFSn: device. However, the print symbiont, which runs as user SYSTEM, opens the file only if it is world readable or there is an entry in the proxy database allowing read access to user SYSTEM.

17.1.4.1 Default User

You can associate a client device with a default user by designating the user with the /UID and /GID qualifiers on the MOUNT command. If you do not specify a user with the /UID and /GID qualifiers, NFS uses the default user --2/--2. If the local user or the NFS client has no proxy for the host serving a DNFS device, all operations performed by that user on that device are seen as coming from the default user (--2/--2).

To provide universal access to world-readable files, you can use the default UID instead of creating a proxy entry for every NFS client user.

Compaq strongly recommends that, for any other purposes, you provide a proxy with a unique UID for every client user. Otherwise, client users may see unpredictable and confusing results when they try to create files.

17.1.5 How the Client Maps UNIX Permissions to OpenVMS Protections

Both OpenVMS and UNIX based systems use a protection mask that defines categories assigned to a file and the type of access granted to each category. The NFS server file protection categories, like those found on UNIX systems, include: user, group and other, each having read (r), write (w), or execute (x) access. The OpenVMS categories are SYSTEM, OWNER, GROUP, and WORLD. Each category can have up to four types of access: READ (R), WRITE, (W), EXECUTE (E), and DELETE (D). The NFS client handles file protection mapping from server to client.

OpenVMS DELETE access does not directly translate to UNIX. A UNIX user can delete a file as long as he or she has write access to the parent directory. The user can see whether or not he or she has permissions to delete a file by looking at the protections on the parent directory. This design corresponds to OpenVMS where the absence of write access to the parent directory prevents users from deleting files, even when protections on the file itself appear to allow delete access. For this reason, the NFS client always displays the protection mask of remote UNIX files as permitting DELETE access for all categories of users. Since a UNIX file system does not have a SYSTEM protection mask (the superuser has all permissions for all files) the NFS client displays the SYSTEM as identical to the OWNER mask.

17.1.6 Guidelines for Working with DNFS Devices

The following list summarizes the guidelines and restrictions associated with DNFS devices:

• BACKUP and RESTORE operations
  The OpenVMS NFS client does not emulate the on-disk structure of actual OpenVMS disks. Therefore, applications that need direct knowledge of the OpenVMS on-disk structure, such as image BACKUP and RESTORE, work differently with DNFSn: volumes than with other volumes.
• File identification
  The NFS client constructs OpenVMS file identifiers (FIDs) "on the fly." The remote NFS server does not store them. Each NFS client constructs its own FIDs, possibly leading to different FIDs of the same file for different NFS clients.
• Disk quotas
  Disk quotas for OpenVMS disks are not applicable to DNFSn: disks.

Because NFS uses UNIX style syntax for file names, valid OpenVMS file names may be invalid on the NFS server and vice versa. The NFS software automatically converts file names to the format required by either the client or server. (NFS always converts file names even when both the NFS client and the NFS server are OpenVMS hosts.)

All name-mapping sequences on the OpenVMS client begin with the "$" escape character. Appendix D lists the rules that govern these conversions and provides a list of character sequences, server characters, and octal values used for NFS name conversion.

17.2 Registering Users in the Proxy Database

Users on your client host must have corresponding accounts on the NFS server host. After making sure client users have appropriate accounts, you must register them with the proxy database. The NFS client, the NFS server, and the PC-NFS daemon all use the proxy database.

If you use TCPIP$CONFIG to configure NFS, the index file TCPIP$PROXY.DAT is created for you. This file is empty until you populate it with proxy entries. If you do not use the configuration procedure, use the CREATE PROXY¹ command to create the empty database file. The file TCPIP$PROXY.DAT resides in the SYS$COMMON:[SYSEXE] directory by default. You can change the location of the proxy database by redefining the logical name TCPIP$PROXY.

Use the following commands to manage the proxy database:

• ADD PROXY
• REMOVE PROXY
• SHOW PROXY

Enter these commands at the TCPIP> prompt. For example:

TCPIP> ADD PROXY username /NFS=type /UID=n /GID=n /HOST=host_name

Changes in the proxy database take effect only after you dismount all DNFSn: devices and remount them. An exception is DNFS0:, which is present if the NFS client driver is loaded and cannot be mounted or dismounted.

Each entry in the proxy database has four fields as defined in Table 17-1.

Table 17-1 Required Fields for NFS Proxy Entries

Field	Meaning
OpenVMS user name	Name of the NFS user's OpenVMS account
Type	Direction of NFS communication allowable to the user. Specify one of the following: O (outgoing). Used by the NFS client. N (incoming). Used by the NFS server. ON (outgoing and incoming). Used by both client and server. D (dynamic). Entry is loaded in the server's dynamic memory. When the NFS server starts, it creates a copy of the proxy database in dynamic memory. (If the account does not exist or the account is disabled, the entry for the account will be missing from dynamic memory.)
UID/GID pair	Remote identity of the user. Required even if both client and server are OpenVMS hosts.
Remote host name	Name of the remote host, which is one of the following: Remote client of the local NFS server Remote server for the local NFS client Both Wildcard ( *) for all hosts

To add a user name to the proxy database, take the following steps:

1. For each NFS user, obtain the OpenVMS user name from the OpenVMS user authorization file (UAF). If a user name is not in the UAF, use the Authorize utility to add it.
2. Obtain the UID/GID pair for each NFS user from the /etc/password file on the NFS server.
3. Enter SHOW PROXY.
4. Enter ADD PROXY for each NFS user you want to add to the proxy database. For example:

   TCPIP> ADD PROXY GANNET /NFS=(OUTGOING,INCOMING) /UID=1111 /GID=22 /HOST=CLIENT1

5. Reenter SHOW PROXY to confirm the new information.

The following illustrates a portion of a proxy database file:

VMS User_name Type User_ID Group_ID Host_name GANNET OND 1111 22 CLIENT1, client1 GEESE OND 1112 22 * GREBE OND 1113 22 client1, client2 GROUSE OD 1114 23 client3 GUILLEMOT OD 1115 23 client3 GULL OD 1116 23 client4

17.3 Mounting Files and Directories

Attaching remote files and directories exported by an NFS server is called mounting. The NFS client identifies each file system by the name of its mount point on the server. The client provides the following MOUNT commands:

• MOUNT
• SHOW MOUNT
• DISMOUNT

Enter these commands at either the TCPIP> prompt or the DCL prompt ($), for example:

TCPIP> MOUNT mount_point /HOST="host" /PATH="/path/name"

or

$ TCPIP MOUNT mount_point /HOST="host" /PATH="/path/name"

When you issue a MOUNT command, the NFS client creates a new DNFS device and mounts the remote file system onto it. For example, the following command mounts, onto local device DNFS2:, the remote directory /usr/users/curlew, which physically resides on NFS server loon.

TCPIP> MOUNT DNFS2: /HOST="loon" /PATH="/usr/users/curlew"

After entering the command, a confirmation message such as the following is displayed:

%DNFS-S-MOUNTED, /users/curlew mounted on DNFS2:[000000]

If you specify DNFS0 in a mount command, the client selects the next available unit number for you, for example:

MOUNT DNFS0:/HOST="loon" /PATH="/usr/curlew" %DNFS-S-MOUNTED, /usr/curlew mounted on DNFS3:[000000]

Qualifiers to the MOUNT command let you modify the way a traditional mount occurs. For example, you may specify background mounting, modify existing mounts, or hide subdirectories from view. See the following sections for more information:

• User-level mounting ( Section 17.3.1)
• Automounting ( Section 17.3.2)
• Background mounting ( Section 17.3.3)
• Overmounting ( Section 17.3.4)
• Occluded mounting ( Section 17.3.5)

See the DIGITAL TCP/IP Services for OpenVMS Management Command Reference manual for a complete list of mount options and command qualifiers.

17.3.1 User-Level Mounting

The NFS client supports shared mounting by using the /SHARE qualifier with the MOUNT command. Any user can mount a file system using the /SHARE qualifier---SYSNAM or GRPNAM privileges are not required. The /SHARE qualifier places the logical name in the job logical name table and increments the volume mount count, regardless of the number of job mounts. When the job logs out, all job mounts are dismounted, which causes the volume mount count to be decremented.

The following example illustrates how to specify a shared mount:

TCPIP> MOUNT DNFS1: /HOST=BART /PATH="/DKA100/ENG" TCPIP> MOUNT DNFS1: /HOST=BART /PATH="/DKA100/ENG" /SHARE

This mount request increments the mount count by one. You must specify the /SHARE qualifier with the same host name and path as used in the initial mount to ensure the mount is seen as a shared mount instead of a new mount request.

With a shared mount, the mount requests increment the mount count by 1 under the following circumstances:

• With an initial /SYSTEM or /GROUP mount.
• With a DCL command MOUNT/SHARE or TCPIP management command MOUNT/SHARE that completes without an error. (This contrasts with overmount, where the previous mounting point is dismounted. This condition can increment or decrement the mount count or leave it unchanged.)

In this way, if the main process of the job logs out, the job mount is deallocated, and the volume mount count decrements by one (if zero, the device is dismounted). OpenVMS handles dismounting differently based on whether you use the TCPIP management command DISMOUNT or the DCL command DISMOUNT. These differences are explained below.

• With the TCPIP command DISMOUNT, the NFS ACP dismounts one or more (in the case of /ALL) mount points. If the mount point being dismounted is the only or last one for the device, the device is dismounted for all users who mounted it, and the mount count is decremented to zero. If more that one mount point exists, the mount point is dismounted along with a specifically shared mount.
• With the DCL command DISMOUNT, the OpenVMS operating system checkes for job mounts first. If a job mount for the specified device exists, the /JOB mount is dismounted, any logical name associated with the /JOB mount is deallocated, and the mount count is decremented by one. If no JOB mount exists, OpenVMS checks for /SYSTEM and /GROUP mounts. If one exists, and the user has the required privilege, the /SYSTEM or /GROUP mount is dismounted, any associated logical name is deallocated, and the mount count is decremented by one. No mount points are dismounted until the mount count reaches zero.
  If the user does not have the required SYSNAM or GRPNAM privilege, the following error message is returned:

  SYSTEM-F-NO-PRIVILEGE, operation requires privilege

  
  If no /SYSTEM or /GROUP mount exists, the following error message is returned:

  %DISM-W-CANNOTDMT, NFSn: cannot be dismounted %SYSTEM -F -DEVNOTMOUNT, device is not mounted

Consider the mount counts in the following sample MOUNT/DISMOUNT sequence:

1. TCPIP> MOUNT DNFS1:/HOST=BART /PATH="/DKA0/ENG"/
   Mount count: 1 system mount, not incremented
2. TCPIP> MOUNT DNFS1:[A] /HOST=BART /PATH="/DKA0/ENG" /SHARE
   Mount count: 2 (incremented)
3. $ MOUNT/SHARE DNFS1:
   Mount count: 3 (incremented)
4. TCPIP> MOUNT DNFS1:[B] /HOST=MARGE /PATH="DKA0/TEST"
   Mount count: 3 (system mount, not incremented)
5. TCPIP> DISMOUNT DNFS1:[A]
   Mount count: 2
6. $ DISMOUNT DNFS1:
   Mount count: 1 (removed mount in example 3, decremented)
7. $ DISMOUNT DNFS1:
   Mount count: 0 (removed mount in example 4, decremented)

The original mount for BART "/ENG" on DNFS1:[A] along with its shared mount is dismounted. The subsequent DISMOUNT commands dismount examples 3 and 4, leaving nothing mounted.