You may have set up proxy mapping such that many incoming users map to one OpenVMS account, causing multiple users to share the same file quota. In such a case, ensure that the FILLM value for this account is large enough to provide satisfactory performance for all the users so associated.
The CHANNELCNT parameter sets the maximum number of channels that a
process can use. Ensure that CHANNELCNT is set large enough to handle
the total number of files accessed by all clients.
14.13.10 OpenVMS SYSGEN Parameters that Impact Performance
The following OpenVMS SYSGEN parameters impact NFS server performance:
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 14.
15.1 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.
15.1.1 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 F
15.1.2 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) --- 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.
The client stores ADFs, as far as available memory allows, in a file attribute cache. When you dismount a directory, the NFS client flushes the cache. It no longer can "reconstruct" an original file. A record-format-recognition algorithm reads the files to determine record attributes:
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$SYSTEM:UCX$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.
15.1.2.2 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, they 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.
15.1.2.3 Creating Customized Default ADFs
You can create customized default ADFs for special applications. To do so:
> ls -a . .. .$ADF$test.gaf;1 test.gaf
> cp .\$ADF\$test.gaf\;1 gaf.adf
$ COPY GAF.ADF SYS$COMMON:[SYSEXE]UCX$GAF.ADF
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 UCX$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 15.2 for instructions on how to add entries to the
proxy database.
15.1.4 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 simply numbers to identify a user on a system.
The proxy database contains entries for each user wishing 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 reload the NFS client software. (Proxy mapping always occurs even when operating in OpenVMS-to-OpenVMS mode.)
When a user on the client host requests file access, the client searches the proxy database for an entry that maps the requester's identity to a corresponding UID/GID pair. If the client finds a match, it sends a message to the server that contains the following:
If the remote server is running OpenVMS, the server scans its copy of the proxy database for an entry that corresponds to the requester's UID/GID. If it finds a valid entry, the server grants access according to the privileges set for that account.
Before sending a user request to the NFS server, the client checks access based on the UNIX-style protection mask. This check occurs on the client host and causes the client to grant or deny access.
The protections set for files located on DNFSn: devices might be different from OpenVMS protection parameters. Some remote file systems do not have system-level file protections (the superuser has all privileges for all files).
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.
15.1.4.1 Default Mapping
It is possible to give client users access to the server file systems even if the user does not have a corresponding account identity on the server system. You accomplish this by creating a proxy identity for the default user (usually the UNIX user "nobody" --2/--2).
If the outgoing UID does not map to an OpenVMS account on the server,
the server may still grant access to the client user, but access is
restricted. The server searches its version of the proxy database for a
entry for the default user UID/GID pair. (See Section 14.1.5 in
Chapter 14 for more information about the default user.) If such an
entry exists, the unmapped user is mapped to that account.
15.1.4.2 Providing Universal Access to World-Readable Files
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.
DIGITAL 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.
15.1.5 How the Client Grants File Access
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 NFS. An NFS 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 is similar 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.
15.1.6 Guidelines for Working with DNFS Devices
The following list summarizes the guidelines and restrictions associated with DNFS devices.
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. It is important to note that 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 F lists the rules that
govern these conversions and provides a list of character sequences,
server characters, and octal values used for NFS name conversion.
15.2 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 UCX$CONFIG to configure NFS, the index file UCX$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 UCX$PROXY.DAT resides in the SYS$COMMON:[SYSEXE] directory by default. You can change the location of the proxy database by redefining the logical name UCX$PROXY.
Use the following commands to manage the proxy database:
Issue these commands at the UCX prompt. For example:
UCX> ADD PROXY username /NFS=type /UID=n /GID=n /HOST=host_name
Changes in the proxy database take effect only after you dismount all DNFSn: devices and remount them. An exception is DNFS0:, which is present if the NFS client driver is loaded and cannot be mounted or dismounted.
Each entry in the proxy database has four fields as defined in Table 15-1.
| Field | Meaning |
|---|---|
| OpenVMS user name | Name of the NFS user's OpenVMS account (no default) |
| Type |
Direction of NFS communication allowable to the user. Specify one of
the following:
|
| UID/GID pair | Remote identity of the user. Required even if both client and server are OpenVMS hosts. |
| Remote host name |
Name of the remote host, which is one of the following:
(No default) |
To add a user name to the proxy database, take the following steps:
UCX> ADD PROXY GANNET /NFS=(OUTGOING,INCOMING) /UID=1111 /GID=22 /HOST=CLIENT1
The following illustrates a portion of a proxy database file:
VMS User_name Type User_ID Group_ID Host_name GANNET OND 1111 22 CLIENT1, client1 GEESE OND 1112 22 * GREBE OND 1113 22 client1, client2 GROUSE OD 1114 23 client3 GUILLEMOT OD 1115 23 client3 GULL OD 1116 23 client4
Attaching remote files and directories exported by an NFS server is called mounting. The NFS client identifies each file system by the name of its mount point on the server. The client provides the following MOUNT commands:
Issue these commands at either the UCX> prompt or the DCL prompt ($), for example:
UCX> MOUNT mount_point /HOST="host" /PATH="/path/name"
or
$ UCX MOUNT mount_point /HOST="host" /PATH="/path/name"
Note
By default, a mount is now considered a system mount and privileges are required unless the /SHARE qualifier is used. See Section 15.3.1 for information on user-level mounting.
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.
UCX> MOUNT DNFS2: /HOST="loon" /PATH="/usr/users/curlew"
After issuing 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: %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:
See the DIGITAL TCP/IP Services for OpenVMS Management Command Reference manual for a complete list of mount options and
commmand qualifiers.
15.3.1 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.
UCX> MOUNT DNFS1: /HOST=BART /PATH="/DKA100/ENG" UCX> 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:
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 UCX management command DISMOUNT or the DCL command DISMOUNT. These differences are explained below.
SYSTEM-F-NO-PRIVILEGE, operation requires privilege
%DISM-W-CANNOTDMT, NFSn: cannot be dismounted %SYSTEM -F -DEVNOTMOUNT, device is not mounted
Consider the mount counts in the sample MOUNT/DISMOUNT sequence shown below.
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.
15.3.2 Automounting
Automounting allows you to mount a remote file system on an as-needed basis. This means that the client automatically and transparently mounts a remote server path as soon as the user accesses the path name. Automounting is convenient for file systems that are inactive for large periods of time. When a user on a system invokes a command to access a remote file or directory, the automount daemon mounts the file and keeps it mounted as long as the user needs it. When a specified amount of time elapses without the file being accessed, it is dismounted. You can specify an inactivity period (5 minutes is the default), after which the software automatically dismounts the path.
You specify automounting and an inactivity interval with the qualifier /AUTOMOUNT=INACTIVITY:OpenVMS_delta_time.
The inactivity interval is the maximum inactive period for the mount attempt. When this period expires, the NFS client dismounts the path name as described below.
In this example, the client automounts directory /usr/webster residing on host robin onto the OpenVMS mount point DNFS67: When it references the path name, the client keeps the path mounted unless it reaches an inactive period of 10 minutes, after which it dismounts the file system. With subsequent references, the client remounts the file system.
UCX> MOUNT DNFS67: /HOST="robin" - _UCX> /PATH="/usr/webster" /AUTOMOUNT=INACTIVITY=00:10:00
Background mounting allows you to retry a file system mount that initially failed. For example, you may have set mount points in your system startup command file so they are automatically mounted every time your system reboots. In this scenario, if the server is unavailable (because, for example, the server is also rebooting), the mount requests fail. With background option set, the client continues to try the mount after the initial failure. The client continues trying up to 10 times at 30-second intervals (default) or for the number of retries and interval you specify.