From: hoffman@xdelta.zko.dec.nospam Sent: Friday, January 07, 2000 9:51 PM To: Info-VAX@Mvb.Saic.Com Subject: OpenVMS Frequently Asked Questions (FAQ), Part 3/4 Archive-name: dec-faq/vms/part3 Posting-Frequency: monthly Last-modified: 7 January 2000 Version: VMS-FAQ-3.TXT(3) Overview ======== This is part 3/4 of the Frequently Asked Questions (FAQ) posting for the comp.os.vms and vmsnet.misc newsgroups. (comp.os.vms is bidirectionally-gatewayed to the INFO-VAX mailing list - see INTRO3 for further details.) It contains answers to frequently asked questions about Compaq's OpenVMS operating system and the computer systems on which it runs. (Please see INTRO5 before posting.) The OpenVMS FAQ is archived in the following locations: http://www.openvms.digital.com/wizard/openvms_faq.html ftp://ftp.digital.com/pub/Digital/dec-faq/OpenVMS.txt ftp://ftp.digital.com/pub/Digital/dec-faq/vms ftp://rtfm.mit.edu/pub/usenet/news.answers/dec-faq/vms comp.answers and news.answers newsgroups Other internet FAQs are generally available in these locations: comp.answers and news.answers newsgroups ftp://rtfm.mit.edu/pub/usenet/... User-created HTML versions of the OpenVMS FAQ are located at: http://www.kjsl.com/vmsfaq http://eisner.decus.org/vms/faq.htm Please do NOT send technical questions to the Frequently Asked Questions (FAQ) editor -- well, please do not email any questions that do not also include the answer(s). Please post these questions to the appropriate newsgroup instead -- and see INTRO5 before posting. To make suggestions for changes or additions to this FAQ list, please send mail to the FAQ editor at hoffman@xdelta.zko.dec.com. Again, the FAQ editor is *not* in a position to answer general questions. Some general notes: The term "VMS" is synonymous with "OpenVMS". "Alpha", "AlphaGeneration" or "AXP" generally refers to any system or product based on or related to Compaq's Alpha processor architecture. OpenVMS manual names mentioned are those as of V7.2 -- names may be different in other editions of the documentation set. World-Wide Web Universal Resource Locator (URL) notation is used for FTP addresses. Many people have contributed to this list, directly or indirectly. In some cases, an answer has been adapted from one or more postings on the comp.os.vms newsgroup. Our thanks to all of those who post answers. The name (or names) at the end of an entry indicate that the information was taken from postings by those individuals; the text may have been edited for this FAQ. These citations are only given to acknowledge the contribution. Although the editor of this FAQ is an employee of Compaq Computer Corporation, this posting is not an official statement of Compaq. AlphaGeneration, AlphaServer, AlphaStation, Alpha AXP, AXP, DEC, DECstation, DECsystem, OpenVMS, ULTRIX, VAX and VMS are trademarks of Compaq. Compaq and the names of Compaq products are trademarks and/or registered trademarks and/or service marks of Compaq Computer Corporation. OSF/1 is a registered trademark of the Open Software Foundation. UNIX is a registered trademark in the United States and other countries, licensed exclusively through X/Open Company Ltd. Other names are properties of their respective owners. Table of Contents - Part 3/4 ____________________________ Other Utilities ======================================== UTIL1. How do I play an audio CD on my workstation? UTIL2. How do I access a MS-DOS floppy disk from OpenVMS? UTIL3. How do I play sound files on an AlphaStation? DECsound doesn't work DCL and command usage ======================================== DCL1. How do I run a program with arguments? DCL2. How can I redefine control keys in DCL? DCL3. How can I clear the screen in DCL? DCL4. How do I do a REPLY/LOG in a batch stream? DCL5. How do I generate a random number in DCL? DCL6. What does the MCR command do? DCL7. How do I change the OpenVMS system prompt? DCL8. Can I do DECnet task-to-task communication with DCL? File System and RMS ======================================== FILE1. How can I undelete a file? FILE2. Why does SHOW QUOTA give a different answer than DIR/SIZE? FILE3. How do I make sure that my data is safely written to disk? FILE4. What are the limits on file specifications and directories? FILE5. What is the largest disk volume size OpenVMS can access? FILE6. What is the maximum file size, and the RMS record size limit? FILE7. How do I write recordable CD media (CD-R) on OpenVMS? FILE8. What I/O transfer size limits exist in OpenVMS? Programming ======================================== PROG1. How do I call from ? PROG2. How do I get the arguments from the command line? PROG3. How do I get a formatted error message in a variable? PROG4. How do I link against SYS$SYSTEM:SYS.STB on an Alpha system? PROG5. How do I do a SET DEFAULT from inside a program? PROG6. How do I create a shareable image transfer vector on an Alpha system? PROG7. How do I turn my Fortran COMMON into a shareable image on Alpha? PROG8. How do I convert between IEEE and VAX floating data? PROG9. How do I get the argument count in a Fortran routine? PROG10. How do I get a unique system ID for licensing purposes? PROG11. What is an executable, shareable, system or UWSS image? PROG12. How do I do a file copy from a program? PROG13. What is a descriptor? PROG14. How many bytes are in a disk block? PROG15. How many bytes are in a memory page? PROG16. How do I create a process under another username? PROG17. Why do lib$spawn, lib$set_symbol fail in detached processes? PROG18. Where can I obtain Bliss, and the libraries and supporting files? PROG19. How can I open a file for shared access? ------------------------------------------------------------ UTIL1. How do I play an audio CD on my workstation? If you've installed the DECwindows examples, you'll find DECW$CDPLAYER.C, .DAT, .EXE, .UIL, and .UID. Copy the .UID and .DAT files to DECW$USER_DEFAULTS: (typically SYS$LOGIN:), define the logical name DECW$CD_PLAYER to be the device name of your CD-ROM drive (eg. DKA400:), give yourself PHY_IO and DIAGNOSE privileges, and run the .EXE. You can also install the image with these privileges. See the source for additional details - note that the comments regarding the need for SYSGEN CONNECT are no longer applicable (at least as of VMS V5.5-2). There's also SYS$EXAMPLES:CDROM_AUDIO.C and .EXE, a non-Motif program. ------------------------------------------------------------ UTIL2. How do I access a MS-DOS floppy disk from OpenVMS? The Compaq Advanced Server (formerly known as PATHWORKS) for OpenVMS product includes an unsupported and undocumented utility called PCDISK, and this tool can read and write various MS-DOS format diskettes. ProGIS in Germany sells a product called VMove which supports DOS files on many different device types. For more information, send mail to info@progis.rmi.de. Engineering Software has a product called VAKSAT which will read, write, and erase files on DOS diskettes. Available for both VAX and Alpha. Contact ed@cityscape.co.uk for more information. MadGoat PC Exchange (PCX) is a utility for copying files to and from MS-DOS format diskettes under VMS, using an RX23 (3.5"), RX26 (3.5"), or RX33 (5.25") diskette drive. For 3.5" diskettes, high-density disks can be read or written; double-density disks are read-only. Only high-density disks are supported on the RX33. http://www.madgoat.com/ ------------------------------------------------------------ UTIL3. How do I play sound files on an AlphaStation? DECsound doesn't work The new AlphaStation systems use a different sound board (Microsoft Sound System) than the earlier DEC 3000 AXP systems, and DECsound, as supplied by DECwindows Motif, doesn't support this board. Compaq offers an optional product, Multimedia Services for OpenVMS: http://www.digital.com/info/SP6424/ which provides a replacement DECsound for this card as well as many other features (an AVI and MPEG player, video capture support, etc.) Ensoniq sound support is expected to be available in January 2000. ------------------------------------------------------------ DCL1. How do I run a program with arguments? The RUN command does not accept arguments. To pass arguments to a program, you must use what is called a "foreign command". For example: $ uudecode :== $disk:[dir]uudecode.exe $ uudecode filespec The leading $ in the symbol definition is what makes it a foreign command. If the device and directory is omitted, SYS$SYSTEM: is assumed. Under OpenVMS V6.2 and later, DCL supports automatic foreign command definition via the logical name DCL$PATH:. An example of a definition of this logical name is: $ DEFINE DCL$PATH SYS$DISK:[],ddcu:[mytooldir],SYS$SYSTEM: DCL will first look for a command in the DCL command table, and if no match is found and if DCL$PATH is defined, it will then look for command procedures and executable images with filenames matching the command specified, in the directories specified via DCL$PATH. The first match found is invoked, and under OpenVMS, the DCL$PATH support will cause a command procedure to be activated in preference to an executable image. For more information on foreign commands or on automatic foreign command support, see the OpenVMS User's Manual. See also question PROG2. If you want to create a detached process that takes arguments from a command line, it must be run under the control of a command line interpreter (CLI) (typically DCL). This is done by placing the command line in a file, specifying SYS$SYSTEM:LOGINOUT.EXE as the image to run and the command file as the input. For example: $ OPEN/WRITE CMD TEMP_INPUT.COM $ WRITE CMD "$ MYCOMMAND arguments" $ CLOSE CMD $ RUN/DETACHED SYS$SYSTEM:LOGINOUT /INPUT=TEMP_INPUT.COM Various OpenVMS library calls (such as lib$spawn(), cli$dcl_parse(), and the C library system() call) require access to a command line interpreter such as DCL to perform requested actions, and will not operate if a CLI is not available. When a CLI is not available, these calls typically return the error status SS$_NOCLI. And as mentioned above, invoke the image LOGINOUT to cause a CLI (such as DCL) to be mapped into and made available in the context of the target process. [Stephen Hoffman] ------------------------------------------------------------ DCL2. How can I redefine control keys in DCL? The DCL DEFINE/KEY command allows you to define function and keypad keys, but not control keys. Also, keys you define with DEFINE/KEY are not recognized inside applications. Many applications which use the SMG$ routines for input have a similar DEFINE/KEY feature. The terminal driver line-editing control keys, including the use of DEL for delete, are not modifiable. ------------------------------------------------------------ DCL3. How can I clear the screen in DCL? The simplest way is the TYPE/PAGE NLA0: command. You can set up a symbol to clear the screen in your LOGIN.COM: $ CLS :== TYPE/PAGE NLA0: ------------------------------------------------------------ DCL4. How do I do a REPLY/LOG in a batch stream? Your terminal must be enabled as an operator terminal before doing the REPLY/LOG, but a batch stream doesn't have a terminal. To make this work, use the following sequence to enable the OPA0: console as the operator terminal; then the REPLY/LOG will be accepted: $ DEFINE/USER SYS$COMMAND _OPA0: $ REPLY/LOG $ DEFINE/USER SYS$COMMAND _OPA0: $ REPLY/ENABLE To disable the system console terminal (OPA0:) as an operator terminal, use the following command: $ DEFINE/USER SYS$COMMAND _OPA0: $ REPLY/DISABLE Also see SYLOGICALS.COM (and SYLOGICALS.TEMPLATE) for information on configuring the behaviour of OPCOM, including the use of the system console (OPA0:) as an operator and the specific contents and behaviour of the system operator log file OPERATOR.LOG. [Arne Vajhøj] [Stephen Hoffman] ------------------------------------------------------------ DCL5. How do I generate a random number in DCL? Here's my random number generator for inclusion into the OVMS FAQ; just do a GOSUB RAND and the global symbol RANDOM will contain a randomly generated number. The user/programmer can feed the generator a ceiling value (__CEIL) or a new seed (__SEED). $! RAND - returns a positive random number ("RANDOM") between 0 and $! __CEIL - 1. $ RAND: $ $ IF F$TYPE(__SEED) .EQS. "" $ THEN $ ! seed the random number generator, ... $ __NOW = F$CVTIME() $ __HOUR = 'F$EXTRACT(11,2,__NOW)' $ __MINUTE = 'F$EXTRACT(14,2,__NOW)' $ __SECOND = 'F$EXTRACT(17,2,__NOW)' $ __TICK = 'F$EXTRACT(20,2,__NOW)' $ $ __SEED == __TICK + (100 * __SECOND) + (6000 * __MINUTE) + - (360000 * __HOUR) $ ! the generator tends to do better with a large, odd seed, ... $ __SEED == (__SEED .OR. 1) $ ! clean up, ... $ DELETEX/SYMBOL __NOW $ DELETEX/SYMBOL __HOUR $ DELETEX/SYMBOL __MINUTE $ DELETEX/SYMBOL __SECOND $ DELETEX/SYMBOL __TICK $ ENDIF $ $ IF F$TYPE(__CEIL) .EQS. "" THEN __CEIL = %X3FFFFFFF $ $ __SEED == __SEED * 69069 + 1 $ $ RANDOM == (__SEED.AND.%X3FFFFFFF)/(%X40000000/__CEIL) $ $ RETURN [sharris@sdsdmvax.fb3.noaa.gov] ------------------------------------------------------------ DCL6. What does the MCR command do? The MCR command runs the specified image, with a default filespec of SYS$SYSTEM:.EXE, and passes any (optional) command line arguments in the same manner as a foreign command. In other words: $ MCR FOO BAR is equivalent to: $ FOO :== $FOO $ FOO BAR It derives from the RSX operating system from which VMS evolved and is still often used as a shortcut for activating images. The MCR command is different from the MCR command line interpreter, which is provided as part of the optional VAX-11 RSX product that provides RSX emulation under VMS. ------------------------------------------------------------ DCL7. How do I change the OpenVMS system prompt? You can use the SET PROMPT command for this purpose. SET PROMPT sets the DCL prompt to the specified string. When you want to display variable information, you will need to establish a tie-in that provides the information to the SET PROMPT command as required. If you wish to display the default directory for instance, you will have to establish a tie between the SET DEFAULT command and the SET PROMPT commands, as there is no direct way to get the default directory as the DCL prompt. You can easily acquire or create a set of DCL command procedures that perform the SET DEFAULT and SET PROMPT for you. These DCL command procedures often use a command such as: $ set prompt='f$env("default")' More advanced users could implement a system service or other intercept, and use these tools to intercept the directory change and reset the prompt accordingly. (This approach likely involves some kernel-mode programming, and requires write access to various undocumented OpenVMS data structures.) There are related tools available from various sources, including the following web sites: o ftp://ftp.hhs.dk/pub/vms/setpmt/ o ftp://ftp.tmesis.com/sys_service_hook.src o James F. Duff has also made available a Macro32 tool known as TIME_PROMPT, a tool that sets the prompt to the current system time. o Many folks have contributed DCL procedures to perform this task. Visit the newsgroup archives for information and examples. Information in this section has been acquired from various postings that have discussed this topic in the comp.os.vms newsgroup in the past, and examples from Arne Vajhoej, Brian Schenkenberger, James Duff, and others. [Stephen Hoffman] ------------------------------------------------------------ DCL8. Can I do DECnet task-to-task communication with DCL? Yes, you can do this with DCL. The OpenVMS DECnet documentation shows various simple examples using the task object and the TYPE command to trigger the execution of a DCL command procedure on a remote node. A slightly more advanced example of using DCL for DECnet task-to-task -- a procedure that acts as both the client and as the server as appropriate, and that uses a basic form of half-duplex communications -- is included: $! x.com $ $! This procedure must be in the user's login directory. $! Requires a self-referential (not reverential :-) proxy: $! UAF> add/prox :: /default $! Author: Stephen Hoffman, OpenVMS Engineering, Compaq $ $ goto 'f$mode()' $INTERACTIVE: $ open/read/write chan 0::"task=x" $ write chan "Hello" $ read chan parameter $ close chan $ write sys$output parameter $ exit $BATCH: $OTHER: $NETWORK: $ open/read/write chan sys$net $ read chan parameter $ write chan "''parameter' yourself!" $ close chan $ exit An example of a run of the above procedure: $ @x Hello yourself! $ DCL does not include support asynchronous I/O, thus a predetermined protocol or a predetermined "turn-around" command sequence must be implemented in order to avoid protocol deadlocks -- cases where both tasks are trying to write or both tasks are trying to read. The task that is writing messages to the network must write (or write and read) a predetermined sequence of messages, or it must write a message that tells the reader that it can now start writing messages. (This is the essence of a basic half-duplex network protocol scheme.) [Stephen Hoffman] ------------------------------------------------------------ FILE1. How can I undelete a file? OpenVMS doesn't have an "undelete" function. However, if you are quick to write-protect the disk (or if you can guarantee that no new files get created or existing files extended), your data is still on the disk and it may be possible to retrieve it. The FLORIAN tool available from the WKU Fileserver claims to be able to do this (see question SOFT1.) Other alternatives here include the DFU tool, available on the OpenVMS Freeware CD-ROM distribution. If you are setting up a user environment for yourself or for others, it is quite easy to use DCL to intercept the DELETE command, using a symbol: $ DEL*ETE :== @SYS$LOGIN:MYDELETE.COM The DELETE symbol will cause the procedure to be invoked whenever the user enters the DELETE command, and it can copy the file(s) to a "trashcan" subdirectory before issuing a "real" DELETE on the files. Other procedures can retrieve the file(s) from the "trashcan" subdirectory, and can (and should) clean out the "trashcan" as appropriate. (Realize that this DELETE symbol can interfere with DELETE/GLOBAL and other similar DCL commands.) [Stephen Hoffman] ------------------------------------------------------------ FILE2. Why does SHOW QUOTA give a different answer than DIR/SIZE? DIR/SIZE doesn't take into account the size of file headers which are charged to your quota. Also, unless you use DIR/SIZE:ALL, you'll see only the "used" size of the file, not the allocated size which is what gets charged against your quota. Also, you may have files in other directories. [Steve Lionel] $ DIR/SIZ=ALL/GRAND [username...] Grand total of D1 directories, F1 files, B1/B2 blocks. $ DIR/SIZ=ALL/GRAND [-]username.DIR Grand total of 1 directory, 1 file, B3/B4 blocks. $ SHOW QUOTA User [username] has B5 blocks used, B6 available, of B7 authorized and permitted overdraft of B8 blocks on disk If the user has no files in other directories and all file-headers are only 1 block, then the following should apply: B5=B2+B4+F1+1 If the diskquota is out of synch, then the system-manager can make a rebuild. [Arne Vajhøj] Also be aware that the DIRECTORY/SIZE command can report larger values than might otherwise be expected when used to evaluate files and/or directories that are alias links -- such as the system roots on OpenVMS system disks -- as the command reports a total that is cumulative over all of the files and directories examined, without regard for which ones might be alias entries and which are not. (In other words, a DIRECTORY/SIZE of an entire OpenVMS system disk will report a disk useage value larger than the (usually more accurate) value reported by the SHOW DEVICE command. This as a result of the alias entries linking each SYS$SYSDEVICE:[SYSCOMMON]SYS*.DIR directory file and the SYS$SYSDEVICE:[000000]VMS$COMMON.DIR file together.) ------------------------------------------------------------ FILE3. How do I make sure that my data is safely written to disk? If your application must absolutely guarantee that data is available, no matter what, there's really no substitute for RMS Journalling. However, you can achieve a good degree of data integrity by issuing a SYS$FLUSH RMS call at appropriate times (if you're using RMS, that is.) If you're using a high-level language's I/O system, check that language's documentation to see if you can access the RMS control blocks for the open file. In C you can use fflush followed by fsync. Note that fsync, which was undocumented for VAX C but is documented for DEC C, takes a file descriptor as an argument, not a *FILE. ------------------------------------------------------------ FILE4. What are the limits on file specifications and directories? A file specification has an aggregate maximum size of 255 characters at present. The node and device specification may be up to 255 characters each - file name and file types may be up to 39 characters each. File versions are from 1 through 32767, though 0 (latest version), -0 (oldest version) and -n (n'th previous version) can be used in most contexts. A file specification may not have more than 8 directories and subdirectories - while it is possible to create subdirectories of greater depth, accessing them is problematic in most cases and this should be avoided. Application developers should use OpenVMS-supplied routines for parsing file specifications - this ensures that changes in what is allowable will not tend to break your application. Consider that various parts of the file specification may contain quoted strings with embedded spaces and other punctuation! Some routines of interest are SYS$FILESCAN, SYS$PARSE and LIB$TRIM_FILESPEC. For further information, see the OpenVMS Guide to File Applications. ------------------------------------------------------------ FILE5. What is the largest disk volume size OpenVMS can access? One Terabyte (2**31 blocks of 2**9 bytes). Prior to the release of V6.0, the OpenVMS file system was limited to disk volumes of 8.5 GB (2**24 blocks) or less. On some systems, there are restrictions in the console program that limit the size of the OpenVMS system disk. Note that data disks are not affected by console program limits. For example, all members of the VAXstation 3100 series are limited to a system disk to 1.073 GB or less due to the console, though larger data disks are possible. Some SCSI disks with capacities larger than 8.6 gigabytes (GB) will require the use of an OpenVMS ECO kit (eg: ALPSCSI04_062 or later) for new SCSI device drivers. Failure to use this ECO can cause "rounding errors" on the SCSI disk device capacity -- OpenVMS will not use nor display the full capacity of the drive -- and "%sysinit-e-error mounting system device status equals 000008C4" (8C4 -> "%SYSTEM-?-FILESTRUCT, unsupported file structure level") errors during bootstrap. (One workaround for the bootstrap when the bitmap is located far into the disk is the use of INIT/INDEX=BEGIN.) The problem here involves the particular extensions and fields used for larger capacity disks within the SCSI specifications and within the various intepretations of same. [Stephen Hoffman] For IDE disk drives: o Versions of DQDRIVER *BEFORE* X-15 topped out at 8.455 GB. Fixed drivers (>="X-15") were shipped in: OpenVMS Alpha V7.2-1, and later V7.2 UPDATE V1.0 ECO, and later V7.1-2 UPDATE V1.0 ECO, and later V7.1-2 UPDATE V3.0 ECO, and later o The newer DQDRIVER driver operates to disks up to 33 GB without (known) problems, and effectively works with rather larger disks (up to circa 137 GB?) but is known to report an incorrect number of "cylinders" with disks above 33 GB. Be aware that a known restriction in certain older versions of the Alpha SRM Console prevents booting most IDE drives larger than 8.455 GB, depending on exactly where the various files are located on the volume. Updated SRM consoles for systems with SRM and IDE drive support are (will be) available. (OpenVMS Engineering has successfully bootstrapped 20GB IDE disks using the appropriate SRM console version.) NOTE: All IDE-related disk sizes listed in this section are stated in units of "disk (base 10) gigabytes" (1GB = 10^9 bytes) and NOT in units of "software (base 2) gigabytes" (1GB = 2^30 (1073741824.) bytes. [Atlant Schmidt] ------------------------------------------------------------ FILE6. What is the maximum file size, and the RMS record size limit? RMS can store individual files of a size up to the maximum supported volume size. Under OpenVMS V6.0 and later, the volume size and the RMS maximum file size limit is 2**31 * 512 bytes -- one terabyte (1 TB). The RMS formats -- sequential, relative, and indexed -- are limited by the one terabyte maximum volume size. RMS relative files are further limited to a number of records that will fit in 32 bits -- 4 billion records. Sequential and indexed formats do not have a record limit. Also see PROG14. [Stephen Hoffman] ------------------------------------------------------------ FILE7. How do I write recordable CD media (CD-R) on OpenVMS? Creation of CD-ROMs using recordable CD media (CD-R) under OpenVMS typically involves one of two approaches: the use of the optional CD-R (`Scribe') capabilities available for the InfoServer or other "offline" hardware packages, or the use of a host-based package such as the CDWRITE13_VMS utility, an OpenVMS port of a Linux tool. OpenVMS has no integrated support for recording CD-R media. OpenVMS can read both ODS2 and ISO9960 format CD-ROMs. InfoServer hardware configurations are no longer availble from Compaq, but may potentially be acquired through other means. The CDWRITE13_VMS package is one example of a host-based package that can be used to create CD-R media. The contact for CDWRITE13_VMS is Dr. Eberhard Heuser-Hofmann. One website that discusses this package is located at: http://www.geocities.com/SiliconValley/Lakes/9999/vmscdwri.html Also see the newest linux-cdwrite package, XCDROAST. Additional information is available via David J. Dachtera at: http://home.earthlink.net/~djesys/vms/cdrom.html Also see: http://www.cd-info.com/CDIC/Technology/CD-R/vms.html http://www.faqs.org/faqs/cdrom/cd-recordable/part1/preamble.html [Stephen Hoffman] ------------------------------------------------------------ FILE8. What I/O transfer size limits exist in OpenVMS? The maximum transfer size is an attribute of the particular I/O device, controller and driver combination; there is no inherent limit imposed by OpenVMS (other than the fact that, today, byte counts and LBNs are generally limited to 32 bits). The maximum size of a device I/O request is limited by the value in UCB$L_MAXBCNT, which is set by the device driver based on various factors. (Also check the setting of the MAXBUF system parameter for buffered I/O transfers, and check the process quotas.) Currently, SCSI drivers limit I/O transfers to FE00(16) bytes, 65024 bytes (decimal). The reasons for this transfer size limitation are largely historical. Similarly, DSSI devices are limited to the same value, this for hardware-specific reasons. Transfers to HSC and HSJ device controllers via the CI are limited to 1,048,576 bytes. Client MSCP-served devices are limited to 65535 bytes -- to help ensure that the I/O fragmentation processing happens on the client and not on the server system. Parts of the OpenVMS I/O subsystem are optimized for data transfers less than 64KB, because (obviously) most I/O operations are (substantially) less than that. OpenVMS can handle larger transfers, if the driver and the device can handle it. Also see FILE4, FILE5 [John Croll] ------------------------------------------------------------ PROG1. How do I call from ? Most OpenVMS system services and RTL routines pass string arguments by descriptor. Languages which support native string data types create descriptors automatically; those which do not (eg., C) require that you set them up explicitly. [eric@tardis.HQ.ileaf.com] There is a lot of information available on how to call system services and Run-Time Library routines, including examples in numerous languages. The best references are: Your language's User Manual OpenVMS Programming Environment Manual OpenVMS Programming Concepts Manual OpenVMS Programming Interfaces: Calling a System Routine OpenVMS Calling Standard In addition, if you are a subscriber to the Compaq Software Information Network (available to those with a software support contract), the support database contains hundreds of worked examples of calling system services and RTL routines, including the one that seems to trip up almost everyone, SMG$CREATE_MENU. [Steve Lionel] Arne Vajhøj has put together a collection of OpenVMS example programs. It can be found at: ftp://ftp.hhs.dk/pub/vms/ [Arne Vajhøj] Additional information and examples for OpenVMS are available via: http://www.openvms.digital.com/wizard/ http://www.openvms.digital.com/freeware/ [Stephen Hoffman] ------------------------------------------------------------ PROG2. How do I get the arguments from the command line? If you're writing a program and want to accept arguments from a foreign command, you can use LIB$GET_FOREIGN to get the command line and parse it yourself, or if you're programming in C, use the normal argc/argv method. To write an application which uses the normal DCL verb/qualifier/parameter syntax for invocation, see the description of the CLI$ routines in the OpenVMS Callable Utility Routines Reference Manual. It is possible to write an application which can be used both ways; if a DCL verb isn't used to invoke the image, the application parses the command line itself. One way to do this is to call CLI$GET_VALUE for a required parameter. If it is not present (or you get an error), call LIB$GET_FOREIGN to get the command line and do the manual parse. See also question DCL1. ------------------------------------------------------------ PROG3. How do I get a formatted error message in a variable? Use the SYS$PUTMSG system service with an action routine that stores the message line(s) in the variable of your choice. Be sure the action routine returns a "false" (low bit clear) function value so that SYS$PUTMSG doesn't then try to display the message (unless you want it to.) See the description of $PUTMSG in the System Services Reference Manual for an example of using an action routine. ------------------------------------------------------------ PROG4. How do I link against SYS$SYSTEM:SYS.STB on an Alpha system? LINK/SYSEXE is the OpenVMS Alpha equivalent of linking against SYS.STB. ------------------------------------------------------------ PROG5. How do I do a SET DEFAULT from inside a program? The problem is that SYS$SETDDIR only changes the default directory - NOT the default disk. The default disk is determined by the logical SYS$DISK. If you want to change the default disk within a program, then call LIB$SET_LOGICAL to change the logical SYS$DISK. You will need to call both LIB$SET_LOGICAL and SYS$SETDDIR to change both default disk and the default directory! [Arne Vajhøj] ------------------------------------------------------------ PROG6. How do I create a shareable image transfer vector on an Alpha system? This is something that was greatly simplified for OpenVMS Alpha. You don't need to create a separate transfer vector module; just use the SYMBOL_VECTOR statement in a linker options file. For example, if your shareable image has two routines named FOO and BAR, the linker options file should contain the following line: SYMBOL_VECTOR=(FOO=PROCEDURE, BAR=PROCEDURE) The Linker manual has more details on this. ------------------------------------------------------------ PROG7. How do I turn my Fortran COMMON into a shareable image on Alpha? You need to add SYMBOL_VECTOR=(=PSECT) to your options file. On OpenVMS VAX all OVR/REL/GBL psects were automatically exported into the shareable image's Global Symbol Table. On OpenVMS Alpha you have to tell the linker that you want this done by means of the PSECT keyword in the SYMBOL_VECTOR options file statement. This has several advantages over OpenVMS VAX. First, you don't have to worry about the address of the psect when you try to create a new, upwardly compatible version of the shareable image. Second, you can control which psects, if any, are made visible outside the shareable image. By default, COMMON PSECTs in DEC Fortran for OpenVMS Alpha (as well as most other OpenVMS Alpha compilers) are NOSHR. On VAX, the default was SHR which required you to change the attribute to NOSHR if you wanted your COMMON to be in a shareable image but not write-shared by all processes on the system. If you do want write-sharing, use: CDEC$ PSECT common-name=SHR in the Fortran source code (the CDEC$ must be begin in column 1) or a linker options file PSECT_ATTR statement to set the COMMON PSECT attribute to SHR. For further information, see the Linker manual. ------------------------------------------------------------ PROG8. How do I convert between IEEE and VAX floating data? In OpenVMS V6.1 there is a routine CVT$CONVERT_FLOAT, documented in the LIB$ Run-Time Library Reference Manual, which can perform conversions between any two of the following floating datatypes: VAX (F,D,G,H), little-endian IEEE (single, double, quad), big-endian IEEE (single, double, quad), CRAY and IBM System\370. DEC Fortran (all platforms) has a feature which will perform automatic conversion of unformatted data during input or output. See the DEC Fortran documentation for information on "non-native data in I/O" and the CONVERT= OPEN statement keyword. For further floating-point related information, see: ftp://ftp.hhs.dk/pub/vms/collection/ieee.zip ------------------------------------------------------------ PROG9. How do I get the argument count in a Fortran routine? On VAX, many programmers would use a MACRO routine which accessed the AP register of the caller to get the address of the argument list and hence the argument count. This was not guaranteed to work on VAX, but usually did. However, it doesn't work at all on OpenVMS Alpha, as there is no AP register. On Alpha systems, you must use a language's built-in function to retrieve the argument count, if any. In Fortran this is IARGCOUNT, which is also available in DEC Fortran on OpenVMS VAX. Note that omitting arguments to Fortran routines is non-standard and is unsupported. It will work in many cases - read the DEC Fortran release notes for additional information. ------------------------------------------------------------ PROG10. How do I get a unique system ID for licensing purposes? Many software developers desire to use a unique hardware ID to "lock" a given copy of their product to a specific system. Most VAX and Alpha systems do not have a unique hardware-set "system ID" that can be used for this purpose. Compaq does not use hardware IDs in its licensing methods and many users consider a hardware-based licensing scheme to be a negative attribute when considering software purchases. Compaq OpenVMS uses a software-based system called the License Management Facility (LMF). This provides for software keys (Product Authorization Keys or PAKS) which support capacity and user-based license checking. Compaq offers an LMF PAK Generator to CSA members -- see ALPHA4. However, if a hardware-based method is required, the most common method is based on an Ethernet adaptor hardware address. Sample source code for implementing this is available at: http://www.openvms.digital.com/wizard/ ------------------------------------------------------------ PROG11. What is an executable, shareable, system or UWSS image? Executable code in OpenVMS typically resides in an image -- an image is a file -- the file extension is typically .EXE -- that contains this code. Common types of images include executable images, shareable images, system images, and protected (UWSS) images. Executable images are programs that can be directly executed. These images can grant enhanced privileges, with an INSTALL of the image with /PRIVILEGE, or can grant enhanced access with the specification of a subsystem identifier on the ACL associated with the image. Shareable images contain code executed indirectly, these images are referenced from executable images and/or from other shareable images. These images can not grant enhanced privileges, even with the use of INSTALL with /PRIVILEGE or a subsystem identifier. These shareable images can be dynamically activated (a LINK that occurs at run-time) via the LIB$FIND_IMAGE_SYMBOL run-time library (RTL) routine. (See `protected images' for information on `privileged shareable images'.) System images are intended to run directly on the VAX or Alpha hardware -- these are normally used for the kernel code that comprises an operating system. Protected images -- also refered to as User-Written System Services (UWSS), or as privileged shareable images -- are similiar in some ways to a standard shareable images, but these images include a `change mode' handler, and execute in an `inner' processor mode (privileged mode; executive or kernel), and code executing in inner modes has implicit SETPRV privilege. Must be INSTALLed with /PROTECT. Note that inner-mode code has restrictions around calling library routines, around calling various system services, and around calling code located in other protected or shareable images. Loadable images and device drivers are images that can be used to add code into the OpenVMS kernel. Pseudo-device drivers are a particularly convenient way to add executable code, with associated driver-defined data structures, into the kernel. The pseudo-device driver includes the UCB and DDB data structures, and a calling interface with support for both privileged and unprivileged access to the driver code via sys$qio[w] calls. A cookbook approach to creating OpenVMS shareable images is available at the (admittedly overly long) URL: http://www.openvms.digital.com/wizard/ [Stephen Hoffman] ------------------------------------------------------------ PROG12. How do I do a file copy from a program? There are several options available for copying files from within a program. Obvious choices include using lib$spawn(), system(), sys$sndjbc() or sys$creprc() to invoke a DCL COPY command. Other common alternatives include using the callable convert routines and the BACKUP application programming interface (V7.1 and later). [Stephen Hoffman] ------------------------------------------------------------ PROG13. What is a descriptor? A descriptor is a data structure that describes a string or an array. Each descriptor contains information that describes the type of the data being referenced, the size of the data, and the address of the data. It also includes a description of the storage used for the data, typically static or dynamic. Descriptors are passed by reference. The following are examples of creating and using descriptors in C: #include #include #include int RetStat; char TxtBuf[TXTSIZ] struct dsc$descriptor StaticDsc = { 0, DSC$K_DTYPE_T, DSC$K_CLASS_S, NULL }; struct dsc$descriptor DynDsc = { 0, DSC$K_DTYPE_T, DSC$K_CLASS_D, NULL }; int DynDscLen = 255; $DESCRIPTOR( ConstDsc, "This is a string" ); /* finish setting up a static descriptor */ StaticDsc.dsc$w_length = TXTSIZ; StaticDsc.dsc$a_pointer = (void *) TxtBuf; /* finish setting up a dynamic descriptor */ RetStat = lib$sget1_dd( &DynDscLen, &DynDsc ); if ( !$VMS_STATUS_SUCCESS( RetStat ) ) return RetStat; /* release the dynamic storage */ RetStat = lib$sfree1_dd( &DynDsc ); if (!$VMS_STATUS_SUCCESS( RetStat )) return RetStat; Static descriptors reference storage entirely under application program control, and the contents of the descriptor data structure can be modified as required (by the application). OpenVMS routines do not modify the contents of a static descriptor, nor do they alter the address or length values stored in the static descriptor. (The term "static" refers to the descriptor data structure, and not necessarily to the storage referenced by the descriptor.) Dynamic descriptors reference storage under the control of the run-time library, and the contents of a dynamic descriptor data structure -- once initialized -- can only be modified under control of run-time library routines. The dynamic storage referenced by the dynamic descriptor is allocated and maintained by the run-time library routines. Various OpenVMS routines do alter the contents of the descriptor data structure, changing the value for the amount and the address of the storage associated with the dynamic descriptor, as required. Routines can obviously access and alter the contents of the storage referenced by the descriptor. OpenVMS languages that include support for strings or arrays are expected to use descriptors for the particular structure. Most OpenVMS languages, such as Fortran and BASIC, use descriptors entirely transparently. Some, like DEC C, require the programmer to explicitly create and maintain the descriptor. For further information on string descriptors, see the _OpenVMS Programming Concepts_ manual, part of the OpenVMS documentation set. [Stephen Hoffman] ------------------------------------------------------------ PROG14. How many bytes are in a disk block? A disk block is the minimum unit of disk storage allocation in OpenVMS. Under OpenVMS VAX and OpenVMS Alpha, the disk volume block size is consistent, with each block containing 512 bytes. The minimum disk allocation granularity actually permissible (in the ODS-2 and ODS-5 volume structures commonly used on OpenVMS) is determined on a per-volume basis, and is typically based on a combination of the total number blocks on the disk volume and the total size of the volume storage bitmap. The allocation granularity is known as the volume cluster factor -- the cluster factor is the number of blocks in a disk cluster, and it is the smallest number of blocks that can be allocated on a particular disk volume. Prior to OpenVMS V7.2, the maximum permissible size of the bitmap requires larger cluster factors as volume sizes increase. Starting with V7.2, the bitmap can be larger, and cluster factors as small as one block can be used. The number of bytes in a file can be determined by multiplying the number of blocks allocated for the file times the number of bytes in a block. For sequential files (only), the FFB (XAB$W_FFB, in the File Header XAB) value can be used to find out how much of the last (XAB$L_EBK) block is used. FFB and EBK are meaningful only for sequential files, and only in a limited context -- partial block allocations are not permitted. For other file formats, the EOF marker is not meaningful. Disk allocations always occur only in units of the cluster factors, which can be from one block up to (potentially) clusters of eighteen blocks or more, depending on the volume cluster factor. OpenVMS assumes that the device driver and the underlying storage device will present the file system with addressable units of storage of 512 bytes in size, or the appearance of same. Various third-party CD-ROM devices, for instance, support only 2048 byte blocks, and such devices are incompatible with the standard OpenVMS device drivers. To determine the number of bytes required for a file from DCL, one option uses the f$file_attributes item EOF, multiplied by the size of a block in bytes (512). This does not account for the unused space in the last block of a sequential file, but it also does not have to differentiate sequential files from other files. [Stephen Hoffman] ------------------------------------------------------------ PROG15. How many bytes are in a memory page? A memory page is the minimum unit of memory allocation in OpenVMS. With OpenVMS VAX, the memory page size matches the disk block size: it is always 512 bytes. With OpenVMS Alpha, the memory page size is variable, and it can range from 8192 bytes (8 kilobytes) up to 64 kilobytes. The current system page size can be determined using the sys$getsyi or f$getsyi PAGE_SIZE item. Programs with hardcoded constants for the memory page size (or page alignment) should always assume a page size of 64 kilobytes. On OpenVMS Alpha, a 512 byte area of memory -- equivilent in size to an OpenVMS VAX memory page -- is refered to as a pagelet. [Stephen Hoffman] ------------------------------------------------------------ PROG16. How do I create a process under another username? Many server processes can operate within the context of the target user using privileges, using calls such as sys$chkpro and (more commonly in this context) sys$check_access as needed to determine if access would be permitted for the specified user within the current security model. With OpenVMS V6.2 and later, the persona system services (SYS$PERSONA_*) can be used to assume the persona of the specified user -- these allow the server to operate as the specified user, in a controlled fashion. The persona services can be used as a "wrapper" around a sys$creprc process creation call, as well -- this will create a seperate process entirely under the assumed persona. Information on the persona system services is included in the OpenVMS V6.2 new features documentation, and in the OpenVMS V7.1 and later system services documentation. These system services exist and are supported in OpenVMS V6.2 and later releases. Typical mechanisms for creating a process under another username include: o personna services around a sys$creprc call. See above. o via DECnet task-to-task, using explicit specification of username and password, or using a DECnet proxy. This creates a network-mode job under the target user. The network-mode job might do little more than a RUN/DETACH of an image passed in via task-to-task -- task-to-task communications are fully available using strictly DCL-to-DCL processing, or using a compiled language and DCL, etc.) o SUBMIT/USER, or the username argument on the sys$sndjbc call. This creates a batch-mode job under the specified username. The batch-mode job might do little more than a RUN/DETACH of an image passed in via a parameter. o the UIC argument on the sys$creprc call. This mimics the UIC of the target user, and is certainly not the prefered mechanism for this task. o Via pseudo-terminals... There are likely a few other mechanisms around... There are various tools available from DECUS and other sources that allow various forms of user impersonation, as well. These tools will require version-dependent kernel code and enhanced privileges for some of (or all of) their operations. [Stephen Hoffman] ------------------------------------------------------------ PROG17. Why do lib$spawn, lib$set_symbol fail in detached processes? The processing within run-time library (RTL) calls such as lib$attach, lib$disable_ctrl, lib$do_command, lib$enable_ctrl, lib$get_symbol, lib$run_program, lib$set_symbol, lib$set_logical, and lib$spawn, is dependent on and requires the presence of a command language interpreter (CLI), such as DCL. Without a CLI present in the current process, these calls will fail with a "NOCLI, no CLI present to perform function" error. Detached processes typically do not have a CLI present. In place of lib$spawn, sys$creprc can often be used. The context of the parent process (symbols and logical names) will not be propogated into the subprocess when sys$creprc is used, though when there is no CLI present in the process this (lack of) propogation is moot. To create a detached process with a CLI, you must specify LOGINOUT as the target image as discussed elsewhere in the FAQ, or only use these calls (and any other calls requiring a CLI) from images that are running in an "interactive", "batch", or "other" mode process. [Stephen Hoffman] ------------------------------------------------------------ PROG18. Where can I obtain Bliss, and the libraries and supporting files? The Bliss language compilers and documentation are available on the OpenVMS Freeware distributions. Bliss language source code that contains the following statement: LIBRARY 'SYS$LIBRARY:STARLET.L32'; or similar requires the presence of the Bliss libraries. These libraries are created on the target system using the Bliss require files, and are built using the following Bliss commands: STARLET.L32 contains the public interfaces to OpenVMS: $ BLISS /LIBRARY=SYS$COMMON:[SYSLIB]STARLET.L32 - SYS$LIBRARY:STARLET.REQ LIB.L32 contains both the public and private interfaces to OpenVMS: $ BLISS /LIBRARY=SYS$COMMON:[SYSLIB]LIB.L32 - SYS$LIBRARY:LIB.REQ+SYS$LIBRARY:STARLET.REQ The equivilent files for Bliss64 are created with: $ BLISS/A64/LIBRARY==SYS$COMMON:[SYSLIB]LIB.L64 - SYS$LIBRARY:LIB.R64+STARLET.REQ+STARLET.R64 $ BLISS/A64/LIBRARY==SYS$COMMON:[SYSLIB]STARLET.L64 - SYS$LIBRARY:STARLET.R64 Some Bliss code may also require the OpenVMS VAX architecture flags. The following is the equivilent of the Alpha ARCH_DEFS.BLI module: ! ! This is the OpenVMS VAX version of ARCH_DEFS.BLI, and ! contains the architectural definitions for conditionally ! compiling OpenVMS Bliss sources for use on VAX systems. ! MACRO VAXPAGE = 1%; MACRO BIGPAGE = 0%; MACRO VAX = ! = 1 if compiled BLISS/VAX %BLISS(BLISS32V)%; ! = 0 if not compiled BLISS/VAX MACRO EVAX = ! = 1 if compiled BLISS/E* ! ! A more appropriate definition can only be used with versions ! of the Bliss compilers that understand the 32E/64E flags. ! %BLISS(BLISS32E) OR %BLISS(BLISS64E)%; ! = 0 if compiled /VAX NOT %BLISS(BLISS32V)%; ! = 0 if compiled /VAX MACRO ADDRESSBITS = %BPADDR%; ! = 32 or 64 based on compiler used [Stephen Hoffman] ------------------------------------------------------------ PROG19. How can I open a file for shared access? When creating a file, it is often useful to allow other applications and utilities -- such as TYPE -- to share read access to the file. This permits you to examine the contents of a log file, for instance. A C source example that demonstrates how to do this is available in topic 2867 in the OpenVMS Ask The Wizard area: http://www.openvms.digital.com/wizard/ Depending on the environment, you may need to use C calls such as fsync and fflush, and -- in specific cases -- the setvbuf(_IONBF) call. [Stephen Hoffman] [End of Part 3/4] --------------------------- pure personal opinion --------------------------- Hoff (Stephen) Hoffman OpenVMS Engineering hoffman#xdelta.zko.dec.com