MOUNT (Utility)

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MOUNT is a utility in OpenVMS that is used to make a disk or a magnetic tape available for processing.


MOUNT  device-name[:][,...] [volume-label[,...]] [logical-name[:]]


On systems with volumes not connected to hierarchical storage controllers, use the ddcu: format. On systems with volumes connected to hierarchical storage controllers, use the node$ddcu: or allocation-class$ddcu:. Names in a volume set should be separated with commas or plus signs.


When mounting a volume, the volume label needs to be provided matching the volume used during the device initialization. Label can be omitted if the volume is mounted privately and /OVERRIDE=IDENTIFICATION is specified. OpenVMS requires disk volume labels to be unique in the first 12 characters within a given domain. For example, disks mounted by different members of the same group using the /GROUP qualifier must be unique.


Defines a 1- to 255-alphanumeric character string logical name to be associated with the volume. If you do not specify a logical name, the MOUNT command assigns the default logical name:

  • DISK$volume-label to individual disk drives
  • DISK$volume-set-name to the device on which the root volume of a disk volume set is mounted.

The table in which the logical name is created depends on whether the device is mounted private (Process), Group (Group), public (System), or clusterwide (Cluster).

Mount Status

Depending on access to the mounted volume, the volume's mount status can be:

  • System/public mount: the volume is mounted /SYSTEM, available to all users on the system. SYSNAM is required to mount volumes public.
  • Process/private mount: the volume is mounted without /SYSTEM, /CLUSTER or /GROUP, is marked MOUNTED ALLOCATED and only available to the user who mounted it.
  • Group mount: the volume is mounted /GROUP and allocated to users of the group. GRPNAM is required to mount volumes /GROUP.
  • Cluster mount: the volume is mounted /SYSTEM or /GROUP on all nodes in the cluster. /CLUSTER should be specified with either /SYSTEM or /GROUP; if it is neither, the use of /SYSTEM is assumed.
  • shareable: the volume is mounted /SHARE and is not allocated. If the device is mounted /NOSHARE (default), the device is allocated.

/WRITE (default) controls whether the volume can be written. To write-lock the volume, use /NOWRITE.

File System

Volumes that are not in the standard format used by OpenVMS (ODS-2 or ODS-5, or ANSI for magnetic tapes) should be mounted /FOREIGN. Target volumes for restoring image backups are also mounted /FOREIGN. To mount a volume currently in Files-11 format with the /FOREIGN qualifier, you must have VOLPRO.

For more information on foreign volumes, see Foreign Volume. The /FOREIGN qualifier is incompatible with the following qualifiers: /ACCESSED, /AUTOMATIC, /BIND, /CACHE, /[NO]CONFIRM, [NO]COPY, /EXTENSION, /HDR3, /INITIALIZE, /LABEL, /PROCESSOR, /QUOTA, /REBUILD, /SHADOW, /OVERRIDE=EXPIRATION, and /WINDOWS.

/MEDIA_FORMAT=CDROM mounts a volume assuming the media to be ISO 9660 (or High Sierra) formatted.

/PROCESSOR requests, for magnetic tapes and ODS-1 disks, that the MOUNT command associate an ancillary control process (ACP) to process the volume. The /PROCESSOR qualifier causes MOUNT to override the default manner in which ACPs are associated with devices. For Files-11 Structure Levels 2 and 5 disks, controls block cache allocation.

You must have the operator user privilege OPER to use the /PROCESSOR qualifier.

Keyword Description
UNIQUE Creates a new process to execute the default ancillary control process (ACP) image supporting the magnetic tape, Files-11 ODS-1, ISO 9660, or High Sierra formatted media being mounted. For Files-11 Structure Levels 2 and 5 disks, allocates a separate block cache.
SAME:device Uses an existing process that is executing the same ACP image supporting the magnetic tape, Files-11 ODS-1, ISO 9660, or High Sierra formatted media being mounted. For Files-11 Structure Levels 2 and 5 disks, takes the block cache allocation from the specified device.
filespec Creates a new process to execute the ACP image specified by the file specification (for example, a modified or a user-written ACP). You cannot use wildcard characters, or node and directory names in the file specification. To use this keyword, you need CMKRNL and OPER privileges.

/UCS_SEQUENCE supplies the escape sequence to select the coded graphic character set, a requirement when mounting an ISO 9660 volume for one of the Supplementary Volume Descriptors (SVDs).

/UNDEFINED_FAT=record-format:[record-attributes:][record-size] establishes default file attributes to be used for records on ISO 9660 media for which no record format has been specified.

Operator Assistance

/ASSIST directs the mount operation to allow operator or user intervention if the mount request fails. Mount /NOASSIST if there is no operator to prevent the system from waiting if a mount fails.

When you specify the /ASSIST qualifier, MOUNT notifies the user and certain classes of operators (DISK) if a failure occurs during the mount operation. If a failure occurs, the operator or user can either abort the operation or correct the error condition to allow the operation to continue. If no operator terminal is enabled to receive and respond to a mount assist request, a message is displayed informing the user of the situation. If a volume is placed in the requested drive, no additional operator response is necessary. If the mount request originates from a batch job and no operator terminal is enabled to receive messages, the mount is aborted.

/COMMENT=string specifies additional information to be included with the operator reqiest when the mount operation requires operator assistance. The value of this qualifier is output to the operator log file and the current SYS$OUTPUT.

/MESSAGE (default) causes mount request messages to be sent to your current SYS$OUTPUT device. If you specify /NOMESSAGE during an operator-assisted mount, messages are not output to SYS$OUTPUT; the operator sees them, however, provided an operator terminal is enabled.


/AUTOMATIC (default) determines whether MOUNT enables or disables automatic volume switching and labeling for magnetic tape or ISO 9660 CD-ROM.

/BLOCKSIZE=n specifies the default block size for magnetic tape volumes.

/CACHE=TAPE_DATA enables write caching if the tape controller supports write caching.

/DENSITY specifies the density at which a magnetic tape is to be written. See Tape Densities for details.

/HDR3 controls whether ANSI standard header label 3 is writte on a magnetic tape volume. By default, header label 3 is written. You can specify the /NOHDR3 qualifier to write magnetic tapes that are to be used on other systems that do not process HDR3 labels correctly.

/INITIALIZE=CONTINUATION specifies that any volume added to the magnetic tape volume set is initialized before you can write to the volume.

/LABEL indicates that the volume is in the standard format used by the OpenVMS operating system; that is, a magnetic tape volume is in the standard ANSI format, or a disk volume is in Files-11 format.

/MEDIA_FORMAT=[NO]COMPACTION enables and controls data compaction and data record blocking on tape drives that support data compaction.

/MULTI_VOLUME determines, for foreign or unlabeled magnetic tape volumes, whether you override MOUNT volume access checks.

/RECORDSIZE specifies the number of characters in each record of a magnetic tape volume.

Volume Characteristics

/ACCESSED: Specifies, for ODS-1 disk volumes, the approximate number of directories that will be in use concurrently on the volume.

/CACHE controls whether caching limits established at system generation time are disabled or overridden. Specify one of more of the following options separated by commas and enclose the list in parentheses:

Keyword Description
DATA (default) and NODATA Enable or disable Extended File Caching (XFC). To enable XFC caching, you must specify the DATA (this is the default value for /CACHE qualifier). To disable XFC, specify NODATA. Note that /NOCACHE is equivalent to /CACHE=NODATA.
EXTENT[=n] and NOEXTENT Enable or disable extent caching. To enable extent caching, you must have the OPER privilege and you must specify n, the number of entries in the extent cache. Note that NOEXTENT is equivalent to EXTENT=0; both disable extent caching.
FILE_ID[=n] and NOFILE_ID Enable or disable file identification caching. To enable file identification caching, you must have the OPER privilege and you must specify n, the number of entries, as a valu e greater than 1. Note that NOFILE_ID is equivalent to FILE_ID=1; both disable file identification caching.
LIMIT=n Specifies the maximum amount of free space in the extent cache in one-thousandths of the currently available free space on the disk.
QUOTA[=n] and NOQUOTA Enable or disable quota caching. To enable quota caching, you must have the OPER privilege and you must specify n, the number of entries in the quota cache. Normally n is set to the maximum number of active users expected for a disk with quotas enabled. Both NOQUOTA and QUOTA=0 disable quota file caching.
TAPE_DATA Enables write caching for a magnetic tape device if the tape controller supports write caching. The /CACHE qualifier is the default for mounting tape devices. You must specify TAPE_DATA to enable write caching. If the tape controller does not support write caching, the keyword is ignored. The write buffer stays enabled even after you dismount the magnetic tape. To disable the write buffer, mount a tape with the /NOCACHE qualifier. If a tape supports compaction, then the default is compaction, and caching is enabled. For tape storage devices that support compaction, the following command is valid:
WRITETHROUGH Disables the deferred write feature for file headers. By default, this feature is enabled, which improves the performance of applications, such as PATHWORKS, that use it. The deferred write feature is not available on Files-11 ODS-1 volumes.

If you do not specify the /CACHE qualifier and it is not implied by the use of the qualifier /MEDIA_FORMAT=COMPACTION, caching is enabled by default.

/DATA_CHECK overrides the read-check (/DATA_CHECK=READ) or write-check (/DATA_CHECK=WRITE) options (or both: /DATA_CHECK=(READ,WRITE)) specified for a volume when it was initialized.

/EXTENSION=n specifies the number of blocks by which disk files are to be extended on the volume unless otherwise specified by an individual command or program request. If you later plan to extend this volume, you can do that without dismounting only up to the volume specified with the /EXTENSION qualifier.

/OWNER_UIC=uic requests that the specified UIC be assigned ownership of the volume while it is mounted, overriding the ownership recorded on the volume. If you are mounting a volume using the /FOREIGN qualifier, requests an owner UIC other than your current UIC.

/PROTECTION specifies the protection code to be assigned to the volume. If you specify the /PROTECTION qualifier when you mount a volume with the /SYSTEM or /GROUP qualifier, the specified protection code overrides any access rights implied by the other qualifiers. If you specify the /FOREIGN qualifier, the execute (E) or create (C) and delete (D) access codes are synonyms for logical I/O (L) and physical I/O (P). You can, however, specify the access codes physical I/O (P) or logical I/O (L), or both, to restrict the nature of input/output operations that different user categories can perform. To use the /PROTECTION qualifier on a Files-11 volume, you must have the user privilege VOLPRO or your UIC must match the UIC written on the volume.

/QUOTA (default) controls whether quotas are to be enforced on the specified disk volume.

/REBUILD controls whether MOUNT performs a rebuild operation on a disk volume.

/WINDOWS=n specifies the number of mapping pointers to be allocated for file windows. The parameter, n, specifies a value from 7 to 80 that overrides the default value specified when the volume was initialized.

Volume Sets

/BIND Creates a volume set of one or more disk volumes or adds one or more volumes to an existing volume set. Specify the volume set label as the value of this qualifier. See the volume set article for more information.

Shadow Sets

See the article on shadow sets for a full description of the following qualifiers.

/CONFIRM causes MOUNT to pause and request confirmation before performing a copy operation on the specified disk device. Must be used with the /SHADOW qualifier.

/COPY enables or disables copy operations on physical devices specified when you mount a shadow set.

/INCLUDE automatically reconstructs a former shadow set to the way it was before the shadow set was dissolved. This qualifier is applicable only if you have the volume shadowing option. It should be used with the /SHADOW qualifier.

/POLICY controls the setup and use of shadow sets.

/SHADOW binds devices into a shadow set.


/MOUNT_VERIFICATION specifies that the device is a candidate for Mount Verification.

/OVERRIDE=keyword inhibits one or more protection checks that the MOUNT command performs:

Keyword Description
ACCESSIBILITY For magnetic tapes only. If the installation allows, this keyword overrides any character in the Accessibility Field of the volume. The necessity of this keyword is defined by the installation. That is, each installation has the option of specifying a routine that the magnetic tape file system will use to process this field.

By default, the OpenVMS operating system provides a routine that checks this field in the following manner:

  • If the magnetic tape was created on a version of OpenVMS that conforms to Version 3 of ANSI, then you must use this keyword to override any character other than an ASCII space.
  • If an OpenVMS protection is specified and the magnetic tape conforms to an ANSI standard that is higher than Version 3, then you must use this keyword to override any character other than an ASCII 1.

To use the ACCESSIBILITY keyword, you must have the user privilege VOLPRO or own the volume.

EXPIRATION For magnetic tapes only. Allows you to override the expiration dates of a volume and its files. Use this keyword when the expiration date in the first file header label of any file that you want to overwrite has not been reached. You must have the user privilege VOLPRO or your UIC must match the UIC written on the volume.
IDENTIFICATION Overrides processing of the volume identifier in the volume label. Use this keyword to mount a volume for which you do not know the label, or for an ISO 9660 volume whose label is not unique in the first 12 characters. Only the volume identifier field is overridden. Volume protection, if any, is preserved. The volume must be mounted /NOSHARE (either explicitly or by default). The /OVERRIDE=IDENTIFICATION qualifier is incompatible with the /GROUP and /SYSTEM qualifiers.
LIMITED_SEARCH Allows the Mount command to search an entire device for a home block, if a home block is
not found at the expected location. By default, the search for a home block is limited to avoid excessive search times if no valid home block is present.
LOCK Directs MOUNT not to write-lock the volume as a consequence of certain errors encountered

while mounting it. Use this keyword when you are mounting a damaged volume to be repaired using the ANALYZE/DISK_STRUCTURE command. You must have VOLPRO privilege or own the volume to use the LOCK keyword.

NO_FORCED_ERROR Directs the Mount command to proceed with shadowing, even though the device or controller does not support forced error handling. Using unsupported SCSI disks can cause members to be removed from a shadow set if certain error conditions arise that cannot be corrected, because some SCSI disks do not implement READL and WRITEL commands that support disk bad block repair.
OWNER_IDENTIFIER For magnetic tapes only. Overrides the processing of the owner identifier field. Use this keyword to interchange protected magnetic tapes between OpenVMS and other operating systems.
SECURITY Allows you to continue mounting a volume if an error is returned because the volume has an invalid SECURITY.SYS file. You must have the user privilege VOLPRO or own the volume to use this keyword.
SETID For magnetic tapes only. Prevents MOUNT from checking the file-set identifier in the first file header label of the first file on a continuation volume. Use this keyword only for ANSI-labeled volumes on which the file-set identifier of the first file on a continuation volume differs from the file-set identifier of the first file of the first volume that was mounted.
SHADOW_MEMBERSHIP Allows you to override the write protection of former shadow set members.
When you mount a volume with this qualifier, the volume shadowing generation number is erased. If you attempt to remount the volume in a shadow set, the volume is considered an unrelated volume and receives a full copy operation from a current shadow set member.

/SUBSYSTEM enables protected subsystems and the processing of subsystem ACEs. By default, only the system disk has /SUBSYSTEM enabled.

/UNLOAD controls whether or not the disk or magnetic tape volume or volumes specified in the MOUNT command are unloaded when they are dismounted.

See also