LINK CP Privilege Class: G
Use the LINK command to make a device that is associated with another virtual
machine available to your virtual machine configuration, based upon information
in that user's VM/SP directory entry. The format of the LINK command is:
+----------+------------------------------------------------------------------+
| LINK | [To] userid vaddr1 [As] vaddr2 [mode] [[PASS=] password] |
+----------+------------------------------------------------------------------+
where:
[To] userid
is the name of the user whose VM/370 directory is to be searched for
device vaddr1. An asterisk (*) is used to specify that the device is
in your own VM/370 directory. If the keyword TO is omitted, the
userid may not be "TO" or "T."
vaddr1 is the virtual device address (cuu) in the VM/SP directory for that
userid.
[As] vaddr2
is the virtual address (cuu) that is to be assigned to the device for
your virtual machine. If the keyword AS is omitted, vaddr may not be
"AS" or "A." If your virtual machine has the ECMODE option, any
address up to X'FFF' is valid; otherwise, any address up to X'5FF' is
valid.
mode is the access mode which consists of up to two letters. The first
letter specifies the primary access mode (read-only, write, or
multiple). The optional second letter indicates the alternate access
mode (read-only or write access) desired if the primary access is not
available. Valid modes are:
R Primary read-only (R/O) access. The read-only link is
established as long as no other user has the disk in write
status. If there is an existing write link to the disk, no link
is given. R is the default mode if the link is to another
userid.
RR Primary read-only access or alternate read-only access. The
read-only link is established even if another user has the disk
in write status. The alternate access of R assures the user
will get the read link no matter what links currently exist to
the disk.
W Primary write access. The write link is established only if
there are no other current links to the disk. If another user
has the disk in read or write status, no link is given.
WR Primary write access or alternate read-only access. If write
access is available, then the write link is established,
otherwise the alternate access of a read-only link is given.
M Primary multiple access. A write link is established unless
another user already has write access to the disk, in which case
no link is given.
MR Primary multiple access or alternate read access. A write link
is established unless another user already has write access to
the disk, in which case a read link is given since it was the
alternate access requested.
Note: Unpredictable results can occur when one user has a read-
only (R or RR) link to a device that is being updated by a user
who has the device in write status (W or WR).
For example, in CMS, when a file is updated, it is moved on the
disk and the directory for the disk is updated. The user with a
read-only link will be using an old copy of the file until the
disk is reaccessed. As a precaution, the user with a read-only
link should reaccess the disk everytime a user with a write link
updates the disk.
MW Primary multiple access or alternate write access. A write link
is established in all cases.
Caution: CMS does not protect a user from loss of data on a disk when
multiple users have write access to the disk. More than one user
writing to the same virtual device will almost always result in a
permanent loss of data. Users should not be linking with MW mode to
obtain the M or MR function. (The M or MR access modes will allow
only one write link to a disk.)
If the mode is omitted and the userid is that of another user, then
the default mode is R. If you are linking to one of your own disks,
the default mode is the access mode as specified in the VM/370
directory for your disk (on the MDISK or LINK control statement).
PASS= password
is a one- to eight-character string that must match the access mode
password for device vaddr1 in the VM/370 directory for the user
(userid) specified. The password should be specified only when the
LINK is executed by a virtual machine (for example, from CMS), since
printing of the password is not suppressed when included with the LINK
command. The access mode password cannot be the same as any of the
access modes (R, RR, W, WR, M, MR, or MW) if the default mode is to be
used.
Usage notes:
1. The access mode password should not be confused with a user password. Up
to three access mode passwords can exist for each disk; these are the read,
write, and multiple passwords.
2. If you link to one of your own disks, no password is required. If another
user has write access to one of your disks when you log on, your access
will be forced read-only (R/O). You can obtain write access by issuing a
link command with an access mode of MW. Now two write links exist to the
disk and the integrity of the data is not guaranteed by CP or CMS.
3. If the link is to a device whose password is ALL, (meaning that any user
can access the device), the password is not required. However, if the link
is to a device whose password is not ALL, a password must be provided. If
a LINK command is issued from a CMS batch job, a password must be provided
even if the access password is ALL.
4. The link established by the LINK command to the vaddr1 device belonging to
userid is summarized in the following table where R = read-only, W = write,
M = multiple, N = no or none, and Y = yes:
Primary access requested R R R R R W W W W W W M M M M M M
Alternate access requested R R R R W
Read password in directory N Y Y Y Y
Write password in directory N Y Y Y Y Y
Multi password in directory N Y Y Y Y Y
Current existing links N R W W N R R W W N R W W W
Access established N R R N R N W N R N R N W W N R W
Responses:
ENTER READ PASSWORD:
XXXXXXXX
Type the read password over the mask to request read-only access to the
desired disk. The mask will only appear on line-mode terminals.
ENTER WRITE PASSWORD:
XXXXXXXX
Type the write password over the mask to request write access to the desired
disk. The mask will only appear on line-mode terminals.
ENTER MULT PASSWORD:
XXXXXXXX
Type the multiple password over the mask to obtain write access to a disk to
which other users may already have access. The mask will only appear on
line-mode terminals.
Note: CP keeps track of unsuccessful link attempts due to invalid
passwords. When a user exceeds 10 incorrect password attempts, the LINK
command is disabled for the remainder of the terminal session.
DASD vaddr2 LINKED R/O
This response indicates that a read-only link to the given disk is
established for a LINK request with a mode of R or RR, and that no other
users are linked to the same disk in read/write mode.
DASD vaddr2 LINKED R/W
This response indicates that a read/write link to the given disk is
established for a LINK request with a mode of W, WR, M, MR, or MW, and that
no other users are linked to the same disk.
DASD vaddr2 LINKED R/O;R/W BY userid ¦ nnn USERS ;R/O BY userid ¦ nnn USERS
This response indicates that a read-only link to the given disk is
established for a LINK request with a mode of RR, but warns that the disk is
in read/write use by some users and possibly in read use by some users. If
only one user has access, the number of users (nnn USERS) is replaced by
userid.
DASD vaddr2 LINKED R/W; R/O BY userid ¦ nnn USERS
This response indicates that a read/write link to the given disk is
established for a LINK request with a mode of M, MR, or MW, and informs you
that the disk is also in read-only use by userid or by nnn users. (No other
users have a read/write link to the disk.)
DASD vaddr2 LINKED R/W;R/W BY userid ¦ nnn USERS ;R/O BY userid ¦ nnn USERS
This response indicates that a read/write link to the given disk is
established for a LINK request with a mode of MW, but warns you that the
disk is also in read/write use by some users and possibly in read use by
some users. If only one user has access, the number of users (nnn USERS) is
replaced by userid.