Pg. of GC20-1819-2 Rev March 30, 1979 by Supp. SD23-9024-1 for 5748-XX8 You can assign a filemode number when you create a file with the CMS editor. To change the filemode number of an existing file, use the
RENAME or COPYFILE commands, or use the FMODE subcommand when you are in
the edit environment. fIL!Q!f: When you assign file definitions to disk files for
programs or CMS command functions, you can specify a filemode number. §!NMQQ: You can specify a filemode number on the GENMCD command line.
To change the filemode number of an eXisting file, use the RENAME or COPYFILE commands.
READCARD: You can assign a filemode number when you specify a file IdentIfIer on the READCARD command line or on a READ control card.
RENAME: When you specify the fileids on the RENAME command, you can specIfy the filemode numbers for the input and/or output files. You can specify filemode numbers for the input and/or output
fileids on the SORT command line.
Managing Your CMS Disks
The number of files you can write on a CMS disk depends on both the size
of the disk and the size of the files that it contains. You can find
out how much space is being used on a disk by using the QUERY DISK command. For example, to see how much space is on your A-disk, you would
enter:
query disk a
The response may be something like this:
LABEL cuu M STAT eYL TYPE BLKSIZE 191 A R/i 5 3330 1024 FILES ELKS USED-(%) ELKS LEFT ELK TOTAL 171 1221-92 107 1328 When a disk is becoming full, you should erase whatever files you no
longer need. Or dump to tape files that you need to keep but do not need
to keep active on disk. When you are executing a command or program that writes a file to
disk, and the disk becomes full in the process, you receive an error
message, and you have to try to clear some space on the disk before you
can attempt to execute the command or program again. To avoid the
delays that such situations cause, you should try to maintain an
awareness of the usage of your disks. If you cannot erase any more
files from your disks, you should contact installation support personnel
about obtaining additional read/write disk space. CMS File Directories
Each disk has a master file directory that contains entries for each
of the CMS files on the disk. When you access a disk, information frem
the master file directory is brought into virtual storage and written
into a user file directory. The user file directory has an entry for
each file that you may access. If you have accessed a disk specifying
only particular files, then the user file directory contains entries
only for those files.
56 IBM VM/370 CMS User's Guide

Page of GC20-1819-2 As Updated April 27, 1981 by TNL SN25-0828 For 5748-XE1 If you have read/write access to a disk, the master file directory
and the user file directory are updated to reflect the current status of
the disk each time you write the file onto disk. Only the master file
directory, however, is updated if there are no open files on the disk,
and only the user file directory is updated when an FSCLOSE macro
command is issued.
with read-only access to a disk, you cannot update the master file
directory or the user file directory; however, if another user is
writing files onto the disk, you can obtain an updated copy of the
master file directory by issuing the ACCESS command for the disk. 1:!Q.te: You should never attempt to write on a disk at the same time as
another user.
The user file directory remains in virtual storage until you issue
the RELEASE command specifying the mode letter or virtual address of the
disk. If you detach a virtual disk (with the CP DETACH command) without
releasinq it, CMS does not know that the disk is no longer part of your
virtual machine. When you attempt to read or write a file on the disk CMS assumes that the disk is still active (because the user file
directory is still in storage) and encounters an error when it tries to
read or write the file.
A similar situation occurs if you detach a disk and then add a new
disk to your virtual machine using the same virtual address as the disk
you detached. For example, if you enter the following sequence of
commands:
cp link user1 191 195 rr rpass
1
access 195 d cp detach 195
cp link user2 193 195 rr rpass2
1
listfile * * d the LISTFILE command produces a list of the files on USER1's 191 disk;
if you attempt to read one of these files, you receive an error message. You must issue the ACCESS command to obtain a copy of the master file
directory for USER2's 193 disk.
The entries in the master file directory are sorted alphamerically by
filename and filetype, to facilitate the CMS search for particular
files. When you are updating disk files, the entries in the user file
directory and master file directory tend to become unsorted as files are
created, updated, and erased. When you use the RELEASE command to
release a read/write disk, the entries are sorted and the master file
directory is rewritten. If you or any other user subsequently access
the disk, the file search may be more efficient. CMS Command Search Order When you enter a command line in the CMS environment, CMS has to locate
the command to execute. If you have EXEC or MODULE files on any of your
accessed disks, CMS treats them as commands; also, they are known as
user-written commands. INote that the password cannot be entered on the command line if the
password suppression facility was specified at sysgen.
Section 4. The CMS File System 57