Adding and Mounting File Systems to the Root File System

If you have appropriate authority, you can create other mountable file systems with their own directory and data file structures, and mount them on a directory in the root file system or in another file system. Each file system can be logically mounted to a directory (mount point) in another file system by using the TSO/E MOUNT command. Use the UNMOUNT command to unmount a file system. To create and mount additional file systems:

Allocate an additional HFS data set by using either the TSO/E ALLOCATE command as shown in the following example or a JCL DD statement similar to that shown in Creating and Mounting the Root File System.
```
   ALLOCATE DSNAME('OMVS.USER.JOE') NEW DSNTYPE(HFS) BLKSIZE(0)
     LRECL(0) RECFM(U) DSORG(PO) SPACE(1,1) CYLINDERS
```
The new data set is allocated with an empty root directory.
Have an authorized user enter a TSO/E MOUNT command to logically mount the new file system in the directory of an existing file system.
```
   MOUNT FILESYSTEM('OMVS.USER.JOE') TYPE(HFS) MOUNTPOINT('/u/joe')
```

You can specify additional file systems to be logically mounted automatically every time z/OS® UNIX is started by adding MOUNT commands to the BPXPRMxx member of SYS1.PARMLIB. The following restrictions apply to mounting file systems:

The mount point must be a directory.
Any files in the directory are not accessible while the file system is mounted.
Only one mount can be active at any time for a mount point.
A file system can be mounted on only one directory at a time.

You can also create special HFS files to perform the following tasks:

Represent hardware devices (character special files).
Allow the use of alias names for HFS files (symbolic links).
Send data from one process to another so that the receiving process reads the data first-in-first-out (FIFO special files, also called named pipes). The term process as used here is defined as either a program that is created by the fork function, or a program that requests z/OS UNIX system services.