NFS Terminology

NFS, which is the Solaris distributed network file system, is the industry's most widely available file-sharing system and has been adopted and shipped by more than 300 vendors. The terms in this discussion are commonly used to describe how resources are shared with NFS and how these terms relate to the automounter.

Server and Client Systems

The terms server and client describe the roles that systems perform when they interact to share resources. These terms are part of general distributed computing terminology and are not specific to either NFS or the automounter.

• A server is a system that shares (exports) file systems so that they are accessible to other systems on the network.

• A client is a system that accesses some or all of its files from one or more servers.

You do not need to set up server file systems in a special way for access by the automounter. As long as the file systems are shared for NFS access, the automounter software can mount and unmount them.

Mount Points

Mount points are directories on a client system that are used as places to attach (or mount) other file systems. When you mount or automount a file system on a mount point, any files or directories that are stored locally in the mount point directory are hidden and inaccessible as long as the file system is mounted. These files are not permanently affected by the mounting process, and they become available again when the file system is unmounted. However, mount directories are usually empty so that existing files are not obscured.

The Virtual File System Table

Each system has a virtual file system table (/etc/vfstab) that specifies which file systems are mounted by default at system boot. This file specifies local UFS (UNIX file system) and NFS file systems that are mounted automatically when a system boots. The /etc/vfstab file has additional entries for file systems, such as swap and proc, that are used by the system.

In addition, the /etc/vfstab file may have entries for pcfs (personal computer file system) and cdrom file systems.

The automounter is an alternative to the /etc/vfstab file for specifying which file systems to mount and unmount. The automounter uses maps because they are more flexible than the /etc/vfstab file and they enable a consistent network-wide view of all file names.

You can, without any conflict, mount some file systems with the /etc/vfstab file and other files with the automounter.

Mount and Unmount

Without the automounter, user file systems are mounted when the system boots from entries in the /etc/vfstab file. When file systems are not automounted, users employ the mount and umount commands—which require superuser privileges—if they need to mount any additional file systems or unmount a mounted file system. The mount command is used to mount a file system. The umount command is used to unmount a file system. When file systems are automounted, users do not need to use the mount and umount commands. Instead, the automounter mounts the file systems and makes them available when a user changes into an autofs directory.

For a description of the types of file systems and for information on how to share, mount, and unmount files, refer to Solaris System Administrator's Guide, Third Edition, by Janice Winsor. (See the bibliography at the end of this book.)

The Mount Table (/etc/mnttab)

The Solaris Operating Environment uses a mount table, which is maintained in the /etc/mnttab file, to keep track of currently mounted file systems. Whenever users mount or unmount a file system with either the mount or umount commands or the automounter, the system modifies the /etc/mnttab file to list the currently mounted file systems.

In previous Solaris releases, the /etc/mnttab mount table was a text-based file that stored information about mounted file systems. This file could get out of sync with the state of mounted file systems. Starting with the Solaris 8 release, /etc/mnttab is an MNTFS file system that provides read-only information directly from the kernel about mounted file systems for the local system.

Because of this structural difference, the following mnttab behavior is changed.

• Programs or scripts cannot write to /etc/mnttab.

• The mount -m option for faking mnttab entries no longer works.

MNTFS requires no administration. See mnttab(4) for more information.

You can display the contents of the /etc/mnttab file with the cat or more commands, but you cannot edit it.