The Mounted File System Table

Whenever you mount or unmount a file system, the /etc/mnttab (mount table) file is modified with the list of currently mounted file systems. You can display the contents of this file with the cat or more commands, but you cannot edit it. Here is an example of an /etc/mnttab file:

$ more /etc/mnttab
/dev/dsk/c0t0d0s0  /  ufs rw,intr,largefiles,onerror=panic,suid,dev=2200000 938557523
/proc   /proc   proc    dev=3180000     938557522
fd      /dev/fd fd      rw,suid,dev=3240000     938557524
mnttab  /etc/mnttab     mntfs   dev=3340000     938557526
swap    /var/run        tmpfs   dev=1   938557526
swap    /tmp    tmpfs   dev=2   938557529
/dev/dsk/c0t0d0s7 /export/home ufs rw,intr,largefiles,onerror=panic,suid,dev=2200007 ...
$

The Virtual File System Table

It would be a very time-consuming and error-prone task to manually mount file systems every time you wanted to access them. To avoid this problem, the virtual file system table (the /etc/vfstab file) provides a list of file systems and how to mount them.

The /etc/vfstab file provides two important features:

• You can specify file systems to automatically mount when the system boots.

• You can mount file systems by using only the mount point name, because the /etc/vfstab file contains the mapping between the mount point and the actual device slice name.

A default /etc/vfstab file is created when you install a system, depending on the selections you make when installing system software. However, you can edit the /etc/vfstab file on a system whenever you want. To add an entry, the main information you need to specify is the device where the file system resides, the name of the mount point, the type of the file system, whether you want the file system to mount automatically when the system boots (by using the mountall command), and any mount options.

The following is an example of an /etc/vfstab file. Comment lines begin with #. This example shows an /etc/vfstab file for a system with two disks (c0t0d0 and c0t3d0).

$ more /etc/vfstab
#device         device          mount           FS      fsck   mount  mount
#to mount       to fsck         point           type    pass   at boot options
/dev/dsk/c0t0d0s0 /dev/rdsk/c0t0d0s0 /          ufs     1       no      -
/proc           -               /proc           proc    -       no      -
/dev/dsk/c0t0d0s1 -                -            swap    -       no      -
swap            -               /tmp            tmpfs   -       yes     -
/dev/dsk/c0t0d0s6 /dev/rdsk/c0t0d0s6 /usr       ufs     2       no      -
/dev/dsk/c0t3d0s7 /dev/rdsk/c0t3d0s7 /test      ufs     2       yes     -
$

In the preceding example, the last entry specifies that a UFS file system on the /dev/dsk/c0t3d0s7 slice will be automatically mounted on the /test mount point when the system boots. Note that, for root (/) and /usr, the mount at boot field value is specified as no, because these file systems are mounted by the kernel as part of the boot sequence before the mountall command is run.

For descriptions of each of the /etc/vfstab fields and information on how to edit and use the file, see Chapter 40, Mounting and Unmounting File Systems (Tasks).

The NFS Environment

NFS is a distributed file system service that can be used to share resources (files or directories) from one system, typically a server, with other systems on the network. For example, you might want to share third-party applications or source files with users on other systems.

NFS makes the actual physical location of the resource irrelevant to the user. Instead of placing copies of commonly used files on every system, NFS allows you to place one copy on one system's disk and let all other systems access it from the network. Under NFS, remote files are virtually indistinguishable from local ones.

A system becomes an NFS server if it has resources to share on the network. A server keeps a list of currently shared resources and their access restrictions (such as read/write or read-only access).

When you share a resource, you make it available for mounting by remote systems.

You can share a resource in these ways:

• By using the share or shareall command

• By adding an entry to the /etc/dfs/dfstab (distributed file system table) file and rebooting the system

For information on how to share resources, see Chapter 40, Mounting and Unmounting File Systems (Tasks). For a complete description of NFS, see "Managing Network File Systems (Overview)" in System Administration Guide: Resource Management and Network Services.

Automounting or AutoFS

You can mount NFS file system resources by using a client-side service called automounting (or AutoFS), which enables a system to automatically mount and unmount NFS resources whenever you access them. The resource remains mounted as long as you remain in the directory and are using a file. If the resource is not accessed for a certain period of time, it is automatically unmounted.

AutoFS provides the following features:

• NFS resources don't need to be mounted when the system boots, which saves booting time.

• Users don't need to know the root password to mount and unmount NFS resources.

• Network traffic might be reduced, since NFS resources are only mounted when they are in use.

The AutoFS service is initialized by the automount utility, which runs automatically when a system is booted. The automountd daemon runs continuously and is responsible for the mounting and unmounting of the NFS file systems on an as-needed basis. By default, the /home file system is is mounted by the automount daemon.

With AutoFS, you can specify multiple servers to provide the same file system. This way, if one of the servers is down, AutoFS can try to mount from another machine.

For complete information on how to set up and administer AutoFS, see System Administration Guide: IP Services.

Determining a File System's Type

You can determine a file system's type by using the following:

• The FS type field in the virtual file system table (/etc/vfstab file)

• The /etc/default/fs file for local file systems

• The /etc/dfs/fstypes file for NFS file systems

How to Determine a File System's Type

This procedure works whether the file system is mounted or not.

Determine a file system's type by using the grep command.

$ grep mount-point fs-table

Information for the mount point is displayed.

Note - If you have the raw device name of a disk slice, you can use the fstyp command to determine a file system's type (if the disk slice contains a file system). For more information, see fstyp(1M).