Solaris File System Types

Solaris file systems can be put into three categories: disk-based, networkbased, and virtual.

Disk-Based File Systems

Disk-based file systems reside on the system’s local disk. Following are the four types of disk-based file systems:

  • UFS The UNIX file system, which is based on the BSD FAT Fast file system (the traditional UNIX file system). The UFS file system is the default disk-based file system used in Solaris.

  • HSFS The High Sierra and ISO 9660 file system, which supports the Rock Ridge extensions. The HSFS file system is used on CD-ROMs and is a read-only file system.

  • PCFS The PC file system, which allows read/write access to data and programs on DOS-formatted disks written for DOS-based personal computers.

  • UDF The Universal Disk Format file system. UDF is the new industry-standard format for storing information on optical media technology called DVD (digital versatile disc or digital video disc).

Network-Based File Systems

Network-based file systems are file systems accessed over the network. Typically, they reside on one system and are accessed by other systems across the network.

The network file system (NFS) or remote file systems are file systems made available from remote systems. NFS is the only available network-based file system. NFS is discussed in detail in Chapter 22, “The NFS Environment.”

Virtual File Systems

VFS, previously called pseudo file systems, are virtual or memory-based file systems that create duplicate paths to other disk-based file systems or provide access to special kernel information and facilities. Most VFS do not use file system disk space, although a few exceptions exist. Cache file systems, for example, use a file system to contain the cache.

Some VFS, such as the temporary file system, might use the swap space on a physical disk. The following is a list of some of the more common types of VFS:

  • SWAPFS A file system used by the kernel for swapping. Swap space is used as a virtual memory storage area when the system does not have enough physical memory to handle current processes.

  • PROCFS The Process File System resides in memory. It contains a list of active processes, by process number, in the /proc directory. Commands such as ps use information in the /proc directory. Debuggers and other development tools can also access the processes’ address space by using file system calls.

  • LOFS The Loopback File System lets you create a new virtual file system. You can access files by using an alternative path name. The entire file system hierarchy looks as though it is duplicated under /tmp/newroot, including any file systems mounted from NFS servers. All files are accessible with a pathname starting from either / or /tmp/newroot.

  • CacheFS The Cache File System lets you use disk drives on local workstations to store frequently used data from a remote file system or CD-ROM. The data stored on the local disk is the cache.

  • TMPFS The temporary file system uses local memory for file system reads and writes. Because TMPFS uses physical memory and not the disk, access to files in a TMPFS file system is typically much faster than to files in a UFS file system. Files in the temporary file system are not permanent; they are deleted when the file system is unmounted and when the system is shut down or rebooted. TMPFS is the default file system type for the /tmp directory in the SunOS system software. You can copy or move files into or out of the /tmp directory just as you would in a UFS /tmp file system. When memory is insufficient to hold everything in the temporary file system, the TMPFS file system uses swap space as a temporary backing store, as long as adequate swap space is present.

  • /var/run /var/run is a temporary file system. /var/run is the repository for temporary system files that are not needed across systems. The /tmp directory continues to be a repository for nonsystem temporary files. Because /var/run is mounted as a memory-based file system rather than a disk-based file system, updates to this directory do not cause unnecessary disk traffic that interferes with systems that are running power-management software.

    The /var/run directory requires no administration and cannot be unmounted with the umount -a or the umountall command.

    For security reasons, root owns /var/run.

  • MNTFS The MNTFS file system type maintains information about currently mounted file systems. MNTFS is described later in this chapter.

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