Ch5-File System PDF

 A file system is a structure of directories used to locate and store files.  The term “file system” is used in several different ways: ◦ To describe the entire file tree from the root directory downward ◦ To describe a particular type of file system: disk-based, n...

 A file system is a structure of directories used to locate and store files.  The term “file system” is used in several different ways: ◦ To describe the entire file tree from the root directory downward ◦ To describe a particular type of file system: disk-based, network-based, or pseudo ◦ To describe the data structure of a disk slice or other media storage device ◦ To describe a portion of a file tree structure that is attached to a mount point on the main file tree so that it is accessible Usually, you can tell from context which meaning is intended.  The Solaris system software uses the virtual file system (VFS) architecture, which provides a standard interface for different file system types.  The kernel handles basic operations, such as reading, writing, and listing files, without requiring the user or program to know about the underlying file system type.  The file system administrative commands provide a common interface that allows you to maintain file systems of differing types.  These commands have two components: a generic component and a component specific to each type of file system.  The generic commands apply to most types of file systems, while the specific commands apply to only one type of file system.  Administering the file system is one of your most important system administration tasks.  The file system story is a complex one, and understanding it can help you more effectively administer file systems.  Making local and remote files available to users. ◦ “Mounting and Unmounting File Systems,” for detailed information.  Connecting and configuring new storage devices when needed.  Designing and implementing a backup schedule and restoring files and file systems as needed. ◦ “Planning a Backup Strategy,” for information on designing a backup schedule. ◦ “Backing Up Files and File Systems,” for detailed information about doing backups. ◦ “Restoring Files and File Systems,” for detailed information about restoring files and file systems.  Checking for and correcting file system damage. File systems are usually checked and corrected at boot time. ◦ “Checking File System Integrity,” for detailed information on how to proceed if the automatic checking fails.  The system software supports three types of file systems: ◦ Disk-based ◦ Network-based ◦ Pseudo USF sunos HSFS  Disk-based file systems are stored on physical media such as hard disks, CD-ROMs, and diskettes.  Disk-based file systems can be written in different formats.  The available formats are: ◦ UFS – UNIX® file system (based on the BSD Fat Fast File system). UFS is the default disk-based file system in SunOS system software. ◦ HSFS – High Sierra and ISO 9660 file system. High Sierra is the first CD-ROM file system; ISO 9660 is the official standard version of the High Sierra File System. ◦ The HSFS file system is used on CD-ROM, and is a readonly file system. SunOS HSFS supports Rock Ridge extensions to ISO 9660, which, when present on a CD-ROM, provide all UFS file system semantics and file types except for writability and hard links. ◦ PCFS – PC file system, which allows read/write access to data and programs on DOS-formatted disks written for DOS-based personal computers. ◦ Each type of disk-based file system is customarily associated with a particular media device:  UFS with hard disk  HSFS with CD-ROM  PCFS with diskette  s5 with hard disk ◦ These associations are not, however, restrictive. For example, CD-ROMs and diskettes can have UFS file systems put on them.  Network-based file systems are file systems accessed over the network.  Typically, network-based file systems are file systems that reside on one system and are accessed by other systems across the network.  NFS is the only available network-based file system.  NFS is the default SunOS distributed file system.  You administer distributed file systems by exporting them from a server and mounting them on individual systems.  Pseudo file systems are virtual or memory- based file systems that provide access to special kernel information and facilities.  Most pseudo file systems do not use file system disk space.  Cache File Systems use a file system to contain the cache.  Some pseudo file systems, such as the temporary file system, may use the swap space on a physical disk.  The Cache File System can be used to improve performance of remote file systems or slow devices such as CD-ROM.  When a file system is cached, the data read from the remote file system or CD-ROM is stored in a cache on the local system.  The TMPFS file system uses local memory for file system reads and writes.  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.  Using TMPFS file systems can improve system performance by saving the cost of reading and writing temporary files to a local disk or across the network.  For example, temporary files are created when you compile a program.  The operating system generates a lot of disk or network activity while manipulating these files. Using TMPFS to hold these temporary files may significantly speed up their creation, manipulation, and deletion.  The TMPFS file system uses swap space as a temporary backing store.  If a system with a TMPFS file system does not have adequate swap space, two problems can occur:  The TMPFS file system can run out of space, just as a regular file system can fill up  Because TMPFS allocates swap space to save file data (if necessary), some programs may not be able to execute because there is not enough swap space.  The LOFS file system lets you create a new virtual file system.  You can access files using an alternative path name.  For example, you can create a loopback mount of / onto /tmp/newroot.  The entire file system hierarchy looks like it is duplicated under /tmp/newroot, including any file systems mounted from NFS servers.  All files are accessible either with a path name starting from /, or with a path name starting from /tmp/newroot.  The PROCFS file system resides in memory.  It contains a list of active processes, by process number, in the /proc directory.  Information in the /proc directory is used by commands like ps.  Debuggers and other development tools can also access the address space of the processes using file system calls.  The following example shows a partial listing of the contents of the /proc directory:  These additional types of pseudo file systems are listed for your information.  They do not require administration.  FIFOFS (first-in first-out) – Named pipe files that give processes common access to data  FDFS (file descriptors) – Provides explicit names for opening files using file descriptors  NAMEFS – Used mostly by STREAMS for dynamic mounts of file descriptors on top of files  Most file system administration commands have a generic and a file system– specific component.  Use the generic commands, which call the file system– specific component.  Table lists the generic file system administrative commands, which are located in the /usr/bin directory.  NFS is a distributed file system that can be used to “tie together” computers  that are running different operating systems.  For example, systems running DOS can share files with systems running UNIX.  NFS makes the actual physical location of the file system irrelevant to the user.  You can use NFS to allow users to see all the relevant files, regardless of location.  Instead of placing copies of commonly used files on every system, When you share a resource, you make it available for mounting by remote systems.  You can share a resource in these ways:  Using the share or shareall command  Adding an entry to the /etc/dfs/dfstab (distributed file system table)  Add one entry to the /etc/dfs/dfstab file for each resource that you want to have shared automatically.  Each entry must be on a separate line, using this syntax:  share [-F nfs] [-o specific-options] [-d "description"] pathname resource  Thank You