Page 156 - DCAP403_Operating System

Unit 8: File Management

/sbin Contains files needed to boot the machine and mount the /usr file system. Most of the Notes

commands used during booting come from the boot image’s RAM disk file system; therefore,
very few commands reside in the /sbin directory.

/tmp Serves as a mount point for a file system that contains system-generated temporary fi les.
/u Symbolic link to the /home directory.

/usr Serves as a mount point for a file system containing files that do not change and can be shared

by machines (such as executable programs and ASCII documentation).
Standalone machines mount a separate local file system over the /usr directory. Diskless and

disk-poor machines mount a directory from a remote server over the /usr fi le system.
/var Serves as a mount point for files that vary on each machine. The /var file system is confi gured as

a file system because the files that it contains tend to grow. For example, it is a symbolic link to

the /usr/tmp directory, which contains temporary work fi les.
Task How will you mount a fi le? Explain.
8.6 File Sharing

In today’s world where the working is a multiuser environment a file is required to be shared

among more than one users. There are several techniques and approaches to effects this operation.

Simple approach is to copy the file at the users local hard disk. This approach essentially creates

to different files, in therefore cannot be treated as fi le sharing.

A file can be shared in three different modes:
1. Read only: The user can only read or copy the fi le.
2. Linked shared: All the users can share the file and can make the changes but the changes

are reflected in the order defined by the operating systems.

3. Exclusive mode: The file is acquired by one single user who can make the changes while
others can only read or copy it.
Sharing can also be done through symbolic links, but there occurs certain problems like concurrent
updation problem, deletion problem. Updation cannot be done simultaneously by two users at
a time, also one cannot delete a file if it in use by another user. The solution for this problem is

done by locking fi le techniques.
8.7 Protection

The data in the computer system should be protected and kept secure. A major concern is to
protect data from both physical damage (reliability) and improper access (protection). There is
a mechanisms in the computer system that a system program or manually it can take the backup

or duplicate the files automatically. File systems can be damaged by hardware problems (such as
errors in reading or writing), power surges or failures, head crashes, dirt, temperature extremes.
Also the data can be lost due to bugs on system. Protection can be provided in many ways. For
a small single-user system, you might provide protection by physically removing the fl oppy
disks and locking them in a desk drawer or file cabinet. In a multi-user system, however, other

mechanisms are needed.
8.8 File System Implementation

The most important issue in file storage is keeping track of which disk blocks go with which

file. Different operating systems use different methods - contiguous allocation and linked list

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