How are devices represented in UNIX?
All devices are represented by files called special files that are located
in/dev directory. Thus, device files and other files are named and accessed
in the same way. A 'regular file' is just an ordinary data file in the
disk. A 'block special file' represents a device with characteristics similar
to a disk (data transfer in terms of blocks). A 'character special file'
represents a device with characteristics similar to a keyboard (data transfer
is by stream of bits in sequential order).
What is 'inode'?
All UNIX files have its description stored in a structure called 'inode'. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode. In addition to descriptions about the file, the inode contains pointers to the data blocks of the file. If the file is large, inode has indirect pointer to a block of pointers to additional data blocks (this further aggregates for larger files). A block is typically 8k.
Inode consists of the following fields:
A Unix directory is a file containing a correspondence between filenames
and inodes. A directory is a special file that the kernel maintains. Only
kernel modifies directories, but processes can read directories. The contents
of a directory are a list of filename and inode number pairs. When new
directories are created, kernel makes two entries named '.' (refers to
the directory itself) and '..' (refers to parent directory).
What are the Unix system calls for I/O?
How do you change File Access Permissions?
Every file has following attributes:
(user permission-group permission-others permission)
To change the access mode, we use chmod(filename,mode).
Each operation is represented by discrete values
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