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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 807
776
CASE STUDY 1: UNIX, LINUX, AND ANDROID
CHAP. 10
disks of its era), there was interest in better file systems almost from the beginning
of the Linux development, which began about 5 years after MINIX 1 was released.
The first improvement was the ext file system, which allowed file names of 255
characters and files of 2 GB, but it was slower than the MINIX 1 file system, so the
search continued for a while. Eventually, the ext2 file system was invented, with
long file names, long files, and better performance, and it has become the main file
system. However, Linux supports several dozen file systems using the Virtual File
System (VFS) layer (described in the next section).
When Linux is linked, a
choice is offered of which file systems should be built into the kernel. Others can
be dynamically loaded as modules during execution, if need be.
A Linux file is a sequence of 0 or more bytes containing arbitrary information.
No distinction is made between ASCII files, binary files, or any other kinds of
files. The meaning of the bits in a file is entirely up to the file’s owner.
The system
does not care. File names are limited to 255 characters, and all the ASCII charac-
ters except NUL are allowed in file names, so a file name consisting of three car-
riage returns is a legal file name (but not an especially convenient one).
By convention, many programs expect file names to consist of a base name and
an extension, separated by a dot (which counts as a character).
Thus
prog.c
is typi-
cally a C program,
prog.py
is typically a Python program, and
prog.o
is usually an
object file (compiler output).
These conventions are not enforced by the operating
system but some compilers and other programs expect them. Extensions may be of
any length, and files may have multiple extensions, as in
prog.java.gz
, which is
probably a
gzip
compressed Java program.
Files can be grouped together in directories for convenience. Directories are
stored as files and to a large extent can be treated like files. Directories can contain
subdirectories, leading to a hierarchical file system.
The root directory is called
/
and always contains several subdirectories. The / character is also used to separate
directory names, so that the name
/usr/ast/x
denotes the file
x
located in the direc-
tory
ast
, which itself is in the
/usr
directory.
Some of the major directories near the
top of the tree are shown in Fig. 10-23.
Directory
Contents
bin
Binary (executable) programs
dev
Special files for I/O devices
etc
Miscellaneous system files
lib
Libraries
usr
User directories
Figure 10-23.
Some important directories found in most Linux systems.
There are two ways to specify file names in Linux, both to the shell and when
opening a file from inside a program. The first way is by means of an
absolute
path
, which means telling how to get to the file starting at the root directory.
An
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