Transcript Chapter One - City University of New York

Exploring the UNIX File
System and File Security
Understanding Files and
Directories
Understanding the UNIX
File System
A file is the basic component for data storage
– UNIX considers everything it interacts with a file
A file system is UNIX’s way of organizing files on
mass storage (disk) devices
– A physical file system is a section of the hard disk that
has been formatted to hold files
The file system is organized in a hierarchical
structure similar to an inverted tree
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Understanding the Standard
Tree Structure
The structure starts at the root level
– Root is the name of the file at this basic level and it is
denoted by the slash character (/)
A directory is a file that can contain other files
and directories
A subdirectory is a directory within a directory
– The subdirectory is considered the child of the parent
directory
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Using UNIX Partitions
The section of the disk that holds a file
system is called a partition
– When installing UNIX, one of the first tasks is
deciding how to partition a storage device, or hard
disk
– Hard disks may have many partitions
UNIX partitions are given names
– Like hda1 and hda2
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Using UNIX Partitions
Storage devices are called peripheral
devices
Peripheral devices connect to the
computer through electronic interfaces
– IDE - Integrated Drive Electronics
– SCSI - Small Computer System Interface
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Exploring the Root File System
UNIX must mount a file system before any
programs can access files on it
To mount a file system is to connect it to
the directory tree structure
The root file system is mounted by the
kernel when the system starts
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Exploring the Root File
System
The root directory contains sub-directories
that contain files:
– /bin contains binaries, or executables needed
to start the system and perform system tasks
– /boot contains files needed by the bootstrap
loader as well as kernel images
– /dev contains system device reference files
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Exploring the Root File
System
Root subdirectories continued:
– /etc contains configuration files that the
system uses when the computer starts
– /lib contains kernel modules, security
information, and the shared library images
– /mnt contains mount points for temporary
mounts by the system administrator
– /proc is a virtual file system allocated in
memory only
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Exploring the Root File
System
Root subdirectories continued:
– /root is the home directory of the root user, or
the system administrator
– /sbin contains essential network programs
used only by the system administrator
– /tmp is a temporary place to store data during
processing cycles
– /var contains subdirectories which have sizes
that often change, such as error logs
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Understanding Paths
and Pathnames
To specify a file or directory, use its
pathname, which follows the branches of
the file system to the desired file
– A forward slash (/) separates each directory
name
– The UNIX command prompt may indicate
your location within the file system
– Use the UNIX pwd command to display the
current path name
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Navigating the File System
To navigate the UNIX directory structure,
use the cd (change directory) command
UNIX refers to a path as either:
– Absolute - begins at the root level and lists all
subdirectories to the destination file
– Relative - begins at your current working
directory and proceeds from there
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Listing Directory Contents
The ls (list)
command displays
a directory’s
contents, including
files and
subdirectories
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Listing Directory Contents
The system
normally uses
hidden files to keep
configuration
information and for
other purposes
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Managing Directories and
Files
mkdir (make directory) command
– Create a new directory
rmdir (make directory) command
– Delete an empty directory
cp (copy) command
– Copy files from one director to another
rm (remove) command
– Delete files
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Setting File Permissions
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Setting File Permissions
File Permissions
r
Owner has read
w
Owner has write
x
Owner has execute
r
Group has read
-
Group does not have write
x
Group has execute
r
Others have read
-
Others do not have write
x
Others have execute
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Setting File Permissions
for Security
chmod command
– To set file permissions
– Settings are read (r), write (w), execute (x)
– The three types of users are owners, groups,
and others
Setting permissions to directories
– Use the execute (x) to grant access
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