1. File System Implementation
A file system must be mounted before it can be accessed.
An unmounted file system is mounted at a mount point.
Operating System Concepts

2. Swap-Space Management
Swap-space - Virtual memory uses disk space as an extension of the main memory.
Swap-space can be:
carved out of the normal file system (Windows)
in a separate disk partition (UNIX).
UNIX does the swapping faster, while changing the size of the swap area is easier on Windows.
Operating System Concepts

3. The UNIX Network File System (NFS)
An implementation and a specification of a software system for accessing remote files across LANs.
Interconnected workstations with independent file systems, allow sharing a part of these file systems in a transparent manner.
A remote directory is mounted over a local file system directory. The mounted directory looks like an integral subtree of the local file system.
If there is a subtree with the same name, descending from the local directory, it will be replaced by the remote subtree.
Specification of the remote directory for the mount operation is nontransparent; the host name of the remote directory and the directory's name have to be provided. Files in the remote directory can then be accessed in a transparent manner.
Subject to access-rights accreditation, potentially any file system (or directory within a file system), can be mounted remotely on top of any local directory.
Operating System Concepts

4. Operating System Concepts
NFS (Cont.)
NFS is designed to operate in a heterogeneous environment of different machines, operating systems, and network architectures.
At the client: Mount operation includes name of remote directory to be mounted and name of server machine storing it.
At the server: Export list – specifies local file systems that server exports for mounting, along with names of machines that are permitted to mount them.
NFS path-name translation is performed by breaking the path into component names and performing a separate NFS lookup call for each directory.
To make lookup faster, a directory name lookup cache on the client’s side holds the location of least recently used remote directories.
Operating System Concepts

5. LDAP - Directory Service
Tim Howes at the University of Michigan develops LDAP as a lightweight directory access protocol on 1998.
It maintains a database with information on the users and computers on your network.
LDAP Versions:
UNIX/LINUX: LDAP, OpenLDAP
There was a pre-"directory services" on UNIXes before LDAP called NIS (or yp); however NIS lacks encryption, object oriented and in most of its versions NIS lacks GUI.
Microsoft: ActiveDirectory
Lotus: Domino/Notes
Novell: NDS and GroupWise
Operating System Concepts

6. Operating System Concepts
LDAP Features
Single Sign-on: A user can use the same username and password to log onto many different machines.
The administrator no longer has to setup a user account on each machine that the user needs access to.
Redirected Profiles/Folder: Users' files are stored in a central location. users' desktop, settings and files appear to follow them to whatever machine they use.
Backing up important files becomes easier.
Group Policy: configuring many computers simultaneously; e.g.: specifying that:
Applications be automatically installed on certain computers.
Certain users cannot use specific programs or Control Panel Applets.
specific machines should not run specific services.
Operating System Concepts

7. Operating System Concepts
LDAP Features (cont.)
Group Hierarchy: Groups can be grouped into bigger groups forming trees of groups.
Can help reducing the needs of multiplied lists.
The data is more organized.
Replication: LDAP can be easily replicated between two or more machines.
Redundancy. If one machine dies, LDAP can continue to run.
All the LDAP servers have up-to-date databases, therefore some users can use different servers; yielding load balancing and better performance.
Interface: LDAP can be accessed by GUI, Command Line Utilities, Shell, JavaScript, Java, Perl and C/C++.
Operating System Concepts

8. Operating System Concepts
LDAP organization
LDAP is well suited for:
Information that is referenced by many entities and applications.
Information that needs to be accessed from more then one location.
Information that is read more often than it is written.
LDAP is not well suited for
Information that changes often. It is not a relational database and for each change it compiles the entire file again.
Operating System Concepts

9. Operating System Concepts
DHCP
DHCP stands for Dynamic Host Configuration Protocol.
DHCP server assigns dynamic IP addresses (identifiers for a computer or device) to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network.
In some systems, the device's IP address can even change while it is still connected.
DHCP also supports a mix of static and dynamic IP addresses.
The client sends its MAC (Media Access Control) address to the dhcp server and gets an IP number.
Dynamic addressing simplifies network administration because DHCP keeps track of IP addresses rather than requiring an administrator to manage the task.
This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address.
Many ISPs use dynamic IP addressing for dial-up users.
Operating System Concepts

10. Operating System Concepts
SAMBA
SAMBA stands for Session Message Block.
SAMBA is a protocol for sharing
files
printers
serial ports
communications abstractions such as named pipes
Using SAMBA, UNIX machines and Windows machines can see and understand each other files and directories.
Operating System Concepts