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File Server

File Server

In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files (such as documents, sound files, photographs, movies, images, databases, etc.) that can be accessed by the workstations that are attached to the same computer network. The term server highlights the role of the machine in the client–server scheme, where the clients are the workstations using the storage. A file server is not intended to perform computational tasks, and does not run programs on behalf of its clients. It is designed primarily to enable the storage and retrieval of data while the computation is carried out by the workstations.

File servers are commonly found in schools and offices, where users use a LAN to connect their client computers.

Types of file servers

A file server may be dedicated or non-dedicated. A dedicated server is designed specifically for use as a file server, with workstations attached for reading and writing files and databases.

File servers may also be categorized by the method of access: Internet file servers are frequently accessed by File Transfer Protocol (FTP) or by HTTP (but are different from web servers, that often provide dynamic web content in addition to static files). Servers on a LAN are usually accessed by SMB/CIFS protocol (Windows and Unix-like) or NFS protocol (Unix-like systems).

Database servers, that provide access to a shared database via a database device driver, are not regarded as file servers as they may require Record locking.

Design of file servers

In modern businesses the design of file servers is complicated by competing demands for storage space, access speed, recoverability, ease of administration, security, and budget. This is further complicated by a constantly changing environment, where new hardware and technology rapidly obsolesces old equipment, and yet must seamlessly come online in a fashion compatible with the older machinery. To manage throughput, peak loads, and response time, vendors may utilize queuing theory to model how the combination of hardware and software will respond over various levels of demand. Servers may also employ dynamic load balancing scheme to distribute requests across various pieces of hardware.

The primary piece of hardware equipment for servers over the last couple of decades has proven to be the hard disk drive. Although other forms of storage are viable (such asmagnetic tape and solid-state drives) disk drives have continued to offer the best fit for cost, performance, and capacity.

Storage

Since the crucial function of a file server is storage, technology has been developed to operate multiple disk drives together as a team, forming a disk array. A disk array typically has cache (temporary memory storage that is faster than the magnetic disks), as well as advanced functions like RAID and storage virtualization. Typically disk arrays increase level of availability by using redundant components other than RAID, such as power supplies. Disk arrays may be consolidated or virtualized in a SAN.

Network-attached storage

Main article: Network-attached storage

Network-attached storage (NAS) is file-level computer data storage connected to a computer network providing data access to heterogeneous clients. NAS devices specifically are distinguished from file servers generally in a NAS being a computer appliance – a specialized computer built from the ground up for serving files – rather than a general purpose computer being used for serving files (possibly with other functions). In discussions of NASs, the term “file server” generally stands for a contrasting term, referring to general purpose computers only.

As of 2010 NAS devices are gaining popularity, offering a convenient method for sharing files between multiple computers. Potential benefits of network-attached storage, compared to non-dedicated file servers, include faster data access, easier administration, and simple configuration.

NAS systems are networked appliances containing one or more hard drives, often arranged into logical, redundant storage containers or RAID arrays. Network Attached Storage removes the responsibility of file serving from other servers on the network. They typically provide access to files using network file sharing protocols such as NFS, SMB/CIFS (Server Message Block/Common Internet File System), or AFP.

Security

File servers generally offer some form of system security to limit access to files to specific users or groups. In large organizations, this is a task usually delegated to what is known as directory services such as openLDAP, Novell’s eDirectory or Microsoft’s Active Directory.

These servers work within the hierarchical computing environment which treat users, computers, applications and files as distinct but related entities on the network and grant access based on user or group credentials. In many cases, the directory service spans many file servers, potentially hundreds for large organizations. In the past, and in smaller organizations, authentication could take place directly at the server itself.

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Squid Proxy Server

Squid Proxy Server

Squid Proxy Server

 

Proxy server

Diagram of two computers connected only via a proxy server. The first computer says to the proxy server: "ask the second computer what the time is".

Communication between two computers (shown in grey) connected through a third computer (shown in red) acting as a proxy. Note that Bob doesn’t know whom the information is going to, which is why proxies can be used to protect privacy.

In computer networks, a proxy server is a server (a computer system or an application) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource available from a different server and the proxy server evaluates the request as a way to simplify and control its complexity. Proxies were invented to add structure and encapsulation to distributed systems.[1]Today, most proxies are web proxies, facilitating access to content on the World Wide Web and providing anonymity.

Squid is a proxy server and web cache daemon. It has a wide variety of uses, from speeding up a web server by caching repeated requests; to caching web, DNS and other computer network lookups for a group of people sharing network resources; to aiding security by filtering traffic. Although primarily used for HTTP and FTP, Squid includes limited support for several other protocolsincluding TLS, SSL, Internet Gopher and HTTPS.

Squid was originally designed to run on Unix-like systems. A Windows port was maintained up to version 2.7, but more current versions are not being developed. Squid is free software released under the GNU General Public License.

Supported operating systems

Squid can run on the following operating systems:

  • AIX
  • BSDI
  • Digital Unix
  • FreeBSD
  • HP-UX
  • IRIX
  • Linux
  • Mac OS X
  • Microsoft Windows
  • NetBSD
  • NeXTStep
  • OpenBSD
  • OS/2 and eComStation
  • SCO OpenServer
  • Solaris
  • UnixWare

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Mailing Solution

 

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Linux Security

Linux Security

Linux Security Modules (LSM) is a framework that allows the Linux kernel to support a variety of computer security models while avoiding favoritism toward any single security implementation. The framework is licensed under the terms of the GNU General Public License and is standard part of the Linux kernel since Linux 2.6. AppArmorSELinuxSmackand TOMOYO Linux are the currently accepted modules in the official kernel.

Design

LSM was designed to provide the specific needs of everything needed to successfully implement a mandatory access control module, while imposing the fewest possible changes to the Linux kernel. LSM avoids the approach of system call interposition as used in Systrace because it does not scale to multiprocessor kernels and is subject to TOCTTOU(race) attacks. Instead, LSM inserts “hooks” (upcalls to the module) at every point in the kernel where a user-level system call is about to result in access to an important internal kernel object such as inodes and task control blocks.

The project is narrowly scoped to solve the problem of access control to avoid imposing a large and complex change patch on the mainstream kernel. It is not intended as a general “hook” or “upcall” mechanism, nor does it support Operating system-level virtualization.

LSM’s access control goal is very closely related to the problem of system auditing, but is subtly different. Auditing requires that every attempt at access be recorded. LSM cannot deliver that, because it would require a great many more hooks, so as to detect cases where the kernel “short circuits” failing system calls and returns an error code before getting near significant objects.

The LSM design is described in the paper Linux Security Modules: General Security Support for the Linux Kernel presented at USENIX Security 2002. At the same conference was the paper Using CQUAL for Static Analysis of Authorization Hook Placement which studied automatic static analysis of the kernel code to verify that all of the necessary hooks have actually been inserted into the Linux kernel.

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