Operating Systems use fast, CPU-addressable main memory to maintain an application’s temporary data as anonymous data and to cache copies of persistent data stored in slower block-based storage devices. However, the use of this faster memory comes at a high cost. Therefore, several techniques have been implemented to use main memory more efficiently in the literature. In this dissertation we introduce three distinct approaches to improve overall system performance by optimizing main memory usage. First, DRAM and host-side caching of file system data are used for speeding up virtual machine performance in today’s virtualized data centers. The clustering of VM images that share identical pages, coupled with data deduplication, has the potential to optimize main memory usage, since it provides more opportunity for sharing resources across processes and across different VMs. In our first approach, we study the use of content and semantic similarity metrics and a new algorithm to cluster VM images and place them in hosts where through deduplication we improve main memory usage. Second, while careful VM placement can improve memory usage by eliminating duplicate data, caches in current systems employ complex machinery to manage the cached data. Writing data to a page not present in the file system page cache causes the operating system to synchronously fetch the page into memory, blocking the writing process. In this thesis, we address this limitation with a new approach to managing page writes involving buffering the written data elsewhere in memory and unblocking the writing process immediately. This buffering allows the system to service file writes faster and with less memory resources. In our last approach, we investigate the use of emerging byte-addressable persistent memory technology to extend main memory as a less costly alternative to exclusively using expensive DRAM. We motivate and build a tiered memory system wherein persistent memory and DRAM co-exist and provide improved application performance at lower cost and power consumption with the goal of placing the right data in the right memory tier at the right time. The proposed approach seamlessly performs page migration across memory tiers as access patterns change and/or to handle tier memory pressure.

The thesis deals with models used in access control to operating systems' resources. The thesis' goals are the theoretical description of these models and their comparison, the description of their implementations in selected operating systems and the description of their utilization in securing typified servers. In the first chapter, the reader is introduced to basic terms and principles of computer security and access control. In the second, also theoretical part, selected access control models are described from different viewpoints, for example their factual specialization, basic rules, principles and evolution. At the end of the chapter, the models are compared to each other according to specified criteria. The third, more practically oriented chapter, continues from the initial, both general and concrete introduction with operating systems, to description of access control model implementations in selected operating systems. At the end of the chapter, these implementations too are compared according to specified criteria. The fourth, final part, is dedicated to the description of the actual securing of a web and file server using operating system level access control means. The end of the chapter is dedicated to the possibilities of using these means to secure web applications. The contribution of this thesis from the theoretical point of view is a well-arranged and compact access control model comparison, and also the merger of the theoretical base with practical use of the described model implementations. The thesis is recommended to people interested in the computer security issues in general and people interested in access control from both theoretical and practical sides, e.g. system administrators or system designers.

The virtualization of IT infrastructure enables the consolidation and pooling of IT resources so that they can be shared over diverse applications to offset the limitation of shrinking resources and growing business needs. Virtualization provides a logical abstraction of physical computing resources and creates computing environments that are not restricted by physical configuration or implementation. Virtualization is very important for cloud computing because the delivery of services is simplified by providing a platform for optimizing complex IT resources in a scalable manner, which makes cloud computing more cost effective. Hypervisor plays an important role in the virtualization of hardware. It is a piece of software that provides a virtualized hardware environment to support running multiple operating systems concurrently using one physical server. Cloud computing has to support multiple operating environments and Hypervisor is the ideal delivery mechanism. The intent of this thesis is to quantitatively and qualitatively compare the performance of VMware ESXi 4.1, Citrix Systems Xen Server 5.6 and Ubuntu 11.04 Server KVM Hypervisors using standard benchmark SPECvirt_sc2010v1.01 formulated by Standard Performance Evaluation Corporation (SPEC) under various workloads simulating real life situations.

The scope of this project describes World Wide Graphics (WWG) a software package that provides instructors with the tools needed to present a web-based presentation to a group of students while having the ability of enhancing the prepared HTML slide with userdrawn graphics and highlighting.

A Distributed Shared Memory(DSM) system consists of several computers that share a memory area and has no global clock. Therefore, an ordering of events in the system is necessary. Synchronization is a mechanism for coordinating activities between processes, which are program instantiations in a system.

This thesis presents the developed taxonomy of the agent-based distributed computing systems. Based on this taxonomy, a design, implementation, analysis and distribution protocol of a multi-agent architecture for internet-based distributed computing system was developed. A prototype of the designed architecture was implemented on Spider III using the IBM Aglets software development kit (ASDK 2.0) and the language Java.

This thesis deals with the implementation of ACP protocol which serves to manage the access for operation system based on L4 microkernel. The theoretical part of the thesis deals with methods of access management in computer networks. It focuses primarily on AAA systems which make access management possible. Furthermore it describes in detail the ACP protocol, the types of messages and their feedback. The next theoretical part is dedicated to operation systems and in particular to their architecture and services. Then we get a closer look at L4 microkernel family, their philosophy and properties. We continue with a detailed description of the L4 application interface and its ways of expansion. The practical section deals with the implemented concept of system for ACP protocol support in computers. General concept is then applied in real implementation of ACP protocol into the L4 operation system environment based on the L4 platform. To assist, I also included a detailed tutorial explaining the modeling and compilation of software for this platform. At this point we describe the methods used at the implementation and the description of particular modules and features. The end of the thesis concludes the information about the ways of testing and the implementation properties.

This Master thesis describes the configuration of operating systems and their capabilities. It introduces differences between configuration of different operating systems according to their specialization, and it introduces advanced configuration of operating systems with third-party applications. The practical part of the thesis is a design of a new computer language aimed at describing a configuration of an operating system and its services. Such a description is used to automatically configure system services by translating it to a sequence of configuration commands. An advantage of the language is its readability by a human, but its similarity with natural languages introduces a certain level of ambiguity. The proposed method of automatic generation of commands deals with the ambiguity by searching and selecting as least as possible destructive commands.

Idag beskärs en stålrulle inom stålindustrin i ett skärverk, stålrullarna delas tillmindre delband med dålig kontroll av skärgradshöjdens kvalitet. Stickprover tas manuelltvilket endast blir ett fåtal stickprover på en stålrulle som har 150 delband ochär 30 kilometer i längd. En hål omsändning för en stålrulle kostar upp mot en miljonkronor och har en negativ klimatpåverkan. En mjukvaruprototyp för detektering avskärgradshöjd med en referenslinje togs fram. Prototypen innehöll en ljussensor, tvåmotorer, en PC och en prototypkonstruktion. Varje uppgift i programvaran tilldeladesen egen tråd. Operativsystem, trådar och algoritmer prestanda testades för mätningav exekveringstider och periodtider. Resultatet visade att en skärgradsdetektorvar möjlig att realisera. Algoritmen för skärgradshöjd med referenslinje detekteradeskärgradshöjden där amplituden var tillräckligt stor. / Today, a steel roll is cut within the steel industry in a cutting factory, the steel rollsare divided to smaller part bands with poor control of the burr height quality. Samplesis taken manually, the amount of samples is too low to know the quality of thesteel roll, the steel rolls can be divided up to 150 times and the length will be 30 kilometers. A whole resend for one steel roll costs up against a million SEK and has anegative climatic impact. One software prototype for detection of burr heights witha reference line was programmed. The prototype contained one light sensor, two motors,a PC and one prototype construction. Each task in the software was allocatedan own thread. Operating systems, threads and algorithms was performance testedfor measurement of execution times and period times. The result showed that a burrheight detector where possible to implement. The algorithm could detect burrheights that were too large related to its reference line.

Internet of Things (IoT) devices are devices with embedded sensors or software. Their usage is becoming more prevalent. They are used for smart homes, traffic tracking, weather data and sensor networks. Often IoT devices communicate wirelessly using low-power protocols. A wireless connection provides an easy way to eavesdrop on personal data or even hijack connections. Thus security measures need to be taken. Our thesis looks at a specific IoT operating system, Contiki-NG, and describes the porting process of a Transportation Layer Protocol (TLS) protocol library, MbedTLS. The porting process consists of specific modules that need to be adapted to the Contiki-NG environment. After porting, example programs that send and receive datawere written to enable performance testing that includes execution time, runtime memory usage and code space. The results of the tests were analyzed and evaluated. The produced implementation from porting MbedTLS to Contiki-NG provides a secure connection between two hosts running the TLS protocol. The highly configurable nature of MbedTLS allows the implementation to be adapted to comply to the resource constraints of platforms supported by Contiki-NG. / Internet of Things (IoT)-enheter är enheter med inbyggda sensorer eller mjukvara. Deras användning blir allt vanligare. De används för smarta hem, trafikspårning, väderdata och sensornätverk. Ofta kommunicerar IoT-enheter trådlöst med protokoll med låg energiförbrukning. En trådlös anslutning ger ett enkelt sätt att avlyssna personuppgifter eller till och med att kapa anslutningar. Därför måste säkerhetsåtgärder vidtas. Vårt examensarbete täcker ett specifikt IoT-operativsystem Contiki-NG och beskriver en portningsprocess av ett TLS-protokollbibliotek (Transportation Layer Protocol), MbedTLS. Portningen består av specifika moduler som behöver anpassas till den ursprungliga Contiki-NG-miljön. Efter portningen skrevs exempelprogram som skickar och tar emot data för att möjliggöra prestandatestning som inkluderar exekveringstid, minnesanvändning och kodutrymme. Resultaten av testerna analyserades och utvärderades. Den framställda implementeringen från att överföra MbedTLS till Contiki- NG gav en säker anslutning mellan de två ändpunkterna som kommunicerar med TLS-protokollet. Den i hög grad konfigurerbara karaktären hos MbedTLS gjorde det möjligt att anpassa implementeringen för att följa resursbegränsningarna för plattformar som stöds av Contiki-NG.