Networking Operating Systems (CO32010)

Transcription

1 Networking Operating Systems (CO32010) 1. Operating Systems 2. Processes and scheduling Objectives: To discuss the advantages of a distributed file system. To outline the different methods of mounting remote file systems onto a file system structure. To outline practical implementations of a distributed file systems, especially NFS. To show how domains can be created and managed, especially using standard protocols, such as NIS. 7. Encryption 3. Distributed processing 8. NT, UNIX and NetWare 4.1 Distributed File Systems 4.2 Active Directories 4.3 Exercises 4.4 Sample exam question 6. Routers 5. Routing protocols 4. Distributed file systems

2 4.1 Distributed file system Administration services Mounted as a local drive Network Localized File storage (rather than accessing a remote file) Networked file system (NFS) Distributed databases Centralized Configuration (passwords, user IDs, and so on)

3 4.2 Advantages of distributed file systems File system mirrors the corporate structure. File systems can be distributed over a corporate network, which might span cities, countries or even continents. The setup of a complete network file system over a corporation can allow the network to mirror the logical setup of the organization, rather than its physical and geographical organization. For example the Sales Department might be distributed around the world, but the network in which they connect to is identical to the way that the Sales Department is organized. Easier to protect the access rights on file systems. In a distributed file system it is typical to have a strong security policy on the file system, and each file will have an owner who can define the privileges on this file. File systems on user computers tend to have limited user security. Increased access to single sources of information. Many users can have access to a single source of information. Having multiple versions of a file can cause a great deal of problems, especially if it is not know as to which one is the most up-to-date. Automated updates. Several copies of the same information can be stored, and when any one of them is updated they are synchronized to keep each of them up-to-date. Users can thus have access to a local copy of data, rather than accessing a remote copy of it. This is called mirroring files.

4 4.3 Advantages of distributed file systems Improved backup facilities. A user s computer can be switched-off, but their files can still be backed-up from the distributed file system. Increased reliability. The distributed file system can have a backbone which is constructed from reliable and robust hardware, which are virtually 100% reliable, even when there is a power failure, or when there is a hardware fault. Larger file systems. In some types of distributed file systems it is possible to build-up large file systems from a network of connected disk drives. Easier to administer. Administrators can easily view the complete file system. Interlinking of databases. Small databases can be linked together to create large databases, which can be configured for a given application. The future may also bring the concept of data mining, where agent programs will search for information with a given profile by interrogating databases on the Internet. Limiting file access. Organizations can setup an organization file structure, in which users can have a limited view of complete file system.

5 4.4 Traditional file structure v. corporate structure UNIX \ \ NDS/ Active Directories orgname orgname users users config config sales sales production production progs progs research research Tree structure fred fred bert bert UK UK Office Office US US Office Office

6 4.5 Flat structures \\ \\ Windows NT NT uses uses a flat flat structure, where nodes join join into into a domain \\bert \\bert \\fred \\fred Network \\freddy Local disk Local disk Local disk Domain Flat structure

7 4.6 Forest of drives v. single tree Single tree /etc Global File system /progs Drives mounted over the network to create a single tree /user /sys Network Forest of drives C: D: E: F: Drives mounted over the network to a forest of drives

8 4.7 NFS services protocol stack Application NFS NIS Presentation XDR XDR defines a common data format for the conversion of data values. Session Transport Network Data link Physical RPC TCP IP Ethernet/ Token Ring RPC defines a a number of procedures which can be executed on the server, such as WRITE, CREATE, and so on. RPC is stateless, where a NFS server waits for a client to contact it for a client to contact it, it then gets a request for a service, and sends back the results.

9 4.8 Some RPC procedures used by NFS No Procedure void NULL(void) attrstat GETATTR(fhandle) attrstat SETATTR(sattrargs) readres READ(readargs) attrstat WRITE(writeargs) diropres CREATE(createargs) stat REMOVE(diropargs) stat RENAME(renameargs) stat LINK(linkargs) diropres MKDIR(createargs) stat RMDIR(diropargs) Name No operation Get file attributes Set file attributes Read from file Write to file Create file Remove file Rename file Create link to file Create symbol link Create directory

10 4.9 RPC procedures and responses NFS server Remotely accessed file system RPC procedures getattr, setattr, read, write, create, remove, rename, link, symlink, mkdir, rmdir, readdir Network RPC response Requested data, parameters or status flag (such as: NFS_OK and NFSERR_PERM) File system either mounted onto a single tree or as a forest of drives NFS client

11 #/etc/protocols #/etc/protocols ip 0 IP ip 0 IP icmp 1 ICMP icmp 1 ICMP ggp 3 GGP ggp 3 GGP tcp 6 TCP tcp 6 TCP Server 4.10 NIS domain Master NIS server maintains: /etc/passwd Domain passwords /etc/groups Domain groups /etc/hosts IP addresses and host names /etc/rpc RPC processes /etc/network Used to map IP address to networks /etc/protocols Known network layer protocols /etc/services Known transport layer protocols #/etc/hosts #/etc/groups #/etc/hosts #/etc/groups bath root::0:root bath root::0:root compuserve other::1:root,hpdb compuserve other::1:root,hpdb niss bin::2:root,bin niss bin::2:root,bin hensa sys::3:root,uucp hensa sys::3:root,uucp janet freds_grp::4:fred,fred2,fred janet freds_grp::4:fred,fred2,fred3 Clients NIS Domain #/etc/passwd #/etc/passwd root:fdec6.32:1:0:super unser:/user:/bin/csh root:fdec6.32:1:0:super unser:/user:/bin/csh fred:jt.06hldisdaa:2:4:fred Blogs:/user/fred:/bin/csh fred:jt.06hldisdaa:2:4:fred Blogs:/user/fred:/bin/csh fred2:jty067sdisfaa:3:4:fred Smith:/user/fred2:/bin/csh fred2:jty067sdisfaa:3:4:fred Smith:/user/fred2:/bin/csh #/etc/rpc #/etc/rpc portmapper portmap sunrpc portmapper portmap sunrpc rstatd rstat rstat_svc rstatd rstat rstat_svc rusersd rusers rusersd rusers nfs nfsprog nfs nfsprog ypserv ypprog ypserv ypprog #/etc/services #/etc/services ftp 21/tcp ftp 21/tcp telnet 23/tcp telnet 23/tcp smtp 25/tcp smtp 25/tcp pop3 110/tcp pop3 110/tcp #/etc/networks #/etc/networks loopback loopback localnet localnet Production Production

12 4.11 NIS master and slave(s) Master NIS Server maintains: /etc/passwd /etc/groups /etc/hosts /etc/rpc /etc/network /etc/protocols /etc/services and so on. NIS Domain Master sends updates to NIS slaves Slave NIS server 2. Client broadcasts an NIS request to the domain Slave NIS server 3. The client then binds to the first server which responds NIS client 1. Client is started

13 4.12 inetd.conf defines the network services that are started # <service_name> <sock_type> <proto> <flags> <user> <server_path> <args> # Echo, discard and daytime are used primarily for testing. echo stream tcp nowait root internal echo dgram udp wait root internal discard stream tcp nowait root internal discard dgram udp wait root internal daytime stream tcp nowait root internal daytime dgram udp wait root internal time dgram udp wait root internal # # These are standard services. ftp stream tcp nowait root /usr/sbin/tcpd /usr/sbin/wu.ftpd telnet stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.telnetd # # Shell, login, exec and talk are BSD protocols. shell stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.rshd login stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.rlogind talk dgram udp wait root /usr/sbin/tcpd /usr/sbin/in.ntalkd ntalk dgram udp wait root /usr/sbin/tcpd /usr/sbin/in.ntalkd # # Pop mail servers pop3 stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.pop3d # bootps dgram udp wait root /usr/sbin/tcpd /usr/sbin/in.bootpd # finger stream tcp nowait daemon /usr/sbin/tcpd /usr/sbin/in.fingerd systat stream tcp nowait guest /usr/sbin/tcpd /usr/bin/ps -auwwx