Networking Operating Systems (CO 32010) Objectives: 2. Processes • To discuss the advantages of a distributed file system. and • To outline the different methods of mounting remote file scheduling systems onto a file system structure. • To outline practical implementations of a distributed file 1. Operating systems, especially NFS. Systems • To show domains can be created and managed, especially using standard protocols, such as 3. Distributed NIS. 7. Encryption 4. 1 4. 2 4. 3 4. 4 processing 8. NT, UNIX and Net. Ware Distributed File Systems Active Directories Exercises Sample exam question 6. Routers 5. Routing protocols http: //www. soc. napier. ac. uk/~bill/nos. html 4. Distributed file systems bill@napier, 2002
4. 1 Distributed file system Administration services Network Mounted as a local drive Localized File storage (rather than accessing a remote file) Distributed databases Networked file system(NFS) http: //www. soc. napier. ac. uk/~bill/nos. html Centralized Configuration (passwords, user IDs, and so on) bill@napier, 2002
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. http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
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. http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
4. 4 Traditional file structure v. corporate structure UNIX NDS/ Active Directories Tree structure http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
4. 5 Flat structures \ \bert \fred Windows NT uses a flat structure, where nodes join into a domain \freddy Network Local disk Domain Flat structure http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
4. 6 Forest of drives v. single tree Single tree Global File system /etc Drives mounted over the network to create a single tree /progs /user /sys Network C: Forest of drives E: D: F: http: //www. soc. napier. ac. uk/~bill/nos. html Drives mounted over the network to a forest of drives bill@napier, 2002
4. 7 NFS services protocol stack XDR defines a common data format for the conversion of data values. 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, it then gets a request for a service, and sends back the results. http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
4. 8 Some RPC procedures used by NFS No. Procedure Name 0 void NULL (void) No operation 1 attrstat GETATTR (fhandle) Get file attributes 2 attrstat SETATTR (sattrargs) Set file attributes 6 readres READ (readargs) Read from file 8 attrstat WRITE (writeargs) Write to file 9 diropres CREATE (createargs) Create file 10 stat REMOVE (diropargs) Remove file 11 stat RENAME (renameargs) Rename file 13 stat LINK (linkargs) Create link to file 14 diropres MKDIR (createargs) Create symbol link 15 stat RMDIR (diropargs) Create directory http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
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 File system either mounted onto a single tree or as a forest of drives http: //www. soc. napier. ac. uk/~bill/nos. html RPC response Requested data, parameters or status flag (such as: NFS_OK and NFSERR_PERM) NFS client bill@napier, 2002
4. 10 NIS domain #/etc/protocols ip 0 icmp 1 ggp 3 tcp 6 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 IP ICMP GGP TCP Server #/etc/groups root: : 0: root other: : 1: root, hpdb bin: : 2: root, bin sys: : 3: root, uucp freds_grp: : 4: fred, fred 2, fred 3 Clients NIS Domain #/etc/rpc portmapper rstatd rusersd nfs ypserv 100000 100001 100002 100003 100004 portmap sunrpc rstat_svc rusers nfsprog ypprog #/etc/hosts 138. 32. 45 198. 4. 6. 3 193. 63. 76. 2 148. 8. 84 146. 176. 2. 3 bath compuserve niss hensa janet #/etc/passwd root: FDEc 6. 32: 1: 0: Super unser: /user: /bin/csh fred: jt. 06 h. Ldi. SDa. A: 2: 4: Fred Blogs: /user/fred: /bin/csh fred 2: jt. Y 067 Sdi. SFa. A: 3: 4: Fred Smith: /user/fred 2: /bin/csh #/etc/services ftp 21/tcp telnet 23/tcp smtp 25/tcp pop 3 110/tcp http: //www. soc. napier. ac. uk/~bill/nos. html #/etc/networks loopback 127. 0. 0. 0 localnet 146. 176. 151. 0 Production 146. 176. 142. 0 bill@napier, 2002
4. 11 NIS master and slave(s) Master NIS Servermaintains: /etc/passwd /etc/groups /etc/hosts /etc/rpc /etc/network /etc/protocols /etc/services and so on. Master sends updates to NIS slaves Slave NIS server NIS Domain 2. Client broadcasts an NIS request to the domain 1. Client is started 3. The client then binds to the first server which responds Slave NIS server http: //www. soc. napier. ac. uk/~bill/nos. html NIS client bill@napier, 2002
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 # # 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 pop 3 stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in. pop 3 d # 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 http: //www. soc. napier. ac. uk/~bill/nos. html bill@napier, 2002
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