Loads the data from the given locations, converts them to character string equivalents and writes the results to a variety of sinks.

Within the /proc/ directory, one can find a wealth of information detailing the system hardware and any processes currently running. In addition, some of the files within the /proc/ directory tree can be manipulated by users and applications to communicate configuration changes to the kernel.It  also know as virtual file system.

• Processes do not share their address space while threads executing under same process share the address space.
• From the above point its clear that processes execute independent of each other and the synchronization between processes is taken care by kernel only while on the other hand the thread synchronization has to be taken care by the process under which the threads are executing
• Context switching between threads is fast as compared to context switching between processes
• The interaction between two processes is achieved only through the standard inter process communication while threads executing under the same process can communicate easily as they share most of the resources like memory, text segment etc

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@three client used into server1.
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@single client .
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@client for server1 rcs file.
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@processing for server
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1.pipes:it is related data only send from one pipe output is giving to another pipe input

to share resouses pipe are used

drawback:itis only related process only communicated

2.message queues:message queues are un related process are also communicate with message queues

drawback:user dont know which process curently works

share memory:memory shared in distributed systems some memory wants to share some files that time it is use full

semaphores
semaphore is integer type and in semaphore resourses give coding like negetive value means process are wants to use perticular resource waiting only

and 0 means no process is waiting

and 1 means one resource is free

and

sockets:sockets also ipc it is comunicate clients and server

with socket system calls connection oriented and connection less also

IPCs are
1.FIFO
2.Message Queue
3.Shared Memory
4.PIPE
5.Semaphore

we can also say the Sockets is one of the IPCs

     FILE *popen ( char *command, char *type);

This standard library function creates a half-duplex pipeline by calling pipe() internally. It then forks a child process, exec the Bourne shell, and executes the “command” argument within the shell. Direction of data flow is determined by the second argument, “type”. It can be “r” or “w”, for “read” or “write”. It cannot be both! popen() returns the pointer to the new file stream or NULL on failure.

Pipes which are created with popen() must be closed with pclose(). popen() and pclose() share a striking resemblance to the standard file stream I/O functions fopen() and fclose().

     int pclose( FILE *stream );

The pclose() function performs a wait4() (waits for process termination) on the process forked by popen(). When it returns, it destroys the pipe and the file stream. Once again, it is synonymous with the fclose() function for normal stream-based file I/O. The pclose() returns wait4() status. If everything is all right it simply returns 0.

We have now began to see how multiple processes may be running on a machine and maybe be controlled (spawned by fork() by one of our programs.

In numerous applications there is clearly a need for these processes to communicate with each exchanging data or control information. There are a few methods which can accomplish this task. We will consider:

• Pipes
• Signals
• Message Queues
• Semaphores
• Shared Memory
• Sockets

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@semaphore with semget,semctl,semop.
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text
@#include<stdio.h>
#include<linux/sem.h>
#include<stdlib.h>
int main()
{
int i,aa,aaa;
union semun u;
u.val=1;
struct sembuf sem1;
sem1.sem_num=0;
sem1.sem_op=-1;
sem1.sem_flg=SEM_UNDO;

aa=semget((key_t)1234,1,IPC_CREAT|0777);
if(aa<0)
{
perror(“semget failure\n”);
goto OUT;
}
aaa=semctl(aa,0,SETVAL,0);
if(aaa<0)
{
perror(“segctl failure\n”);
goto OUT;
}
semop(aa,&sem1,0);
for(i=1;i<=3;i++)
{
printf(“hello i m into critical section =%d\n”,getpid());
sleep(2);
printf(” i m into critical section =%d\n”,getpid());
sleep(2);
printf(“bye i m into critical section =%d\n”,getpid());

}

sem1.sem_num=0;
sem1.sem_op=1;
sem1.sem_flg=SEM_UNDO;
semop(aa,&sem1,0);
return 0;
OUT:
return -1;
}
@

The Dynamic Host Configuration Protocol is used by computers for requesting Internet Protocol parameters, such as an IP address from a network server. The protocol operates based on the client-server model. DHCP is very common in all modern networks^[1] ranging in size from home networks to large campus networks and regional Internet service provider networks. Most residential network routers receive a globally unique IP address within the provider network. Within a local network, DHCP assigns a local IP address to devices connected to the local network.

When a computer or other networked device connects to a network, its DHCP client software in the operating system sends a broadcast query requesting necessary information. Any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, time servers. On receiving a request, the server may respond with specific information for each client, as previously configured by an administrator, or with a specific address and any other information valid for the entire network, and the time period for which the allocation (lease) is valid. A host typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When an assignment is refreshed by the client computer, it initially requests the same parameter values, but may be assigned a new address from the server, based on the assignment policies set by administrators.

On large networks that consist of multiple links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets.

Depending on implementation, the DHCP server may have three methods of allocating IP-addresses:

• dynamic allocation: A network administrator reserves a range of IP addresses for DHCP, and each client computer on the LAN is configured to request an IP address from the DHCP server during network initialization. The request-and-grant process uses a lease concept with a controllable time period, allowing the DHCP server to reclaim (and then reallocate) IP addresses that are not renewed.
• automatic allocation: The DHCP server permanently assigns an IP address to a requesting client from the range defined by the administrator. This is like dynamic allocation, but the DHCP server keeps a table of past IP address assignments, so that it can preferentially assign to a client the same IP address that the client previously had.
• static allocation: The DHCP server allocates an IP address based on a preconfigured mapping to each client’s MAC address. This feature is variously called static DHCP assignment by DD-WRT, fixed-address by the dhcpd documentation, address reservation by Netgear, DHCP reservation or static DHCP by Cisco and Linksys, and IP address reservation or MAC/IP address binding by various other router manufacturers.

DHCP is used for Internet Protocol version 4 (IPv4), as well as IPv6. While both versions serve the same purpose, the details of the protocol for IPv4 and IPv6 are sufficiently different that they may be considered separate protocols.^[2] IPv6 devices may alternatively use stateless address autoconfiguration. IPv4 hosts may use link-local addressing to achieve limited local connectivity.