- The signal() command can be used in 3 modes :-
(i) Default mode (Terminate the process)
SIG_DFL –> is used in place of func.
(ii) Ignore the signal
SIG_IGN –> is used in place of func.
(iii) User defined mode
User defined function is used in place of func.

- The signal command returns the function which is setup to handle the signal, SIG_DFL or SIG_IGN in 3rd, 1st and 2nd cases respectively.

- They can also be used to sent from one process to another as a way of passing information or modifying behaviour.

- As default, if a process receives any signal, process will be terminated immediately.
- Usually a core dump file is created.

- The signals are defined by including header file signal.h
- They all begn with “SIG”.
- There are 64 signals in LINUX.
- The can be listed using command :-
kill -l
- Some of the signals are :-

Signal Name       Description
SIGABORT          Process Abort
SIGALRM           Alarm Clock
SIGFPE            Floating Point Exception
SIGHUP            Hangup
SIGILL            Illegal Instruction
SIGINT            Terminal Interrupt
SIGKILL           Kill (can’t be caught or ignored)
SIGPIPE           Write on a pipe with no reader
SIGQUIT           Terminal Quit
SIGSEGV           Invalid memory segment access (Segmentation Fault)
SIGTERM           Termination
SIGUSR1           User-defined signal 1
SIGUSR2           User-defined signal 2

SIGCHLD           Child process has stopped or exited
SIGCONT           Continue exexuting, if stopped
SIGSTOP           Stop Executing (Can’t be caught or ignored)
SIGTSTP           Terminal stop signal
SIGTTIN           Background process trying to read
SIGTTOU           Background process trying to write

- SIGINT can be called using Ctrl-C
- A signal has 3 steps:-
1) raise
2) catch
3) ignore/handle

RCS file: request.h,v
Working file: request.h
head: 1.19
branch:
locks: strict
root: 1.19
access list:
symbolic names:
keyword substitution: kv
total revisions: 19;    selected revisions: 19
description:
It contains struct request
It is format of basic client request.
It contains client PID, 2 objects,operation to be performed.
—————————-
revision 1.19    locked by: root;
date: 2016/01/06 10:22:24;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.18
date: 2016/01/04 11:02:29;  author: root;  state: Exp;  lines: +1 -1
maximum clients are changed from 1000 to 10000.
—————————-
revision 1.17
date: 2016/01/04 10:39:25;  author: root;  state: Exp;  lines: +1 -1
No. of MAX_CLIENT increased to 1000.
—————————-
revision 1.16
date: 2016/01/01 02:30:39;  author: root;  state: Exp;  lines: +1 -1
No. of clients = 100
—————————-
revision 1.15
date: 2016/01/01 02:13:15;  author: root;  state: Exp;  lines: +2 -0
signal.h is included.
—————————-
revision 1.14
date: 2015/12/21 09:54:15;  author: root;  state: Exp;  lines: +1 -1
CIIENT_MAX = 5
—————————-
revision 1.13
date: 2015/12/21 09:45:17;  author: root;  state: Exp;  lines: +1 -1
No. of clients increased to 1114.
—————————-
revision 1.12
date: 2015/12/21 09:27:52;  author: root;  state: Exp;  lines: +1 -1
No. of clients is 114.
—————————-
revision 1.11
date: 2015/12/21 09:13:31;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.10
date: 2015/12/21 09:07:47;  author: root;  state: Exp;  lines: +1 -1
No. of clients is increased from 4 to 5.
—————————-
revision 1.9
date: 2015/12/21 08:50:23;  author: root;  state: Exp;  lines: +1 -1
No. of MAX_CLIENT becomes 4
—————————-
revision 1.8
date: 2015/12/21 07:09:44;  author: root;  state: Exp;  lines: +1 -0
*** empty log message ***
—————————-
revision 1.7
date: 2015/12/21 05:56:59;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.6
date: 2015/12/21 05:52:10;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.5
date: 2015/12/21 05:50:03;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.4
date: 2015/12/21 05:46:10;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.3
date: 2015/12/21 05:32:51;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.2
date: 2015/12/21 05:27:31;  author: root;  state: Exp;  lines: +1 -1
Macro of REQUESTFIFO is redefined which contains a %d which will be its PID.
—————————-
revision 1.1
date: 2015/12/21 04:56:38;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: adder.c,v
Working file: adder.c
head: 1.4
branch:
locks: strict
root: 1.4
access list:
symbolic names:
keyword substitution: kv
total revisions: 4;    selected revisions: 4
description:
adder has command line arguments which contains File Descriptors of pipe.
adder read request from server for adding 2 objects
adder write result(int) into server.
—————————-
revision 1.4    locked by: root;
date: 2016/01/06 08:52:29;  author: root;  state: Exp;  lines: +1 -1
signal is removed.
—————————-
revision 1.3
date: 2016/01/01 02:07:16;  author: root;  state: Exp;  lines: +2 -1
alarm signal is send to server after it writes result to server
—————————-
revision 1.2
date: 2015/12/21 09:59:14;  author: root;  state: Exp;  lines: +1 -1
print statement decreased.
—————————-
revision 1.1
date: 2015/12/21 04:40:12;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: client1.c,v
Working file: client1.c
head: 1.15
branch:
locks: strict
root: 1.15
access list:
symbolic names:
keyword substitution: kv
total revisions: 15;    selected revisions: 15
description:
It open the requestfifo
Write request for addition using struct request to server
Then, it reads result(int) from server.
Before reading result “resultfifo” is being created by client.
Different clients uses same requestfifo but they have unique resultfifo which is created by client itself.
—————————-
revision 1.15    locked by: root;
date: 2015/12/21 10:05:47;  author: root;  state: Exp;  lines: +5 -5
print staements removed
—————————-
revision 1.14
date: 2015/12/21 06:16:33;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.13
date: 2015/12/21 06:11:20;  author: root;  state: Exp;  lines: +7 -7
name of arr changes to client_fifo
—————————-
revision 1.12
date: 2015/12/21 05:59:17;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.11
date: 2015/12/21 05:56:32;  author: root;  state: Exp;  lines: +3 -3
arr data type changes from char * to string.
—————————-
revision 1.10
date: 2015/12/21 05:52:06;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.9
date: 2015/12/21 05:50:02;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.8
date: 2015/12/21 05:46:08;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.7
date: 2015/12/21 05:41:58;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.6
date: 2015/12/21 05:39:43;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.5
date: 2015/12/21 05:35:20;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.4
date: 2015/12/21 05:34:03;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.3
date: 2015/12/21 05:32:47;  author: root;  state: Exp;  lines: +1 -0
*** empty log message ***
—————————-
revision 1.2
date: 2015/12/21 05:27:08;  author: root;  state: Exp;  lines: +3 -1
sprintf() is used for creating client address.
—————————-
revision 1.1
date: 2015/12/21 04:42:31;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: client2.c,v
Working file: client2.c
head: 1.3
branch:
locks: strict
root: 1.3
access list:
symbolic names:
keyword substitution: kv
total revisions: 3;    selected revisions: 3
description:
client2 request for subtraction from the server.
It writes its request from requestfifo.
And it creates the resultfifo.
And it reads result from server through resultfifo.
—————————-
revision 1.3    locked by: root;
date: 2015/12/21 10:06:09;  author: root;  state: Exp;  lines: +4 -4
print staements removed
>
—————————-
revision 1.2
date: 2015/12/21 06:36:30;  author: root;  state: Exp;  lines: +7 -4
client_fifo is introduced.
—————————-
revision 1.1
date: 2015/12/21 05:09:19;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: client3.c,v
Working file: client3.c
head: 1.4
branch:
locks: strict
root: 1.4
access list:
symbolic names:
keyword substitution: kv
total revisions: 4;    selected revisions: 4
description:
This client request for multiplication.
It writes request to server through requestfifo.
It creates resultfifo.
It reads result from server through resultfifo.
—————————-
revision 1.4    locked by: root;
date: 2015/12/21 10:06:20;  author: root;  state: Exp;  lines: +5 -5
print staements removed
—————————-
revision 1.3
date: 2015/12/21 06:37:03;  author: root;  state: Exp;  lines: +7 -4
client_fifo is introduced.
—————————-
revision 1.2
date: 2015/12/21 05:16:34;  author: root;  state: Exp;  lines: +1 -1
Values of objects changed.
—————————-
revision 1.1
date: 2015/12/21 05:14:09;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: client4.c,v
Working file: client4.c
head: 1.3
branch:
locks: strict
root: 1.3
access list:
symbolic names:
keyword substitution: kv
total revisions: 3;    selected revisions: 3
description:
This client request for modulo (%)
—————————-
revision 1.3    locked by: root;
date: 2015/12/21 10:06:24;  author: root;  state: Exp;  lines: +3 -3
print staements removed
—————————-
revision 1.2
date: 2015/12/21 09:36:57;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.1
date: 2015/12/21 08:49:24;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: client5.c,v
Working file: client5.c
head: 1.2
branch:
locks: strict
root: 1.2
access list:
symbolic names:
keyword substitution: kv
total revisions: 2;    selected revisions: 2
description:
Client5 request for divide operation.
—————————-
revision 1.2    locked by: root;
date: 2015/12/21 10:06:27;  author: root;  state: Exp;  lines: +5 -5
print staements removed
—————————-
revision 1.1
date: 2015/12/21 09:05:44;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: divide.c,v
Working file: divide.c
head: 1.4
branch:
locks: strict
root: 1.4
access list:
symbolic names:
keyword substitution: kv
total revisions: 4;    selected revisions: 4
description:
It is used for accepting request for divide i.e when operation=’/’
—————————-
revision 1.4    locked by: root;
date: 2016/01/06 08:52:44;  author: root;  state: Exp;  lines: +1 -1
signal is removed.
—————————-
revision 1.3
date: 2016/01/01 02:08:20;  author: root;  state: Exp;  lines: +3 -2
alarm signal is send to server after it writes result to server
—————————-
revision 1.2
date: 2015/12/21 09:59:36;  author: root;  state: Exp;  lines: +1 -1
print statement decreased.
—————————-
revision 1.1
date: 2015/12/21 09:06:02;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: modulo.c,v
Working file: modulo.c
head: 1.5
branch:
locks: strict
root: 1.5
access list:
symbolic names:
keyword substitution: kv
total revisions: 5;    selected revisions: 5
description:
This gives result of modulo
—————————-
revision 1.5    locked by: root;
date: 2016/01/06 08:52:52;  author: root;  state: Exp;  lines: +1 -1
signal is removed.
—————————-
revision 1.4
date: 2016/01/01 02:08:33;  author: root;  state: Exp;  lines: +3 -2
alarm signal is send to server after it writes result to server
..
—————————-
revision 1.3
date: 2015/12/21 09:59:41;  author: root;  state: Exp;  lines: +1 -1
print statement decreased.
—————————-
revision 1.2
date: 2015/12/21 08:53:15;  author: root;  state: Exp;  lines: +1 -1
print statement changes.
—————————-
revision 1.1
date: 2015/12/21 08:49:48;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: multiplier.c,v
Working file: multiplier.c
head: 1.4
branch:
locks: strict
root: 1.4
access list:
symbolic names:
keyword substitution: kv
total revisions: 4;    selected revisions: 4
description:
It read request from server from pipe for multiplication purpose.
It prosses the request and get the result.
result is written to server through pipe.
—————————-
revision 1.4    locked by: root;
date: 2016/01/06 08:52:59;  author: root;  state: Exp;  lines: +1 -1
signal is received.
—————————-
revision 1.3
date: 2016/01/01 02:08:39;  author: root;  state: Exp;  lines: +2 -1
alarm signal is send to server after it writes result to server
—————————-
revision 1.2
date: 2015/12/21 09:59:45;  author: root;  state: Exp;  lines: +1 -1
print statement decreased.
—————————-
revision 1.1
date: 2015/12/21 04:46:24;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: server.c,v
Working file: server.c
head: 1.46
branch:
locks: strict
root: 1.46
access list:
symbolic names:
keyword substitution: kv
total revisions: 46;    selected revisions: 46
description:
Ii can handle only 1 client in this revision.
requestfifo is created.
It reads the request from client.
A pipe is created by server.
This pipe is used to send request to adder.
Then, it read result(int) from adder.
through pipe.
It writes result to the client using resultfifo (of respectice client).
—————————-
revision 1.46    locked by: root;
date: 2016/01/06 10:22:21;  author: root;  state: Exp;  lines: +0 -10
*** empty log message ***
—————————-
revision 1.45
date: 2016/01/06 09:13:03;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.44
date: 2016/01/06 08:53:09;  author: root;  state: Exp;  lines: +3 -3
signal is removed.
wait() is used instead of pause().
—————————-
revision 1.43
date: 2016/01/04 11:04:33;  author: root;  state: Exp;  lines: +1 -0
rfd and wfd are printed.
—————————-
revision 1.42
date: 2016/01/04 11:00:31;  author: root;  state: Exp;  lines: +2 -0
The pipe fd’s are closed.
—————————-
revision 1.41
date: 2016/01/04 10:41:42;  author: root;  state: Exp;  lines: +1 -0
Print statement added to show which no. of cient is accessing th server.
—————————-
revision 1.40
date: 2016/01/04 03:32:19;  author: root;  state: Exp;  lines: +1 -1
No, of clients determination corrected.
—————————-
revision 1.39
date: 2016/01/04 03:11:11;  author: root;  state: Exp;  lines: +1 -0
No.of clients Printed.
—————————-
revision 1.38
date: 2016/01/04 03:05:30;  author: root;  state: Exp;  lines: +4 -4
2nd argument of read or write corrected.
—————————-
revision 1.37
date: 2016/01/04 03:03:31;  author: root;  state: Exp;  lines: +28 -28
array of variables changed to simple variables
—————————-
revision 1.36
date: 2016/01/04 02:54:37;  author: root;  state: Exp;  lines: +2 -3
*** empty log message ***
—————————-
revision 1.35
date: 2016/01/04 02:52:44;  author: root;  state: Exp;  lines: +2 -1
*** empty log message ***
—————————-
revision 1.34
date: 2016/01/04 02:46:38;  author: root;  state: Exp;  lines: +2 -6
close() command is removed.
—————————-
revision 1.33
date: 2016/01/04 02:43:10;  author: root;  state: Exp;  lines: +2 -1
*** empty log message ***
—————————-
revision 1.32
date: 2016/01/04 02:37:50;  author: root;  state: Exp;  lines: +2 -3
*** empty log message ***
—————————-
revision 1.31
date: 2016/01/04 02:36:11;  author: root;  state: Exp;  lines: +6 -7
while is used instead of for loop.
—————————-
revision 1.30
date: 2016/01/01 02:12:09;  author: root;  state: Exp;  lines: +1 -1
ce
—————————-
revision 1.29
date: 2016/01/01 02:08:42;  author: root;  state: Exp;  lines: +12 -1
pause is used instead of wait() before reading result from pipe through calculating client.
—————————-
revision 1.28
date: 2015/12/21 10:10:28;  author: root;  state: Exp;  lines: +2 -2
print removed.
—————————-
revision 1.27
date: 2015/12/21 10:06:30;  author: root;  state: Exp;  lines: +5 -5
print staements removed
—————————-
revision 1.26
date: 2015/12/21 09:56:25;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.25
date: 2015/12/21 09:50:03;  author: root;  state: Exp;  lines: +2 -2
Print statement corrected.
—————————-
revision 1.24
date: 2015/12/21 09:41:27;  author: root;  state: Exp;  lines: +1 -0
sleep is replaced by wait()
—————————-
revision 1.23
date: 2015/12/21 09:38:51;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.22
date: 2015/12/21 09:36:59;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.21
date: 2015/12/21 09:07:13;  author: root;  state: Exp;  lines: +4 -0
divide is also included in operations.
—————————-
revision 1.20
date: 2015/12/21 08:50:02;  author: root;  state: Exp;  lines: +4 -0
modulo choice is added to switch(req.opr)
—————————-
revision 1.19
date: 2015/12/21 08:26:26;  author: root;  state: Exp;  lines: +1 -1
loop is executing one more time.
—————————-
revision 1.18
date: 2015/12/21 08:21:43;  author: root;  state: Exp;  lines: +1 -1
ce
—————————-
revision 1.17
date: 2015/12/21 08:19:40;  author: root;  state: Exp;  lines: +3 -3
Print statement before writion for calculation added.
—————————-
revision 1.16
date: 2015/12/21 08:11:55;  author: root;  state: Exp;  lines: +1 -1
ce
—————————-
revision 1.15
date: 2015/12/21 08:10:57;  author: root;  state: Exp;  lines: +6 -6
Changes in addresses in read and write statements.
—————————-
revision 1.14
date: 2015/12/21 08:00:30;  author: root;  state: Exp;  lines: +2 -2
*** empty log message ***
—————————-
revision 1.13
date: 2015/12/21 07:47:37;  author: root;  state: Exp;  lines: +2 -2
&(req+i) changes to (&req+i)
—————————-
revision 1.12
date: 2015/12/21 07:45:49;  author: root;  state: Exp;  lines: +16 -9
req change to req[i] for client i.
—————————-
revision 1.11
date: 2015/12/21 07:31:19;  author: root;  state: Exp;  lines: +14 -10
fd[i] changes to fd
—————————-
revision 1.10
date: 2015/12/21 07:12:56;  author: root;  state: Exp;  lines: +5 -5
res changes to res[MAX_SIZE]
—————————-
revision 1.9
date: 2015/12/21 07:07:57;  author: root;  state: Exp;  lines: +35 -35
fd become fd[MAX_CLIENT]
rfd[4] and wfd[4] becomes rfd[MAX_CLIENT][4] and wfd[MAX_CLIENT][4].
count changes to count[MAX_CLIENT]
—————————-
revision 1.8
date: 2015/12/21 06:58:49;  author: root;  state: Exp;  lines: +2 -2
sleep removed.
—————————-
revision 1.7
date: 2015/12/21 06:55:16;  author: root;  state: Exp;  lines: +2 -0
*** empty log message ***
—————————-
revision 1.6
date: 2015/12/21 06:18:23;  author: root;  state: Exp;  lines: +1 -1
client_fifo data type changes from char to string.
—————————-
revision 1.5
date: 2015/12/21 06:16:43;  author: root;  state: Exp;  lines: +1 -1
sprintf() is used for getting RESULTFIFO name.
—————————-
revision 1.4
date: 2015/12/21 06:11:34;  author: root;  state: Exp;  lines: +3 -1
client_fifo is used for RESULT_FIFO.
—————————-
revision 1.3
date: 2015/12/21 05:06:34;  author: root;  state: Exp;  lines: +3 -3
+,-,* are replaced by ‘+’,’-’,’*’ respectively in switch case of operation.
—————————-
revision 1.2
date: 2015/12/21 05:04:10;  author: root;  state: Exp;  lines: +13 -3
execl() for subtractor and multiplier are also included along with addition in a switch case which depend on operand of the request by the client.
—————————-
revision 1.1
date: 2015/12/21 04:47:51;  author: root;  state: Exp;
Initial revision
=============================================================================

RCS file: subtractor.c,v
Working file: subtractor.c
head: 1.11
branch:
locks: strict
root: 1.11
access list:
symbolic names:
keyword substitution: kv
total revisions: 11;    selected revisions: 11
description:
It reads request from server through pipe for subtraction purpose.
It processes the request and get the result.
result is send to server by the pipe.
—————————-
revision 1.11    locked by: root;
date: 2016/01/06 08:53:35;  author: root;  state: Exp;  lines: +2 -2
kill() is removed.
signal is not used.
—————————-
revision 1.10
date: 2016/01/04 10:56:49;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.9
date: 2016/01/04 10:56:16;  author: root;  state: Exp;  lines: +4 -3
*** empty log message ***
—————————-
revision 1.8
date: 2016/01/04 10:52:54;  author: root;  state: Exp;  lines: +2 -1
*** empty log message ***
—————————-
revision 1.7
date: 2016/01/04 10:51:58;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.6
date: 2016/01/04 10:51:23;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.5
date: 2016/01/04 10:50:54;  author: root;  state: Exp;  lines: +1 -1
*** empty log message ***
—————————-
revision 1.4
date: 2016/01/04 10:47:34;  author: root;  state: Exp;  lines: +1 -1
exit function is used instead of return.
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revision 1.3
date: 2016/01/01 02:09:33;  author: root;  state: Exp;  lines: +3 -2
alarm signal is send to server after it writes result to server
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revision 1.2
date: 2015/12/21 09:59:50;  author: root;  state: Exp;  lines: +1 -1
print statement decreased.
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revision 1.1
date: 2015/12/21 04:52:26;  author: root;  state: Exp;
Initial revision
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