Signals
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- A signal is an event generated by UNIX/LINUX system in response to some condition.
- On receipt of a signal, process may in turn take some action.
- Signals are generated by some error conditions such as:-
* Memory Segment Violation
* Floating Point Processor error
* Illegal Instruction etc.
- They are generated by shell and terminal handlers.
- They cause interrupts.

- 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