Signals---Concepts

1.Signal Concepts

Signals are software interrupts,which can be generated by following kind of conditions:

a.The terminal-generated signals occur when users press certain terminal keys

(ctrl + C | delete:SIGINT)

b.Hardware exceptions generate signals(devide by 0,invalid memory reference,SIGSEGV)

c.calling kill function allows a process to send any signal to another process or process group

d.kill command provides interface to the kill function.

e.Software conditions can generate signals when something happens about which the process should be notified.(SIGURG:out-of-band data arrives over a network connection;SIGPIPE:generatd when a process writes to a pipe after the reader of the pipe has terminated;SIGALRM:generated when an alram clock set by the process expires)

 

2.Signal Handling

disposition of the signal or the action associated with the signal:

a.Ignore the signal.(SIG_ING)

b.catch the signal.(signal handler installed by calling sigaction or signal function)

c.apply default action for the signal.

***SIGKILL and SIGSTOP can never be caught or ignored ****

***default action for most signals is terminate the process ***

 

3.List of signals

SIGABRT  abnormal termination(abort)

SIGALRM  time expired(alarm)

SIGBUS   hardware fault

SIGCANCEL thread library internal use

SIGCHLD  change in status of child(stopped,continued,termination)

SIGCONT  continue stopped process

SIGEMT   hardware fault

SIGFPE   arithmetic exception

SIGFREEZE checkpoint freeze

SIGHUP    hangup

SIGILL    illegal instruction

SIGINFO   status request from keyboard

SIGINT    terminal interrupt character

SIGIO     asynchronous I/O

SIGIOT    hardware fault

SIGKILL   termination

SIGLWP    thread library internal use

SIGPIPE   write to a pipe with no reader

SIGPOLL   pollable event(poll)

SIGPROF   profiling time alarm(settimer)

SIGPWR    power fail/restart

SIGQUIT   terminal quit character(Ctrl + \)

SIGSEGV   invalid memory reference

SIGSTKFLT  coprocessor stack fault

SIGSTOP   stop

SIGSYS    invalid system call

SIGTERM   termination

SIGTHAW   checkpoint thaw

SIGTRAP   hardware fault

SIGTSTP   terminal stop character

SIGTTIN   background read from control tty

SIGTTOU   background write to control tty

SIGURG    urgent conditions(sockets)

SIGUSR1   user-defined signals

SIGUSR2   user-defined signals

SIGVTALRM  virtual time alarm(settimer)

SIGWAITING   thread library internal use   ignore

SIGWINCH     terminal window size change   ignore

SIGXCPU      CPU limit exceeded

SIGXFSZ      file size limit exceeded

SIGXRES      resource control exceeded     ignore