Working with the Unix OS

Processes I
F_SETFL set status flags via arg
F_GETFL return status flags via arg
F_GETLK, F_SETLK, F_SETLKW record locking
#include device specific operations
int ioctl (int fildes, unsigned long request, char *arg);
intended for device specific operations
! signals
Notification to a process that an event has occurred "software interrupt" usually occur asynchronously.
- by one process to another process
- by the kernel to a process
#include
Name Description Default action
ISIGALRM Alarm clock Terminate
ISIGBUS Bus error Terminate core
ISIGCLD Death of child process Discarded
ISIGEMT EMT instruction Terminate core
ISIGFPE FPE instruction Terminate core
ISIGHUP Hangup Terminate
ISIGILL Illegal instruction Terminate core
ISIGINT Interrupt character Terminate
ISIGIOT IOT instruction Terminate core
ISIGKILL Kill Terminate
ISIGPIPE Write on pipe no one read it Terminate
ISIGPOLL Select event on stream device Terminate
ISIGPWR Power fail Terminate
ISIGQUIT Quit character Terminate core
ISIGSEGV Segmentation violation Terminate core
ISIGSYS Bad argument to system call Terminate core
ISIGTERM Software termination signal Terminate
ISIGTRAP Trace trap Terminate core
ISIGUSRl User defined signal 1 Terminate
ISIGUSR2 User defined signal 1 Terminate
- How and when are signals sent?
1. kill system call (kill is a misnomer)
allows a process to sending process and send a signal to another process. To send a signal, the receiving
process must both have the same effective user ID.
2. kill command
is also used to send signals
3. terminal-generated signals e.g. interrupt character AC generates SIGINT signal
4. hardware conditions e.g. floating point error generates SIGFPE error
5. software conditions
the kernel causes signals to be generated e.g. SIGURG out-of-band data arrives on a socket
- What can a process do with a signal?
1. Provide a function called a signal handler
2. Ignore a signal (except SIGKILL terminate any process)
3. Allow the default action to occur
- To handle a signal from within a process:
#include
int (*signal (int sig, void (*func) (in))) (int);
signal: is a function that returns a pointer to a function that returns an integer.
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