CMPSC 311 - Introduction to Systems Programming Signals

Vocabulary flashcards covering key terms from the lecture notes on UNIX signals and process control.

Control flow

The sequence of instructions a CPU reads and executes from startup to shutdown.

Exceptional control flow

Mechanisms that allow a system to react to events, enabling exception processing.

Exception

An event that disrupts normal execution and requires handling.

Exception processing

The handling of an exception when control flow is diverted from its normal path.

Exception return

Optional mechanism to resume normal execution after an exception is handled.

Interrupt

A low‑level mechanism that interrupts CPU execution to handle hardware/software events.

Trap

A software-generated exception used to transfer control to the operating system.

Fault

An error condition that causes abnormal program behavior and requires handling.

Abort

An unrecoverable error leading to process termination.

Process context switch

High‑level OS/hardware mechanism to switch CPU context between processes.

Signals

Asynchronous notifications sent by the OS to a process to notify events, handled by a signal handler.

Nonlocal jumps (setjmp/longjmp)

C runtime facility to transfer control nonlocally between function calls.

UNIX signal definition

A signal is a special message sent through the OS to tell a process of a command or event.

Signal

A message delivered by the OS to a process to notify an event and trigger a handler.

Signal handler

Function executed when a signal is delivered.

SIGHUP

Hangup signal (POSIX).

SIGINT

Interrupt signal (ANSI).

SIGQUIT

Quit signal (POSIX).

SIGABRT

Abort signal (ANSI).

SIGFPE

Floating-point exception signal (ANSI).

SIGKILL

Kill signal (unblockable in POSIX).

SIGSEGV

Segmentation fault signal (ANSI).

SIGTERM

Termination signal (ANSI).

SIGSTKFLT

Stack fault signal.

SIGCHLD

Child status has changed signal (POSIX).

SIGCONT

Continue signal (POSIX).

SIGSYS

Bad system call signal (ANSI).

SIGILL

Illegal instruction signal (ANSI).

SIGTRAP

Trace trap signal (POSIX).

SIGIOT

IOT trap (4.2 BSD).

SIGBUS

BUS error signal (4.2 BSD).

SIGUSR1

User-defined signal 1 (POSIX).

SIGUSR2

User-defined signal 2 (POSIX).

SIGSTOP

Stop, unblockable signal (POSIX).

SIGCONT (again)

Continue signal (POSIX).

SIGSYS (again)

Bad system call signal (ANSI).

PID

Process ID; a unique identifier for a running process.

ps

Process status utility; lists PIDs and related process information.

kill

Program that sends signals to processes; defaults to SIGTERM if no signal is given.

killall

Program that sends signals to all instances of a named program.

raise

System call for a process to send a signal to itself.

User-defined signal handlers

Custom functions that handle specific signals instead of the default handler.

signal

Legacy API to set a signal handler.

sighandler_t

Type of a signal handler function pointer.

signal handler

The function invoked when a specified signal is delivered.

Function pointer

A pointer that can refer to a function, be passed as an argument, and be invoked.

sigaction

System call to specify signal handling with greater control than signal.

SA_NODEFER

Flag to prevent blocking of the signal while its handler runs.

SA_ONSTACK

Flag to use an alternate signal stack for the handler.

SA_RESETHAND

Flag to restore the default action after the handler is invoked.

struct sigaction

Data structure used by sigaction to define the handler and options.

Graceful shutdown

Proper shutdown with resource cleanup and synchronization to storage.

Signal vs. sigaction

sigaction provides more control (blocking, stacks, reset behavior) than the basic signal API.