Key Concepts in Operating Systems and Process Management

file descriptor

An integer index pointing into the kernel's open file table.

fread() and fwrite()

Only when the buffer needs to be filled or emptied.

short count

When read() or write() processes fewer bytes than requested.

const in a pointer parameter

It prevents the function from modifying the data pointed to.

process environment

A list of strings containing name/value pairs (e.g., PATH=/usr/bin).

pipe | in Bash

Sends stdout of one program to stdin of another.

GDB (GNU Debugger)

Pause/resume execution and inspect variables during debugging.

stack segment

Function params, local variables, and CPU state.

exit handler

A function that runs when exit() or return from main() occurs, but not on abnormal termination.

abnormal termination

When a process is terminated due to a signal with a default terminate disposition (e.g. SIGKILL).

signal mask

Blocks delivery of signals until they are unmasked.

signal disposition

The behavior assigned to a signal: default, ignore, or custom handler.

asynchronous signal handling

Signals can interrupt the program at any time.

orphaned processes

They are adopted by the init or systemd process.

execve()

Replaces the current process image with a new program.

race condition

When output depends on the order of execution between processes or threads accessing shared resources.

fork() + printf() output

Any interleaving of parent/child printf() calls due to concurrent execution (e.g. 2A1A, 1AA2, etc.).

errno

A global variable set when system calls fail; holds the error code.

malloc()

Scans the heap for available memory and allocates dynamically; expands heap if necessary.

virtual memory

An abstraction of memory that can exceed physical RAM and offers isolation and security.