Linux signals are a fundamental aspect of the operating system, providing a mechanism for processes to communicate with each other and respond to various events. Each signal serves a specific purpose, from controlling processes to notifying them about events or requesting specific actions. In this comprehensive guide, we will explore the most commonly used Linux signals and their respective functions.
Usage: Typically sent to a process when its controlling terminal is closed.
Purpose: This signal is often used to instruct daemons to reload configuration files or restart after an update.
Usage: Sent when the user presses Ctrl+C in the terminal.
Purpose: It instructs a process to interrupt its execution, allowing for a graceful termination.
Usage: Similar to SIGINT, but typically generates a core dump in addition to termination.
Purpose: Used for debugging and identifying the state of a process when it quits unexpectedly.
Usage: Sent to a process when it attempts to execute an illegal machine instruction.
Purpose: Indicates a serious problem with the execution of the program.
Usage: Typically used by debuggers to set breakpoints in a program.
Purpose: Allows for debugging and monitoring of processes.
Usage: Sent by the abort() function when a critical error occurs.
Purpose: Indicates a severe problem and requests the program to terminate.
Usage: Sent when a process makes a faulty memory access to a misaligned address.
Purpose: Indicates a hardware-related problem or a bug in the program.
Usage: Sent when a process executes an illegal floating-point operation.
Purpose: Indicates arithmetic errors like division by zero or overflow.
Usage: Forcefully terminates a process.
Purpose: Provides a quick way to stop a misbehaving or unresponsive process.
Usage: Reserved for user-defined purposes.
Purpose: Customizable signal for specific application needs.
Usage: Sent when a process attempts to access a restricted memory area.
Purpose: Indicates a serious programming error, often due to a bug.
Usage: Reserved for user-defined purposes.
Purpose: Another customizable signal for specific application needs.
Usage: Sent when a process attempts to write to a pipe with no readers.
Purpose: Indicates a broken pipe situation and allows processes to handle it.
Usage: Sent when a timer set by the alarm() function expires.
Purpose: Allows for time-sensitive operations or periodic tasks.
Usage: Requests a process to terminate.
Purpose: Allows a process to perform cleanup before exiting, considered more graceful than SIGKILL.
This guide covers the first fifteen signals commonly used in Linux. In the next part, we’ll explore the remaining signals and their applications.
Usage: Sent to a process when it experiences a stack overflow or stack underflow.
Purpose: Indicates a problem with the stack, usually due to a bug.
Usage: Sent to a parent process when a child process changes its status.
Purpose: Allows a parent process to monitor and handle changes in its child processes.
Usage: Instructs a stopped process to continue its execution.
Purpose: Resumes the execution of a process that was stopped by SIGSTOP or SIGTSTP.
Usage: Halts the execution of a process.
Purpose: Temporarily suspends a process, and it can be resumed later with SIGCONT.
Usage: Sent when the user presses Ctrl+Z in the terminal.
Purpose: Similar to SIGSTOP, but allows the process to be moved to the background.
Usage: Sent to a background process that attempts to read from the terminal.
Purpose: Prevents background processes from reading from the terminal.
Usage: Sent to a background process that attempts to write to the terminal.
Purpose: Prevents background processes from writing to the terminal.
Usage: Sent when urgent data is present on a socket.
Purpose: Informs a process about the arrival of out-of-band data.
Usage: Sent when a process exceeds its CPU time limit.
Purpose: Indicates a process consuming excessive CPU time.
Usage: Sent when a process attempts to create a file that exceeds the file size limit.
Purpose: Indicates an attempt to create a file that exceeds system limits.
Usage: Sent when a virtual timer set by setitimer() expires.
Purpose: Useful for periodic tasks that need to be performed at regular intervals.
Usage: Sent when a profiling timer set by setitimer() expires.
Purpose: Used for collecting profiling information about a process.
Usage: Sent to a process when the terminal window size changes.
Purpose: Allows a process to adjust its layout or behavior based on the new window size.
Usage: Sent when asynchronous I/O events occur.
Purpose: Used for asynchronous I/O operations.
Usage: Sent when a power failure or similar critical power event occurs.
Purpose: Indicates that the system is about to lose power.
Usage: Sent when a process makes a system call that is not implemented.
Purpose: Indicates a problem with system call invocations.
Usage: Reserved for real-time user-defined signals.
Purpose: Customizable signals for real-time applications.
This comprehensive guide covers all 64 signals available in Linux. Understanding signals is crucial for system administrators, developers, and anyone working with Linux systems, providing insights into process control and communication. Feel free to refer to this guide whenever you encounter signals in your Linux journey.
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