{"id":411,"date":"2026-09-08T22:39:52","date_gmt":"2026-09-08T14:39:52","guid":{"rendered":"http:\/\/www.digicreatorbina.com\/blog\/?p=411"},"modified":"2026-09-08T22:39:52","modified_gmt":"2026-09-08T14:39:52","slug":"how-does-a-process-receive-and-handle-signals-42a8-8126ac","status":"publish","type":"post","link":"http:\/\/www.digicreatorbina.com\/blog\/2026\/09\/08\/how-does-a-process-receive-and-handle-signals-42a8-8126ac\/","title":{"rendered":"How does a process receive and handle signals?"},"content":{"rendered":"

In the realm of operating systems, signals play a crucial role in inter – process communication and system management. As a trusted process supplier, I’ve witnessed firsthand the significance of how processes receive and handle these signals. Understanding this mechanism not only provides insights into the inner workings of an operating system but also helps in optimizing the performance and stability of processes in a production environment. Process<\/a><\/p>\n

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Signal Basics<\/h3>\n

Before delving into how a process receives and handles signals, let’s clarify what signals are. Signals are software interrupts sent to a process to notify it of an event. These events can range from something as simple as a user pressing Ctrl + C on the terminal, which sends the SIGINT signal, to more serious events such as a segmentation fault (SIGSEGV). In Unix – like operating systems, signals are identified by integers, and each number corresponds to a specific type of event.<\/p>\n

There are two broad categories of signals: real – time signals and non – real – time signals. Non – real – time signals, also known as standard signals, are numbered from 1 to 31. They are not queued, which means that if multiple instances of the same non – real – time signal are sent to a process before it can handle them, only one instance will be delivered. Real – time signals, numbered from 32 to 64, are queued. This means that if multiple real – time signals of the same type are sent, the process will receive and handle each one.<\/p>\n

How a Process Receives Signals<\/h3>\n

The kernel is the intermediary between the source of the signal and the target process. When an event triggers a signal, the kernel is responsible for delivering that signal to the appropriate process. There are several ways a signal can be generated:<\/p>\n

User – initiated Signals<\/h4>\n

A user can send signals to a process using commands such as kill<\/code> or pkill<\/code> in the terminal. For example, if a user wants to terminate a misbehaving process, they can use the command kill - 9 <PID><\/code>, where <PID><\/code> is the process ID of the target process. The -9<\/code> option corresponds to the SIGKILL signal, which forces the process to terminate immediately.<\/p>\n

Inter – process Signaling<\/h4>\n

Processes can also send signals to each other using system calls. For instance, in C programming, the kill()<\/code> system call can be used to send a signal from one process to another. Here is a simple example of a process sending a SIGUSR1 signal to another process:<\/p>\n

#include <stdio.h>\n#include <signal.h>\n#include <unistd.h>\n\nint main() {\n    pid_t target_pid = 1234; \/\/ Replace with the actual PID\n    if (kill(target_pid, SIGUSR1) == -1) {\n        perror("kill");\n    }\n    return 0;\n}\n<\/code><\/pre>\n
System – generated Signals<\/h4>\n
The kernel can generate signals in response to system events. For example, when a child process terminates, the kernel sends a SIGCHLD signal to the parent process. Similarly, if a process tries to access memory that it doesn’t have permission to access, the kernel sends a SIGSEGV signal.<\/p>\n
Signal Delivery<\/h3>\n
Once a signal is generated, the kernel checks if the target process is eligible to receive it. There are several things the kernel needs to consider:<\/p>\n
Signal Mask<\/h4>\n
Each process has a signal mask, which is a set of signals that are currently blocked. If a signal is blocked, the kernel will not deliver it immediately. Instead, it will be pending until the signal is unblocked. A process can set its signal mask using system calls such as sigprocmask()<\/code>. For example, if a process wants to block the SIGINT signal, it can use the following code:<\/p>\n
#include <stdio.h>\n#include <signal.h>\n\nint main() {\n    sigset_t set;\n    sigemptyset(&set);\n    sigaddset(&set, SIGINT);\n    if (sigprocmask(SIG_BLOCK, &set, NULL) == -1) {\n        perror("sigprocmask");\n    }\n    \/\/ The process is now immune to SIGINT\n    return 0;\n}\n<\/code><\/pre>\n
Signal Disposition<\/h4>\n
The disposition of a signal determines how the process will handle it when it is delivered. There are three possible dispositions:<\/p>\n
    \n
  1. Default Action<\/strong>: Each signal has a default action associated with it. For example, the default action of SIGINT is to terminate the process, while the default action of SIGCHLD is to be ignored.<\/li>\n
  2. Ignore<\/strong>: A process can choose to ignore a signal by setting its disposition to SIG_IGN. For instance, if a process wants to ignore the SIGTERM signal, it can use the following code:<\/li>\n<\/ol>\n
    #include <stdio.h>\n#include <signal.h>\n\nint main() {\n    signal(SIGTERM, SIG_IGN);\n    \/\/ The process will now ignore SIGTERM\n    return 0;\n}\n<\/code><\/pre>\n
      \n
    1. Catch and Handle<\/strong>: A process can also define a signal handler function to be called when a specific signal is received. This allows the process to take custom actions in response to the signal.<\/li>\n<\/ol>\n
      Signal Handling<\/h3>\n
      When a signal is delivered to a process and its disposition is set to catch and handle, the process will execute the corresponding signal handler function. The signal handler is just like any other function in the program, but it has a specific signature. In C, the general form of a signal handler function is:<\/p>\n
      void signal_handler(int signum) {\n    \/\/ Handle the signal here\n    printf("Received signal %d\\n", signum);\n}\n<\/code><\/pre>\n
      To set a signal handler for a specific signal, a process can use the signal()<\/code> or sigaction()<\/code> system calls. The sigaction()<\/code> is generally preferred over signal()<\/code> because it provides more control over signal handling, such as the ability to block other signals while the handler is executing.<\/p>\n
      #include <stdio.h>\n#include <signal.h>\n\nvoid signal_handler(int signum) {\n    printf("Received signal %d\\n", signum);\n}\n\nint main() {\n    struct sigaction sa;\n    sa.sa_handler = signal_handler;\n    sigemptyset(&sa.sa_mask);\n    sa.sa_flags = 0;\n    if (sigaction(SIGUSR1, &sa, NULL) == -1) {\n        perror("sigaction");\n    }\n    \/\/ The process will now call signal_handler when SIGUSR1 is received\n    while (1) {\n        sleep(1);\n    }\n    return 0;\n}\n<\/code><\/pre>\n
      Considerations in Signal Handling<\/h3>\n
      When writing signal handlers, there are several important considerations:<\/p>\n
      Reentrancy<\/h4>\n
      Signal handlers can interrupt the normal flow of a process at any time. This means that they need to be reentrant, i.e., they should not rely on global variables in an unsafe way or call non – reentrant functions. For example, functions like malloc()<\/code> and printf()<\/code> are not reentrant and should be avoided in signal handlers.<\/p>\n
      Asynchronous – safety<\/h4>\n
      Signal handlers are asynchronous events. They can occur at any point in the execution of the main program. Therefore, signal handlers should be as simple as possible and avoid complex operations that could interfere with the main program.<\/p>\n
      Our Expertise as a Process Supplier<\/h3>\n
      As a process supplier, we understand the importance of efficient signal handling in ensuring the stability and performance of your processes. Our solutions are designed to optimize the signal reception and handling mechanisms in your applications. We offer a range of services, including custom – built process modules that are engineered to handle signals gracefully, reducing the risk of crashes and data loss.<\/p>\n
      <\/p>\n
      Our team of experts has in – depth knowledge of operating system internals and signal mechanisms. We can provide you with tailored advice on how to design your processes to handle signals effectively. Whether you are dealing with real – time applications that require strict signal handling or background processes that need to respond to user – initiated signals, we have the expertise to help you.<\/p>\n
      Contact Us for Procurement and Discussion<\/h3>\n
      Auto Forks<\/a> If you are interested in improving the signal reception and handling capabilities of your processes, we invite you to reach out to us for a procurement discussion. Our team is ready to answer all your questions and provide you with detailed information about our products and services. By working with us, you can ensure that your processes are robust, reliable, and efficient in handling signals.<\/p>\n
      References<\/h3>\n