How to trigger a process from another process in linux?

@adolf 

There are multiple ways to trigger one process from another process in Linux. Here are a few common methods:

1. Signals: One process can send a signal to the other process to trigger a specific action. Common signals include SIGTERM, SIGINT, and SIGKILL. The kill command can be used to send signals to processes using their Process ID (PID). For example, to send a SIGTERM signal, use the command: kill -TERM
2. Pipes: Processes can communicate with each other through pipes. A pipe enables the output of one process to be directly used as the input of another process. This can be used to trigger a process by feeding it specific input from another process. Pipes are created using the | (pipe) symbol in the command line. For example:
3. System calls: Processes can communicate indirectly through system calls like fork() and exec(). The fork() system call can create a new process, and the child process can be used to trigger an action in another process using the exec() system call. This allows the child process to replace itself with a different process.
4. IPC (Inter-Process Communication) mechanisms: Linux provides several IPC mechanisms such as shared memory, message queues, and sockets. These mechanisms allow processes to communicate and trigger each other through shared memory or messaging.
5. File-based communication: Processes can communicate through files. One process can write specific data into a file, and the other process can monitor the file for changes and trigger a corresponding action.

The method to use depends on the specific requirements and nature of the processes involved.

@adolf 

Here is an example showing how to use a signal to trigger a process from another process:

Sender process (Process 1) sending a signal to receiver process (Process 2):

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#!/bin/bash

# Get the PID of the receiver process
RECEIVER_PID=<PID of Process 2>

# Sending a SIGUSR1 signal to the receiver process
kill -SIGUSR1 $RECEIVER_PID

Receiver process (Process 2) handling the signal and triggering an action:

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#!/bin/bash

# Signal handler function
handle_signal() {
    echo "Signal received! Triggering an action..."
    # Perform the action here
}

# Registering the signal handler function for SIGUSR1
trap 'handle_signal' SIGUSR1

# Infinite loop to keep the process running
while true; do
    sleep 1
done

In this example, the sender process sends a SIGUSR1 signal to the receiver process. The receiver process has a signal handler function registered for SIGUSR1, which triggers an action when the signal is received. The receiver process continues running in an infinite loop to keep listening for signals.

You can run both scripts in separate terminals to observe how the sender process triggers an action in the receiver process using signals.