Parent process and child process in linux

Difference Between Process, Parent Process, and Child Process

Running program is a process . From this process, another process can be created. There is a parent-child relationship between the two processes. This can be achieved using a library function called fork(). fork() function splits the running process into two processes, the existing one is known as parent and the new process is known as a child. Here is a program that demonstrates this:

C

Before Forking After Forking Before Forking After Forking

Explanation: All the statements after the fork() are executed twice:

1. Once by the parent process.
2. The second time the statements are executed by the child process.

Let’s discuss the following concepts in more detail:

Process: A process is a program under execution i.e an active program. A process is more than the program code, it includes the following:

On the contrary program code is only a text section.

A process changes its state as it executes. The new state partially depends on the current activity of a process. The different states of the process during its execution are:

A process control block and process table are associated with each of the processes. It contains the following important information about the process:

1. Process state.
2. Process number.
3. Program counter.
4. List of files and registers.
5. CPU information.
6. Memory information, etc.

Parent Process: All the processes are created when a process executes the fork() system call except the startup process. The process that executes the fork() system call is the parent process. A parent process is one that creates a child process using a fork() system call. A parent process may have multiple child processes, but a child process only one parent process.

On the success of a fork() system call:

• The Process ID (PID) of the child process is returned to the parent process.
• 0 is returned to the child process.

On the failure of a fork() system call,

Child Process: A child process is created by a parent process in an operating system using a fork() system call. A child process may also be known as subprocess or a subtask.

• A child process is created as a copy of its parent process.
• The child process inherits most of its attributes.
• If a child process has no parent process, then the child process is created directly by the kernel.
• If a child process exits or is interrupted, then a SIGCHLD signal is sent to the parent process to inform about the termination or exit of the child process.

Why Do We Need to Create A Child Process?
Sometimes there is a need for a program to perform more than one function simultaneously. Since these jobs may be interrelated so two different programs to perform them cannot be created. For example: Suppose there are two jobs: copy contents of source file to target file and display an animated progress bar indicating that the file copy is in progress. The GIF progress bar file should continue to play till file copy is taking place. Once the copying process is finished the playing of the GIF progress bar file should be stopped. Since both these jobs are interrelated they cannot be performed in two different programs. Also, they cannot be performed one after another. Both jobs should be performed simultaneously.

At such times fork() is used to create a child process and then write the program in such a manner that file copy is done by the parent and displaying of the animated GIF file is done by the child process.

Program 1: The task here is to show how to perform two different but interrelated jobs simultaneously. Hence, the actual code for file copying and playing the animated GIF file has been skipped only the approach for performing 2 jobs simultaneously is shown.

Источник

How can a parent and child process communicate in Linux?

How can a parent and child process communicate in Linux?

The inter communication between a child process and a parent process can be done through normal communication schemes such as pipes, sockets, message queues, shared memories. There are special ways to inter communicate which has advantage of the relationships.

How parent processes communicate with child process?

In this post, the communication between child and parent processes is done using kill() and signal(), fork() system call.

1. fork() creates the child process from the parent.
2. The parent can then send messages to child using the pid and kill().
3. The child picks up these signals with signal() and calls appropriate functions.

How do you communicate between processes in Linux?

Inter-process communication in Linux: Shared storage

1. Shared files.
2. Shared memory (with semaphores)
3. Pipes (named and unnamed)
4. Message queues.
5. Sockets.
6. Signals.

What is parent and child process in Linux?

A child process is a process created by a parent process in operating system using a fork() system call. A child process is created as its parent process’s copy and inherits most of its attributes. If a child process has no parent process, it was created directly by the kernel.

Can 2 Linux processes have the same parent process?

Since PID is an unique identifier for a process, there’s no way to have two distinct process with the same PID.

How do I see parent processes in Linux?

To see what the parent process is we can use the ps command with the $PPID environment variable.

How do you find the PID of the parent process?

10 Answers To use the alias, a PID must be supplied. For the single process, just pass the PID, like: ps j 1234 . To get parent PID of the current process, use echo $$ . Run top with whatever options you want, like -u username and -p PID .

What are the commands in Linux?

which command in Linux is a command which is used to locate the executable file associated with the given command by searching it in the path environment variable. It has 3 return status as follows: 0 : If all specified commands are found and executable.

What is PS in bash?

The ps (i.e., process status) command is used to provide information about the currently running processes, including their process identification numbers (PIDs). A process, also referred to as a task, is an executing (i.e., running) instance of a program.

What is ps command for?

The ps command enables you to check the status of active processes on a system, as well as display technical information about the processes. This data is useful for administrative tasks such as determining how to set process priorities.

What is PS output?

ps stands for process status. It reports a snapshot of current processes. It gets the information being displayed from the virtual files in /proc filesystem. The output of ps command is as follows $ ps. PID TTY STAT TIME CMD.

What is ps and top command?

ps enables you to see all your processes, or just the processes used by certain users, for example root or yourself. top should be used to see which processes are most active, ps could be used to see which processes you (or any other user) are running currently.

Which command is used to manage process?

Any running program or a command given to a Linux system is called a process….Summary:

Command	Description
ps	Give the status of processes running for a user
ps PID	Gives the status of a particular process
pidof	Gives the Process ID (PID) of a process
kill PID	Kills a process

How a process is created in Linux?

A new process can be created by the fork() system call. The new process consists of a copy of the address space of the original process. fork() creates new process from existing process. Existing process is called the parent process and the process is created newly is called child process.

Is the Linux kernel a process?

From the process management point of view, the Linux kernel is a preemptive multitasking operating system. As a multitasking OS, it allows multiple processes to share processors (CPUs) and other system resources. Each CPU executes a single task at a time.

What is the first process in Linux?

Init process is the mother (parent) of all processes on the system, it’s the first program that is executed when the Linux system boots up; it manages all other processes on the system. It is started by the kernel itself, so in principle it does not have a parent process. The init process always has process ID of 1.

Where are processes stored in Linux?

In linux, the “process descriptor” is struct task_struct [and some others]. These are stored in kernel address space [above PAGE_OFFSET ] and not in userspace. This is more relevant to 32 bit kernels where PAGE_OFFSET is set to 0xc0000000. Also, the kernel has a single address space mapping of its own.

How many processes can Linux handle?

On 64-bit systems, pid_max can be set to any value up to 2^22 (PID_MAX_LIMIT, approximately 4 million). So to answer your question, if processes are just sitting there doing nothing than you are most likely going to spawn enough processes to reach the default limit of 32768.

How do you see what services are running in Linux?

Method-1: Listing Linux Running Services with service command. To display the status of all available services at once in the System V (SysV) init system, run the service command with the –status-all option: If you have multiple services, use file display commands (like less or more) for page-wise viewing.

What are the different process categories in Linux?

There are three primary categories of processes in Linux and each serves different purposes. These can be categorized into three distinct sets: interactive, automated (or batch) and daemons.

How does the kernel manage processes?

To let the kernel manage processes, each process is represented by a process descriptor that includes information about the current state of the process. When the kernel stops the execution of a process, it saves the current contents of several processor registers in the process descriptor.

What is Process hierarchy in Linux?

In normal ps command we have to look manually on PID and PPID number to know the relation between processes. In hierarchial format, child processes are shown under the parent process which makes it easy for us to look upon.

What is the use of top command in Linux?

top command is used to show the Linux processes. It provides a dynamic real-time view of the running system. Usually, this command shows the summary information of the system and the list of processes or threads which are currently managed by the Linux Kernel.

How do I find the top 5 processes in Linux?

top Command to View Linux CPU Load To quit the top function, press the letter q on your keyboard. Some other useful commands while top is running include: M – sort task list by memory usage. P – sort task list by processor usage.

How do I find the top 10 processes in Linux?

How To Check Top 10 CPU Consuming Process In Linux Ubuntu

1. -A Select all processes. Identical to -e.
2. -e Select all processes. Identical to -A.
3. -o User-defined format. Option of ps allows to specify the output format.
4. –pid pidlist process ID.
5. –ppid pidlist parent process ID.
6. –sort Specify sorting order.
7. cmd simple name of executable.
8. %cpu CPU utilization of the process in “##.

How do I find the top process in Linux?

top. The top command is the traditional way to view your system’s resource usage and see the processes that are taking up the most system resources. Top displays a list of processes, with the ones using the most CPU at the top. To exit top or htop, use the Ctrl-C keyboard shortcut.

Recent Posts

Источник