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What does the fork function return?
RETURN VALUE Upon successful completion, fork() returns 0 to the child process and returns the process ID of the child process to the parent process. Otherwise, -1 is returned to the parent process, no child process is created, and errno is set to indicate the error.
Why do we need file descriptor?
A file descriptor is a number that uniquely identifies an open file in a computer’s operating system. It describes a data resource, and how that resource may be accessed. When a program asks to open a file — or another data resource, like a network socket — the kernel: Creates an entry in the global file table.
Does fork copy file descriptor table?
The program does a fork(). The new child process gets a copy of its parent’s file descriptor table, but the file description is not copied. Entry number 3 in both processes’ file tables points to the same struct file . The parent process waits while the child process writes.
Does fork return twice?
fork does not return two values. Right after a fork system call you simply have two independent processes executing the same code, and the returned pid from fork is the only way to distinguish which process are you in – the parent or the child.
In which hand we should hold fork and spoon?
However, if you are eating spaghetti or tagliatelle, then it makes sense to hold the fork in your right hand (presuming you’re right-handed) and a spoon in the left – this way you can hold the prongs of your fork up to the bowl of the spoon in order to help you twirl the pasta strands onto your fork.
* The child inherits copies of the parent’s set of open file descrip- tors. Each file descriptor in the child refers to the same open file description (see open (2)) as the corresponding file descriptor in the parent.
Why are file descriptors shared between forked shells?
The shell opens outputfile once, when starting the redirection, and then passes the file handle to the somecmd and othercmd, processes it fork s off. Given the grouping, the user might not be wrong to expect to get the output of both commands to end up in outputfile, the same way they would end up on the screen.
Why do I need to fork a program in Linux?
One reason is to create a new thread of control within the same program (which was originally only possible in POSIX by creating a new process); the other is to create a new process running a different program. In the latter case, the call to fork () is soon followed by a call to one of the exec functions.
What happens when one of them closes a file descriptor?
They are independent. WRT what happens when one of them closes a file descriptor, see the answer to the first question. Whenever fork () makes a new child, the file descriptors are not retained at all – they are changed. Although the file will be a duplicate, it will have a different file descriptor.