The tag has no usage guidance.

learn more… | top users | synonyms

3
votes
1answer
202 views

COW and fork - how many frames

Consider process P that owns 10 physical frames. Suppose process P calls fork() and creates a child process Q. How many physical frames does the child initially own, without copy-on-write? 10 How ...
3
votes
1answer
2k views

Program stall under user but runs under root

I am running R job under a normal user john and root. Interestingly, the program stalls under john user but runs quickly under root. Using strace, I found that when john runs the R, the process stalls ...
5
votes
4answers
304 views

Coloring output of forked processes

I have a runscript that starts some processes and sends them to the background mongod & pid_mongo=$! redis-server & pid_redis=$! # etc. All these processes then output concurrently to ...
3
votes
2answers
1k views

What sets a child's STDERR, STDOUT, and STDIN?

If a program runs fork() what sets standard streams STDOUT, STDIN and STDERR?
7
votes
2answers
8k views

How does copy-on-write in fork() handle multiple fork?

According to Wikipedia (which could be wrong) When a fork() system call is issued, a copy of all the pages corresponding to the parent process is created, loaded into a separate memory location by ...
4
votes
2answers
2k views

Fork call and recursion

#include <stdio.h> #include <stdlib.h> #include <string.h> int main(int argc, char *argv[]) { fork(); fork(); fork(); puts("hi"); return 0; } This program ...
30
votes
4answers
6k views

What's the difference between running a program as a daemon and forking it into background with '&'?

What are the practical differences from a sysadmin point of view when deploying services on a unix based system?
3
votes
1answer
79 views

How is the inherited file descritor vulnerability dealt with in Unices?

Ulrich Drepper describes a vulnerability in programs that have open file descriptors then they fork() and execve() without lots of very careful locking in place. He also talks about new kernel ...
4
votes
3answers
8k views

Fork bomb on a Mac?

I just learned about a fork bomb, an interesting type of a denial of service attack. Wikipedia (and a few other places) suggest using :(){ :|:& };: on UNIX machines to fork the process an infine ...
14
votes
3answers
9k views

When do you need 'nohup' if you're already forking using '&'?

First this question is related but definitely not the same as this very nice question: Difference between nohup, disown and & I want to understand something: when I do '&', I'm forking ...
1
vote
1answer
4k views

Apache cannot fork: cannot allocate memory

I am running apache on Fedora with mod_perl. The server forks a process to send an email frequently - and the fork exits. Suddenly, I got: Cannot fork: Cannot allocate memory. There was plenty of ...
33
votes
2answers
4k views

Why is the default process creation mechanism fork?

The UNIX system call for process creation, fork(), creates a child process by copying the parent process. My understanding is that this is almost always followed by a call to exec() to replace the ...
9
votes
5answers
14k views

How to totally fork a shell command that is using redirection

I've written quite a few shell scripts over the years (but I'm certainly not a sysadmin) and there's something that always caused me troubles: how can I fork a shell command immune to hangups in the ...
5
votes
1answer
242 views

Why is the following command killing a system?

Anyone understand the following code , running in bash ? :(){ :|:& };: It seems to be a "fork" bomb on Linux.
2
votes
1answer
665 views

There is no bash indicator prompt after a forked process terminates

I am reading the book Advanced Programming in the Unix Environment. There is a test program to test the fork function. It works well in my Ubuntu. But what I confused is that why there is no command ...
2
votes
3answers
2k views

Fork: Negative return value

From the fork(2) man page: RETURN VALUE On success, the PID of the child process is returned in the parent, and 0 is returned in the child. On failure, -1 is returned in the parent, no ...
10
votes
5answers
3k views

Process descendants

I'm trying to build a process container. The container will trigger other programs. For example - a bash script that launches running background tasks with '&' usage. The important feature I'm ...
9
votes
3answers
16k views

Does bash support forking similar to C's fork()?

I have a script that I would like to fork at one point so two copies of the same script are running. For example, I would like the following bash script to exist: echo $$ do_fork() echo $$ If this ...
9
votes
4answers
4k views

Why should a child of a vfork or fork call _exit() instead of exit()?

From the man page of vfork(): vfork() differs from fork() in that the parent is suspended until the child makes a call to execve(2) or _exit(2). The child shares all memory with its ...
10
votes
2answers
5k views

What's the difference between fork() and vfork()?

I would like to understand in detail the difference between fork() and vfork(). I was not able to digest the man page completely. I would also like to clarify one of my colleagues comment "In ...
16
votes
4answers
9k views

After fork(), where does the child begin its execution?

I'm trying to learn UNIX programming and came across a question regarding fork(). I understand that fork() creates an identical process of the currently running process, but where does it start? For ...