You had the right idea but you're never calling pipe(). So that wouldn't work no matter what you do.
Of course, with four sets of pipes to deal with, you're inevitably going to end up blocking if you don't use something like select() to inform you when any of them are ready to be read or written -- when reading or writing to them won't cause your program to stall. You should set them nonblocking, too.
Is there a way to monitor certain processes and if they hang too long to kill them, but certain scripts which are expected to take a long time to let them go?
Thank you
Richard (4 Replies)
Hi
Is there an easy way to identify and group currently running processes into OS processes and APP processes. Not all applications are installed as packages.
Any free tools or scripts to do this?
Many thanks. (2 Replies)
Hi All,
I am running 25 background process from a Unix shell script which calls a single Oracle procedure with different paramenters each time.
These 25 process creates 25 different files.
When i run these 25 Background SQLPLUS processes, few files are not created completly but if i run 25... (1 Reply)
I had issues with processes locking up. This script checks for processes and kills them if they are older than a certain time.
Its uses some functions you'll need to define or remove, like slog() which I use for logging, and is_running() which checks if this script is already running so you can... (0 Replies)
I need help with understanding this in C-programming style(the systemcalls only):
Three processes communicates via two pipes. (when the processes creates all stdin is the keyboard and all stdout is the screen)
This is how the communication goes:
Process 2 stdin (keyboard) and stdout goes via... (3 Replies)
I am trying to get a better understanding of pipes and processes. I have code in which I link 3 processes A,B,C. I have A->B->C but how would I go about getting C->A?
Here is my code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
main()
{
pid_t A, B, C;
int fd;
int fd2;
... (1 Reply)
We have a production server at a client site running AIX. And recently when users are trying to connect to it via telnet, it prompts "No more multiple IP addresses to connect".
Can I know what does this error mean? and how to rectify this?
Thanks. (2 Replies)
It appears i cant connect linux VPS server via SSH or i cant SCP any file to it and i cant wget any file TO it (from inside it) while CSF (Config Server Firewall, LFD is running. Just after isntall in default configuration and after changing TESTING mode to LIVE mode.
Trying to wget & install... (1 Reply)
Greetings Experts,
I am working for a bank client and have a question on connect-direct and SFTP.
We are using Linux RedHat servers. We use connect-direct to transfer (NDM) files from one server to another server. At times, we manually transfer the files using SFTP from one server to another... (2 Replies)
Discussion started by: chill3chee
2 Replies
LEARN ABOUT CENTOS
pipe2
PIPE(2) Linux Programmer's Manual PIPE(2)NAME
pipe, pipe2 - create pipe
SYNOPSIS
#include <unistd.h>
int pipe(int pipefd[2]);
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <fcntl.h> /* Obtain O_* constant definitions */
#include <unistd.h>
int pipe2(int pipefd[2], int flags);
DESCRIPTION
pipe() creates a pipe, a unidirectional data channel that can be used for interprocess communication. The array pipefd is used to return
two file descriptors referring to the ends of the pipe. pipefd[0] refers to the read end of the pipe. pipefd[1] refers to the write end
of the pipe. Data written to the write end of the pipe is buffered by the kernel until it is read from the read end of the pipe. For fur-
ther details, see pipe(7).
If flags is 0, then pipe2() is the same as pipe(). The following values can be bitwise ORed in flags to obtain different behavior:
O_NONBLOCK Set the O_NONBLOCK file status flag on the two new open file descriptions. Using this flag saves extra calls to fcntl(2) to
achieve the same result.
O_CLOEXEC Set the close-on-exec (FD_CLOEXEC) flag on the two new file descriptors. See the description of the same flag in open(2) for
reasons why this may be useful.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EFAULT pipefd is not valid.
EINVAL (pipe2()) Invalid value in flags.
EMFILE Too many file descriptors are in use by the process.
ENFILE The system limit on the total number of open files has been reached.
VERSIONS
pipe2() was added to Linux in version 2.6.27; glibc support is available starting with version 2.9.
CONFORMING TO
pipe(): POSIX.1-2001.
pipe2() is Linux-specific.
EXAMPLE
The following program creates a pipe, and then fork(2)s to create a child process; the child inherits a duplicate set of file descriptors
that refer to the same pipe. After the fork(2), each process closes the descriptors that it doesn't need for the pipe (see pipe(7)). The
parent then writes the string contained in the program's command-line argument to the pipe, and the child reads this string a byte at a
time from the pipe and echoes it on standard output.
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char *argv[])
{
int pipefd[2];
pid_t cpid;
char buf;
if (argc != 2) {
fprintf(stderr, "Usage: %s <string>
", argv[0]);
exit(EXIT_FAILURE);
}
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
cpid = fork();
if (cpid == -1) {
perror("fork");
exit(EXIT_FAILURE);
}
if (cpid == 0) { /* Child reads from pipe */
close(pipefd[1]); /* Close unused write end */
while (read(pipefd[0], &buf, 1) > 0)
write(STDOUT_FILENO, &buf, 1);
write(STDOUT_FILENO, "
", 1);
close(pipefd[0]);
_exit(EXIT_SUCCESS);
} else { /* Parent writes argv[1] to pipe */
close(pipefd[0]); /* Close unused read end */
write(pipefd[1], argv[1], strlen(argv[1]));
close(pipefd[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
}
}
SEE ALSO fork(2), read(2), socketpair(2), write(2), popen(3), pipe(7)COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-02-14 PIPE(2)