Run a process in the background
Note: The
daemon() function provides portability. In
QNX Neutrino programs, use
procmgr_daemon() instead.
See fork() to understand the implications of using
daemon() instead of procmgr_daemon().
Synopsis:
#include <stdlib.h>
int daemon( int nochdir,
int noclose );
Arguments:
- nochdir
- If this argument is 0, the current working directory is changed to the root
directory (/).
- noclose
- If this argument is 0, standard input, standard output, and standard error
are redirected to /dev/null.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The daemon() function allows programs to detach themselves from
the controlling terminal and run in the background as system daemons.
If daemon() is called with a noclose value of 0 and fails,
then the states of file descriptors 0, 1, and 2 (STDIN_FILENO,
STDOUT_FILENO, and STDERR_FILENO) are undefined.
Note:
The controlling terminal behaves as in Unix System V, Release 4.
An
open() on a terminal device not already associated with
another session causes the device to become the controlling terminal for
that process.
If you are using the High
Availability Manager (HAM), daemon() notifies the HAM of the new
process change. If the calling process is being monitored, the HAM switches to monitor the
new process that daemon() creates. For more information, see the High Availability
Framework Developer's Guide.
Returns:
Zero for success, or -1 if an error occurs
(errno is set).
Errors:
- EAGAIN
- Insufficient resources are available to create the child process.
For example, you might have exceeded the maximum number of processes
permitted; see the RLIMIT_NPROC resource for
getrlimit().
- EBADF
- A problem occurred when daemon() was duplicating a file descriptor.
For example, another thread might have opened or closed a file descriptor while the
daemon() was occurring.
You can add synchronization around the operations that involve file descriptors,
or try calling daemon() again.
- ENOMEM
- The process requires more memory than the system is able to supply.
- EPERM
- One of the following occurred:
- The calling process doesn't have PROCMGR_AID_FORK or
PROCMGR_AID_PGRP abilities; see
procmgr_ability().
- (QNX Neutrino 7.0.1 or later) The calling process's priority is above the permitted range.
- The process group ID of a process other than the calling process matches the process
ID of the calling process. This is unlikely to occur.
Classification:
Legacy Unix
| Safety: |
|
|---|
| Cancellation point |
No |
| Interrupt handler |
No |
| Signal handler |
Yes |
| Thread |
See fork() for more information |