I wish to make a process run in the background, but only one instance of it, and not many,
so when the program is loaded, it has to check whether another instance of the same
program is running and if so to exit. How do I do this ?
If your system supports the semget() and semop() calls that are included in one of the optional features in the POSIX standards, you can use semget() to get access to a semaphore with a key that is known to your daemon. After getting the semaphore ID you can use semop() with an array of two operations at the start of your program. These operations are:
If the semop() call fails with EAGAIN, another daemon is already running and owns the semaphore. If the semop() call succeeds, this daemon owns the semaphore until it terminates. (It doesn't matter if this daemon terminates due to receipt of an uncaught signal or terminates normally by calling exit, the SEM_UNDO flag will release ownership of the semaphore when the daemon terminates.)
If you don't have access to a similar set of semaphore operations, a common approach is to atomically create (with open flags O_CREAT | O_EXCL) a lock file and write the PID of the daemon that created the lock into the lock file. The daemon should then remove the lock file before it exits. (If the daemon is killed before it can remove the lock file, another daemon won't be able to start until you manually remove the lock file.)
This User Gave Thanks to Don Cragun For This Post:
Hi,
I have to write a daemon process, which performs certain operations in the background.
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rish (1 Reply)
Hello,
I need to run a command on remote Linux using the ssh command from my local machine. I am able to execute the command on remote machine using ssh but it's behaving strangely.
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Hello,
I am new to this forum and this is my first post here...
I have never worked on either Pro*C or Multithreading..Now, i have to write a Pro*C, Multithreading daemon process.. I dont know where to start.. Can anybody help me with examples?
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I have a scenario where I need to find if a process is a daemon process or not. This check needs to be done from within the process. I know there are no direct API's to do so. I have explored these options.
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Hi All,
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Hi,
HI ,
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Discussion started by: nks342
3 Replies
LEARN ABOUT MOJAVE
sem_unlink
SEM_UNLINK(2) BSD System Calls Manual SEM_UNLINK(2)NAME
sem_unlink -- remove a named semaphore
SYNOPSIS
#include <semaphore.h>
int
sem_unlink(const char *name);
DESCRIPTION
The named semaphore named name is removed. If the semaphore is in use by other processes, then name is immediately disassociated with the
semaphore, but the semaphore itself will not be removed until all references to it have been closed. Subsequent calls to sem_open() using
name will refer to or create a new semaphore named name.
If successful, sem_unlink() will return 0. Otherwise, -1 is returned and errno is set, and the state of the semaphore is unchanged.
ERRORS
sem_unlink() succeeds unless:
[EACCES] Permission is denied to be remove the semaphore.
[ENAMETOOLONG] name exceeded PSEMNAMLEN characters.
[ENOENT] The named semaphore does not exist.
SEE ALSO sem_close(2), sem_open(2), semctl(2), semget(2), semop(2)HISTORY
sem_unlink() is specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995).
Darwin June 8, 2000 Darwin