9 More Discussions You Might Find Interesting
1. Solaris
Hi,
Can somebody please explain me what semaphores are? there purpose? and there effects?
Thanks in advance:) (0 Replies)
Discussion started by: Laxxi
0 Replies
2. Solaris
Hi, I've used the following way to set ssh public key authentication and it is working fine on Solaris 10, RedHat Linux and SuSE Linux servers without any problem. But I got error 'Server refused our key' on Solaris 8 system. Solaris 8 uses SSH2 too. Why? Please help. Thanks.
... (1 Reply)
Discussion started by: aixlover
1 Replies
3. UNIX for Dummies Questions & Answers
I am having problem with semaphores. I am trying to protect line where process prints so that every process with print in proper order.This is the code..
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/types.h>
union... (3 Replies)
Discussion started by: joker40
3 Replies
4. UNIX for Advanced & Expert Users
Hello, first of all I apologize if this thread is not in the correct section of this forum, but this one just seemed the most appropriate.
The question I have does not concern Unix specifically, it applies to virtually any OS, however it is in Unix where I learned about this problem.
So, the... (8 Replies)
Discussion started by: Watto86
8 Replies
5. Programming
been searching around on how to use an up and down function with semaphores but i can't find an example. i looked into using: "semop" but i have no idea how to use it. I have been able to declared the semaphores using semget and initializing them using semctl. (7 Replies)
Discussion started by: ddx08
7 Replies
6. Shell Programming and Scripting
Hi Friends,
If i execute this command it comes back with 300 lines:
ipcs|grep cerebrus >>> i would like to clear the semaphores but ipcrm can remove one id at a time. is there a quicker way of removing semaphores maybe using awk?
Regards, (1 Reply)
Discussion started by: kekanap
1 Replies
7. Programming
Hi there,
Could someone please confirm which POSIX semaphore routines should be used for a multiprocess (and not multithreaded) environment?
sys/sem.h definitely works. but the routines, semget, semctl, semop are pretty unwieldy. So, I am looking for an easier way out.
From the man pages... (2 Replies)
Discussion started by: qntmteleporter
2 Replies
8. UNIX for Dummies Questions & Answers
Hi all,
I am using HP 10.20 on A 9000/785. My question is:
If I am the only person logged in as root at the moment, how many "semaphore proccesses" should I have?? Is it only one, or it is relevant to other system proccesses?
Here is what I get listing the current semaphores
# ipcs -sp... (1 Reply)
Discussion started by: guest100
1 Replies
9. Programming
Dear Reader,
I'm in a multiprocess environment working with shared mem and semaphores as mutex.. The problem is -- If one of the process hooked up with the semaphore and accessing the shared mem, terminates abruptly ( or got killed ), other process which are in want of the semaphore are... (1 Reply)
Discussion started by: joseph_shibu
1 Replies
semget(2) System Calls Manual semget(2)
NAME
semget - get set of semaphores
SYNOPSIS
DESCRIPTION
returns the semaphore identifier associated with key.
A semaphore identifier and associated data structure and set containing nsems semaphores are created for key if one of the following is
true:
key is equal to This call creates a new identifier, subject to available resources. The identifier is never returned by another
call to until it has been released by a call to The identifier should be used among the calling process and its descendents; how-
ever, it is not a requirement. The resource can be accessed by any process having the proper permissions.
key does not already have a semaphore identifier associated with it, and (semflg & is "true".
Specific behavior can be requested by ORing the following masks into semflg.
Create a semaphore identifier if one does not already exist for key.
If is specified and key already has a semaphore identifier associated with it, return an error.
The low-order 9 bits of semflg are the semaphore operation permissions which are defined in glossary(9).
Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:
In the operation-permission structure, and are set equal to the effective-user-ID of the calling process, while and are set to the
effective-group-ID of the calling process.
The low-order 9 bits of are set equal to the low-order 9 bits of semflg.
is set equal to the value of nsems.
is set equal to 0 and is set equal to the current time.
Security Restrictions
Some or all of the actions associated with this system call are subject to compartmental restrictions. See compartments(5) for more infor-
mation about compartmentalization on systems that support that feature. Compartmental restrictions can be overridden if the process pos-
sesses the privilege (PRIV_COMMALLOWED). Processes owned by the superuser may not have this privilege. Processes owned by any user may
have this privilege, depending on system configuration.
See privileges(5) for more information about privileged access on systems that support fine-grained privileges.
EXAMPLES
The following call to returns a semid associated with the key returned by If a semid associated with the key does not exist, a new semid,
set of 4 semaphores, and associated data structure will be created. If a semid for the key already exists, the semid is simply returned.
RETURN VALUE
Upon successful completion, a non-negative integer, namely a semaphore identifier, is returned. Otherwise, a value of -1 is returned and
is set to indicate the error.
ERRORS
fails if one or more of the following is true:
nsems is either less than or equal to zero or greater than the system-imposed limit.
A semaphore identifier exists for
key, but operation permission as specified by the low-order 9 bits of semflg would not be granted.
A semaphore identifier exists for
key, but the number of semaphores in the set associated with it is less than nsems, and nsems is not equal to zero.
A semaphore identifier does not exist for
key and (semflg & is "false".
A semaphore identifier is to be created,
but the system-imposed limit on the maximum number of allowed semaphore identifiers system wide would be exceeded.
A semaphore identifier exists for
key but is "true".
SEE ALSO
ipcrm(1), ipcs(1), semctl(2), semop(2), stdipc(3C).
STANDARDS CONFORMANCE
semget(2)