Re: [Jack-Devel] semaphore, permission denied

On Monday 17 February 2014 16:17:14 David Santamauro wrote:
> It turns out that a listing of /dev/shm showed that the named semaphore
> had a permission of 700 for some reason. Changing it to 755 cured this
> problem.
> 
> Of course, how that could happen is baffling.

You haven't mentioned which version of JACK you are using. Named semaphores 
are created by JACK like this:

	sem_open(fName, O_CREAT | O_RDWR, 0777, value);

This is a POSIX API call where also the permission tuple is given, so if a 
semaphore of the given name does not exist, it will be created by the OS with 
the given permission tuple, masked against the process' permission tuple.

I currently don't see a reason why JACK could be blamed for the semaphore 
being created with 700 there. My guess is that it might be caused by incorrect 
permissions being set to the JACK server binary. From the sem_open() man page:

	"If  O_CREAT  is specified in oflag, then two additional arguments must 
	be supplied. The mode argument specifies the permissions to be placed on 
	the new semaphore, as for open(2) ... The permissions settings  are  
	masked  against  the  process umask ... If O_CREAT is specified, and a 
	semaphore with the given name already exists, then mode and value are 
	ignored."

CU
Christian

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