SEMGET

Section: System Calls (2)
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BSD mandoc
NetBSD

NAME

semget - get semaphore set

SYNOPSIS

Fd #include <sys/types.h> Fd #include <sys/ipc.h> Fd #include <sys/sem.h> Ft int Fn semget key_t key int nsems int semflg

DESCRIPTION

The Fn semget system call returns the semaphore identifier associated with Fa key .

A new set containing Fa nsems semaphores is created if either Fa key is equal to IPC_PRIVATE, or Fa key does not have a semaphore set associated with it, and the IPC_CREAT bit is set in Fa msgflg.

If a new set of semaphores is created, the data structure associated with it (the semid_ds structure, see semctl(2)) is intialized as follows:

sem_perm.cuid and sem_perm.uid are set to the effective uid of the calling process.
sem_perm.gid and sem_perm.cgid are set to the effective gid of the calling process.
sem_perm.mode is set to the lower 9 bits of Fa msgflg .
sem_nsems is set to the value of Fa nsems
sem_ctime is set to the current time
sem_otime is set to 0

RETURN VALUES

Fn semget returns a non-negative semaphore identifier if successful. Otherwise, -1 is returned and errno is set to reflect the error.

ERRORS

Bq Er EACCESS: The caller has no permission to access a semaphore set already associated with Fa key.
Bq Er EEXIST: Both IPC_CREAT and IPC_EXCL are set in Fa msgflg , and a semaphore set is already associated with Fa key .
Bq Er EINVAL: nsems is less than 0 or greater than the system limit for the number in a semaphore set.
A semaphore set associated with Fa key exists, but has fewer semaphores than the number specified in Fa nsems .
Bq Er ENOSPC: A new set of semaphores could not be created because the system limit for the number of semaphores or the number of semaphore sets has been reached.
Bq Er ENOENT: IPC_CREAT was not set in Fa msgflg and no semaphore set associated with Fa key was found.

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Time: 16:28:59 GMT, April 18, 2022