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Power 6/32 Unix version 1.21

.TH SEMGET 2
.SH NAME
semget \- get set of semaphores
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/ipc.h>
.br
.B #include <sys/sem.h>
.PP
.nf
.BR "int semget (key, nsems, semflg)
.B key_t key;
.B int nsems, semflg;
.fi
.SH DESCRIPTION
.I Semget
returns the semaphore identifier associated with
.IR key .
.PP
A semaphore identifier and associated data structure and set containing
.I nsems
semaphores
(see
.IR intro (2))
are created for
.I key
if one of the following are true:
.IP
.I Key
is equal to
.SM
.BR IPC_PRIVATE .
.IP
.I Key
does not already have a semaphore identifier associated with it, and
.RI ( semflg " & "
.SM
.BR IPC_CREAT\*S )
is ``true''.
.PP
Upon creation, the data structure associated with the new semaphore
identifier is initialized as follows:
.IP
.BR Sem_perm.cuid ", " sem_perm.uid ,
.BR sem_perm.cgid ", and " sem_perm.gid
are set equal to the effective user
.SM ID
and effective group
.SM ID\*S,
respectively, of the calling process.
.IP
The low-order 9 bits of
.B sem_perm.mode
are set equal to the low-order 9 bits of
.IR semflg .
.IP
.B Sem_nsems
is set equal to the value of
.IR nsems .
.IP
.B Sem_otime
is set equal to 0 and
.B sem_ctime
is set equal to the current time.
.PP
.I Semget
fails if one or more of the following are true:
.TP 15
\s-1[EINVAL]\s+1
.I Nsems
is either less than or equal to zero or greater than the system-imposed limit.
.TP
\s-1[EACCES]\s+1
A semaphore identifier exists for
.IR key ,
but operation permission (see
.IR intro (2))
as specified by the low-order 9 bits of
.I semflg
would not be granted. 
.TP
\s-1[EINVAL]\s+1
A semaphore identifier exists for
.IR key ,
but the number of semaphores in the set associated with it is less than
.IR nsems " and " nsems
is not equal to zero.
.TP
\s-1[ENOENT]\s+1
A semaphore identifier does not exist for
.I key
and
.RI ( semflg " &"
.SM
.BR IPC_CREAT\*S )
is ``false''.
.TP
\s-1[ENOSPC]\s+1
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.
.TP
\s-1[ENOSPC]\s+1
A semaphore identifier is to be created but
the system-imposed limit on the maximum number of
allowed semaphores system wide
would be exceeded.
.TP
\s-1[EEXIST]\s+1
A semaphore identifier exists for
.I key
but
.RI "((" semflg " & "
.SM
.RB IPC_CREAT\*S ") and ("
.IR semflg " & "
.SM
.BR IPC_EXCL\*S "))"
is ``true''.
.br
.if \n()s .bp
.SH "RETURN VALUE"
Upon successful completion,
a non-negative integer,
namely a semaphore identifier, is returned.
Otherwise, a value of \-1 is returned and
.I errno\^
is set to indicate the error.
.SH SEE ALSO
intro(2), semctl(2), semop(2).
.\"	@(#)semget.2	6.2 of 9/6/83

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