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Power 6/32 Unix version 1.21

.TH SEMCTL 2
.SH NAME
semctl \- semaphore control operations
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/ipc.h>
.br
.B #include <sys/sem.h>
.PP
.nf
.B "int semctl (semid, semnum, cmd, arg)"
.B int semid, cmd;
.B int semnum;
.B union semun {
.RS
.ta 8n 28n
.nf
.B int val;
.B struct semid_ds \(**buf;
.B ushort \(**array;
.fi
.RE
.B } arg;
.tr ~~
.SH DESCRIPTION
.I Semctl
provides a variety of semaphore control operations as specified by
.IR cmd .
.PP
The following
.IR cmd s
are executed with respect to the semaphore specified by
.IR semid " and " semnum:
.RS
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B GETVAL
Return the value of semval (see
.IR intro (2)).
.SM {READ}
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B SETVAL
Set the value of semval to
.IR arg.val .
.SM {ALTER}
When this cmd is successfully executed, the semadj value corresponding to the
specified semaphore in all processes is cleared.
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B GETPID
Return the value of sempid.
.SM {READ}
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B GETNCNT
Return the value of semncnt.
.SM {READ}
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B GETZCNT
Return the value of semzcnt.
.SM {READ}
.RE
.PP
The following
.IR cmd s
return and set, respectively, every semval in the set of semaphores.
.RS
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B GETALL
Place semvals into array pointed to by
.IR arg.array .
.SM {READ}
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B SETALL
Set semvals according to the array pointed to by
.IR arg.array .
.SM {ALTER}
When this cmd is successfully executed the semadj values corresponding to each
specified semaphore in all processes are cleared.
.RE
.PP
The following
.IR cmd s
are also available:
.RS
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B IPC_STAT
Place the current value of each member of the data structure associated with
.I semid
into the structure pointed to by
.IR arg.buf .
The contents of this structure are defined in
.IR intro (2).
.SM {READ}
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B IPC_SET
Set the value of the following members of the data structure associated with
.I semid
to the corresponding value found in the structure pointed to by
.IR arg.buf :
.SP 1v
.RS
.nf
.B sem_perm.uid
.B sem_perm.gid
.B "sem_perm.mode /\(** only low 9 bits \(**/"
.fi
.RE
.IP
This cmd can only be executed by a process that has an effective user
.SM ID
equal to either that of super-user or to the value of
.B sem_perm.uid
in the data structure associated with
.IR semid .
.TP \w'\fBIPC_RMID\fP\ \ \ 'u
.SM
.B IPC_RMID
Remove the semaphore identifier specified by
.I semid
from the system and destroy the set of semaphores and data structure
associated with it.
This cmd can only be executed by a process that has an effective user
.SM ID
equal to either that of super-user or to the value of
.B sem_perm.uid
in the data structure associated with
.IR semid .
.PP
.I Semctl
fails if one or more of the following are true:
.TP 15
\s-1\%[EINVAL]\s+1
.I Semid
is not a valid semaphore identifier.
.TP
\s-1\%[EINVAL]\s+1
.I Semnum
is less than zero or greater than
.BR sem_nsems .
.TP
\s-1\%[EINVAL]\s+1
.I Cmd
is not a valid command.
.TP
\s-1\%[EACCES]\s+1
Operation permission is denied to the calling process (see
.IR intro (2)).
.TP
\s-1\%[ERANGE]\s+1
.I Cmd
is
.SM
.B SETVAL
or
.SM
.B SETALL
and the value to which semval is to be set is greater than
the system imposed maximum.
.TP
\s-1\%[EPERM]\s+1
.I Cmd
is equal to
.SM
.B IPC_RMID
or
.SM
.B IPC_SET
and the effective user
.SM ID
of the calling process is not equal to that of super-user and it is
not equal to the value of
.B sem_perm.uid
in the data structure associated with
.IR semid .
.TP
\s-1\%[EFAULT]\s+1
.I Arg.buf
points to an illegal address.
.SH "RETURN VALUE"
Upon successful completion,
the value returned depends on
.I cmd\^
as follows:
.PD 0
.RS
.TP 1.5i
.SM
.B GETVAL
The value of semval.
.TP
.SM
.B GETPID
The value of sempid.
.TP
.SM
.B GETNCNT
The value of semncnt.
.TP
.SM
.B GETZCNT
The value of semzcnt.
.TP
All others
A value of 0.
.RE
.PP
.PD
Otherwise, a value of \-1 is returned and
.I errno\^
is set to indicate the error.
.SH SEE ALSO
intro(2), semget(2), semop(2).
.\"	@(#)semctl.2	6.2 of 9/6/83

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