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.TH SHMCTL 2
.SH NAME
shmctl \- shared memory control operations
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/ipc.h>
.br
.B #include <sys/shm.h>
.PP
.nf
.B int shmctl (shmid, cmd, buf)
.B int shmid, cmd;
.B struct shmid_ds \(**buf;
.fi
.SH DESCRIPTION
.I Shmctl
provides a variety of shared memory control operations as specified by
.IR cmd .
The following
.IR cmd s
are available:
.RS
.TP \w'IPC_RMID\ \ \ 'u
.SM
.B IPC_STAT
Place the current value of each member of the data structure associated with
.I shmid
into the structure pointed to by
.IR buf .
The contents of this structure are defined in
.IR intro (2).
.SM {READ}
.TP
.SM
.B IPC_SET
Set the value of the following members of the data structure associated with
.I shmid
to the corresponding value found in the structure pointed to by
.IR buf :
.nf
.RS
shm_perm.uid
shm_perm.gid
shm_perm.mode /\(** only low 9 bits \(**/
.fi
.RE
.IP
This \fIcmd\fP 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 shm_perm.uid
in the data structure associated with
.IR shmid .
.TP
.SM
.B IPC_RMID
Remove the shared memory identifier specified by
.I shmid
from the system and destroy the shared memory segment and data structure
associated with it.
This \fIcmd\fP 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 shm_perm.uid
in the data structure associated with
.IR shmid .
.PP
.I Shmctl
will fail if one or more of the following are true:
.TP 15
.SM
\%[EINVAL]
.I Shmid
is not a valid shared memory identifier.
.TP
.SM
\%[EINVAL]
.I Cmd
is not a valid command.
.TP
.SM
\%[EACCES]
.I Cmd
is equal to
.B IPC_STAT
and
.SM {READ}
operation permission is denied to the calling process (see
.IR intro (2)).
.TP
.SM
\%[EPERM]
.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 shm_perm.uid
in the data structure associated with
.IR shmid .
.TP
.SM
\%[EFAULT]
.I Buf
points to an illegal address.
.SH "RETURN VALUE"
Upon successful completion, a value of 0 is returned. Otherwise, a
value of \-1 is returned and
.I errno\^
is set to indicate the error.
.SH SEE ALSO
intro(2), shmget(2), shmop(2).
.\"	@(#)shmctl.2	6.2 of 9/6/83

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