MSGCTL(2) MSGCTL(2)
NAME
msgctl - message control operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgctl (msqid, cmd, buf)
int msqid, cmd;
struct msqidds *buf;
DESCRIPTION
msgctl provides a variety of message control operations as
specified by cmd. The following cmds are available:
IPCSTAT Place the current value of each member of the
data structure associated with msqid into the
structure pointed to by buf. The contents of
this structure are defined in intro(2).
{READ}
IPCSET Set the value of the following members of the
data structure associated with msqid to the
corresponding value found in the structure
pointed to by buf:
msg_perm.uid
msg_perm.gid
msg_perm.mode /* only low 9 bits */
msg_qbytes
This cmd can only be executed by a process
that has an effective user ID equal to either
that of super user, or to the value of
msgperm.cuid or msgperm.uid in the data
structure associated with msqid. Only super
user can raise the value of msgqbytes.
IPCRMID Remove the message queue identifier specified
by msqid from the system and destroy the
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MSGCTL(2) MSGCTL(2)
message queue and data structure associated
with it. This cmd can only be executed by a
process that has an effective user ID equal
to either that of super user, or to the value
of msgperm.cuid or msgperm.uid in the data
structure associated with msqid.
msgctl will fail if one or more of the following are true:
[EINVAL] Msqid is not a valid message queue
identifier.
[EINVAL] Cmd is not a valid command.
[EACCES] Cmd is equal to IPCSTAT and {READ} operation
permission is denied to the calling process
[see intro(2)].
[EPERM] Cmd is equal to IPCRMID or IPCSET. The
effective user ID of the calling process is
not equal to that of super user, or to the
value of msgperm.cuid or msgperm.uid in the
data structure associated with msqid.
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MSGCTL(2) MSGCTL(2)
[EPERM] Cmd is equal to IPCSET, an attempt is being
made to increase to the value of msgqbytes,
and the effective user ID of the calling
process is not equal to that of super user.
[EFAULT] Buf points to an illegal address.
SEE ALSO
intro(2), msgget(2), msgop(2).
DIAGNOSTICS
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
Page 3 May 1989