msgctl(2)msgctl(2)NAMEmsgctl - message control operations
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgctl(int msqid, int cmd, .../* struct msqid_ds *buf */);
DESCRIPTIONmsgctl provides a variety of message control operations as specified by
cmd. The following cmds are available:
IPC_STAT 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).
IPC_SET 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 access permission bits */
msg_qbytes
This cmd can only be executed by a process that has an
effective user ID equal to the value of msg_perm.cuid or
msg_perm.uid in the data structure associated with msqid, or
by a process that has the super-user privilege.
A process with the super-user privilege can raise the value of
msg_qbytes.
IPC_RMID
Remove the message queue identifier specified by msqid from the
system and destroy the 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 msg_perm.cuid or msg_perm.uid in the data structure
associated with msqid.
msgctl fails if one or more of the following are true:
EACCES cmd is IPC_STAT and operation permission is denied to the
calling process [see intro(2)].
EFAULT buf points to an illegal address.
EINVAL msqid is not a valid message queue identifier.
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msgctl(2)msgctl(2)
EINVAL cmd is not a valid command.
EINVAL cmd is IPC_SET and msg_perm.uid or msg_perm.gid is not
valid.
EOVERFLOW cmd is IPC_STAT and uid or gid is too large to be stored
in the structure pointed to by buf.
EPERM cmd is IPC_RMID or IPC_SET, the effective user ID of the
calling process is not equal to the value of msg_perm.cuid
or msg_perm.uid in the data structure associated with
msqid and the process does not have the super-user
privilege.
EPERM cmd is IPC_SET, an attempt is being made to increase to
the value of msg_qbytes, and the calling process does not
have the super-user privilege.
SEE ALSOintro(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.
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