msgctl - Perform message control operations
#include <sys/msg.h>
int msgctl(
int msqid,
int cmd,
struct msqid_ds *buf );
Application developers might want to specify #include
statements for <sys/types.h> and <sys/ipc.h> before the
one for <sys/msg.h> if programs are being developed for
multiple platforms. The additional #include statements
are not required on Tru64 UNIX systems or by ISO or X/Open
standards, but may be required on other vendors' systems
that conform to these standards.
Interfaces documented on this reference page conform to
industry standards as follows:
msgctl(): XSH4.0, XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Specifies the message queue ID. Specifies the type of
command. The possible commands and the operations they
perform are as follows: Queries the message queue ID by
copying the contents of its associated data structure into
the buf structure. The process must have mandatory read
access to the message queue with respect to all access
control policies. Sets the message queue ID by copying
values found in the buf structure into corresponding
fields in the msqid_ds structure associated with the message
queue ID. This operation is restricted. The effective
user ID of the calling process must be equal to that of
superuser or equal to the value of msg_perm.uid or
msg_perm.cuid in the associated msqid_ds structure. Only
superuser can raise the value of msg_qbytes. Removes the
message queue ID and deallocates its associated msqid_ds
structure. This operation is restricted. The effective
user ID of the calling process must be equal to that of
superuser or equal to the value of msg_perm.uid or
msg_perm.cuid in the associated msqid_ds structure.
Points to an msqid_ds structure. This structure is used
only with the IPC_STAT and IPC_SET commands. With
IPC_STAT, the results of the query are copied to this
structure. With IPC_SET, the values in this structure are
used to set the corresponding fields in the msqid_ds
structure associated with the message queue ID. In either
case, the calling process must have allocated the structure
before making the call.
The msgctl() function allows a process to query or set the
contents of the msqid_ds structure associated with the
specified message queue ID. It also allows a process to
remove the message queue ID and its associated msqid_ds
structure. The cmd value determines which operation is
performed.
The IPC_SET command uses the user-supplied contents of the
buf structure to set the following members of the msqid_ds
structure associated with the message queue ID: The
owner's user ID. The owner's group ID. The access modes
for the queue. Only the low-order nine bits are set. The
maximum number of bytes on the queue. The time of the
last successful IPC_SET operation.
Upon successful completion, msgctl() returns a value of 0
(zero). Otherwise, a value of -1 is returned and errno is
set to indicate the error.
The msgctl() function sets errno to the specified values
for the following conditions: The cmd parameter is
IPC_STAT, but the calling process does not have read permission.
[Tru64 UNIX] The cmd parameter is IPC_STAT or
IPC_SET, and an error occurred in accessing the buf structure.
The msqid parameter is not a valid message queue
ID, or the cmd parameter is not a valid command. One of
the following occurred: The cmd parameter is equal to
either IPC_RMID or IPC_SET, and the calling process does
not have appropriate privilege. The cmd parameter is
equal to IPC_SET, and an attempt is being made to increase
the value of the msg_qbytes parameter when the calling
process does not have the superuser privilege.
Functions: msgget(2), msgrcv(2), msgsnd(2)
Data Structures: msqid_ds(4)
Standards: standards(5)
msgctl(2)
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