Originální popis anglicky:
msgctl - message control operations
Návod, kniha: Linux Programmer's Manual
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
int msgctl(int msqid, int cmd,
struct msqid_ds *buf);
This function performs the control operation specified by
cmd on the
message queue with identifier
msqid. Legal values for
cmd are:
- IPC_STAT
- Copy info from the message queue data structure associated
with msqid into the structure pointed to by buf. The caller
must have read permission on the message queue.
- IPC_SET
- Write the values of some members of the msqid_ds
structure pointed to by buf to the message queue data structure,
updating also its msg_ctime member. The following members of the
structure can be updated:
msg_perm.uid
msg_perm.gid
msg_perm.mode /* only lowest 9-bits */
msg_qbytes
The calling process must have appropriate (probably, root) privileges or its
effective user-ID must be that of the creator (msg_perm.cuid) or
owner (msg_perm.uid) of the message queue. Appropriate privilege
(Linux: the CAP_IPC_RESOURCE capability) is required to raise the
msg_qbytes value beyond the system parameter MSGMNB.
- IPC_RMID
- Immediately remove the message queue and its associated
data structure, awakening all waiting reader and writer processes (with an
error return and errno set to EIDRM). The calling process
must have appropriate (probably, root) privileges or its effective user-ID
must be either that of the creator or owner of the message queue.
On success, the return value will be
0, otherwise
-1 with
errno indicating the error.
On failure,
errno is set to one of the following:
- EACCES
- The argument cmd is equal to IPC_STAT or
MSG_STAT, but the calling process does not have read permission on
the message queue msqid, and does not have the CAP_IPC_OWNER
capability.
- EFAULT
- The argument cmd has the value IPC_SET or
IPC_STAT, but the address pointed to by buf isn't
accessible.
- EIDRM
- The message queue was removed.
- EINVAL
- Invalid value for cmd or msqid.
- EPERM
- The argument cmd has the value IPC_SET or
IPC_RMID, but the effective user ID of the calling process is not
the creator (as found in msg_perm.cuid) or the owner (as found in
msg_perm.uid) of the message queue, and the process is not
privileged (Linux: it does not have the CAP_SYS_ADMIN
capability).
Various fields in a
struct msqid_ds were shorts under Linux 2.2 and have
become longs under Linux 2.4. To take advantage of this, a recompilation under
glibc-2.1.91 or later should suffice. (The kernel distinguishes old and new
calls by a IPC_64 flag in
cmd.)
SVr4, SVID. SVID does not document the EIDRM error condition.
msgget(2),
msgrcv(2),
msgsnd(2),
ipc(5),
capabilities(7)