msgctl(2)msgctl(2)Namemsgctl - message control operations
int msgctl (msqid, cmd, buf)
int msqid, cmd;
struct msqid_ds, buf;
The system call provides 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
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.mode /* only low 9 bits */
This cmd can be executed only by a process that has an effective user
ID that is equal to superuser or the value of either msg_perm.uid or
msg_perm.cuid in the data structure associated with msqid. Only the
superuser 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 associ‐
ated with it. This command can only be executed by a process
that has an effective user ID equal to either that of the supe‐
ruser or to the value of msg_perm.uid in the data structure
associated with msquid.
Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and errno is set to indicate the error.
The system call fails under the following conditions:
[EINVAL] The msqid is not a valid message queue identifier.
[EINVAL] The cmd is not a valid command.
[EACCES] The cmd is equal to IPC_STAT and read operation permis‐
sion is denied to the calling process. For further
[EPERM] The cmd is equal to IPC_RMID or IPC_SET and the effec‐
tive user ID of the calling process is not equal to that
of the superuser or to the value of msg_perm.uid in the
data structure associated with msqid.
[EPERM] The cmd is equal to IPC_SET, an attempt is being made to
increase to the value of msg_qbytes, and the effective
user ID of the calling process is not equal to that of
[EFAULT] The buf points to an illegal address.
See Alsomsgget(2), msgop(2)msgctl(2)