| MSGCTL(2) | System Calls Manual | MSGCTL(2) | 
msgctl —
#include <sys/msg.h>
int
  
  msgctl(int
    msqid, int cmd,
    struct msqid_ds
  *buf);
msgctl() system call performs control operations on
  the message queue specified by msqid.
Each message queue has a msqid_ds structure associated with it which contains the following members:
    struct ipc_perm msg_perm; /* msg queue permission bits */
    msgqnum_t msg_qnum;       /* # of msgs in the queue */
    msglen_t  msg_qbytes;     /* max # of bytes on the queue */
    pid_t     msg_lspid;      /* pid of last msgsnd() */
    pid_t     msg_lrpid;      /* pid of last msgrcv() */
    time_t    msg_stime;      /* time of last msgsnd() */
    time_t    msg_rtime;      /* time of last msgrcv() */
    time_t    msg_ctime;      /* time of last msgctl() */
The ipc_perm structure used inside the
    msgid_ds structure is defined in
    <sys/ipc.h> and contains the
    following members:
    uid_t cuid;  /* creator user id */
    gid_t cgid;  /* creator group id */
    uid_t uid;   /* user id */
    gid_t gid;   /* group id */
    mode_t mode; /* permission (lower 9 bits) */
The operation to be performed by msgctl()
    is specified in cmd and is one of:
IPC_STATIPC_SETMSGMNB from
      <sys/msg.h>) are silently
      truncated to that limit.IPC_RMIDThe permission to read from or write to a message queue (see msgsnd(2) and msgrcv(2)) is determined by the msg_perm.mode field in the same way as is done with files (see chmod(2)), but the effective uid can match either the msg_perm.cuid field or the msg_perm.uid field, and the effective gid can match either msg_perm.cgid or msg_perm.gid.
msgctl() will fail if:
EPERM]IPC_SET or
      IPC_RMID and the caller is not the super-user, nor
      does the effective uid match either the msg_perm.uid
      or msg_perm.cuid fields of the data structure
      associated with the message queue.
    An attempt was made to increase the value of
        msg_qbytes through
        IPC_SET, but the caller is not the
      super-user.
EACCES]IPC_STAT and the
      caller has no read permission for this message queue.EINVAL]cmd is not a valid command.
EFAULT]msgctl system call conforms to
  X/Open System Interfaces and Headers Issue 5
  (“XSH5”).
| August 25, 1999 | NetBSD 9.4 |