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problem in msgctl() system call
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msgctl(2) System Calls Manual msgctl(2) NAME
msgctl - Performs message control operations SYNOPSIS
#include <sys/msg.h> int msgctl( int msqid, int cmd, struct msqid_ds *buf); Application developers may 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. STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: msgctl(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
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 manda- tory 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 supe- ruser or equal to the value of msg_perm.uid or msg_perm.cuid in the associated msqid_ds structure. Points to a 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. DESCRIPTION
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 opera- tion 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 msgctl() operation that changed the structure. RETURN VALUES
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. ERRORS
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. 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. RELATED INFORMATION
Functions: msgget(2), msgrcv(2), msgsnd(2) Data Structures: msqid_ds(4) Standards: standards(5) delim off msgctl(2)
