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msgctl(2) [sunos man page]

msgctl(2)							   System Calls 							 msgctl(2)

NAME
msgctl - message control operations SYNOPSIS
#include <sys/msg.h> int msgctl(int msqid, int cmd, struct msqid_ds *buf); DESCRIPTION
The msgctl() function provides a variety of 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 defined in intro(2). 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.uid msg_perm.gid msg_perm.mode /* access permission bits only */ msg_qbytes This command can be executed only by a process that has either the {PRIV_IPC_OWNER} privilege or an effective user ID equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid. Only a process with the {PRIV_SYS_IPC_CONFIG} privilege 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 associated with it. This cmd can only be executed by a process that has an effective user ID either with appropriate privi- leges asserted in the effective set or equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associ- ated with msqid. The buf argument is ignored. RETURN VALUES
Upon successful completion, msgctl() returns 0. Otherwise, it returns -1 and sets errno to indicate the error. ERRORS
The msgctl() function will fail if: EACCES The cmd argument is IPC_STAT and operation permission is denied to the calling process (see intro(2)). EFAULT The buf argument points to an illegal address. EINVAL The msqid argument is not a valid message queue identifier; or the cmd argument is not a valid command or is IPC_SET and msg_perm.uid or msg_perm.gid is not valid. EOVERFLOW The cmd argument is IPC_STAT and uid or gid is too large to be stored in the structure pointed to by buf. EPERM The cmd argument is IPC_RMID or IPC_SET, the {PRIV_SYS_IPC_OWNER} privilege is not asserted in the effective set of the calling process, and is not equal to the value of msg_perm.cuid or msg_perm.uid in the data structure associated with msqid. The cmd argument is IPC_SET, an attempt is being made to increase to the value of msg_qbytes, and the {PRIV_SYS_IPC_CONFIG} privilege is not asserted in the effective set of the calling process. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
intro(2), msgget(2), msgrcv(2), msgsnd(2), attributes(5), privileges(5), standards(5) SunOS 5.10 22 Mar 2004 msgctl(2)

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MSGCTL(2)						     Linux Programmer's Manual							 MSGCTL(2)

NAME
msgctl - message control operations SYNOPSIS
#include <sys/types.h> #include <sys/ipc.h> #include <sys/msg.h> int msgctl(int msqid, int cmd, struct msqid_ds *buf); DESCRIPTION
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 (probably, root) privileges are 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. RETURN VALUE
On success, the return value will be 0, otherwise -1 with errno indicating the error. ERRORS
On failure, errno is set to one of the following: EACCES The argument cmd is equal to IPC_STAT but the calling process does not have read permission on the message queue msqid. 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 calling process has insufficient privileges to execute the command. NOTES
The IPC_INFO, MSG_STAT and MSG_INFO control calls are used by the ipcs(8) program to provide information on allocated resources. In the future these may be modified as needed or moved to a proc file system interface. 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 recom- pilation under glibc-2.1.91 or later should suffice. (The kernel distinguishes old and new calls by a IPC_64 flag in cmd.) CONFORMING TO
SVr4, SVID. SVID does not document the EIDRM error condition. SEE ALSO
ipc(5), msgget(2), msgsnd(2), msgrcv(2) Linux 2.4.1 2001-02-18 MSGCTL(2)

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