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msgctl(2)

HP-UX 11i Version 3: February 2007
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NAME

msgctl() — message control operations

SYNOPSIS

#include <sys/msg.h>

int msgctl(int msqid, int cmd, struct msqid_ds *buf);

DESCRIPTION

msgctl() 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 glossary(9). This command requres the DACREAD privilege to operate on a message queue not permitted by access modes. This command requires the COMMALLOWED privilege to operate on a message queue in a different compartment.

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 /* only low 9 bits */ msg_qbytes

This cmd can only be executed by a process that has the OWNER privilege or has an effective user ID equal to the value of either msg_perm.uid or msg_perm.cuid in the data structure associated with msqid. Only a user with the LIMIT privilege can raise the value of msg_qbytes.

WARNING: Programs compiled on HP-UX revisions prior to HP-UX 11i v1 use old 16-bit msqid_ds structure fields (obtained via IPC_STAT) which can describe queue sizes only up to 64 KBytes. Care must be taken such that queues shared with such programs are not made larger than 64 KBytes (65535). Or, those existing programs should be recompiled. Or, the system administrator should restrict the MSGMNB kernel tunable parameter to 64 KBytes or less.

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 the OWNER privilege or has an effective user ID equal to the value of either msg_perm.uid or msg_perm.cuid in the data structure associated with msqid.

Security Restrictions

Some or all of the actions associated with this system call are subject to compartmental restrictions. See compartments(5) for more information about compartmentalization on systems that support that feature.

Compartmental restrictions can be overridden if the process possesses the COMMALLOWED privilege (PRIV_COMMALLOWED). Processes owned by the superuser may not have this privilege. Processes owned by any user may have this privilege, depending on system configuration.

Some or all of the actions associated with this system call require the DACREAD, LIMIT, or OWNER privileges (PRIV_DACREAD, PRIV_LIMIT or PRIV_OWNER). Processes owned by the superuser have these privileges. Processes owned by other users may have one or more of these privileges, depending on system configuration.

See privileges(5) for more information about privileged access on systems that support fine-grained privileges.

RETURN VALUE

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

msgctl() fails if one or more of the following is true:

EINVAL

msqid is not a valid message queue identifier.

EINVAL

cmd is not a valid command, or the command contains invalid parameters.

EACCES

cmd is equal to IPC_STAT and Read operation permission is denied to the calling process (see message operation permissions in glossary(9)).

EPERM

cmd is equal to IPC_RMID or IPC_SET and the calling process does not have the OWNER privilege or the effective user ID of the calling process is not equal to the value of either msg_perm.uid or msg_perm.cuid in the data structure associated with msqid.

EPERM

cmd is equal to IPC_SET, an attempt is being made to increase to the value of msg_qbytes, and the user does not have the LIMIT privilege.

EFAULT

buf points to an illegal address. Reliable detection of this error is implementation dependent.

STANDARDS CONFORMANCE

msgctl(): SVID2, SVID3, XPG2, XPG3, XPG4

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