msgctl.2 (2010 09)

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msgctl(2) msgctl(2)

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 des-

troy 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,orOWNER

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:

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (2 pages)

PAGE 1
msgctl(2) msgctl(2) NAME msgctl() - message control operations SYNOPSIS #include 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).
PAGE 2
msgctl(2) msgctl(2) [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.