HP-UX Reference (11i v3 07/02) - 2 System Calls (vol 5)

m
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 glos-
sary(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 ker-
nel 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 exe-
cuted 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 asso-
ciated 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: February 2007 − 1 − Hewlett-Packard Company 239