Hi All,
First of all thanks for reading this post.
In my application, I am trying to create a new message queue . I am attaching the code below.
But mq_open is return -1 with EFAULT as error code. This is a part of my big application So for checking the method i wrote a sample code with the same method and tried to create a message queue. It was working perfectly fine.
I run strace for the program to get the details of the bug.
(i have attached the entire strace for reference.)
In that it is mentioned as
Please help me to get out of this issue. Thanks again,
Parvathy
Ok, I'm sure this is a total newbie question, but I think I'm in the right place, no?
I'm trying to call a perl module from a cgi script - Mail::Sendmail - and my web host installed the module in a directory that doesn't seem to be accessible, at least not the way I'm trying. But I thought you... (1 Reply)
Hi,
Is there any system call which changes the time of symbolic link apart from utime? or if tere is no system call any other option of how to do it?
Thanks (4 Replies)
I need to write a script that can find a bad record (for example: there is date field colom but value provided in the file for this field is N/A) then script shoud searches this pattern and then insert the whole record into the bad file.
Example:
File1
Name designation dateOfJoining... (1 Reply)
I need to write a script that can find a bad record (for example: there is date field colom but value provided in the file for this field is N/A) then script shoud searches this pattern and then insert the whole record into the bad file.
Example:
File1
Name designation dateOfJoining... (2 Replies)
Hi All
I have a dedicated backup server running ubuntu 10.04, which has recently been rebuilt (same OS, just different h/w)
This is used to receive ufsdump output from a number of Solaris servers, using the following syntax:
ufsdump 1uf :/path/to/backup/file /fs/to/be/backed/up
This has... (1 Reply)
Hi ,
One of my zone went down and when i booted it up i could see the pool in degraded state with some check sum errors . we have brought the pool online after scrubbing. But few files are showing this error
Bad exchange descriptor
Please let me know how to remove these files (2 Replies)
I'm learning SED command. And while doing that i got to this place where i'm taking a copy of my existing file. The code i used is -
sed -n '/Storm/ w Storm.txt' books.txt
As expected, the file 'books.txt' is read , and lines with 'Storm' is put in to the new file 'Storm.txt'. However, it also... (4 Replies)
Discussion started by: justo
4 Replies
LEARN ABOUT V7
mq_setattr
MQ_GETATTR(3) Linux Programmer's Manual MQ_GETATTR(3)NAME
mq_getattr, mq_setattr - get/set message queue attributes
SYNOPSIS
#include <mqueue.h>
int mq_getattr(mqd_t mqdes, struct mq_attr *attr);
int mq_setattr(mqd_t mqdes, const struct mq_attr *newattr,
struct mq_attr *oldattr);
Link with -lrt.
DESCRIPTION
mq_getattr() and mq_setattr() respectively retrieve and modify attributes of the message queue referred to by the message queue descriptor
mqdes.
mq_getattr() returns an mq_attr structure in the buffer pointed by attr. This structure is defined as:
struct mq_attr {
long mq_flags; /* Flags: 0 or O_NONBLOCK */
long mq_maxmsg; /* Max. # of messages on queue */
long mq_msgsize; /* Max. message size (bytes) */
long mq_curmsgs; /* # of messages currently in queue */
};
The mq_flags field contains flags associated with the open message queue description. This field is initialized when the queue is created
by mq_open(3). The only flag that can appear in this field is O_NONBLOCK.
The mq_maxmsg and mq_msgsize fields are set when the message queue is created by mq_open(3). The mq_maxmsg field is an upper limit on the
number of messages that may be placed on the queue using mq_send(3). The mq_msgsize field is an upper limit on the size of messages that
may be placed on the queue. Both of these fields must have a value greater than zero. Two /proc files that place ceilings on the values
for these fields are described in mq_overview(7).
The mq_curmsgs field returns the number of messages currently held in the queue.
mq_setattr() sets message queue attributes using information supplied in the mq_attr structure pointed to by newattr. The only attribute
that can be modified is the setting of the O_NONBLOCK flag in mq_flags. The other fields in newattr are ignored. If the oldattr field is
not NULL, then the buffer that it points to is used to return an mq_attr structure that contains the same information that is returned by
mq_getattr().
RETURN VALUE
On success mq_getattr() and mq_setattr() return 0; on error, -1 is returned, with errno set to indicate the error.
ERRORS
EBADF The message queue descriptor specified in mqdes is invalid.
EINVAL newattr->mq_flags contained set bits other than O_NONBLOCK.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
+---------------------------+---------------+---------+
|Interface | Attribute | Value |
+---------------------------+---------------+---------+
|mq_getattr(), mq_setattr() | Thread safety | MT-Safe |
+---------------------------+---------------+---------+
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
NOTES
On Linux, mq_getattr() and mq_setattr() are library functions layered on top of the mq_getsetattr(2) system call.
EXAMPLE
The program below can be used to show the default mq_maxmsg and mq_msgsize values that are assigned to a message queue that is created with
a call to mq_open(3) in which the attr argument is NULL. Here is an example run of the program:
$ ./a.out /testq
Maximum # of messages on queue: 10
Maximum message size: 8192
Since Linux 3.5, the following /proc files (described in mq_overview(7)) can be used to control the defaults:
$ uname -sr
Linux 3.8.0
$ cat /proc/sys/fs/mqueue/msg_default
10
$ cat /proc/sys/fs/mqueue/msgsize_default
8192
Program source
#include <mqueue.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE);
} while (0)
int
main(int argc, char *argv[])
{
mqd_t mqd;
struct mq_attr attr;
if (argc != 2) {
fprintf(stderr, "Usage: %s mq-name
", argv[0]);
exit(EXIT_FAILURE);
}
mqd = mq_open(argv[1], O_CREAT | O_EXCL, S_IRUSR | S_IWUSR, NULL);
if (mqd == (mqd_t) -1)
errExit("mq_open");
if (mq_getattr(mqd, &attr) == -1)
errExit("mq_getattr");
printf("Maximum # of messages on queue: %ld
", attr.mq_maxmsg);
printf("Maximum message size: %ld
", attr.mq_msgsize);
if (mq_unlink(argv[1]) == -1)
errExit("mq_unlink");
exit(EXIT_SUCCESS);
}
SEE ALSO mq_close(3), mq_notify(3), mq_open(3), mq_receive(3), mq_send(3), mq_unlink(3), mq_overview(7)COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 MQ_GETATTR(3)