How do I see message queue in Linux?

Use the Unix command ipcs to get a list of defined message queues, then use the command ipcrm to delete the queue.

Is Msgrcv a blocking call?

The msgsnd(2) and msgrcv(2) functions can be performed as either blocking or non-blocking operations. A blocked message operation remains suspended until one of the following three conditions occurs: The call succeeds. The process receives a signal.

How do I clear message queue in Linux?

Using a ipcrm command we can remove the single queue at a time. or else using a msgctl() we can remove that.

What does Msgrcv return?

Returned value

If successful, msgrcv() returns a value equal to the number of bytes actually placed into the mtext field of the user-defined buffer pointed to by msgp. A value of zero indicates that only the mtype field was received from the message queue.

How do I find my SMTP queue in Linux?

Viewing email in Linux using postfix’s mailq and postcat

  1. mailq – print a list of all queued mail.
  2. postcat -vq [message-id] – print a particular message, by ID (you can see the ID along in mailq ‘s output)
  3. postqueue -f – process the queued mail immediately.

How do I see pending emails in Linux?

Check mail queue
We use Redhat server , we always use mailq to check any pending mail in mailq , when run the command mailq , it shows all existing pending mail would advise how to write a script to show the pending mails which are older than 24 hours , ( if possible , then send this pending mail info to…

What is blocking call in kernel?

In the current kernel design, blocking calls are calls where the kernel returns only when the request is complete (or error happens). These calls usually take longer amounts of time and usually lead your process to be scheduled out. For instance, many IO calls are blocking.


IPC_NOWAIT. If the message queue is full, then the message is not written to the queue, and control is returned to the calling process. If not specified, then the calling process will suspend (block) until the message can be written.

How do you clean a Mailq?

To purge the mail queue, we will use the postsuper -d command. This command has two execution options: To purge a single email from the queue, use the postsuper -d [message id] command. To purge all email from the queue, use the postsuper -d ALL command.

How do I flush Mailq in sendmail?

If you want to delete all queued mail just cd to /var/spool/mqueue/ and delete all files. Note: Please make sure you are removing all /var/spool/mqueue/ files if you did something wrong with rm -rvf with * you may damage your system.

What is Msgctl?

The msgctl() function allows the caller to control the message queue specified by the msqid parameter. A message queue is controlled by setting the cmd parameter to one of the following values: IPC_RMID (0x00000000) Remove the message queue identifier msqid from the system and destroy any messages on the message queue.

What is the INT Msgflg?

DESCRIPTION top. The msgget() system call returns the System V message queue identifier associated with the value of the key argument. It may be used either to obtain the identifier of a previously created message queue (when msgflg is zero and key does not have the value IPC_PRIVATE), or to create a new set.

How do I find my SMTP server queue?

To hunt for a message, go to Exchange System Manager -> Administrative Groups -> your administrative group -> Servers -> the problematic server -> Queues. When you select the Queues container, Exchange System Manager will display all of the server’s SMTP queues in the console’s details pane.

How do I check my mail queue?

Use Queue Viewer to view the properties of a message. In the Exchange Toolbox, in the Mail flow tools section, double-click Queue Viewer to open the tool in a new window. In Queue Viewer, select the Messages tab to see the list of messages that are currently queued for delivery in your organization.

How do I check my mail queue in sendmail?

To check what is currently sitting in the sendmail mail queue use the sendmail -bp command or its alias mailq. This post looks at basic usage of this command and the output from viewing the mail queue.

Is read () a blocking call?

In blocking mode read() will block; in non-blocking mode if there is no data it will return -1 with errno set to EAGAIN or EWOULDBLOCK depending in your platform.

Is write () a blocking call?

Succinctly, both read() and write() can be blocking or non-blocking, depending on circumstances.

What is IPC V?

System V IPC is the name given to three interprocess communication mechanisms that are widely available on UNIX systems: message queues, semaphore, and shared memory. Message queues System V message queues allow data to be exchanged in units called messages.

What is message queue in Linux?

Message queues allow one or more processes to write messages which will be read by one or more reading processes. Linux maintains a list of message queues, the msgque vector; each element of which points to a msqid_ds data structure which fully describes the message queue.

What is Mailq?

The mailq command prints a list of messages that are in the mail queue. The mailq command is the same as the sendmail -bp command. Specify the -v flag to display message priority.

How do I check mail queue in sendmail?

What is Ipc_stat?

Description. IPC_STAT. Copy information from the kernel data structure associated with msqid into the msqid_ds structure pointed to by buf. The caller must have read permission on the message queue.

What is Ipc_perm structure?

ipc_perm structure that specifies the access permissions on the semaphore set. sem_otime. Time of last semop(2) system call. sem_ctime. Time of last semctl(2) system call that changed a member of the above structure or of one semaphore belonging to the set.

Why we are using Msgget?

The msgget function is used either to create a new message queue or to locate an existing queue based on a key. Message queues are implemented by UNIX System Services, and allow messages of multiple types to be queued.

What is Msgget key?

The msgget() function returns the message queue identifier associated with the argument key. A message queue identifier, associated message queue and data structure (see <sys/msg. h>) are created for the argument key if one of the following is true: The argument key is equal to IPC_PRIVATE.