System V Message Queues in Debian 6.x/Knoppix 6.x

A message queue is a System V IPC object that allows different or unrelated processes to exchange messages. Any process can create a message queue, modify it and leave it for other processes to modify later on. Any process can immediately remove a message queue regardless of whether another process is using it. Message queues exist until they are removed or system shutdown.

The data strucuture of the message queue object is:

struct msqid_ds

{

  struct ipc_perm msg_perm;

  msgqnum_t msg_qnum;    /* no of messages on queue */

  msglen_t msg_qbytes;   /* bytes max on a queue */

  pid_t msg_lspid;       /* PID of last msgsnd(2) call */

  pid_t msg_lrpid;       /* PID of last msgrcv(2) call */

  time_t msg_stime;      /* last msgsnd(2) time */

  time_t msg_rtime;      /* last msgrcv(2) time */

  time_t msg_ctime;      /* last change time */

};

Both commands list all the message queue objects in use on the system:

cat /proc/sysvipc/msg;

ipcs -q; ipcs -q -t; ipcs -q -p; ipcs -q -c; ipcs -q -l; ipcs -q -u;

Create message queue objects on the system:

ipcmk -Q -p <permission bits>;

Remove message queue objects from the system:

ipcrm -Q <msg key>;

ipcrm -q <msg id>;

Do you have a suggestion about how to improve this blog? Let's talk about it. Contact me at David.Brenner.Jr@Gmail.com or 720-584-5229.

Comments

The meaning of time in reinforcement learning

Reinforcement learning (RL) is one of three basic machine learning paradigms, alongside supervised learning and unsupervised learning. Reinforcement learning is concerned with how software agents ought to take actions in an environment in order to maximize the notion of cumulative reward through the process of trial and error. In reinforcement learning an agent starts at an empty state then analyzes the available datasets according to a policy of positive states and negative states. Rather than being explicitly taught as in supervised learning the correct set of actions for performing a task, reinforcement learning uses rewards as signals for positive states and punishments as signals for negative states. The agent obtains the best path to a desirable reward as a cumulation of positive states and negative states. As compared to unsupervised learning, reinforcement learning is different in terms of goals. While the goal in unsupervised learning is to find similarities and differences...

Old idea of encrypted, anonymous group chats

Encrypted, Anonymous Group Chats An owner of the chat connects through multiple VPNs, like NordVPN and SurfShark which are the most popular. Then the owner obtains access to an email provider hosted in a country outside the United States. Once the new email account has been setup and ready to use, the owner shares the login username and login password of that email account with the participants. The idea is to never send/receive any emails, only exchange messages saved as drafts in the email account. The drafts don't get sent/received anywhere. It's also important to note that messages are saved as new drafts without subject-line and recipient-info. Ideally there will be at most two drafts in the account at a time. When the chat is finished the email account is deleted. Whenever the participants are ready to chat, the participants login to that email account and compose a new email. They will write a message and encrypt it with PGP, then save it as a new draft without subjec...

Uploading files through Secure WebDAV using DAVfs

WebDAV is a protocol that facilitates uploading and downloading files through HTTP (port 80) and HTTPS (port 443). Whenever a WebDAV service is being ran over SSL it is called Secure WebDAV. DAVfs is a file system interface to the WebDAV protocol, it works with WebDAV and Secure WebDAV. The command mount uses DAVfs to recognize a WebDAV share as a regular file system so that other tools, scripts, services, and users can access the share's contents (as a file system with actual directories). Here's an easy solution for uploading files to your WebDAV account. These instructions work on Linux, FreeBSD, Solaris, and probably other distributions too. 1. Make a local directory for transferring files. mkdir <your directory>; 2. Stop other processes and users from interfering with your transfers. chown root:root <your directory> && chmod 770 <your directory>; 3. Mount your online cloud share using davfs. Enter your password when the prompt appears askin...

David Brenner Jr

Search This Blog