Insider Tips: Locks

Competitive Thinking

Article from Issue 50/2005
Author(s):

A genuine multitasking system like Linux runs many processes concurrently. Programs must compete for data access. Assigning locks to files ensures exclusive access and prevents the possibility of data.

Most Linux machines have an MTA, a Mail Transfer Agent. This can be Postfix, Exim or even Sendmail. The MTA either uses a Fetchmail process or TCP to fetch email messages. When the MTA finds a message addressed to the local user, it passes the message on to the Local Delivery Agent (LDA). And the LDA stores the message in a mailbox file, after possibly taking a detour via a filter such as Procmail. If two messages arrive at the same time, the MTA will hand both of them to an LDA process at the same (see Figure 1). Each process will then attempt to write to the same mailbox file, again at the same time. If you are lucky, the messages end up in the right file, but in the wrong order, but you are far more likely to lose a file as the processes overwrite each other’s data.

Buy this article as PDF

Express-Checkout as PDF
Price $2.95
(incl. VAT)

Buy Linux Magazine

SINGLE ISSUES
 
SUBSCRIPTIONS
 
TABLET & SMARTPHONE APPS
Get it on Google Play

US / Canada

Get it on Google Play

UK / Australia

Related content

  • Hypermail

    Hypermail converts email messages to HTML and allows you to group your messages in tidy archives.

  • Samba for Clusters

    Samba Version 3.3 and the CTDB lock manager provide full cluster support.

  • Kernel News

    Chronicler Zack Brown reports on the latest news, views, dilemmas, and developments within the Linux kernel community.

  • ReiserFS Without Big Kernel Lock

    Even though reiserfs belongs to the veterans of journaling filesystems and established ext3 and ext4 as standard Linux filesystems, a new patch serves to markedly improve it.

  • Ask Klaus!

    Klaus Knopper is the creator of Knoppix and co-founder of LinuxTag expo. He works as a teacher, programmer, and consultant. If you have a configuration problem, or if you just want to learn more about how Linux works, send your questions to: klaus@linux-magazine.com

comments powered by Disqus

Direct Download

Read full article as PDF:

Admin_Workshop_Locks.pdf (135.38 kB)

News