Understanding /dev

 in
This article gives us a basic introduction to device files and their uses.
Optimizing /dev

If you wish to get every possible millisecond out of your system, there are a few things you should know about directories in UNIX file systems. (Though technically I'm talking about the implementation of the EXT2 file system, the points apply to almost all UNIX file systems.)

First note that though the command ls always displays the directory in a sorted order, directories are not stored with their entries sorted. Instead, each new entry is placed as close to the front of the directory as possible.

To find a file in a directory, the file name is compared with the first file in the directory. If it doesn't match, the second name is checked, and so on until either a match is found, or the end of the directory is reached. Consequently, if you have a large number of files in a directory and are frequently opening the last file in the directory, your CPU is doing a lot of comparisons. If, however, you could control the order of the entries, so as to place the most-frequently-used entries at the beginning of the directory, this would not be such an issue.

If you want to redo the internal ordering of the entries in /dev, boot from a floppy and then mount your primary file system. If your regular file system is mounted as /mnt, your regular device directory is /mnt/dev. Create a new directory called /mnt/dev2. Now you can move device files from /mnt/dev to /mnt/dev2. You will probably want to start with /mnt/dev/zero and /mnt/dev/null, as these two are opened far more frequently than any other devices.

If that sounds like a hassle, then don't bother with it. You probably won't notice any difference unless you are running on an old 386. Furthermore, the new directory cache under development in the 2.1.x kernel series will most likely make this a non-issue.

Serial Port Devices

Preston Crow grew up in Boise, Idaho. He has a Master's degree in Computer Science from Dartmouth College and hopes to soon upgrade to a Ph.D. He now works for the Open Group in Cambridge, MA, where he lives with his brilliant wife. He can be reached via e-mail at Preston.F.Crow@Dartmouth.edu.

______________________

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix