sendmail, 4th Edition

Using qf, df, and xf Subdirectories

Beginning with V8.10, sendmail allows the qf, df, and xf files to reside in separate directories. One advantage to this is that it produces directories that are one-third smaller. Another advantage is that each part can reside on a separate disk for further performance enhancements.

This feature is enabled by simply creating the appropriately named subdirectories, or symbolic links, in each queue directory. The names of those subdirectories or symbolic links are the literals qf, df, and xf. But be aware that you should not create those directories or links when mail is already queued. If you do, that queued mail will disappear from sendmail’s view and will never be delivered. If you need to make the change while mail is queued, first stop sendmail, and then execute the following commands and restart sendmail:

# mkdir df qf xf
# chmod 700 df qf xf
# mv df?* df/           ← if mail is already queued
# mv qf?* qf/           ← if mail is already queued
# mv xf?* xf/           ← if mail is already queued

Here, we first create the new subdirectories in the queue directory. Then we reduce their permissions to the narrow ones that match the queue directory. Finally, if queued mail already existed in the queue directory, we move that mail into the new subdirectories where sendmail will find it.

Because xf files are empty for all successfully delivered mail, there is a penalty for creating and deleting those files just because they might be needed. When performance is of concern, you can ...