Chapter 16. Debug sendmail with -d

The -d command-line switch allows you to observe sendmail’s inner workings in detail. But note that sendmail’s various debugging switches differ from vendor to vendor and from version to version. This chapter is specific to V8.13 sendmail. These switches are perhaps best used with a copy of the sendmail source by your side.

Also note that many of the internal details shown here will change as sendmail continues to evolve and improve.

What’s New with V8.13

Although there are no additional, useful debugging switch settings in V8.13, there is one new debugging command-line switch described next.

The New -D Debug File Switch

The -D command-line switch is used to redirect sendmail’s debugging output (16.1[3ed]) into a file for later examination. It is used as in the following example, where file is the name of an existing or new file:

-D file

The -D command-line switch (if used) must precede the -d switch on the same command-line, otherwise the following error will print, and all debugging output will be printed to the standard output (possibly causing you to miss seeing the error):

-D file must be before -d

The file specified with -D must live in a directory that is writable by the user running sendmail. If the file does not exist, it will be created. If the file already exists, it will be silently appended to.

Extra care must be exercised when using the -D command-line switch as root because the target file will be appended to, even if it is a symbolic link ...

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