What does .Er mean in a man page?

Question

in a man page I'm editing I see the following:

.Er ENOENT ENOENT

what exactly does that mean? I looked in the man(1) man page but don't see anything about how to read the raw files.

Answer 1

Take a look at HPUX man(5):

.ER errorname punctuation

• errorname is an error name that corresponds to a value assigned to errno by a function and described in the ERRORS section of a manpage. It is displayed in roman, enclosed in square brackets. For example, .ER EIO . is displayed as [EIO].

Answer 2

For the specifics about .Er, see mdoc(7):

The ‘.Er’ errno macro specifies the error return value for section 2, 3, and 9 library routines. The second example below shows ‘.Er’ used with the ‘.Bq’ general text domain macro, as it would be used in a section two manual page.

       Usage: .Er ⟨errno type⟩ ...

                .Er ENOENT      ENOENT
                .Er ENOENT ) ;  ENOENT);
                .Bq Er ENOTDIR  [ENOTDIR]

 The default width is 17n.

In general, see groff_mdoc(7) on how to write manual pages.