On a sendmail-style system, the user emma wants her incoming mail copied to emma@example.net while a copy is still filed in her own mailbox on this host. Listing her plain login name in the file would send that local copy back through alias and .forward expansion again. Which single line in ~emma/.forward names her local delivery in the form that stops the re-expansion?
LPIC-1 Exam 102-500, objective 108. Essential system services medium
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The options
Not correct emma, emma@example.net
Wrong on a sendmail-style MTA. The bare name emma is expanded again, which re-reads the same .forward file, so the delivery agent reports a forwarding loop instead of filing a local copy. (Postfix is more forgiving and delivers to the mailbox in this case, but the portable idiom, and the one the exam expects, is the backslash form.)
Correct \emma, emma@example.net
Correct. The leading backslash marks the local recipient as final: no further alias or .forward expansion is applied to it, so one copy lands in emma's local mailbox and one goes to the remote address.
Not correct /var/mail/emma, emma@example.net
Wrong. This hard-codes a path instead of letting the delivery agent file the message where the site's mailbox configuration says it should go, so it breaks the moment the host uses Maildir, a home mailbox or a different spool directory, and the write happens with the user's own rights. The supported way to say deliver to me locally is the backslash form.
Not correct keep, emma@example.net
Wrong. There is no keep keyword in the .forward format; that syntax belongs to Sieve filtering. Here keep would be read as a local user name and fail to resolve.
Why
A .forward file holds the same kind of comma-separated destination list as the right-hand side of an aliases entry, and it is owned and edited by the user rather than by root. Prefixing a local name with a backslash marks that name as final, so no further alias or .forward expansion is applied to it: that is the standard idiom for keep a copy here and also send it on. Without the backslash a sendmail-style MTA expands the name again and aborts on the forwarding loop; Postfix special-cases it and delivers to the mailbox, but the backslash form works everywhere.
Where this comes from
- Cited
- manual page aliases(5)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 108 and space the ones you get wrong.
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