A legacy host runs in.telnetd under xinetd. The service must stay enabled, but only clients in the management network 10.0.5.0/24 may reach it. Which attribute in /etc/xinetd.d/telnet expresses that?
LPIC-1 Exam 102-500, objective 110. Security medium
Machine-checked — no person has signed for it. This question was read against the source cited below by an automated pass, which found no contradiction. That is a weaker claim than it sounds: the same kind of process wrote the question, so it can confirm its own mistake.
Treat it as a good draft rather than as settled fact, and read the source below before you rely on it. It is not used in mock exams here — only questions a person has signed for are.
How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct only_from = 10.0.5.0/24
Correct. only_from lists the remote addresses to which the service is offered. Anything not listed is refused before the server program is started.
Not correct no_access = 10.0.5.0/24
Wrong, and inverted. no_access lists the remote addresses that must be refused, so this line would block precisely the management network and admit everyone else.
Not correct bind = 10.0.5.0
Wrong. bind (also spelled interface) names a local address on this host for the service to listen on. It restricts which of the server's own interfaces answer, not which clients may connect.
Not correct access_times = 10:00-05:24
Wrong. access_times restricts the hours of the day during which the service may be used. It is a real xinetd attribute but has nothing to do with source addresses.
Why
xinetd carries its own access control, so a wrapped service can be filtered without TCP wrappers: only_from is the allow list and no_access the deny list, and if an address matches both the more specific mask wins. Contrast this with bind, which chooses a local listening address. Each service gets its own file under the directory named by the includedir line in /etc/xinetd.conf.
Where this comes from
- Cited
- manual page xinetd.conf(5)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 110 and space the ones you get wrong.
More questions on this objective
- During an audit you must list every file under /usr that has the set-user-ID bit set, regardless of what its other permission bits are. Which command does that? machine-checked
- You locked the password of the account `intern` and confirmed that its hash in /etc/shadow now begins with an exclamation mark. The intern nevertheless still reaches a shell on the host over SSH, without being prompted for anything. What is going on, and what actually stops it? machine-checked
- You have just been added to a sudo rule on a host and want sudo itself to report which commands you are allowed to run there, without running any of them. Type the complete command. machine-checked
- A daemon started from your bash session keeps hitting a 'too many open files' error. Which command raises the limit on open file descriptors for the current shell and the processes it starts to 4096? machine-checked
- You are about to take a server down for maintenance and want ordinary users refused at login for the next hour, with an explanatory message, while root can still get in. On a system using PAM's pam_nologin, creating which file achieves this? machine-checked
- Which two commands report the users who are logged in right now, rather than a history of past logins? (Choose two.) machine-checked