A monitoring script calls ping and must never block: it should send exactly four echo requests to 192.0.2.10 and then exit. Which option enforces that?
LPIC-1 Exam 102-500, objective 109. Networking fundamentals easy
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The options
Correct ping -c 4 192.0.2.10
Correct. -c is the count of echo requests to send. After four have been sent and the last reply has been waited for, ping exits and reports its summary statistics.
Not correct ping -w 4 192.0.2.10
Wrong for the stated requirement. -w is a deadline in seconds; ping stops after four seconds, which on a fast link is many more than four packets and on a slow one may be fewer.
Not correct ping -i 4 192.0.2.10
Wrong. -i sets the interval between packets to four seconds. Without a count, ping still runs until it is interrupted, only more slowly.
Not correct ping -t 4 192.0.2.10
Wrong. On Linux, -t sets the IP time-to-live of the outgoing packets, limiting how many hops they survive. It does not bound the run. (The count semantics belong to Windows ping, which uses -n.)
Why
Without -c, Linux ping runs until interrupted, which is why unattended use always pairs it with -c or -w. -c bounds the number of packets, -w bounds the elapsed time, and the two can be combined so that whichever limit is reached first ends the run. ping's exit status is 0 when at least one reply arrived, 1 when no reply packet arrived at all, and 2 on other errors, which is what a script should test.
Where this comes from
- Cited
- manual page ping(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 109 and space the ones you get wrong.
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