if the linux server is down how we have to connect the server and access it as a linux admin

With the physical console, or ILO/DRAC card if you've one installed.

i didn't get u. it is asked in my interview

You asked a vague question, I've given you two answers, if you don't understand them then google them.

Physical Console - Keyboard / Screen attached to the server.
ILO/DRAC Card - Provides a virtual physical console through hardware, also works when the server is in a powered down state, as long as there's power to the PSUs.

ILO is HP's branding for this card, DRAC is Dells.

Sometime you can also access through serial console port if it's plugged. (ttySx)

he gave you 2 great answers, that to be blunt if you dont understand you should not be interviewing for a Linux admin job.

1 members found this post helpful.

...and since you couldn't answer the question in an interview, it's kind of late now, isn't it? There aren't 'standard' answers to interview questions...they are asked to see how you think and troubleshoot problems. And you need to spell out your words and write clearly, if you're going to be working in a professional environment.

since this is in the networking sub-forum: SSH, telnet, rlogin, numerous third-party software packages.... you're spoiled for choice really.

and if this really was an interview question, you should have asked back "down in what way"? not booting at all? not connecting to the network? not providing a specific network service(s), or providing it unsatisfactorily?

oh and FWIW, serial console access usually requires already-enabled console= parameters in the APPENDs to the kernel line in your bootloader config, as well as the requisite terminal hardware/emulation software on the other end.

not that that helps much at this point

Physical console is almost available when server is down as long as the power dont interrupt!!!