[CentOS] Anyway to ensure SSH availability?

[Brian Mathis]

On Wed, Jun 29, 2011 at 4:15 PM, Emmanuel Noobadmin
<centos.admin at gmail.com> wrote:
> On 6/30/11, Rainer Duffner <rainer at ultra-secure.de> wrote:
>> Yes, it's called "out of band management".
>> Have dial-in access to IPMI/iLO interfaces or just an APC remote
>> controlled power-switch to power-off the server.
>
> I don't want to reboot the server everytime something like that
> happens. I'll expect pretty nasty problems will develop after a few
> dozen unclean shutdowns like that.
>
> Would ILO work on a server that's unresponsive due to heavy load? The
> actual network access isn't a problem so dial up isn't necessary. The
> other problem is the server in question probably doesn't have ILO
> features on the mainboard.


Doing a hard power-off is extreme, but could be the last resort option.

ILO is just one product (by HP) that provides out-of-band management
for servers.  Dell has DRAC, and there are others.  They allow you
access to the server's console as if you are standing there, as well
as other functions like power on/off, virtual CD drive, etc...  These
are usually built-in to the server so you can't really add-on later.

You can get similar functionality by using a remote IP-based KVM.
They only provide the remote console, not power on/off or virtual CD.
For a single server, a low cost option is the Lantronix Spider or
Spider Duo.  It provides a remote console for a single server for a
few hundred $$$s.

An alternative that is usable for Linux servers is a remote serial
console; it allows you to ssh into it and then connect to the serial
port of the server.  You will need to setup the bios, grub, and a
serial getty to be able to login to a server this way.  wti.com makes
a good one that I currently use.

All of these solutions are "out of band" meaning they do not directly
interface with the operating system, so if there's a problem with the
server, they are not affected by it.

Your name suggests you are new to sysadmin.  One of the lessons here
is to always have at least 1 method of out of band management as part
of the non-negotiable requirements for a server, especially a remote
one.

-☙ Brian Mathis ❧-