Can't do ssh key login because of SElinux

This one really threw me off. I buld a rhel-6.1 test box, and I couldn't get in using the root ssh key I loaded into ssh-agent. The `ssh-copy-id` worked fine. However, I was getting prompted for the account password (not my key's password). Here's what I saw and here's how to get around it.

How To Change Timezone to UTC on RHEL5

Did you know there's a difference between GMT and UTC? I didn't. I haven't found it stated succinctly on the web, but it has to do with leap seconds and the increase of them due to tidal deceleration. Tidal deceleration is like how it is difficult to move a big tub of water around due to the inertia being in liquid form absorbing energy. The point is, I needed to change the timezone on some servers and here are my notes.

How to set the mail relay on a rhel6 box

rhel6 uses postfix by default (very nice). I've been used to changing the DS line in /etc/mail/ Now, what you do is:

postconf -e "relayhost = [myrelay.fqdn]"

It can't hurt to make sure you have the right setup. Here's what I have on one of my rhel6 systems

What services are running on my Linux box?

The answer is technically /bin/ps -ef. But what you really want is /bin/netstat -plunt. Netstat prints network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. The switches that make this possible and handy are:

How to get ALL then FC info you need (and more!)

Here's the cheet sheet to using native FC tools and drivers (tested on rhel5):

pWWN = cat /sys/class/fc_host/host[0-9]/port_name
WWN = cat /sys/class/fc_host/host[0-9]/node_name
online? = cat /sys/class/fc_host/host[0-9]/port_state
Speed = cat /sys/class/fc_host/host[0-9]/speed
HBA overview = cat /sys/class/fc_host/host[0-9]/symbolic_name
/sys/class/fc_host/host[0-9]/device/scsi_host\:host[0-9] is same as /sys/class/scsi_host/host[0-9]
HBA make = cat /sys/class/scsi_host/host[0-9]/model_desc
HBA model = cat /sys/class/scsi_host/host[0-9]/model_name
Firmware rev = cat /sys/class/scsi_host/host[0-9]/fw_version
Driver version = cat /sys/class/scsi_host/host[0-9]/driver_version
rescan scsi bus (use VERY wisely) = echo "- - -" > /sys/class/scsi_host/host[0-9]/scan
issue lip (use even MORE wisely) = echo 1 > /sys/class/fc_host/host[0-9]/issue_lip

It's a good cheet sheet, but you'll need more understanding to make this useful for your troubleshooting. Read on.

How to Get VMware Cluster To Use Different CPU Types

In case you didn't think it through (like I didn't), you can't vMotion guests from one type of CPU to another. And when I say type, I don't just mean AMD to Intel, I mean different models and generations. For example, you can't go from Family 6, Model 46 (2Eh) = Nehalem-EX to Family 6, Model 47 (2Fh) = Westmere-EX/E7... at least not live. It makes sense. However, there is one exception: EVC.

How do you scan for new luns on linux?

I always forget this one. How exactly do you find those new fibre channel luns you carved and presented to the host? The zoning is there, but you need to have the OS look for it.

Well, if you have power path or other vendor software it will be different and I'll document that as well some day. Using the native software in RHEL 5.1 or greater, you do this.

Power Notes

I am have spent a LOT of time in data centers, but that doesn't mean I always remember all the details.

Recepticle types:
L5-20 = power outlet you have at home {add pictures}. 120V with up to 20A draw (16A safe {80%})
L6-20 = 208V, 20A
L6-30 = 208V, 30A
Add in the exadata fiasco here (60A!!)

KVA v. Watts
Bascially, Watts is a meausre of max power, KVA is complicated, but is a better number as it accounts for resistance, heat and other imprefections of this imperfect world.


62,400 repetitions make a truth.

Aldous Huxley
Brave New World


Notes on RHEL Server as a desktop

I've been using RHEL5 as my desktop since 9/2009. I thought it was best to work on the same OS as the servers. Ultimately, I think that was a bad idea and I will be switching to Fedora soon. Here's my notes to remind me how to do things I rarely do.

growisofs -dvd-compat -Z /dev/dvd=RHEL6.0-20100715.2-Server-i386-DVD1.iso


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