Nagios: check_http, using the --invert-regex option

Some times you want to check that something is running or working correctly and you work out tests for that. Other times you want to know when something is broken and throwing error messages. This is about the latter, a proper HTTP 200 code is great and all, but what if the page is just showing "Too Many Connections" instead of your home page? My old check_http command for this server used to look like, well, check_http. I didn't check anything about it specifically, just that it was returning a 200 code.

Today however I knew I needed something more in depth. Our database server lost its local network connection, but still was available over the public IP, which is what I test against. Once we re-directed the SQL requests to the public IP address of the server everything started working again, until we ran across "Too Many Connections". The database server kept all of the "local" connections open and thus we ate up the rest.

So, how to test for this scenario? After reading through the man pages of check_http I saw this little gem "--invert-regex Return CRITICAL if found, OK if not". This I knew was exactly what I was looking for! If it sees our error codes it will go Critical! Now to put this gem into practice. Here is where the man pages fall short. There is no explanation on HOW to use this, just that it exists. I tried the obvious to me "check_http -H hostname.com -w 3 -c 5 --invert-regex 'Some string'", but that didn't work. OK, lets try "check_http -H hostname.com -w 3 -c 5 --invert-regex='Some string'" nope that errored out with " option `--invert-regex' doesn't allow an argument".

Third times the charm right?

"check_http -H hostname.com -w 3 -c 5 -r 'Some string' --invert-regex '"

# HTTP OK HTTP/1.1 200 OK - 0.355 second response time |time=0.354966s;3.000000;5.000000;0.000000 size=12975B;;;0

Yes, as it turns out third time is the charm. So that got me thinking some more. How can I ensure that the page is rendering correctly, and if it isn't fail but in a specific way?

"check_http -H hostname.com -w 3 -c 5 -r 'Some string I want in my page' -r 'Some string I don't want to see' --invert-regex '"

You can add more than one -r to the check_http command and it will require all of them to be present for the test to pass, and if one of them fails then it will go critical! Perfect!

If you have any more insight into using the check_http command in Nagios I want to hear about it. We are always running into new failure scenarios that we didn't anticipate and I want to know about them before one of my users tells me about it.

Bash: Finding files between two dates in the current directory

Today my boss asked me for a bash command (or script) to find some files between two dates.

Thanks to Jadu Saikia over at Unstableme his post UNIX BASH scripting: Find Files between two dates, I had a starting point.

This will find all files between the two dates (20071019 & 20071121) in this case.

find . -type f -exec ls -l --time-style=full-iso {} \; | awk '{print $6,$NF}' | awk '{gsub(/-/,"",$1);print}' | awk '$1>= 20071019 && $1<= 20071121 {print $2}'

Now, if you want just PGP files you would do:

find *.pgp -type f -exec ls -l --time-style=full-iso {} \; | awk '{print $6,$NF}' | awk '{gsub(/-/,"",$1);print}' | awk '$1>= 20071019 && $1<= 20071121 {print $2}'

The second request that my boss was looking for with this is the file size, something that was being left out by awk. So we can fix that by updating the command to:

find *.pgp -type f -exec ls -lh --time-style=full-iso {} \; | awk '{print $6,$NF,$5}' | awk '{gsub(/-/,"",$1);print}' | awk '$1>= 20090624 && $1<= 20090901 {print $2,$3}'

We added in a $5 to the first awk command, and the final one had $3 added to it. Also I like human readable file sizes so I added -h to the ls command.

Howto Make a T1 Crossover Cable

I learned this one about a month ago while turning up the T1 connection for my fax server. The tech that installed the Cisco equipment left us with a crossover cable, but a data one, so I cut the ends off and re-crimped the cable like so:

You only have to worry about 4 of the 8 wires if you are using typical cat-5 cable like I did.

1 <—> 4
2 <—> 5
4 <—> 1
5 <—> 2
Or if you go by colors like I do
Side 1 (left is cable end, clip underneath):
Pin 1: Orange White
Pin 2: Orange Solid
Pin 3: none
Pin 4: Blue Solid
Pin 5: Blue White
Pin 6: none
Pin 7: none
Pin 8: none

Side 2 (left is cable end, clip underneath):
Pin 1: Blue Solid
Pin 2: Blue White
Pin 3: none
Pin 4: Orange White
Pin 5: Orange Solid
Pin 6: none
Pin 7: none
Pin 8: none

Then you are done!

How do I disable PS2 Parental Controls?

Again this is one of those things that I had to figure out and I wanted some place to keep it just in case I needed it again. I realize that this won't come in handy for anyone actually reading this blog, but still.

While watching a DVD hit "Select" on the controller. While on the menu find the icon called "Setup". Click it and then find "Custom Setup". Now go down to the "Parental Control" and change the settings to your liking. I choose "Off" because I never want to be bothered by the parental control features.

To save your changes eject and take out the DVD, which will kick the PS2 back to the setup screen. Then turn off the power or reset it.

Reset the maintenance counter on an HP 4000 Laserjet

There are two methods to resetting the maintenance counter on an HP 4000 Laserjet printer.

The first method is the fastest, but may not work due to many different board revisions.
1. Turn the printer off.
2. Hold down the "Item" key (the minus side of the button) and "Value" key (the minus side).
3. Turn the printer on.
4. Wait for "RESET MAINTENANCE COUNT" to be displayed and then release both keys.

If this method fails, like it did for me, you will have to enter service mode. This mode is generally reserved for service technicians and really the only reason to go into it is to reset the maintenance counter.

To get into service mode:
1 Hold down "Select" and "Cancel Job" while turning on the printer until all of the lights on the Control Panel are lit. Note that if the Control Panel reads INITIALIZING, the keys were released too soon.
2 Press the right side of the "Menu" key, then press "Select". The message SERVICE MODE is displayed.
3. Press "Menus" once to display SERVICE MENU.
4. Once it says SERVICE MENU press ITEM to scroll through service mode items.
5. Once on the Maintenance Counter screen, press "Select" on each number in the Maintenance counter. You can change them by hitting the "Value" key to the left or right and move between the digits by using the "Item" key.
6. To exit the Service Mode press [Go].

Mediawiki System Requirements

I am going to be installing Meidawiki for our internal use and I had a little trouble finding the System Requirements for the software. Just posting it here so I can find it easily again in the future.

http://www.mediawiki.org/wiki/Manual:Installation_requirements

Ghostscript Convert PDF to TIFF

Again this is mainly for my reference, but someone may have trouble finding the solution like I did earlier today.

On Windows be sure to add "C:\Program Files\gs\gs8.64\bin" to your PATH, then run the following command.

gswin32c -dNOPAUSE -q -r300 -sDEVICE=tiffg4 -dBATCH -sOutputFile=[YOUR_OUTPUT_FILENAME.TIFF] [YOUR_INPUT_FILENAME.PDF]

Similarly on Linux you can run the command below.

gs -dNOPAUSE -q -r300 -sDEVICE=tiffg4 -dBATCH -sOutputFile=[YOUR_OUTPUT_FILENAME.TIFF] [YOUR_INPUT_FILENAME.PDF]

There are also possibilities to script this, and when you can do that you should. I haven't found the need to bring it to that point yet as I just had to do four files today, but should this come up again I will be scripting it in some fashion and posting the results here.

Thank you to StackOverflow for the solution to my problem. Also one of the other solutions to this is to use a recursive search of a directory with PowerShell to convert files.

Creating a RAID 5 Array in software on CentOS 5.3

In order to create a RAID 5 array entirely in software on Linux you need to do a few things.

First I used three Identical drives, same speed, size, make, and model. This may not be a requirement, but

it will defiantly help the process. For RAID 5 you will need at least three partitions of the same size.

I picked up a four disk internal hot-swap enclosure from Addonics (http://www.addonics.com/products/raid_system/ae4rcs35nsa.asp) and

a hot-swap capable raid card. Once I got everything physically installed in the server case I booted into CentOS 5.3

and got on the command line. The first thing you need to do is create partitions on the blank drives and set them to be

Linux raid autodetect (Hex value of fd). To do this run fdisk /dev/sdX where X is the drive(s) that you want to partition for the RAID array.

For me this was SDC, SDD, SDE but you results will vary.

fdisk /dev/sdc

n [ENTER]

e [ENTER]

4 [ENTER]

[ENTER]

[ENTER]

n [ENTER]

l [ENTER]

t [ENTER]

5 [ENTER]

fd [ENTER]

w [ENTER]

You will want to create an Extended partition so choose n for New partition. If you get stuck you can hit m to get the help menu.

After you hit n type e for Extended. Then you will have to enter a partition number, I choose 4 for all of my drives.

After that you n again and then choose l for logical partition type. Again it will ask for a partition number 1-4 are for primary and thus not an option,

so I choose 5 for all of my drives.

Once the logical partitions are created hit t to change the partition type. If you are unsure what to use hit l, but in this case we already know that we want to

use type fd for the Linux RAID auto.

Once the type has been changed you can type w to write this info to the drive and start on the next one.

fdisk /dev/sdd

n [ENTER]

e [ENTER]

4 [ENTER]

[ENTER]

[ENTER]

n [ENTER]

l [ENTER]

t [ENTER]

5 [ENTER]

fd [ENTER]

w [ENTER]

fdisk /dev/sde

n [ENTER]

e [ENTER]

4 [ENTER]

[ENTER]

[ENTER]

n [ENTER]

l [ENTER]

t [ENTER]

5 [ENTER]

fd [ENTER]

w [ENTER]

Now that we have three (the minimum) partitions for our RAID device we have to create it in CentOS. Here we will use a tool called mdadm to create the

actual RAID device in Linux.

/sbin/mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sdc5 /dev/sdd5 /dev/sde5 [ENTER]

Once this returns back, and it should be pretty quick, you will have a RAID 5 device. To check the status of it run:

/sbin/mdadm --detail /dev/md0

/dev/md0:

Version : 00.90.03

Creation Time : Wed Jul 8 09:14:19 2009

Raid Level : raid5

Array Size : 2930271744 (2794.52 GiB 3000.60 GB)

Used Dev Size : 1465135872 (1397.26 GiB 1500.30 GB)

Raid Devices : 3

Total Devices : 3

Preferred Minor : 0

Persistence : Superblock is persistent

Update Time : Fri Jul 10 11:20:02 2009

State : clean

Active Devices : 3

Working Devices : 3

Failed Devices : 0

Spare Devices : 0

Layout : left-symmetric

Chunk Size : 64K

UUID : 53f6f95a:9e33f5ba:7ac8ef3e:0a40921a

Events : 0.2

Number Major Minor RaidDevice State

0 8 21 0 active sync /dev/sdc5

1 8 37 1 active sync /dev/sdd5

2 8 53 2 active sync /dev/sde5

Now for me after I first created the RAID device the state was listed as clean, degraded, rebuilding. There was a place for the percentage rebuilt and

/dev/sde5 was listed as spare. It took the better part of a day for the rebuild to finish, given that it was a three terabyte device I am not surprised by that.

Once the rebuild was done I had to create a Physical volume for LVM to be able to manage the RAID device.

pvcreate /dev/md0

After that I was able to use system-config-lvm to create the storage volume and format the drive.