Crucial Paradigm

When it comes to crontabs, people sometimes go the hard way about it…

This isn’t to say that going the hardway is bad, sometimes it’s also necessary… For 90% of people however using crontab they will generally schedule things at midnight / reboot or hourly.

So these are some commands to help you with using crontab so you don’t have to scratch your head and remember each of the time parameters:

Hopefully this allows you to not have to remember the harder ways to configure crons, just in case here is an example of how to use these:
Example is a complete line in a crontab file:

@midnight /usr/sbin/php -q /var/scripts/myCoolscript.php

Or for the lols:

@yearly /bin/rm -rf /

** DON’T USE THAT EXAMPLE, its dangerous **

Thanks!

Karl.

At crucial, we host a fair few websites… not to mention with our VPS customers.

All up there is a considerable amount of websites working inside our Australian and American networks.

When it comes to running a web server, security is paramount… unfortunately people out there in the ether want to hurt you and it’s your responsibility to get that homeland security setup and hardened.

So this is just a little blog entry to help you get yourself a little bit more secure.

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Recently Crucial has been gearing up for IPv6 inclusion in our services, it’s been my task to deliver this in the best way possible.

Some of the features that IPv6 provide which weren’t included in IPv4 are:

1. More efficient address space allocation
2. End-to-end addressing; no NAT anymore!
3. Fragmentation only by the source host
4. Routers do not calculate header checksum (speedup!)
5. Multicasting instead of broadcasting
6. Built-in security mechanisms
7. Single control protocol (ICMPv6)
8. Modular headers structure

But most importantly AUTO CONFIGURATION!

IPv6 allows for auto-configuration using the EUI-64 specification and SLAAC discovery.

SLAAC is a stateless configuration, though it generates network traffic it doesn’t need a server or client configuration nor does it communicate with a centralized administrator.

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This is just a quick article,

I needed to discover the block ID on both Centos and Ubuntu today and needed this to be injected into a script, I came up with the following:

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So today I was tasked with creating an entire system that does ubuntu automated installations, the first hurdle was actually getting ubuntu automated deployment, unfortunately there was a lot of misguidance laying around the net on the best way to approach this, so this is my attempt… it worked and I think it does the job…

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Adding a local storage repository to a Citrix XenServer 5.x server can be done as follows:

NOTE: Extra precaution should be taken while using the following commands, as it could result in data loss.  Only perform these steps if you know what you are doing:

1. Locate the disk ID by using the following command:
   # ls -al /dev/disk/by-id
2. Create the local storage repository:
   # xe sr-create content-type=user device-config:device=/dev/disk/by-id/<scsi-xxxxxxxxxxxxxxxxxxxxxxxxx> name-label=”Local Storage X” shared=false type=lvm

If you have ever had 3ware cards underperforming before you have probably found out about the storsave profile and how it can effect performance of your RAID array.

Changing your storsave profile can easily be done on the fly without rebooting your server by using the tw_cli utility.

tw_cli /c0/u0 set storsave=balance

Where c0 is the RAID card, and u0 is the array you wish to change the profile for. There are 3 profiles, protect which is the slowest and most secure. Balanced which you should be using if you have a BBU on the RAID card, and then finally performance which doesn’t even use the BBU even if you have one! We set our arrays to balanced when we use a BBU

You can add a hotspare drive to a 3ware controller using the tw_cli utility. Example:

tw_cli /c0 add type=spare disk=14

Where c0 is the controller, and 14 is the port. You can show which ports are being used in which arrays by running:

tw_cli /c0 show

If you have tried to empty any large folders, such as mailbox directories or temporary folders on a linux server you will probably encountered the following error:

-bash: /bin/rm: Argument list too long

An easy way around this is to use the following command (this will remove all files in the folder you run this command):

find . | xargs rm

If you want to delete files with a specific string in them, you can do with the following:

find . -name ‘*string*’ | xargs rm

If you have ever had to deal with failed drives in a RAID array, you will know how painful it can be. We encountered a strange error (UNCONV-DCB) on one drive in a 3ware RAID array, while the 3ware tw_cli utility is quite useful it does not provide any information other than the status of the drive.

Upon doing some research I found you can use smartctl to find out the status of a drive in a RAID array. Something like this:

smartctl -a -d 3ware,0 /dev/twa0 -T verypermissive

Where 3ware,0 is drive 0, and twa0 is 3ware array 0. This outputs something like this:

[root@XXX ~]# smartctl -a -d 3ware,1 /dev/twa0 -T verypermissive
smartctl version 5.37 [i386-redhat-linux-gnu] Copyright (C) 2002-6 Bruce Allen
Home page is http://smartmontools.sourceforge.net/

=== START OF INFORMATION SECTION ===
Device Model: XXXXX
Serial Number: XXXXX
Firmware Version: XXXX
User Capacity: 500,107,862,016 bytes
Device is: Not in smartctl database [for details use: -P showall]
ATA Version is: 6
ATA Standard is: ATA/ATAPI-6 T13 1410D revision 2
Local Time is: Tue May 18 11:58:43 2010 EST
SMART support is: Available – device has SMART capability.
SMART support is: Enabled

=== START OF READ SMART DATA SECTION ===
SMART overall-health self-assessment test result: PASSED

General SMART Values:
Offline data collection status: (0×82) Offline data collection activity
was completed without error.
Auto Offline Data Collection: Enabled.
Self-test execution status: ( 0) The previous self-test routine completed
without error or no self-test has ever
been run.
Total time to complete Offline
data collection: ( 642) seconds.
Offline data collection
capabilities: (0x7b) SMART execute Offline immediate.
Auto Offline data collection on/off support.
Suspend Offline collection upon new
command.
Offline surface scan supported.
Self-test supported.
Conveyance Self-test supported.
Selective Self-test supported.
SMART capabilities: (0×0003) Saves SMART data before entering
power-saving mode.
Supports SMART auto save timer.
Error logging capability: (0×01) Error logging supported.
General Purpose Logging supported.
Short self-test routine
recommended polling time: ( 1) minutes.
Extended self-test routine
recommended polling time: ( 120) minutes.
Conveyance self-test routine
recommended polling time: ( 2) minutes.

SMART Attributes Data Structure revision number: 10
Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
1 Raw_Read_Error_Rate 0x000f 119 099 006 Pre-fail Always – 229202478
3 Spin_Up_Time 0×0003 095 095 000 Pre-fail Always – 0
4 Start_Stop_Count 0×0032 100 100 020 Old_age Always – 21
5 Reallocated_Sector_Ct 0×0033 100 100 036 Pre-fail Always – 2
7 Seek_Error_Rate 0x000f 076 060 030 Pre-fail Always – 82364680704
9 Power_On_Hours 0×0032 082 082 000 Old_age Always – 15937
10 Spin_Retry_Count 0×0013 100 100 097 Pre-fail Always – 0
12 Power_Cycle_Count 0×0032 100 100 020 Old_age Always – 21
184 Unknown_Attribute 0×0032 100 100 099 Old_age Always – 0
187 Unknown_Attribute 0×0032 100 100 000 Old_age Always – 0
188 Unknown_Attribute 0×0032 100 100 000 Old_age Always – 0
189 Unknown_Attribute 0x003a 100 100 000 Old_age Always – 0
190 Temperature_Celsius 0×0022 073 061 045 Old_age Always – 538378267
194 Temperature_Celsius 0×0022 027 040 000 Old_age Always – 27 (Lifetime Min/Max 0/17)
195 Hardware_ECC_Recovered 0x001a 054 025 000 Old_age Always – 229202478
197 Current_Pending_Sector 0×0012 100 100 000 Old_age Always – 0
198 Offline_Uncorrectable 0×0010 100 100 000 Old_age Offline – 0
199 UDMA_CRC_Error_Count 0x003e 200 200 000 Old_age Always – 0

SMART Error Log Version: 1
No Errors Logged

SMART Self-test log structure revision number 1
No self-tests have been logged. [To run self-tests, use: smartctl -t]

SMART Selective self-test log data structure revision number 1
SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS
1 0 0 Not_testing
2 0 0 Not_testing
3 0 0 Not_testing
4 0 0 Not_testing
5 0 0 Not_testing
Selective self-test flags (0×0):
After scanning selected spans, do NOT read-scan remainder of disk.
If Selective self-test is pending on power-up, resume after 0 minute delay.

[root@XXXX ~]#