Ubuntu apt-get history

for Ubuntu admin you can track apt-get history at

/var/log/apt/history.log

for a brief

and

for more detail at

/var/log/apt/term.log

mdadm cheat sheet

Mdadm Cheat Sheet

1. Create a new RAID array

Create (mdadm –create) is used to create a new array:

mdadm --create --verbose /dev/md0 --level=1 /dev/sda1 /dev/sdb2

or using the compact notation:

mdadm -Cv /dev/md0 -l1 -n2 /dev/sd[ab]1

2. /etc/mdadm.conf

/etc/mdadm.conf or /etc/mdadm/mdadm.conf (on debian) is the main configuration file for mdadm. After we create our RAID arrays we add them to this file using:

mdadm --detail --scan >> /etc/mdadm.conf

or on debian

mdadm --detail --scan >> /etc/mdadm/mdadm.conf

3. Remove a disk from an array

We can’t remove a disk directly from the array, unless it is failed, so we first have to fail it (if the drive it is failed this is normally already in failed state and this step is not needed):

mdadm --fail /dev/md0 /dev/sda1

and now we can remove it:

mdadm --remove /dev/md0 /dev/sda1

This can be done in a single step using:

mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1

4. Add a disk to an existing array

We can add a new disk to an array (replacing a failed one probably):

mdadm --add /dev/md0 /dev/sdb1

5. Verifying the status of the RAID arrays

We can check the status of the arrays on the system with:

cat /proc/mdstat

or

mdadm --detail /dev/md0

The output of this command will look like:

cat /proc/mdstat

Personalities : [raid1]

md0 : active raid1 sdb1[1] sda1[0]

104320 blocks [2/2] [UU]

md1 : active raid1 sdb3[1] sda3[0]

19542976 blocks [2/2] [UU]

md2 : active raid1 sdb4[1] sda4[0]

223504192 blocks [2/2] [UU]

here we can see both drives are used and working fine – U. A failed drive will show as F, while a degraded array will miss the second disk -

Note: while monitoring the status of a RAID rebuild operation using watch can be useful:

watch cat /proc/mdstat

6. Stop and delete a RAID array

If we want to completely remove a raid array we have to stop if first and then remove it:

mdadm --stop /dev/md0

mdadm --remove /dev/md0

and finally we can even delete the superblock from the individual drives:

mdadm --zero-superblock /dev/sda

#Clone partition table

sfdisk -d /dev/sda | sfdisk /dev/sdb

(this will dump the partition table of sda, removing completely the existing partitions on sdb, so be sure you want this before running this command, as it will not warn you at all).

There are many other usages of mdadm particular for each type of RAID level, and I would recommend to use the manual page (man mdadm) or the help (mdadm –help) if you need more details on its usage. Hopefully these quick examples will put you on the fast track with how mdadm works.

Reference :

http://www.ducea.com/2009/03/08/mdadm-cheat-sheet/

ubuntu snmp

I've install cacti to a server which will poll the data from linux box, installed snmp.

To test polling data from cacti to linux box,

#snmpwalk -c public -v 2c [ip-address]

In ubuntu if you want to allow other host to view this data you need to modified

"/etc/default/snmp "

SNMPDOPTS='-Lsd -Lf /dev/null -u snmp -g snmp -I -smux -p /var/run/snmpd.pid [ip-address]'

apache http auth with cgi

If you are using apache http auth with cgi, you have a few more things to do.

You need to enable .htaccess

RewriteEngine On

RewriteRule .* - [E=REMOTE_USER:%{HTTP:Authorization},L]

mysql open query log without changing my.cnf and restart

Use mysql client connect to server

#show variables like 'general%';

+------------------+----------------------------+

| Variable_name | Value |

+------------------+----------------------------+

| general_log | OFF |

| general_log_file | /var/run/mysqld/mysqld.log |

+------------------+----------------------------+

This 2 vaiables control mysql query logging.

To turn query log on :

SET GLOBAL general_log_file = '/var/log/mysql/sql-log.log' ;

SET GLOBAL general_log = 1

To turn query log off :

SET GLOBAL general_log = 0 ;

SET GLOBAL general_log_file = '/var/run/mysqld/mysqld.log';

Notice: This is for mysql 5.1 only. For mysql 5.0, those variable is not available. you need editing my.cnf and restart.

Page cache and pdflush: Theory of operation and tuning for write-heavy loads

For write-heavy option in system, some kernel option must be adjusted. Here are link to article about some kernel options that might help.

Please refer to : http://www.westnet.com/~gsmith/content/linux-pdflush.htm

perc H200 hardware raid utility in linux

I just bought server coming with hardware raid PERC H200 (Dell).

By the time of this blog, I understand that it use chipset from LSI here are out put from

#lspci --n

LSI Logic / Symbios Logic SAS2008 PCI-Express Fusion-MPT SAS-2 [Falcon] [1000:0072] (rev 03)

Unfortunately, the monitoring software for this h/w raid is not open. You have to download sas2ircu bin code. The program will display raid status.

I've downloaded from this link :

http://www.natecarlson.com/2010/08/23/lsi-command-line-utility-for-sas2-non-raid-controllers/#comments

Please visit for usage:

http://hwraid.le-vert.net/wiki/LSIFusionMPTSAS2#a2.Linuxkerneldrivers