Managing Swap space in Red Hat Linux

1. To extend a swap logical volume

a. Disable swapping for the concerned logical volume
# swapoff -v /dev/VolGroup00/LogVol05

b. Extend the logical volume by 1GB
# lvm lvresize /dev/VolGroup00/LogVol05 -L +1G

c. Format the logical volume
# mkswap /dev/VolGroup00/LogVol05

d. Enable the swap device
# swapon -va


2. To reduce a swap logical volume

a. Disable swapping for the concerned logical volume
# swapoff -v /dev/VolGroup00/LogVol05

b. Reduce the logical volume by 512MB
# lvm lvresize /dev/VolGroup00/LogVol05 -L -512M

c. Format the logical volume
# mkswap /dev/VolGroup00/LogVol05

d. Enable the swap device
# swapon -va


3. To list all the configured swap devices:

# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/dev/mapper/VolGroup00-LogVol05         partition       6062072 2180    -1


4. To list the total/used/free swap space:

# free -tm
             total       used       free     shared    buffers     cached
Mem:          7983       7918         65          0        585       4943
-/+ buffers/cache:       2389       5594
Swap:         5919          2       5917
Total:       13903       7920       5982


5. To create a swap file of size 100MB :

# dd if=/dev/zero of=/swap1 bs=1024 count= 102400
# chmod 0600 /swap1
# mkswap /swap1
# swapon /swap1

Finally add the below entry in /etc/fstab so that it enables on every boot.

/swap1          swap            swap    defaults        0 0


6. To enable swap space on a file :

# swapon -v /swap1


7. To disable swap space on a file :

# swapoff -v /swap1

Software RAID in Red Hat Linux

To create a linear RAID array:

# mdadm --create --verbose /dev/md0 --level=linear --raid-devices=2 /dev/sdb /dev/sdc
# mdadm --detail --brief /dev/md0 >> /etc/mdadm.conf


To create a striped RAID array (RAID-0):

# mdadm --create --verbose /dev/md0 --level=0 --raid-devices=2 /dev/sdb /dev/sdc
# mdadm --detail --brief /dev/md0 >> /etc/mdadm.conf


To create a mirrored RAID array (RAID-1):

# mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc
# mdadm --detail --brief /dev/md0 >> /etc/mdadm.conf


To start a RAID Array:

# mdadm --assemble /dev/md0 /dev/sdb /dev/sdc /dev/sdd

                                                    OR

# mdadm --scan --assemble --uuid=a26bf396:31389f83:0df1722d:f404fe4c


To list all software raid arrays and their component devices:

# cat /proc/mdstat
Personalities : [linear]
md0 : active linear sdd[0]
      10485752 blocks super 1.2 0k rounding

md1 : active linear sde[0]
      52428792 blocks super 1.2 0k rounding

unused devices:




 
To query a software raid array :

# mdadm --query /dev/md1
/dev/md1: 129.100GiB linear 1 devices, 0 spares. Use mdadm --detail for more detail.


To list details of a RAID array:

# mdadm --detail /dev/md1
/dev/md1:
        Version : 1.2
  Creation Time : Thu Dec 11 09:32:37 2011
     Raid Level : linear
     Array Size : 52428792 (50.00 GiB 53.69 GB)
   Raid Devices : 1
  Total Devices : 1
    Persistence : Superblock is persistent

    Update Time : Thu Dec 11 09:32:37 2011
          State : clean
 Active Devices : 1
Working Devices : 1
 Failed Devices : 0
  Spare Devices : 0

       Rounding : 0K

           Name : server123:1  (local to host server123)
           UUID : c5804771:253326af:e062f685:cab35fed
         Events : 0

    Number   Major   Minor   RaidDevice State
       0       8       32        0      active sync   /dev/sdc


To examine a RAID array:

# mdadm --examine /dev/md0


To add a raid disk device and extend a linear software raid array :

# mdadm --detail /dev/md3 | tail -n 3
    Number   Major   Minor   RaidDevice State
       0       8        1        0      active sync   /dev/sdc
       1       8       17        1      active sync   /dev/sdd

# mdadm --grow /dev/md3 --add /dev/sde


To remove a RAID array:

# mdadm --stop /dev/md3
# mdadm --remove /dev/md3
# mdadm --zero-superblock /dev/sdc /dev/sdd

MySQL - Part 1

Packages required:
mysql - contains client programs, configuration files and documentation
mysql-server - contains server daemon, startup script and various administrative files and directories
mysql-devel - contains libraries and header files for development purpose

Optional packages:
php-mysql - contains a shared library to allow PHP applications access MySQL databases
mod_auth_mysql - contains tools to authorize Apache Web server access from data in a MySQL database
perl-DBD-MySQL - contains a perl interface to MySQL databases
mysql-bench - contains scripts for benchmarking MySQL databases
MySQL-python - contains a Python interface to MySQL
qt-MySQL - MySQL drivers for QT SQL classes
mysql-administrator - GUI based tool to manage MySQL databases


Server daemon: mysqld

Startup script: /etc/init.d/mysqld

Configuration file: /etc/my.cnf

Log file: /var/log/mqsqld.log

Few Tips for beginners:

1. To set password for root user in MySQL (this is different from the root password in OS):

# mysqladmin -u root password mypasswd

You need to mention this password whenever you run a mysql command.
To make it easy, you can add the password to the file /root/.my.cnf and change the permission to 600

Here is a sample content of /root/.my.cnf

[client]
mypassword


2. What happens when you start MySQL server for the first time:

It creates tables for 2 databases mysql and test. And the information is stored in the /var/lib/mysql/mysql and /var/lib/mysql/test directories, respectively.

3. How to start mqsql command ?

$ mysql -u root
Enter password: *********

Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 13

Server version: 5.0.37 Source distribution
Type 'help;' or '\h' for help. Type '\c' to clear the buffer

mysql>

If you want to connect to mysql on a remote server, use -h hostname or ipaddress to the end of the command.


Some mysql interface commands :

1. Shows the version, connected database, remote or local connection,etc...

mysql> status

2. To create a new database :

mysql> CREATE DATABASE mydb;

You can also create a database using mysqladmin command as below

# mysqladmin -u root -p create

3. To list all the databases on your mysql server :

mysql> SHOW DATABASES;

4. Before working on a database, make it as your current database.

mysql> USE mydb;

5. To create a table:

mysql> CREATE TABLE employee (
-> name      varchar(20)    not null,
-> empid       varchar(6)    not null,
-> phonenumber     varchar(10)    not null,
-> city           varchar(20)    not null,
-> state          varchar(20)    not null,
-> zipcode        varchar(10)    not null
-> );

6. To show all tables in your current database :

mysql> SHOW tables;

7. To display the format of the "employee" table :

mysql> DESCRIBE employee;

8. To add data to the table "employee" :

mysql> INSERT INTO employee
-> VALUES ('Mike','112233','2349871239',
-> 'Philadelphia','PA','11227');

9. To list the contents of the table:

mysql> SELECT * FROM employee;

10. To load data from a text file into a table:

$ mysql -u root -p
Enter password: *******
mysql> USE mydb
Database changed
mysql> LOAD DATA INFILE "/tmp/emp.txt" INTO TABLE employee;
Query OK, 5 rows affected (0.04 sec)
Records: 5  Deleted: 0 Skipped: 0 Warnings: 0

How to integrate Red Hat Satellite with VMWare (ESX)

You can integrate Red Hat Satellite with VMWare ESX Hypervisor so that you can just use one license "Red Hat Enterprise Linux for Virtual Datacenters, Standard" per ESX.

Here is the procedure to make your satellite talk to ESX hypervisor to retrive the UUIDs

1. Register a VMWare based Linux server on Satellite

2. Install virt-who package

# yum install virt-who

3. Add the following lines onto /etc/sysconfig/virt-who

4. Enable and restart virt-who service

# chconfig virt-who on

# service virt-who restart

5. Now virt-who will populate all your hypervisors on RedHat satellite webUI.

6. Go to Content > Content host. Here you will find some systems with UUID. These are all hypervisors reported by your virt-who service.

7. Select a hypervisor > Subscription > Add > Select virtual datacenter subscription. > attach.
Follow this step for all hypervisors available on web UI.

8. Now on your virt-who server execute the following command to list out the hypervisors inherited virtual datacenter subscription.
This subscription contains the pool id. Note down this pool id.

# subscription-manager list --available

9. Now subscribe your system

# subscription-manager subscribe --pool=