Step 1: Create public and private keys using ssh-key-gen on local-host

jsmith@local-host$ [Note: You are on local-host here]

jsmith@local-host$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/jsmith/.ssh/id_rsa):[Enter key]
Enter passphrase (empty for no passphrase): [Press enter key]
Enter same passphrase again: [Pess enter key]
Your identification has been saved in /home/jsmith/.ssh/id_rsa.
Your public key has been saved in /home/jsmith/.ssh/id_rsa.pub.
The key fingerprint is:
33:b3:fe:af:95:95:18:11:31:d5:de:96:2f:f2:35:f9 jsmith@local-host

Step 2: Copy the public key to remote-host using ssh-copy-id

jsmith@local-host$ ssh-copy-id -i ~/.ssh/id_rsa.pub remote-host
jsmith@remote-host’s password:
Now try logging into the machine, with “ssh ‘remote-host’”, and check in:

.ssh/authorized_keys

to make sure we haven’t added extra keys that you weren’t expecting.

Note: ssh-copy-id appends the keys to the remote-host’s .ssh/authorized_key.

Step 3: Login to remote-host without entering the password

jsmith@local-host$ ssh remote-host
Last login: Sun Nov 16 17:22:33 2008 from 192.168.1.2
[Note: SSH did not ask for password.]

jsmith@remote-host$ [Note: You are on remote-host here]

The above 3 simple steps should get the job done in most cases.

We also discussed earlier in detail about performing SSH and SCP from openSSH to openSSH without entering password.

If you are using SSH2, we discussed earlier about performing SSH and SCP without password from SSH2 to SSH2 , from OpenSSH to SSH2 and from SSH2 to OpenSSH.

Using ssh-copy-id along with the ssh-add/ssh-agent

When no value is passed for the option -i and If ~/.ssh/identity.pub is not available, ssh-copy-id will display the following error message.

jsmith@local-host$ ssh-copy-id -i remote-host
/usr/bin/ssh-copy-id: ERROR: No identities found

If you have loaded keys to the ssh-agent using the ssh-add, then ssh-copy-id will get the keys from the ssh-agent to copy to the remote-host. i.e, it copies the keys provided by ssh-add -L command to the remote-host, when you don’t pass option -i to the ssh-copy-id.

jsmith@local-host$ ssh-agent $SHELL

jsmith@local-host$ ssh-add -L
The agent has no identities.

jsmith@local-host$ ssh-add
Identity added: /home/jsmith/.ssh/id_rsa (/home/jsmith/.ssh/id_rsa)

jsmith@local-host$ ssh-add -L
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAsJIEILxftj8aSxMa3d8t6JvM79DyBV
aHrtPhTYpq7kIEMUNzApnyxsHpH1tQ/Ow== /home/jsmith/.ssh/id_rsa

jsmith@local-host$ ssh-copy-id -i remote-host
jsmith@remote-host’s password:
Now try logging into the machine, with “ssh ‘remote-host’”, and check in:

.ssh/authorized_keys

to make sure we haven’t added extra keys that you weren’t expecting.
[Note: This has added the key displayed by ssh-add -L]

Three Minor Annoyances of ssh-copy-id

Following are few minor annoyances of the ssh-copy-id.

1. Default public key: ssh-copy-id uses ~/.ssh/identity.pub as the default public key file (i.e when no value is passed to option -i). Instead, I wish it uses id_dsa.pub, or id_rsa.pub, or identity.pub as default keys. i.e If any one of them exist, it should copy that to the remote-host. If two or three of them exist, it should copy identity.pub as default.
2. The agent has no identities: When the ssh-agent is running and the ssh-add -L returns “The agent has no identities” (i.e no keys are added to the ssh-agent), the ssh-copy-id will still copy the message “The agent has no identities” to the remote-host’s authorized_keys entry.
3. Duplicate entry in authorized_keys: I wish ssh-copy-id validates duplicate entry on the remote-host’s authorized_keys. If you execute ssh-copy-id multiple times on the local-host, it will keep appending the same key on the remote-host’s authorized_keys file without checking for duplicates. Even with duplicate entries everything works as expected. But, I would like to have my authorized_keys file clutter free.

If you like this article, please bookmark it on Delicious and Stumble it.

Post from: The Geek Stuff

3 Steps to Perform SSH Login Without Password Using ssh-keygen & ssh-copy-id

1. Download DELL OMSA

Go to DELL support website -> click on “Drivers & Downloads” -> choose your server model (in my case, I selected PowerEdge 2850) -> choose the operating system -> scroll-down and expand ‘Systems Management’ -> Click on ‘OpenManage Server Administrator Managed Node’ -> Click on OM_5.5.0_ManNode_A00.tar.gz to download it. You can directly download it to your Linux server as shown below.

# mkdir -p /usr/local/omsa
# cd /usr/local/omsa
# wget http://ftp.us.dell.com/sysman/OM_5.5.0_ManNode_A00.tar.gz

2. Install DELL OMSA

Perform an express OMSA installation as shown below. After the installation, check /var/log/srvadmin.log for any installation errors.

# gzip -d OM_5.5.0_ManNode_A00.tar.gz
# tar xvf OM_5.5.0_ManNode_A00.tar
# sh linux/supportscripts/srvadmin-install.sh --express
Installing the selected packages.

Preparing...                ###################################### [100%]
   1:srvadmin-omilcore      ###################################### [  8%]
     To start all installed services without a reboot,
     enter the following command:  srvadmin-services.sh  start
   2:srvadmin-syscheck      ###################################### [ 15%]
   3:srvadmin-deng          ###################################### [ 23%]
   4:srvadmin-omauth        ###################################### [ 31%]
   5:srvadmin-omacore       ###################################### [ 38%]
   6:srvadmin-jre           ###################################### [ 46%]
   7:srvadmin-ipmi          ###################################### [ 54%]
   8:srvadmin-hapi          ###################################### [ 62%]
   9:srvadmin-isvc          ###################################### [ 69%]
  10:srvadmin-cm            ###################################### [ 77%]
  11:srvadmin-iws           ###################################### [ 85%]
  12:srvadmin-omhip         ###################################### [ 92%]
  13:srvadmin-storage       ###################################### [100%]

3. Start DELL OMSA Services

Invoke the srvadmin-services.sh script to start the OMSA services as shown below.

# sh linux/supportscripts/srvadmin-services.sh start
Starting Systems Management Device Drivers:
Starting dell_rbu:                                         [  OK  ]
Starting ipmi driver:                                      [  OK  ]
Starting Systems Management Data Engine:
Starting dsm_sa_datamgr32d:                                [  OK  ]
Starting dsm_sa_eventmgr32d:                               [  OK  ]
Starting DSM SA Shared Services:                           [  OK  ]
Starting DSM SA Connection Service:                        [  OK  ]

4. Access OMSA from web browser

By default, OMSA web application runs on Port 1311 . Login to OMSA from web using the URL: https://{omsa-server-ip-address}:1311 using root as shown below. Please note that you can login only using HTTPS.

5. Check overall system health of the server

To check the overall system health of various hardware components, expand system menu and click on ‘Main System Chassis’, which will display the health of Memory, CPU etc., as shown below.

6. Clear System Event Log on DELL PowerEdge Servers

Sometimes you will see hardware error messages on the front side of the server even after the problem is fixed.  To clear this false alarm,  you have to clear the hardware’s Embedded System Management (ESM) Log. To clear hardware event logs, login to DELL OMSA -> Click on Logs TAB -> click on Clear Log.

7. Create RAID (Virtual Disk) group using OMSA

To create a new raid group, click on Storage -> select “Create Virtual Disk” from the drop-down menu next to “PERC 4e/Di”, as shown below. -> Click on Execute -> and follow the on-screen instructions to create a new RAID group.

You can also create RAID using PERC/CERC Bios Configuration Utility as explained in Step-by-Step Guide to Configure Hardware RAID on DELL servers with Screenshots.

Once the RAID group is created, to view the RAID, click on Storage -> “PERC 4e/Di (Embedded)” -> Click on “Virtual Disks” -> Click on “Virtual Disks 0″ -> This will display the details of the physical disks of that particular RAID group as shown below.

Post from: The Geek Stuff

How To Manage Dell Servers using OMSA - OpenManage Server Administrator On Linux

1. Get basic information about information_schema

show databases command will display the information_schema in the database list. information_schema is not a physical database.  When you perform select on the information_schema tables, it pulls the data from the real database and other system variables.

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| bugs               |
| mysql              |
| sugarcrm           |
+--------------------+
4 rows in set (0.00 sec)

Following are the tables (views) available in the information_schema database.

mysql> use information_schema;
mysql> show tables;
+---------------------------------------+
| Tables_in_information_schema          |
+---------------------------------------+
| CHARACTER_SETS                        |
| COLLATIONS                            |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS                               |
| COLUMN_PRIVILEGES                     |
| KEY_COLUMN_USAGE                      |
| PROFILING                             |
| ROUTINES                              |
| SCHEMATA                              |
| SCHEMA_PRIVILEGES                     |
| STATISTICS                            |
| TABLES                                |
| TABLE_CONSTRAINTS                     |
| TABLE_PRIVILEGES                      |
| TRIGGERS                              |
| USER_PRIVILEGES                       |
| VIEWS                                 |
+---------------------------------------+
17 rows in set (0.00 sec)

2. Query to display tables with more than 1000 rows

Using the above mentioned information_schema tables you can build your own query to get metadata information. This example displays the MySQL tables that have more than 1000 rows.

mysql> select concat(table_schema,'.',table_name) as table_name,table_rows
    -> from information_schema.tables where table_rows > 1000
    -> order by table_rows desc;

+----------------------------------+------------+
| table_name                       | table_rows |
+----------------------------------+------------+
| bugs.series_data                 |      52778 |
| bugs.bugs_activity               |      26436 |
| bugs.longdescs                   |      21473 |
| bugs.email_setting               |       5370 |
| bugs.attachments                 |       4714 |
| bugs.attach_data                 |       4651 |
| bugs.cc                          |       4031 |
| bugs.bugs                        |       2190 |
| bugs.namedqueries_link_in_footer |       1228 |
+----------------------------------+------------+
9 rows in set (0.04 sec)

3. Query to list all tables without primary key

This example gives a list of all the tables without primary key.

SELECT CONCAT(t.table_name,".",t.table_schema) as table_name
FROM information_schema.TABLES t
LEFT JOIN information_schema.TABLE_CONSTRAINTS tc
ON t.table_schema = tc.table_schema
AND t.table_name = tc.table_name
AND tc.constraint_type = 'PRIMARY KEY'
WHERE tc.constraint_name IS NULL
AND t.table_type = 'BASE TABLE';

4. Implement history data for tables using information_schema

Putting the MySQL information_schema to Use article implements a history database using the information schema. The first half of this article describes the requirements for the history database, and a generic design to implement it. The second half describes the stepwise construction of code-generator that creates the SQL to construct and load the history database. The code-generator is driven by the information schema and some features of the information schema are discussed in detail.

5. Query to list top 5 largest tables in the database

This examples gives the top 5 largest space occupying tables in the database along with it’s size in MB.

mysql> SELECT concat(table_schema,'.',table_name) table_name,
    -> concat(round(data_length/(1024*1024),2),'M') data_length
    -> FROM information_schema.TABLES
    -> ORDER BY data_length DESC LIMIT 5;

+--------------------+-------------+
| table_name         | data_length |
+--------------------+-------------+
| bugs.attach_data   | 706.89M     |
| bugs.longdescs     | 3.45M       |
| bugs.bugs_activity | 1.45M       |
| bugs.series_data   | 0.75M       |
| bugs.attachments   | 0.51M       |
+--------------------+-------------+
5 rows in set (0.05 sec)

Additional References:

• Information_schema table documentation from MySQL
• Clickable diagram of MySQL information_schema data dictionary
  

Post from: The Geek Stuff

Overview of MySQL information_schema Database With Practical Examples

dmidecode command reads the system DMI table to display hardware and BIOS information of the server. Apart from getting current configuration of the system, you can also get information about maximum supported configuration of the system using dmidecode. For example, dmidecode gives both the current RAM on the system and the maximum RAM supported by the system.

This article provides an overview of the dmidecode and few practical examples on how to use dmidecode command.

1. Overview of dmidecode

Distributed Management Task Force maintains the DMI specification and SMBIOS specification. The output of the dmidecode contains several records from the DMI (Desktop Management interface) table.

Following is the record format of the dmidecode output of the DMI table.

Record Header: Handle {record id}, DMI type {dmi type id}, {record size} bytes
Record Value: {multi line record value}

• record id: Unique identifier for every record in the DMI table.
• dmi type id: Type of the record. i.e BIOS, Memory etc.,
• record size: Size of the record in the DMI table.
• multi line record values: Multi line record value for that specific DMI type.

Sample output of dmidecode command:

# dmidecode | head -15

# dmidecode 2.9
SMBIOS 2.3 present.
56 structures occupying 1977 bytes.
Table at 0×000FB320.

Handle 0xDA00, DMI type 218, 11 bytes
OEM-specific Type
        Header and Data:
                DA 0B 00 DA B0 00 17 03 08 28 00

Handle 0×0000, DMI type 0, 20 bytes
BIOS Information
        Vendor: Dell Computer Corporation
        Version: A07
        Release Date: 01/13/2004

Get the total number of records in the DMI table as shown below:

# dmidecode | grep ^Handle | wc -l
56

(or)

# dmidecode | grep structures
56 structures occupying 1977 bytes.

2. DMI Types

DMI Type id will give information about a particular hardware component of your system. Following command with type id 4 will get the information about CPU of the system.

# dmidecode -t 4
# dmidecode 2.9
SMBIOS 2.3 present.

Handle 0×0400, DMI type 4, 35 bytes
Processor Information
        Socket Designation: Processor 1
        Type: Central Processor
        Family: Xeon
        Manufacturer: Intel
        ID: 29 0F 00 00 FF FB EB BF
        Signature: Type 0, Family 15, Model 2, Stepping 9
        Flags:
                FPU (Floating-point unit on-chip)
                VME (Virtual mode extension)
                DE (Debugging extension)
                PSE (Page size extension)
                TSC (Time stamp counter)
                MSR (Model specific registers)

Following are the different DMI types available.

       Type   Information
       ----------------------------------------
          0   BIOS
          1   System
          2   Base Board
          3   Chassis
          4   Processor
          5   Memory Controller
          6   Memory Module
          7   Cache
          8   Port Connector
          9   System Slots
         10   On Board Devices
         11   OEM Strings
         12   System Configuration Options
         13   BIOS Language
         14   Group Associations
         15   System Event Log
         16   Physical Memory Array
         17   Memory Device
         18   32-bit Memory Error
         19   Memory Array Mapped Address
         20   Memory Device Mapped Address
         21   Built-in Pointing Device
         22   Portable Battery
         23   System Reset
         24   Hardware Security
         25   System Power Controls
         26   Voltage Probe
         27   Cooling Device
         28   Temperature Probe
         29   Electrical Current Probe
         30   Out-of-band Remote Access
         31   Boot Integrity Services
         32   System Boot
         33   64-bit Memory Error
         34   Management Device
         35   Management Device Component
         36   Management Device Threshold Data
         37   Memory Channel
         38   IPMI Device
         39   Power Supply

Instead of type_id, you can also pass the keyword to the -t option of the dmidecode command. Following are the available keywords.

       Keyword     Types
       ------------------------------
       bios        0, 13
       system      1, 12, 15, 23, 32
       baseboard   2, 10
       chassis     3
       processor   4
       memory      5, 6, 16, 17
       cache       7
       connector   8
       slot        9

For example, to get all the system baseboard related information execute the following command, which will display the type_id 2 and 10

# dmidecode -t baseboard
# dmidecode 2.9
SMBIOS 2.3 present.

Handle 0×0200, DMI type 2, 9 bytes
Base Board Information
        Manufacturer: Dell Computer Corporation
        Product Name: 123456
        Version: A05
        Serial Number: ..CN123456789098.

Handle 0×0A00, DMI type 10, 14 bytes
On Board Device 1 Information
        Type: SCSI Controller
        Status: Enabled
        Description: LSI Logic 53C1030 Ultra 320 SCSI
On Board Device 2 Information
        Type: SCSI Controller
        Status: Enabled
        Description: LSI Logic 53C1030 Ultra 320 SCSI
On Board Device 3 Information
        Type: Video
        Status: Enabled
        Description: ATI Rage XL PCI Video
On Board Device 4 Information
        Type: Ethernet
        Status: Enabled
        Description: Broadcom Gigabit Ethernet 1
On Board Device 5 Information
        Type: Ethernet
        Status: Enabled
        Description: Broadcom Gigabit Ethernet 2

3. Get Physical Memory (RAM) information using dmidecode

What is the maximum RAM supported by the system? In this example, this system can support maximum 8GB of RAM.

# dmidecode -t 16
# dmidecode 2.9
SMBIOS 2.3 present.

Handle 0×1000, DMI type 16, 15 bytes
Physical Memory Array
        Location: System Board Or Motherboard
        Use: System Memory
        Error Correction Type: Multi-bit ECC
        Maximum Capacity: 8 GB
        Error Information Handle: Not Provided
        Number Of Devices: 4

How much memory can I expand to? From /proc/meminfo you can find out the total current memory of your system as shown below.

# grep MemTotal /proc/meminfo
MemTotal:      1034644 kB

In this example, the system has 1GB of RAM. Is this 1 x 1GB (or) 2 x 512MB (or) 4 x 256MB? This can be figured out by passing the type id 17 to the dmidecode command as shown below. Please note in the example below, if you have to expand upto 8GB of maximum RAM, you need to remove the existing 512MB from slot 1 and 2, and use 2GB RAM on all the 4 memory slots.

# dmidecode -t 17
# dmidecode 2.9
SMBIOS 2.3 present.

Handle 0×1100, DMI type 17, 23 bytes
Memory Device
        Array Handle: 0×1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 512 MB  [Note: Slot1 has 512 MB RAM]
        Form Factor: DIMM
        Set: 1
        Locator: DIMM_1A
        Bank Locator: Not Specified
        Type: DDR
        Type Detail: Synchronous
        Speed: 266 MHz (3.8 ns)

Handle 0×1101, DMI type 17, 23 bytes
Memory Device
        Array Handle: 0×1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 512 MB [Note: Slot2 has 512 MB RAM]
        Form Factor: DIMM
        Set: 1
        Locator: DIMM_1B
        Bank Locator: Not Specified
        Type: DDR
        Type Detail: Synchronous
        Speed: 266 MHz (3.8 ns)

Handle 0×1102, DMI type 17, 23 bytes
Memory Device
        Array Handle: 0×1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: No Module Installed [Note: Slot3 is empty]
        Form Factor: DIMM
        Set: 2
        Locator: DIMM_2A
        Bank Locator: Not Specified
        Type: DDR
        Type Detail: Synchronous
        Speed: 266 MHz (3.8 ns)

Handle 0×1103, DMI type 17, 23 bytes
Memory Device
        Array Handle: 0×1000

        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: No Module Installed [Note: Slot4 is empty]
        Form Factor: DIMM
        Set: 2
        Locator: DIMM_2B
        Bank Locator: Not Specified
        Type: DDR
        Type Detail: Synchronous
        Speed: 266 MHz (3.8 ns)

4. Get BIOS information using dmidecode

# dmidecode -t bios
# dmidecode 2.9
SMBIOS 2.3 present.

Handle 0×0000, DMI type 0, 20 bytes
BIOS Information
        Vendor: Dell Computer Corporation
        Version: A07
        Release Date: 01/13/2004
        Address: 0xF0000
        Runtime Size: 64 kB
        ROM Size: 4096 kB
        Characteristics:
                ISA is supported
                PCI is supported
                PNP is supported
                BIOS is upgradeable
                BIOS shadowing is allowed
                ESCD support is available
                Boot from CD is supported
                Selectable boot is supported
                EDD is supported
                Japanese floppy for Toshiba 1.2 MB is supported (int 13h)
                5.25″/360 KB floppy services are supported (int 13h)
                5.25″/1.2 MB floppy services are supported (int 13h)
                3.5″/720 KB floppy services are supported (int 13h)
                8042 keyboard services are supported (int 9h)
                Serial services are supported (int 14h)
                CGA/mono video services are supported (int 10h)
                ACPI is supported
                USB legacy is supported
                LS-120 boot is supported
                BIOS boot specification is supported
                Function key-initiated network boot is supported

Handle 0×0D00, DMI type 13, 22 bytes
BIOS Language Information
        Installable Languages: 1
                en|US|iso8859-1
        Currently Installed Language: en|US|iso8859-1

5. View Manufacturer, Model and Serial number of the equipment using dmidecode

You can get information about the make, model and serial number of the equipment as shown below:

# dmidecode -t system
# dmidecode 2.9
SMBIOS 2.3 present.

Handle 0×0100, DMI type 1, 25 bytes
System Information
        Manufacturer: Dell Computer Corporation
        Product Name: PowerEdge 1750
        Version: Not Specified
        Serial Number: 1234567
        UUID: 4123454C-4123-1123-8123-12345603431
        Wake-up Type: Power Switch

Handle 0×0C00, DMI type 12, 5 bytes
System Configuration Options
        Option 1: NVRAM_CLR:  Clear user settable NVRAM areas and set defaults
        Option 2: PASSWD:  Close to enable password

Handle 0×2000, DMI type 32, 11 bytes
System Boot Information
        Status: No errors detected

Post from: The Geek Stuff

How To Get Hardware Information On Linux Using dmidecode Command

1. How to mount Tmpfs

# mkdir -p /mnt/tmp

# mount -t tmpfs -o size=20m tmpfs /mnt/tmp

The last line in the following df -k shows the above mounted /mnt/tmp tmpfs file system.

# df -k
Filesystem      1K-blocks  Used     Available Use%  Mounted on
/dev/sda2       32705400   5002488  26041576  17%   /
/dev/sda1       194442     18567    165836    11%   /boot
tmpfs           517320     0        517320    0%    /dev/shm
tmpfs           20480      0        20480     0%    /mnt/tmp

2. How to mount Ramfs

# mkdir -p /mnt/ram

# mount -t ramfs -o size=20m ramfs /mnt/ram

The last line in the following mount command shows the above mounted /mnt/ram ramfs file system.

# mount
/dev/sda2 on / type ext3 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
/dev/sda1 on /boot type ext3 (rw)
tmpfs on /dev/shm type tmpfs (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
tmpfs on /mnt/tmp type tmpfs (rw,size=20m)
ramfs on /mnt/ram type ramfs (rw,size=20m)

You can mount ramfs and tmpfs during boot time by adding an entry to the /etc/fstab.

3. Ramfs vs Tmpfs

Primarily both ramfs and tmpfs does the same thing with few minor differences.

• Ramfs will grow dynamically.  So, you need control the process that writes the data to make sure ramfs doesn’t go above the available RAM size in the system. Let us say you have 2GB of RAM on your system and created a 1 GB ramfs and mounted as /tmp/ram. When the total size of the /tmp/ram crosses 1GB, you can still write data to it.  System will not stop you from writing data more than 1GB. However, when it goes above total RAM size of 2GB, the system may hang, as there is no place in the RAM to keep the data.
• Tmpfs will not grow dynamically. It would not allow you to write more than the size you’ve specified while mounting the tmpfs. So, you don’t need to worry about controlling the process that writes the data to make sure tmpfs doesn’t go above the specified limit. It may give errors similar to “No space left on device”.
• Ramfs uses swap.
• Tmpfs does not use swap.

4. Disadvantages of Ramfs and Tmpfs

Since both ramfs and tmpfs is writing to the system RAM, it would get deleted once the system gets rebooted, or crashed. So, you should write a process to pick up the data from ramfs/tmpfs to disk in periodic intervals. You can also write a process to write down the data from ramfs/tmpfs to disk while the system is shutting down. But, this will not help you in the time of system crash.

If you want your process to write faster, opting for tmpfs is a better choice with precautions about the system crash.

This article was written by SathiyaMoorthy. He is working at bksystems, interested in writing articles and  contribute to open source in his leisure time. The Geek Stuff welcomes your tips and guest articles.

Post from: The Geek Stuff

Overview of RAMFS and TMPFS on Linux

1. Enable switch.cfg in nagios.cfg

Uncomment the switch.cfg line in /usr/local/nagios/etc/nagios.cfg as shown below.

[nagios-server]# grep switch.cfg /usr/local/nagios/etc/nagios.cfg
cfg_file=/usr/local/nagios/etc/objects/switch.cfg

2. Add new hostgroup for switches in switch.cfg

Add the following switches hostgroup to the /usr/local/nagios/etc/objects/switch.cfg file.

define hostgroup{
hostgroup_name  switches
alias           Network Switches
}

3. Add a new host for the switch to be monitered

In this example, I’ve defined a host to monitor the core switch in the /usr/local/nagios/etc/objects/switch.cfg file. Change the address directive to your switch ip-address accordingly.

define host{
use             generic-switch
host_name       core-switch
alias           Cisco Core Switch
address         192.168.1.50
hostgroups      switches
}

4. Add common services for all switches

Displaying the uptime of the switch and verifying whether switch is alive are common services for all switches. So, define these services under the switches hostgroup_name as shown below.

# Service definition to ping the switch using check_ping
define service{
use                     generic-service
hostgroup_name          switches
service_description     PING
check_command           check_ping!200.0,20%!600.0,60%
normal_check_interval   5
retry_check_interval    1
}

# Service definition to monitor switch uptime using check_snmp
define service{
use                     generic-service
hostgroup_name          switches
service_description     Uptime
check_command           check_snmp!-C public -o sysUpTime.0
}

5. Add service to monitor port bandwidth usage

check_local_mrtgtraf uses the Multil Router Traffic Grapher - MRTG. So, you need to install MRTG for this to work properly. The *.log file mentioned below should point to the MRTG log file on your system.

define service{
use			        generic-service
host_name			core-switch
service_description	Port 1 Bandwidth Usage
check_command		check_local_mrtgtraf!/var/lib/mrtg/192.168.1.11_1.log!AVG!1000000,2000000!5000000,5000000!10
}

6. Add service to monitor an active switch port

Use check_snmp to monitor the specific port as shown below. The following two services monitors port#1 and port#5. To add additional ports, change the value ifOperStatus.n accordingly. i.e n defines the port#.

# Monitor status of port number 1 on the Cisco core switch
define service{
use                  generic-service
host_name            core-switch
service_description  Port 1 Link Status
check_command        check_snmp!-C public -o ifOperStatus.1 -r 1 -m RFC1213-MIB
}

# Monitor status of port number 5 on the Cisco core switch
define service{
use                  generic-service
host_name            core-switch
service_description  Port 5 Link Status
check_command	       check_snmp!-C public -o ifOperStatus.5 -r 1 -m RFC1213-MIB
}

7. Add services to monitor multiple switch ports together

Sometimes you may need to monitor the status of multiple ports combined together. i.e Nagios should send you an alert, even if one of the port is down. In this case, define the following service to monitor multiple ports.

# Monitor ports 1 - 6 on the Cisco core switch.
define service{
use                   generic-service
host_name             core-switch
service_description   Ports 1-6 Link Status
check_command         check_snmp!-C public -o ifOperStatus.1 -r 1 -m RFC1213-MIB, -o ifOperStatus.2 -r 1 -m RFC1213-MIB, -o ifOperStatus.3 -r 1 -m RFC1213-MIB, -o ifOperStatus.4 -r 1 -m RFC1213-MIB, -o ifOperStatus.5 -r 1 -m RFC1213-MIB, -o ifOperStatus.6 -r 1 -m RFC1213-MIB
}

8. Validate configuration and restart nagios

Verify the nagios configuration to make sure there are no warnings and errors.

# /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

Total Warnings: 0
Total Errors:   0
Things look okay - No serious problems were detected during the pre-flight check

Restart the nagios server to start monitoring the VPN device.

# /etc/rc.d/init.d/nagios stop
Stopping nagios: .done.

# /etc/rc.d/init.d/nagios start
Starting nagios: done.

Verify the status of the switch from the Nagios web UI: http://{nagios-server}/nagios as shown below:

9. Troubleshooting

Issue1: Nagios GUI displays “check_mrtgtraf: Unable to open MRTG log file” error message for the Port bandwidth usage

Solution1: make sure the *.log file defined in the check_local_mrtgtraf service is pointing to the correct location.

Issue2: Nagios UI displays “Return code of 127 is out of bounds - plugin may be missing” error message for Port Link Status.

Solution2: Make sure both net-snmp and net-snmp-util packages are installed. In my case, I was missing the net-snmp-utils package and installing it resolved this issue as shown below.

[nagios-server]# rpm -qa | grep net-snmp
net-snmp-libs-5.1.2-11.el4_6.11.2
net-snmp-5.1.2-11.el4_6.11.2

[nagios-server]# rpm -ivh net-snmp-utils-5.1.2-11.EL4.10.i386.rpm
Preparing…       ########################################### [100%]
1:net-snmp-utils   ########################################### [100%]

[nagios-server]# rpm -qa | grep net-snmp
net-snmp-libs-5.1.2-11.el4_6.11.2
net-snmp-5.1.2-11.el4_6.11.2
net-snmp-utils-5.1.2-11.EL4.10

Note: After you’ve installed net-snmp and net-snmp-utils, re-compile and re-install nagios plugins as explained in “6. Compile and install nagios plugins” in the Nagios 3.0 jumpstart guide.

Post from: The Geek Stuff

How To Monitor Network Switch and Ports Using Nagios

Around The Geek World is a monthly summary of interesting articles and news around the geek world with my brief comment.

I hope you enjoy this collection of interesting geek articles for October 2008.

• 7 online blunders - One of the 7 blunders mentioned in this article is: Using single password for all online accounts, which is a major mistake done by lot of people. The article I wrote a while back about creating a strong passwords talks about 10 common sense about passwords.




• 15 of The Hottest Wearable Gadgets [Pics and Video] - One of the 15 wearable gadgets is a “Wi-Fi detector T-Shirt” - when you’re in the range of a wi-fi- signal, the bars on the shirt light up. Is this geeky or spooky?




• World first for sending data using quantum cryptography - Anything around cryptography is always fascinating for me, because of the complex algorithms involved. For the first time, the transmission of data secured by quantum cryptography is demonstrated within a commercial telecommunications network.




• Wikipedia adopts Ubuntu for its server infrastructure - Ubuntu is the best Linux distro for desktop. But, it can also be an excellent choice for server infrastructure. Don’t beleive me? Ask Wikipedia team, who are migrating 400+ servers from RedHat+Fedora combination to Ubuntu.




• RAID 5 vs RAID 10: Recommended RAID For Safety and Performance - At work, for all I/O intensive database servers, I use RAID 10. If you are debating whether to use RAID 5 of RAID 10, Vivek has clearly explained why you should choose RAID 10 in this article.




• 10 Handy Productivity Tools in Linux - Some applications mentioned in this list are must-have for Linux desktop environment. Freemind is an excellent mind-mapping tool. If you are new to mind-mapping concept, it will take little practice to use this tool effectively. Once you get the hang of it, you will not execute any major project without a mind-map.




• Easy Vertical Centering with CSS - Excellent tutorial with screenshots on how to perform vertical centering in CSS effectively.




• Programmers Salary Policy - Geek Hero Webcomic - Your salary increment is directly proportionate to the total lines of code you write. How many lines of code can you write to do 1 + 1?




• Increase your productivity by using 2 monitors - USAToday is very late in talking about this, as most of us have been using dual monitors for ages now.  Look at the amount of digg comments (close to 300) on such a simple article.




• 1000+ Free High Resolution Photoshop Brush Sets - Some of them are very specific to certain versions of photoshop. But, you’ll definitely find several good brush sets for the version you are using, as there are so many of them.




• 14 Best Linux Distro - Debian, Fedora, OpenSUSE, Mandriva and Ubuntu are in the list as you would expect.  Did your favorite distro made it to this list?




• Effect of the Depression on Technology - October is pretty bad month for WallStreet and US economy in general. As a geek, you may be interested to know how it affects technology. As mentioned in the article, open source will benefit from this economy slow down,  as companies will now turn to open source to save some cash.




• Why did Linus Torvalds start a blog? - Hear it from him directly.




• 10 Useful articles about Database design - Excellent collection of all DB design related articles. If you are DBA, DB architect, or DB programmer, you should definitely bookmark this.




• What is the single most influential book every programmer should read? - You can spend lot of time reading through the user’s answers for this question. My amazon wish-list grew 25%, as I’ve added several books recommended in the article to my wish-list.




• If you steal source code, don’t ask for help fixing it - Is it OK to decompile someone’s code and use it? Just read the comment section of this post to hear various opinions from users.




• Hilarious comments from reddit users about Gmail’s new feature that will stop sending mails that you’ll regret later.  Geek getting drunk and sending emails — can anything be more hilarious than that?




Post from: The Geek Stuff

Around The Geek World - Oct 2008

Bugzilla error message:
The file you are trying to attach is 1396 kilobytes (KB) in size. Non-patch
attachments cannot be more than 1000 KB. 

We recommend that you store your attachment elsewhere on the web,
and then insert the URL to it in a comment, or in the URL field for this bug. 

Alternately, if your attachment is an image, you could convert it to a
compressible format like JPG or PNG and try again.

1. Change the maxattachmentsize parameter in Bugzilla

Login to bugzilla and click on “Parameters” link next to the “Edit” section in the footer area. This will display bugzilla configuration menu as shown below. Click on “Attachments” menu-item to display all bugzilla attachment related configuration parameters. Change the values of maxattachmentsize to 3000 for a 3MB limit.

Fig - Bugzilla configuration Menu

maxattachmentsize is the maximum size (in kilobytes) of non-patch attachments. Bugzilla will not accept attachments greater than this number of kilobytes in size. To accept attachments of any size (subject to the limitations of your server software), set this value to zero.

2. Change the max_allowed_packet parameter in MySQL database

Add max_allowed_packet=3M to the MySQL configuration file:/etc/my.cnf as shown below.

[db-server]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
max_allowed_packet=3M

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

[client]
socket=/var/lib/mysql/mysql.sock

Restart the MySQL database for the new max_allowed_packet parameter to take effect.

[db-server]# /etc/rc.d/init.d/mysqld restart
Stopping MySQL:                                            [  OK  ]
Starting MySQL:                                            [  OK  ]

After the above two changes, you can upload attachments upto 3MB on bugzilla. Also, sometimes when you are restoring a MySQL backup, you may get the following error message.

Got a packet bigger than 'max_allowed_packet' bytes

To resolve this issue, increase the max_allowed_packet as explained above to 32MB or more.

Post from: The Geek Stuff

Increase Bugzilla Attachment Size Using MySQL max_allowed_packet

1. Get DELL Service Tag on remote Windows system

Login to the Windows remote-host using VNC or remote desktop connection. Use WMIC on Windows to get service tag as shown below.

C:\>wmic bios get serialnumber
SerialNumber
ABCDEF1

Following WMIC command will give make and model number along with service tag.

C:\>wmic csproduct get vendor,name,identifyingnumber
IdentifyingNumber    Name                Vendor
ABCDEF1              PowerEdge 2950      Dell Inc.

If VNC or remote desktop connection to the remote-host is not available,  execute the following from the local-host to get the service tag of the remote-host.

C:\>wmic /user:administrator /node:remote-host bios get serialnumber
SerialNumber
ABCDEF1
[Note: Replace remote-host with the machine name of your remote-host.]

2. Get DELL Service Tag on remote Linux system

Login to the Linux remote-host using SSH. Use dmidecode on Linux to get service tag as shown below.

[remote-host]# dmidecode -s system-serial-number
ABCDEF1

3. Get DELL Express Service Code From Service Tag

Service Tag is a base-36 integer.  Once you have the Service Tag, you can calculate express service code yourself. Express Service Code is base-10 decimal integer of Service Tag. Dell uses express service code mainly for their support call-routing. When you call dell support, their automated call-routing system may ask you to enter express service code, which you can easily enter in your telephone, as it is just a bunch of numbers, instead of characters.

Use the following online tools to find express service code from service tag and vice-versa.

• Creativyst Dell-Number Widget
• Dell PC service tag/code converter from PowerDog Industries

If you own systems other than DELL, such as HP, IBM, Sony, Toshiba, Acer etc., how do you find out serial number? Does the same method explained above works for you (or) Do you use a different method to identify serial numbers? Please leave your comment.

Post from: The Geek Stuff

View DELL Service Tag and Express Service Code From Linux and Windows

1. OpenSSH to OpenSSH
2. OpenSSH to SSH2
3. SSH2 to SSH2

In this article, I’ll explain how to perform ssh and scp from SSH2 (local-host) to OpenSSH (remote-host) with no password.

1. Identify local-host and remote-host SSH version

In this example, local-host is running SSH2 and remote-host is running OpenSSH.

[local-host]$ ssh -V
ssh: SSH Secure Shell 3.2.9.1 (non-commercial version) on i686-pc-linux-gnu

[remote-host]$ ssh -V
OpenSSH_4.3p2, OpenSSL 0.9.8b 04 May 2006

2. Generate SSH2 authentication key pair on the local-host using ssh-keygen2

On SSH2, ssh-keygen will be a soft-link to the ssh-keygen2 as shown below.

[local-host]$ ls -l /usr/local/bin/ssh-keygen
lrwxrwxrwx  1 root root 11 Jul 31  2006 /usr/local/bin/ssh-keygen -> ssh-keygen2

[local-host]$ ssh-keygen
Generating 2048-bit dsa key pair
7 o.oOo..oOo.o
Key generated.
2048-bit dsa, jsmith@local-host, Sun Oct 19 2008 14:49:42 -0700
Passphrase : [Enter the password here]
Again      :
Private key saved to /home/jsmith/.ssh2/id_dsa_2048_a
Public key saved to /home/jsmith/.ssh2/id_dsa_2048_a.pub

The public key and private key are stored in .ssh2 folder under your home directory. In this example, it is under /home/jsmith/.ssh2.

You should not share the private key with anybody.

By default ssh-keygen2 generates DSA (Digital Signature Algorithm) key pair. You can also generate RSA key pair as shown below.

[local-host]$ ssh-keygen -t rsa

3. Copy SSH2 public key from local-host to remote-host that is running OpenSSH

Copy local-host:/home/jsmith/.ssh2/id_dsa_2048_a.pub file to  remote-host:/home/jsmith/.ssh/id_dsa_1024_a.pub. Perform a vi /home/jsmith/.ssh/id_dsa_1024_b.pub on the remote-host and copy the content of the public key from the local-host.

[remote-host]$ vi /home/jsmith/.ssh/id_dsa_1024_a.pub
—- BEGIN SSH2 PUBLIC KEY —-
Subject: jsmith
Comment: “2048-bit dsa, jsmith@local-host Sun Oct 19 2008 14:49:42 -070\0″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—- END SSH2 PUBLIC KEY —-

4. On remote-host, convert SSH2 public key to OpenSSH public key

This should be executed on the remote-host that is running OpenSSH. Only OpenSSH can convert keys back and forth between OpenSSH and SSH2 format.

[remote-host]$ ssh-keygen -i -f ~/.ssh/id_dsa_1024_a.pub > \
~/.ssh/id_dsa_1024_a_openssh.pub

Copy the converted OpenSSH public key from ~/.ssh/id_dsa_1024_a_openssh.pub file to the authorized_keys file as shown below.

[remote-host]$ vi ~/.ssh/authorized_keys
ssh-dss 5iGSvMtmBBj8wQdegAEBALVa6VKtALZkydlOiPasikEQfujH07tjW+OffaRufFD
G0VQESjq+YlVTWcXxStz0xGlvJ/dayVqBvvHzMao8bwGC+HFUtH1un7uyIEwOqU1fNzEpgh
C97s143S8zBcTAGtdegte3IqmlLbp/ZCd6bcJLvZEepMz96nlNB4NJ5UYIfdgXNhf/TrJD8
COWQst6jsP6RG/WrpHiI4QVDM6tZVZ4CnGjm1QPkRnf/o5YMFJZRo4Iwc7+bgYrIyywBZnf
LL7TRTk9TBfWzgJHy/y1tTtCMvVooWvFZbG5AiV3de63MxBaD0o68SASyXZzVM+MabXhjcd
XFY2vjq2vJxOzunEAAAAVAOTeOzDCnj3K5iGSvMtmBBj8wQGHAAABAA38sGpHEfSxLx5MjQ
dFYXpHCaZ/xuKPXr4DFugGl8MRDU8TwioNE9kRi0Ko/kB5LTHuGhMPHGshMJeVGiPQTrt9N
AzgYyJeT9RB9VZadgElMvQ9S0+fo6ipOA==

5. Login from the local-host to remote-host using the SSH key authentication

Perform ssh from local-host (SSH2) to remote-host (OpenSSH) as shown below to verify whether the key based authentication works properly.

[local-host]$ [You are on local-host here]

[local-host]$ ssh -l jsmith remote-host
Host key not found from database.
Key fingerprint:
bitaz-navun-gogus-mptop-ljilk-qwlem-ftrtm-llmak-topok-zuiof-bnmix
You can get a public key’s fingerprint by running
% ssh-keygen -F publickey.pub on the keyfile.
Are you sure you want to continue connecting (yes/no)? yes
Host key saved to /home/jsmith/.ssh2/hostkeys/key_22_remote-host.pub
host key for remote-host, accepted by jsmith Sun Oct 19 2008 15:06:42 -0700

Passphrase for key “/home/jsmith/.ssh2/id_dsa_2048_a” with comment “2048-bit
dsa, jsmith@local-host, Sun Oct 19 2008 14:49:42 -0700″:[Enter password]
Last login: Sun Oct 19 14:01:48 2008 from 192.168.1.10

[remote-host]$ [You are on remote-host here]

Note: If you get the following error while performing the ssh or scp from local-host to remote-host, please refer to How to resolve Algorithm negotiation failed issue on SSH, to fix this issue.

[local-host]$ ssh -l jsmith remote-host
warning: Authentication failed.
Disconnected; key exchange or algorithm negotiation failed
(Algorithm negotiation failed.)

There are two ways to perform ssh and scp without entering the password:

1. No passphrase: While creating key pair, leave the passphrase empty. Use this option for the automated batch processing. for e.g. if you are running a cron job to copy files between machines this is suitable option. You can skip the next step steps for this method.
2. Use passphrase and SSH Agent: If you are using ssh and scp interactively from the command-line and you don’t want to use the password everytime you perform ssh or scp, I don’t recommend the previous option (no passphrase), as you’ve eliminated one level of security in the ssh key based authentication. Instead, use the passphrase while creating the key pair and use SSH Agent to perform ssh and scp without having to enter the password everytime as explained in the steps below.

6. Start the SSH Agent on local-host

The SSH Agent will be running in the background to hold the private keys and perform ssh and scp without having to enter the passphrase several times.

[local-host]$ ssh-agent $SHELL

7. Load the private key to the SSH agent on the local-host

[local-host]$ ssh-add

Adding identity: /home/jsmith/.ssh2/id_dsa_2048_a.pub
Need passphrase for /home/jsmith/.ssh2/id_dsa_2048_a (2048-bit dsa,
jsmith@local-host, Sun Oct 19 2008 14:49:42 -0700).
Enter passphrase:[Enter your passphrase here]

8. Perform SSH or SCP from local-host to remote-home without entering the password

[local-host]$ [You are on local-host here]

[local-host]$ ssh -l jsmith remote-host
Last login: Sun Oct 19 14:20:48 2008 from 192.168.1.10

[remote-host]$ [You are on remote-host here]

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Post from: The Geek Stuff

How To Perform SSH and SCP Without Password from SSH2 to OpenSSH