IP Address Configuration in UBUNTU

IP Addressing

The following section describes the process of configuring your systems IP address and default gateway needed for communicating on a local area network and the Internet.

Temporary IP Address Assignment

For temporary network configurations, you can use standard commands such as ip, ifconfig and route, which are also found on most other GNU/Linux operating systems. These commands allow you to configure settings which take effect immediately, however they are not persistent and will be lost after a reboot.

To temporarily configure an IP address, you can use the ifconfig command in the following manner. Just modify the IP address and subnet mask to match your network requirements.

sudo ifconfig eth0 10.0.0.100 netmask 255.255.255.0

To verify the IP address configuration of eth0, you can use the ifconfig command in the following manner.

ifconfig eth0

eth0      Link encap:Ethernet  HWaddr 00:15:c5:4a:16:5a 

          inet addr:10.0.0.100  Bcast:10.0.0.255  Mask:255.255.255.0

          inet6 addr: fe80::215:c5ff:fe4a:165a/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:466475604 errors:0 dropped:0 overruns:0 frame:0

          TX packets:403172654 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000

          RX bytes:2574778386 (2.5 GB)  TX bytes:1618367329 (1.6 GB)

          Interrupt:16

To configure a default gateway, you can use the route command in the following manner. Modify the default gateway address to match your network requirements.

sudo route add default gw 10.0.0.1 eth0

To verify your default gateway configuration, you can use the route command in the following manner.

route -n

Kernel IP routing table

Destination     Gateway         Genmask         Flags Metric Ref    Use Iface

10.0.0.0        0.0.0.0         255.255.255.0   U     1      0        0 eth0

0.0.0.0         10.0.0.1        0.0.0.0         UG    0      0        0 eth0

If you require DNS for your temporary network configuration, you can add DNS server IP addresses in the file/etc/resolv.conf. The example below shows how to enter two DNS servers to /etc/resolv.conf, which should be changed to servers appropriate for your network. A more lengthy description of DNS client configuration is in a following section.

nameserver 8.8.8.8

nameserver 8.8.4.4

If you no longer need this configuration and wish to purge all IP configurations from an interface, you can use the ip command with the flush option as shown below.

ip addr flush eth0

Note:
	Flushing the IP configuration using the ip command does not clear the contents of /etc/resolv.conf. You must remove or modify those entries manually.

Dynamic IP Address Assignment (DHCP Client)

To configure your server to use DHCP for dynamic address assignment, add the dhcp method to the inet address family statement for the appropriate interface in the file /etc/network/interfaces. The example below assumes you are configuring your first Ethernet interface identified as eth0.

auto eth0

iface eth0 inet dhcp

By adding an interface configuration as shown above, you can manually enable the interface through the ifup command which initiates the DHCP process via dhclient.

sudo ifup eth0

To manually disable the interface, you can use the ifdown command, which in turn will initiate the DHCP release process and shut down the interface.

sudo ifdown eth0

Static IP Address Assignment

To configure your system to use a static IP address assignment, add the static method to the inet address family statement for the appropriate interface in the file /etc/network/interfaces. The example below assumes you are configuring your first Ethernet interface identified as eth0. Change the address, netmask, and gateway values to meet the requirements of your network.

auto eth0

iface eth0 inet static

address 10.0.0.100

netmask 255.255.255.0

gateway 10.0.0.1

By adding an interface configuration as shown above, you can manually enable the interface through the ifup command.

sudo ifup eth0

To manually disable the interface, you can use the ifdown command.

sudo ifdown eth0

Loopback Interface

The loopback interface is identified by the system as lo and has a default IP address of 127.0.0.1. It can be viewed using the ifconfig command.

ifconfig lo

lo        Link encap:Local Loopback 

          inet addr:127.0.0.1  Mask:255.0.0.0

          inet6 addr: ::1/128 Scope:Host

          UP LOOPBACK RUNNING  MTU:16436  Metric:1

          RX packets:2718 errors:0 dropped:0 overruns:0 frame:0

          TX packets:2718 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0

          RX bytes:183308 (183.3 KB)  TX bytes:183308 (183.3 KB)

By default, there should be two lines in /etc/network/interfaces responsible for automatically configuring your loopback interface. It is recommended that you keep the default settings unless you have a specific purpose for changing them. An example of the two default lines are shown below.

auto lo

iface lo inet loopback

Creation of raw device for oracle table Space datafiles.

Creation of raw device for oracle table Space datafiles. (Unix Team Activity)

Recently the following storage has been created (on UAT):

/dev/sdao

/dev/sdap

Each of the above raw devices is hosted from the XP1024 storage array, and can accommodate 5 x 8gb devices to be allocated to the database.

The following instructions assume that the user is root, and the oracle environments are fully down.

1)     Partition the new devices using fdisk following below partition table for cylinder guidance, repeating for all new devices sdao and sdap, start on serverdb1:

# fdisk /dev/sdao

Disk /dev/sdao: 42.9 GB, 42949672960 bytes

255 heads, 63 sectors/track, 5221 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System

/dev/sdao1               1        1045     8393931   83  Linux

/dev/sdao2            1046        2090     8393962+  83  Linux

/dev/sdao3            2091        3135     8393962+  83  Linux

/dev/sdao4            3136        5221    16755795    5  Extended

/dev/sdao5            3136        4180     8393931   83  Linux

/dev/sdao6            4181        5221     8361801   83  Linux

And…

Disk /dev/sdap: 44.1 GB, 44197360640 bytes

255 heads, 63 sectors/track, 5373 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System

/dev/sdap1               1        1075     8634906   83  Linux

/dev/sdap2            1076        2150     8634937+  83  Linux

/dev/sdap3            2151        3225     8634937+  83  Linux

/dev/sdap4            3226        5373    17253810    5  Extended

/dev/sdap5            3226        4300     8634906   83  Linux

/dev/sdap6            4301        5373     8618841   83  Linux

2)     Once the above partitions tables have been added and written to serverdb1, go to serverdb2 and fdisk the same devices. The partitions tables should already be populated as per serverdb1, just ensure you write the partition tables to commit these changes.

3)     Backup /etc/DATA_RAC_RAW file on serverdb1 and serverdb2 and edit /etc/DATA_RAC_RAW to reflect the addition of the new devices, e.g.

# cp /etc/DATA_RAC_RAW /etc/DATA_RAC_RAW.preCMxxxxx

Append the following new entries in /etc/DATA_RAC_RAW onto the end of the existing files

/dev/eudata/unused24_8g:/dev/sdao1:c:162:266:8010

/dev/eudata/unused25_8g:/dev/sdao2:c:162:267:8010

/dev/eudata/unused26_8g:/dev/sdao3:c:162:268:8010

/dev/eudata/unused27_8g:/dev/sdao5:c:162:269:8010

/dev/eudata/unused28_8g:/dev/sdao6:c:162:270:8010

/dev/eudata/unused29_8g:/dev/sdap1:c:162:271:8010

/dev/eudata/unused30_8g:/dev/sdap2:c:162:272:8010

/dev/eudata/unused31_8g:/dev/sdap3:c:162:273:8010

/dev/eudata/unused32_8g:/dev/sdap5:c:162:274:8010

/dev/eudata/unused33_8g:/dev/sdap6:c:162:275:8010

4)     For each newly added device, make the character devices on serverdb1 and serverdb2

Using the above devices (repeat for all new devices), example:

# mknod /dev/eudata/unused24_8g c 162 266

# chown oracle:dba /dev/eudata/unused24_8g

Note that the minor number (266 in this case) must be unique in the OS and therefore must be incremented with each new device, 266…267… as per the above entries in the /etc/DATA_RAC_RAW file

mknod /dev/eudata/unused24_8g c 162 266

mknod /dev/eudata/unused25_8g c 162 267

mknod /dev/eudata/unused26_8g c 162 268

mknod /dev/eudata/unused27_8g c 162 269

mknod /dev/eudata/unused28_8g c 162 270

mknod /dev/eudata/unused29_8g c 162 271

mknod /dev/eudata/unused30_8g c 162 272

mknod /dev/eudata/unused31_8g c 162 273

mknod /dev/eudata/unused32_8g c 162 274

mknod /dev/eudata/unused33_8g c 162 275

5)     Bind new raw devices on both nodes, serverdb1 first, then serverdb2

Using the above example device (repeat for all new devices):

# raw /dev/eudata/unused24_8g /dev/sdao1

raw /dev/eudata/unused25_8g /dev/sdao2

raw /dev/eudata/unused26_8g /dev/sdao3

raw /dev/eudata/unused27_8g /dev/sdao5

raw /dev/eudata/unused28_8g /dev/sdao6

raw /dev/eudata/unused29_8g /dev/sdap1

raw /dev/eudata/unused20_8g /dev/sdap2

raw /dev/eudata/unused31_8g /dev/sdap3

raw /dev/eudata/unused32_8g /dev/sdap5

raw /dev/eudata/unused33_8g /dev/sdap6

-- At this point we have successfully added the new devices to Linux. The devices (“unused*”) will be ready to allocate when necessary, and can be allocated without any disruption to the Oracle environment as steps 1-5 have been completed.

6)     Release the system to the dba’s to add the new devices to oracle and test.

Linux Command History Advanced Features

Linux Command History Advanced Features

“History” command is a very important command in Linux to check the last executed commands in your system. We can use “history” command in some advanced manner with using some extra functionality. You can find this command more enjoyable by using following document.

1.    Display Time Format using HISTSIZEFORMAT

When you run simple “history” it displays only number of command and last running command. For auditing purpose the time for running command is important. Timestamp can be added in history command as shown below.

# export HISTTIMEFORMAT="%F %T "

# history | more

   1  2012-09-12 10:48:00 ls

   2  2012-09-12 10:48:07 history

   3  2012-09-12 10:48:24 ls -ltr

   4  2012-09-12 10:54:57 ls

   5  2012-09-12 10:55:05 ls -ltr

   6  2012-09-12 10:55:22 cat ff_unix

2.    Search the history using Control+R

When you’ve already executed a very long command, you can simply search history using a keyword and re-execute the same command without having to type it fully. Press Control+R and type the keyword. In the following example, I searched for red, which displayed the previous command “cat /etc/redhat-release” in the history that contained the word red.In the following example, I searched for red, which displayed the previous command “cat /etc/redhat-release” in the history that contained the word red.

# [Press Ctrl+R from the command Prompt, which will display reverse –i-search prompt.]

(reverse-i-search)`red': cat /etc/redhat-release

[Note: Press enter when you you see command, which will execute from history.]

[root@qmailprd ~]# cat /etc/redhat-release

Red Hat Enterprise Linux Server release 6.2 (Santiago)

Sometimes you want to edit a command from history before executing it. For e.g. you can search for httpd, which will display service httpd stop from the command history, select this command and change the stop to start and re-execute it again as shown below.

# [Press Ctrl+R from the command prompt,which will display the reverse-i-search prompt]

(reverse-i-search)`httpd': service httpd stop

[Note: Press either left arrow or right arrow key when you see your

command, which will display the command for you to edit, before executing it]

# service httpd start

3.    Repeat previous command quickly using 4 different methods

Sometime you may end up repeating the previous commands for various reasons. Following are the 4 different ways to repeat the last executed command.

1.    Use the up arrow to view the previous command and press enter to execute it.

2.    Type !! and press enter from the command line

3.    Type !-1 and press enter from the command line.

4.    Press Control+P will display the previous command, press enter to execute it

4. Execute a specific command from history

In the following example, If you want to repeat the command #998, you can do !998 as shown below

  997  vi pop3d-ssl

  998  pwd

  999  openssl s_client -connect localhost:993 -quiet

 1000  history

 1001  cat /etc/issue

 1002  cat /etc/redhat-realease

 1003  history

[root@qmailprd ~]# !998

pwd

/root

5. Execute previous command that starts with a specific word

Type ! followed by the starting few letters of the command that you would like to re-execute. In the following example, typing !ps and enter, executed the previous command starting with ps, which is ‘ps aux | grep http’.

[root@qmailprd ~]# !ps

ps -ef | grep http

root      1830     1  0 Aug03 ?        00:00:35 /usr/sbin/httpd

apache   22502  1830  0 Sep16 ?        00:00:00 /usr/sbin/httpd

apache   22503  1830  0 Sep16 ?        00:00:00 /usr/sbin/httpd

6. Control the total number of lines in the history using HISTSIZE

Append the following two lines to the .bash_profile and relogin to the bash shell again to see the change. In this example, only 1500 command will be stored in the bash history.

# vi ~/.bash_profile

HISTSIZE=1500

HISTFILESIZE=1500

7. Change the history file name using HISTFILE

By default, history is stored in ~/.bash_history file. Add the following line to the .bash_profile and relogin to the bash shell, to store the history command in .commandline_warrior file instead of .bash_history file. I’m yet to figure out a practical use for this. I can see this getting used when you want to track commands executed from different terminals using different history file name.

# vi ~/.bash_profile

HISTFILE=/root/.commandline_warrior

8. Eliminate the continuous repeated entry from history using HISTCONTROL

In the following example pwd was typed three times, when you do history, you can see all the 3 continuous occurrences of it. To eliminate duplicates, set HISTCONTROL to ignoredups as shown below.

# pwd

# pwd

# pwd

# history | tail -4

44  pwd

45  pwd

46  pwd [Note that there are three pwd commands in history, after

executing pwd 3 times as shown above]

47  history | tail -4

# export HISTCONTROL=ignoredups

# pwd

# pwd

# pwd

# history | tail -3

56  export HISTCONTROL=ignoredups

57  pwd [Note that there is only one pwd command in the history, even after

executing pwd 3 times as shown above]

58  history | tail -4

9. Erase duplicates across the whole history using HISTCONTROL

The ignoredups shown above removes duplicates only if they are consecutive commands. To eliminate duplicates across the whole history, set the HISTCONTROL to erasedups as shown below.

# export HISTCONTROL=erasedups

# pwd

# service httpd stop

# history | tail -3

38  pwd

39  service httpd stop

40  history | tail -3

# ls -ltr

# service httpd stop

# history | tail -6

35  export HISTCONTROL=erasedups

36  pwd

37  history | tail -3

38  ls -ltr

39  service httpd stop

[Note that the previous service httpd stop after pwd got erased]

40  history | tail -6

10. Force history not to remember a particular command using HISTCONTROL

When you execute a command, you can instruct history to ignore the command by setting HISTCONTROL to ignorespace AND typing a space in front of the command as shown below. I can see lot of junior sysadmins getting excited about this, as they can hide a command from the history. It is good to understand how ignorespace works. But, as a best practice, don’t hide purposefully anything from history.

# export HISTCONTROL=ignorespace

# ls -ltr

# pwd

#  service httpd stop [Note that there is a space at the beginning of service,

to ignore this command from history]

# history | tail -3

67  ls -ltr

68  pwd

69  history | tail -3

 

11. Clear all the previous history using option -c

Sometime you may want to clear all the previous history, but want to keep the history moving forward.

# history -c

12. Subtitute words from history commands

When you are searching through history, you may want to execute a different command but use the same parameter from the command that you’ve just searched.

In the example below, the !!:$ next to the vi command gets the argument from the previous command to the current command.

# ls anaconda-ks.cfg

anaconda-ks.cfg

# vi !!:$

vi anaconda-ks.cfg

In the example below, the !^ next to the vi command gets the first argument from the previous command (i.e cp command) to the current command (i.e vi command).

# cp anaconda-ks.cfg anaconda-ks.cfg.bak

anaconda-ks.cfg

# vi  !^

vi anaconda-ks.cfg

 

 

13. Substitute a specific argument for a specific command.

In the example below, !cp:2 searches for the previous command in history that starts with cp and takes the second argument of cp and substitutes it for the ls -l command as shown below.

# cp ~/longname.txt /really/a/very/long/path/long-filename.txt

# ls -l !cp:2

ls -l /really/a/very/long/path/long-filename.txt

In the example below, !cp:$ searches for the previous command in history that starts with cp and takes the last argument (in this case, which is also the second argument as shown above) of cp and substitutes it for the ls -l command as shown below.

# ls -l !cp:$

ls -l /really/a/very/long/path/long-filename.txt

14. Disable the usage of history using HISTSIZE

If you want to disable history all together and don’t want bash shell to remember the commands you’ve typed, set the HISTSIZE to 0 as shown below.

# export HISTSIZE=0

# history

# [Note that history did not display anything]

15. Ignore specific commands from the history using HISTIGNORE

Sometimes you may not want to clutter your history with basic commands such as pwd and ls. Use HISTIGNORE to specify all the commands that you want to ignore from the history. Please note that adding ls to the HISTIGNORE ignores only ls and not ls -l. So, you have to provide the exact command that you would like to ignore from the history.

# export HISTIGNORE="pwd:ls:ls -ltr:"

# pwd

# ls

# ls -ltr

# service httpd stop

# history | tail -3

79  export HISTIGNORE="pwd:ls:ls -ltr:"

80  service httpd stop

81  history

[Note that history did not record pwd, ls and ls -ltr]