How to configure the DNS in Unix and Linux servers?

How to configure the DNS in Unix and Linux servers?


A) Steps:

First Create the file called /etc/resolv.conf - which includes the primary and secondary DNS server IP address for UNIX system, its your own DNS server.

# touch /etc/resolv.conf
# vi /etc/resolv.conf (Add the following lines to it)
domain test-lob.com  
nameserver ipaddress
nameserver ipaddress
Where, nameserver IP: It is IP of first DNS server and secondary DNS server of test-lob.com.


Search test-lob.com: Default domain name to search.

For example, if you type command nslookup www, it will search it as www.test-lob.com

For AIX Enable the name resolving using DNS as follows:
Edit the file /etc/netsvc.conf so that the “host =” will be pointing to local and dns as in the following
hosts=local,bind

For Solaris and Linux, Enable the name resolving using DNS as follows:
Edit the file /etc/nsswitch.conf so that the “host:” will be pointing to local and dns as in the following
hosts: files dns

B). VALIDATION REQUIREMENTS
Check with nslookup it should be able to resolve the host to IP and IP to host as in the following example
# nslookup
Default Server: change.test-lob.com
Address: 10.14.15.16
> lotus

Server: change.test-lob.com
Address: 10.14.15.16

Name: lotus.test-lob.com
Address: 10.120.12.6

Resolve from IP to host:
nslookup 10.120.12.6

Server: change.test-lob.com
Address: 10.14.15.16


Name: lotus.test-lob.com
Address: 10.120.12.6


C). ROLL BACK
AIX:
Remove the entries you have added in the /etc/netsvc.conf , so that the server will point to local host configuration file ( /etc/hosts ) only.

LINUX & SOLARIS:
Remove the entries you have added in the /etc/nsswitch.conf so that the server will point to local host configuration file ( /etc/hosts ) only.

How to mirror the rootvg in AIX?

How to mirror the rootvg in AIX?

How to mirror the rootvg in AIX?

This procedure is to assume the rootvg having hdisk0 and we need to take a mirror to hdisk1. 

Pre-Work:

                   Make sure the hdisk0 and the hdisk1 are in the same size. check the size with the #bootinfo -s hdisk1" command

          
Steps:

     

1. Add hdisk1 to rootvg:
         extendvg rootvg hdisk1

2. Mirror rootvg to hdisk1:
         mirrorvg rootvg hdisk1 (or smitty mirrorvg)

3. Create boot images on hdisk1:
         bosboot -ad /dev/hdisk1

4. Add hdisk1 to the bootlist:

                                     bootlist -m normal hdisk0 hdisk1  

Validation:

Validation:

·         Execute the below commands and ensure that the number of PPs is double than number than LPs.

             # lsvg –l rootvg

rootvg:

LV NAME   TYPE       LPs     PPs     PVs  LV STATE      MOUNT POINT

hd5                 boot       1       2       2    closed/syncd  N/A

hd6                 paging     105     210     2    open/syncd    N/A

hd8                 jfs2log    1       2       2    open/syncd    N/A

hd4                 jfs2       16      32      2    open/syncd    /

hd2                 jfs2       40      80      2    open/syncd    /usr

hd9var              jfs2       40      80      2    open/syncd    /var

hd3                 jfs2       40      80      2    open/syncd    /tmp

hd1                 jfs2       16      32      2    open/syncd    /home

hd10opt             jfs2       40      80      2    open/syncd    /opt

Rollback:

1. Un-Mirror rootvg to hdisk0:

unmirrorvg rootvg hdisk1

2. Reduce the hdisk0 from Rootvg

reducevg rootvg hdisk1

3. delete the bootimage from hdisk1

chpv -c hdisk1

4. Add hdisk0 only to the bootlist:

bootlist -m normal hdisk0

Downtime details:

·        No downtime required.

How to recover a deleted file in aix?

How to recover a deleted file in aix?

It is possible to recover the file using the "fsdb" command (filesystem debugger). when,

No new files have been created on the filesystem.

No files have been extended.

The filesystem is able to be unmounted.

Warning: I have test this in my test server. This is undocumented one. You may facing the critical problem when you follow the below steps on your systems. So try this at your own risk. Please avoid directly try this with your production servers. Here is the output for your reference.

# lsvg -l testvg

testvg:

LV NAME             TYPE       LPs   PPs   PVs  LV STATE      MOUNT POINT

loglv00             jfs2log    1     1     1    closed/syncd  N/A

#

# crfs -a size=256M -v jfs2 -g testvg -m /new            à create a "/new" FS

File system created successfully.

261932 kilobytes total disk space.

New File System size is 524288

#

# lsvg -l testvg

testvg:

LV NAME             TYPE       LPs   PPs   PVs  LV STATE      MOUNT POINT

loglv00             jfs2log    1     1     1    closed/syncd  N/A

fslv00              jfs2       16    16    1    closed/syncd  /new

#

# mount /new         à mount the /new FS

#

# lsvg -l testvg

testvg:

LV NAME             TYPE       LPs   PPs   PVs  LV STATE      MOUNT POINT

loglv00             jfs2log    1     1     1    open/syncd    N/A

fslv00              jfs2       16    16    1    open/syncd    /new

#

# cd /new

#

# ls -l

total 0

drwxr-xr-x   2 root     system          256 Apr 03 16:47 lost+found

#

# cat >> film         à Create a file named “film”

Hi this is the test file. I want to use this file for recovery test

^C#

#

# cat film

Hi this is the test file. I want to use this file for recovery test

#

# ls –il        à check the inode number of the file “film”. That is 4

total 8

    4 -rw-r--r--   1 root     system           68 Apr 03 16:49 film

    3 drwxr-xr-x   2 root     system          256 Apr 03 16:47 lost+found

#

#

# rm film     à remove the file “film”

#

# ls -l

total 0

drwxr-xr-x   2 root     system          256 Apr 03 16:47 lost+found

#

# cd ~

#

# umount /new     à unmount the /new FS

#

# lsvg -l testvg

testvg:

LV NAME             TYPE       LPs   PPs   PVs  LV STATE      MOUNT POINT

loglv00             jfs2log    1     1     1    closed/syncd  N/A

fslv00              jfs2       16    16    1    closed/syncd  /new

#

# fsdb /dev/fslv00       à use the “fsdb ” to recover the deleted  file.

File System:                    /dev/fslv00

File System Size:               523864  (512 byte blocks)

Aggregate Block Size:           4096

Allocation Group Size:          8192    (aggregate blocks)

> dir 2

 idotdot = 2

 3      lost+found

> 

> i 4     à provide the inode number of our deleted file. That is 4

Inode 4 at block 33, offset 0x800:

[1] di_fileset:         16                 [18] di_inostamp:       0x4d98ead4

[2] di_number:          4               [19] di_gen:            3940655789

[3] di_size:    0x0000000000000044      [20] di_ixpxd.len:      4

[4] di_nblocks: 0x0000000000000001      [21] di_ixpxd.addr1:    0x00

[5] di_nlink:           0               [22] di_ixpxd.addr2:    0x00000021

[6] di_mode:            0x000081a4           di_ixpxd.address:  33

                 0100644 -rw-r--r--      [24] di_uid:            0

                                        [25] di_gid:            0

[9] di_atime.tj_nsec:   0x1e8a1025      [26] di_atime.tj_sec:0x000000004d98eb7d

[10] di_ctime.tj_nsec:  0x0ca85614      [27] di_ctime.tj_sec:0x000000004d98ebac

[11] di_mtime.tj_nsec:  0x1af63892      [28] di_mtime.tj_sec:0x000000004d98eb77

[12] di_otime.tj_nsec:  0x03b74a9a      [29] di_otime.tj_sec:0x000000004d98eb24

[13] di_ea.flag:        0x00            [30] di_ea.len:         0

     EAv1                               [31] di_ea.addr1:       0x00

[15] di_ea.nEntry:      0x00            [32] di_ea.addr2:       0x00000000

[16] di_ea.type:        0x0000               di_ea.address:     0

                                        [34] di_ea.nblocks:     0

change_inode: [m]odify, [e]a, [t]ree, or e[x]it > m     à choose “m” to modify

Please enter: field-number value > 5  1   à  put the field number is 5, change the di_nlink value to 1

Inode 4 at block 33, offset 0x800:

[1] di_fileset:         16              [18] di_inostamp:       0x4d98ead4

[2] di_number:          4               [19] di_gen:            3940655789

[3] di_size:    0x0000000000000044      [20] di_ixpxd.len:      4

[4] di_nblocks: 0x0000000000000001      [21] di_ixpxd.addr1:    0x00

[5] di_nlink:           1               [22] di_ixpxd.addr2:    0x00000021

[6] di_mode:            0x000081a4           di_ixpxd.address:  33

                 0100644 -rw-r--r--      [24] di_uid:            0

                                        [25] di_gid:            0

[9] di_atime.tj_nsec:   0x1e8a1025      [26] di_atime.tj_sec:0x000000004d98eb7d

[10] di_ctime.tj_nsec:  0x0ca85614      [27] di_ctime.tj_sec:0x000000004d98ebac

[11] di_mtime.tj_nsec:  0x1af63892      [28] di_mtime.tj_sec:0x000000004d98eb77

[12] di_otime.tj_nsec:  0x03b74a9a      [29] di_otime.tj_sec:0x000000004d98eb24

[13] di_ea.flag:        0x00            [30] di_ea.len:         0

     EAv1                               [31] di_ea.addr1:       0x00

[15] di_ea.nEntry:      0x00            [32] di_ea.addr2:       0x00000000

[16] di_ea.type:        0x0000               di_ea.address:     0

                                        [34] di_ea.nblocks:     0

change_inode: [m]odify, [e]a, [t]ree, or e[x]it > x    à exit

> quit

#

# fsck -yp /dev/fslv00     à run fsck to repaired the  inconsistencies.

The current volume is: /dev/fslv00

Primary superblock is valid.

J2_LOGREDO:log redo processing for /dev/fslv00

logredo start at:  1301867616 sec and end at  1301867616 sec

Primary superblock is valid.

*** Phase 1 - Initial inode scan

*** Phase 2 - Process remaining directories

*** Phase 3 - Process remaining files

*** Phase 4 - Check and repair inode allocation map

File system inode map is corrupt (FIXED)

Superblock marked dirty because repairs are about to be written.

*** Phase 5 - Check and repair block allocation map

Block allocation map is corrupt (FIXED)

Inodes not connected to the root directory

         tree have been detected.  Will reconnect.

File system is clean.

Superblock is marked dirty (FIXED)

All observed inconsistencies have been repaired.

#

# mount /new   à mount the /new FS

# lsvg -l testvg

testvg:

LV NAME             TYPE       LPs   PPs   PVs  LV STATE      MOUNT POINT

loglv00             jfs2log    1     1     1    open/syncd    N/A

fslv00              jfs2       16    16    1    open/syncd    /new

#

# cd /new  à goto the /new FS

#

# ls -l

total 0

drwxr-xr-x   2 root     system          256 Apr 03 16:47 lost+found

#

# cd lost+found   à go to lost+found dir

#

# pwd

/new/lost+found

#

# ls -l

total 8

-rw-r--r--   1 root     system           68 Apr 03 16:49 4     à you can see the deleted file in the name of your inode number

#

# cat 4   à confirm the file content

Hi this is the test file. I want to use this file for recovery test

#

# mv 4 /new/.      à move the file to the exact place where it was before

#

# pwd

/new/lost+found

# cd ..

#

# pwd

/new

# ls -l

total 8

-rw-r--r--   1 root     system           68 Apr 03 16:49 4

drwxr-xr-x   2 root     system          256 Apr 03 16:55 lost+found

#

# cat 4

Hi this is the test file. I want to use this file for recovery test

#

# mv 4 film  à change the name of the recovered file to the old one.

#

# ls -l

total 8

-rw-r--r--   1 root     system           68 Apr 03 16:49 film   à the deleted file has been recovered.

drwxr-xr-x   2 root     system          256 Apr 03 16:55 lost+found