Category Archives: Linux

Reclaim Space in a VM on Thin or Thick VMDKs

[root@rac1 ~]$ yum install zerofree
updates/metalink | 12 kB 00:00
updates | 4.5 kB 00:00
updates/primary_db | 4.3 MB 00:21
Setting up Install Process
Resolving Dependencies
Running transaction check
Package zerofree.i686 0:1.0.1-8.fc15 will be installed
Finished Dependency Resolution

Dependencies Resolved

Package Arch Version Repository Size
zerofree i686 1.0.1-8.fc15 fedora 20 k

Transaction Summary
Install 1 Package

Total download size: 20 k
Installed size: 20 k
Is this ok [y/N]: y
Downloading Packages:
zerofree-1.0.1-8.fc15.i686.rpm | 20 kB 00:00
Running Transaction Check
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Installing : zerofree-1.0.1-8.fc15.i686 1/1

zerofree.i686 0:1.0.1-8.fc15

For Debian/Ubuntu:
[root@rac1 ~]$ apt-get install zerofree
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 17 not upgraded.
Need to get 7,272 B of archives.
After this operation, 61.4 kB of additional disk space will be used.
Get:1 oneiric/universe zerofree amd64 1.0.1-2ubuntu1 [7,272 B]
Fetched 7,272 B in 0s (41.5 kB/s)
Selecting previously deselected package zerofree.
(Reading database ... 22748 files and directories currently installed.)
Unpacking zerofree (from .../zerofree_1.0.1-2ubuntu1_amd64.deb) ...
Processing triggers for man-db ...
Setting up zerofree (1.0.1-2ubuntu1) ...

Then you need to mount the partition as read-only and run zerofree on it. If you need perform this on your OS/root partition, then power off your VM and attach the OS disk to another Linux VM. Here is how it looks like:

[root@rac1 ~]$ mount -o remount,ro /dev/mapper/test-lvol0
[root@rac1 ~]$ zerofree -v /dev/mapper/test-lvol0

How to Add Linux route ?

You can use any one of the following tool to add, display, delete Linux kernel routing table:

(a) route command : show / manipulate the IP routing table on Linux.

(b) ip command : show / manipulate routing, devices, policy routing and tunnels on Linux.

Display your current routing table

Open the Terminal or login to server using ssh/console. Type the  following command to display routing table:

# route
# route -n


 # ip route show
 # ip route list

Linux add a default route using route  command

Route all traffic via gateway connected via eth0 network interface:

 # route add default gw eth0

Linux add a default gateway (route) using ip command

Route all traffic via gateway connected via eth0 network interface:

 # ip route add dev eth0

Verify newly added route ip in the Linux kernel routing table

To verify new routing table, enter:
 # ip route list
 # route -n

How do I make routing changes persistent across reboots?

To make route entry persistent in the Linux kernel routing table, you need to modify config file as per your Linux distributions.

RHEL/CentOS/Fedora/Scientific Linux persistent routing configuration

Edit /etc/sysconfig/network and set default gateway IP address:
# vi /etc/sysconfig/network
Sample outputs:


You can add additional static route for eth0 by editing /etc/sysconfig/network-scripts/route-eth0 file as follows: via

The above config sets static routing for network via router.

Debian / Ubuntu Linux persistence static routing configuration

Edit /etc/network/interfaces file, enter:
# vi /etc/network/interfaces
Append the following in eth0 section:

up route add -net netmask gw
down route del -net netmask gw

Save and close the file.

Generic method to add persistent static routing on Linux

The following method works with almost all Linux distributions.

Edit /etc/rc.d/rc.local or /etc/rc.local, enter
# vi /etc/rc.local
Append the following line:

/sbin/ip route add dev eth0

Save and close the file.

ifconfig command not found on CentOS 7

On CentOS 6.x and before, ifconfig command by default used to  shipped. Whereas in minimal installed CentOS 7 , I have not found ifconfig command.

This will give you the error , ifconfig command not found.

To get the ifconfig command into our system , run the below given command

yum install net-tools

Now check the ifconfig command and its path in system (which and whereis command will help)

ifconfig -a
which ifconfig
whereis ifconfig

How I got to know net-tools package need to be installed

Using yum command with provides or whatprovides options help to give you list of package which is required for that particular command.

As per man page of yum :

provides or whatprovides
Is used to find out which package provides some feature or file. Just use a specific name or a file-glob-syntax wildcards to list the packages available or installed that provide that feature or file.

We have used the below given command to find which package provides the ifconfig command.

yum provides ifconfig

Below screenshot is last section of command output.


How to Rescan new LUN’s added in Linux, HP-UX, Aix, Solaris ?


1. Rescan the devices:

ioscan -fnC <disk|tape>

2. Generate device files:

 insf -e

3. Verify the new devices:

 ioscan -funC <disk|tape>


1. Rescan the devices ):

 cfgmgr -vl fcsx

Where x is FC adapter number

2. Verify the new devices:

 lsdev -Cc <disk|tape>


The rescan in Linux is HBA-specific.

For QLogic:

echo scsi-qlascan > /proc/scsi/qla<model#>/<adapter instance>

For Emulex:

 sh lpfc<adapter-instance>

For each identified device, run the following:

echo scsi add-single-device <host> <channel> <ID> <lun> >   /proc/scsi/scsi


1. Determine the FC channels:

 cfgadm -al

2. Force rescan :

 cfgadm -o force_update -c configure cx

Where x is the FC channel number

3. Force rescan at HBA port level:

 luxadm -e forcelip /dev/fc/fpx

4. Force rescan on all FC devices:

 cfgadm -al -o show_FCP_dev

5. Install device files:


6. Display all Qlogic HBA ports

 luxadm -e port

7. Display HBA port information

 luxadm -v display <WWPN>

8. Display HBA port information

 luxadm -e dump_map

Notes If one specific SANclient is missing a drive, please verify that your zoning is correct. Please also make sure the host initiator and VTL™s target ports are showing online via the Fibre Channel switch. (Check HBA link light and check the cable.)


How to Mount NFS From Linux To AIX

Linux :

  1. SSH to the Linux box
  2. Add an entry in the /etc/hosts to add the AIX server IP and hostname, if it is not already there
  3. Specify the file system to be exported in the /etc/exports file
    /data X.X.X.X
  4. Start the nfs service, if it has not already been started
    [root@linux ~]# service nfs status
    rpc.mountd (pid 3170) is running…
    nfsd (pid 3167 3166 3165 3164 3163 3162 3161 3160) is running…
    rpc.rquotad (pid 3145) is running…
    [root@linux ~]# service nfs restart
    Shutting down NFS mountd: [ OK ]
    Shutting down NFS daemon: [ OK ]
    Shutting down NFS quotas: [ OK ]
    Shutting down NFS services: [ OK ]
    Starting NFS services: [ OK ]
    Starting NFS quotas: [ OK ]
    Starting NFS daemon: [ OK ]
    Starting NFS mountd: [ OK ]
  5. Run the exportfs command to export the file system
    # exportfs -a


  1. Add an entry in the /etc/hosts for the Linux box, if it is not already there.
  2. Run the showmount command to check if AIX can see the exported file system
    # showmount -e X.X.X.X 
  3. Create a directory to mount the NFS
    # mkdir /data 
  4. Run the mount command to mount the exported NFS
    # mount X.X.X.X:/data /data 
  5. If not able to mount and the error message is “vmount: operation not permitted“, run the command below. Detailed explanation here.
    #  nfso -p -o nfs_use_reserved_ports=1
  6. Try the mount command again.
  7. If successful, try to access the directory.

Where are yum downloaded packages saved in linux?

The packages will be saved in /var/cache/yum/<repo-name>/packages/

You have to edit the /etc/yum.conf
from : keepcache=0 to : keepcache=1

keepcache=0  { Remove packages after successful instillation }

keepcache=1  { Keep packages after successful instillation }

[root@sip3 base]# cat /etc/yum.conf

# Note: yum-RHN-plugin doesn't honor this.

installonly_limit = 5

# PUT YOUR REPOS HERE OR IN separate files named file.repo
# in /etc/yum.repos.d
[rootsip3 base]#

How to configure Proxy Settings for the Unix / Linux Console

You can use the following methods to configure your console to use a proxy server so that console based programs like wget could get connect to the internet through the proxy.

1 – Set the environment variable
# export http_proxy=http://DOMAIN\USERNAME:PASSWORD@SERVER:PORT/

In the above configuration you can ommit the DOMAIN\USERNAME:PASSWORD@ part if you are not using proxy authentication.

Note: If you get the following error when you try to use wget, you might have to pass the proxy authentication credentials to wget as arguments.

Connecting to SERVER:PORT... connected.
Proxy request sent, awaiting response... 407 Proxy Authentication Required
11:14:45 ERROR 407: Proxy Authentication Required.
1.1 – Passing proxy authentication credentials to wget as arguments
$ wget --proxy-user "DOMAIN\USERNAME" --proxy-passwd "PASSWORD" URL
2 – Configure the proxy settings in the .bashrc
If you want set the proxy for all the users you can do it in the system wide .bashrc file.

nano /etc/bash.bashrc#proxy settings

Note: The system wide .bashrc file may not be available in all Linux systems and only can be used if you are using the bash shell

2.1 – Having an alias for wget with proxy
If you don’t want to pass the proxy arguments to wget all the time, you create an alias for wget in the .bashrc file

alias wget 'wget --proxy-user "DOMAIN\USERNAME" --proxy-passwd "PASSWORD"'

How to Unzip Multiple Files from Linux / Unix single Command Line

bash-3.2# ls *.zip

Problem :

bash-3.2# unzip *.zip
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:
caution: filename not matched:

Solution :

Use single quotes [ ‘  ‘ ]
bash-3.2# unzip ‘*.zip’
inflating: 146470-08/LEGAL_LICENSE.TXT
inflating: 146470-08/prepatch
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/EST
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/tab/
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/tab/
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Broken_Hill
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Eucla
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Melbourne
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Sydney
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Adelaide
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Perth
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Lord_Howe
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Hobart
inflating: 146470-08/SUNWcsu/reloc/usr/share/lib/zoneinfo/Australia/Currie