X11 connection rejected because of wrong authentication.

When you need to run an X window application over SSH.
You ssh -X into the remote machine, running X applications works fine, until you
sudo or su to another user to run an X application , You get the following error.
"X11 connection rejected because of wrong authentication.

X connection to localhost:10.0 broken (explicit kill or server shutdown)."

or if you connected using putty the error will read.
“Xlib: PuTTY X11 proxy: wrong authentication protocol attempted”.


How to fix?


ssh cgerada@remote-server -X


cgerada $ su – oracle
oracle‘s Password:
oracle $ xclock


"X11 connection rejected because of wrong authentication.
X connection to localhost:10.0 broken (explicit kill or server shutdown)".

or if you connected with putty the error reads


"Xlib: PuTTY X11 proxy: wrong authentication protocol attempted
xclock Xt error: Can’t open display: localhost:10.0"


On newer versions of  OpenSSH Server releases, you can simply enable “ForwardX11Trusted yes” in the /etc/ssh/sshd_config file and restart the OpenSSH server.
If you’re using an older version of  OpenSSH Server release then
You need to temporarily transfer the authorization to the other account. First, get the key from your account:
cgerada $ xauth list
fileserver/unix:10  MIT-MAGIC-COOKIE-96951c0622f80fd52186129dd06f2f6
Next, sudo/su to the other account and add the authorization key.
cgerada $ su – oracle
oracle $ xauth add fileserver/unix:10  MIT-MAGIC-COOKIE-96951c0622f80fd52186129dd06f2f6
Now, you should be able to start any X Windows application, 
oracle $ xclock

Installing Fedora 16 on a System that can not boot GPT Labelled Disks

Some Systems Particularly Fujitsu Siemens Life books, Apple Macs and some others,
Cannot Boot If the Hard drive is Formatted using this Newer GPT  format.

Fedora 16 uses the new GPT format since it does have some benefits.
However if you want to install Fedora 16 on a Lifebook or an Apple mac, you need to do the following.

You need to pass parameter nogpt to the Fedora installer.

To do this, at the initial bootloader menu for the Fedora installation, where you can select to install, install in basic graphics mode, boot to the rescue mode and so on, hit the Tab key, then edit the command line for the Fedora installer and add the word nogpt.  you can do this when using the Live CD or the Complete distribution DVD.

Then install as normal and your Machine should now boot and work as expected.

Do not choose custom partitioning layout, You must let the system create it's own layout first and then if you want , You can edit what it creates to suite your requirements. If you choose custom layout, the 1MB problematic BootBios partition is created and this will give you the following error "
"you have not created a bootloader stage1 target device"

mount.nfs: access denied by server while mounting

If your nfs mounts stop working
and mount-a gives you the following error.
mount.nfs: access denied by server while mounting /blah_blah_blah/blah_blah


Chances are, your machine has been upgraded and now uses the NFS version 4 as default nfs version
 instead of 3

To fix this issue you need to explicitly tell nfs to mount your share using the older nfs version 3

simply add nfsvers=3  to your nfs mount stanza in your /etc/fstab file


eg
vi /etc/fstab


192.168.1.10:/shared/files  /mnt/files nfs soft,intr,nfsvers=3 0 0

save the file and type
mount -a  

Your nfs mounts will now work.

Resolve transparency issues with Guake

If you set Guake to start automatically when your computer starts, depending on how quickly your Gnome session loads, there  may be an issue with it starting before Gnome has completed it's full initialization. 

when this happens, the transparency in quake does not work as it should, You cannot see the windows behind the Guake terminal, It lets you see your Background wallpaper only.

A solution for this is to delay the start up of Guake, so that Gnome is allowed to initialize fully before Guake starts.

To do this , run 

gnome-session-properties

under startup-programs edit your entry for Guake.

and add  sleep 8 && infront of guake, 
like so

 sleep 8 && guake 

This gives guake an 8 second delay before starting, and should be enough to let Gnome fully initialize, and your transparency will work as it should.

Problem mounting a LVM

To  manually mount a drive that contains a LVM (Logical Volume)
do the following.

lvdisplay

will output info about your logical volume
the important thing to note here is
the line which says VG Name
VG Name               vg_lvm

sometimes you will get a lv status as not available
to make it available type

vgchange -a y

this will activate any LVMS that werent active and make them available.

then to mount the LVM simply type

mount /dev/vg_lvm   /mnt

Problem installing Oracle Virtual box extension pack

If you would like to use the USB ports on your virtual machine in virtual box.
You need to install the virtual box extension pack available from the download section at www.virtualbox.org

However opening the downloaded extension pack from virtualbox and clicking the install button, sometimes gives the following error

"Failed to install the Extension Pack Oracle_VM_VirtualBox_Extension_Pack-.vbox-extpack.  The installer failed with exit code 127: The value for the SHELL variable was not found the /etc/shells file    This incident has been reported..  Result Code: NS_ERROR_FAILURE (0x80004005) Component: ExtPackManager Interface: IExtPackManager "

I find that installing the extension pack using the command line fixes this problem.
simply cd into the folder were the extension pack you downloaded resides,
and type the following. replacing the xxxx with the version of the extension pack you downloaded.

 sudo VBoxManage extpack install --replace Oracle_VM_VirtualBox_Extension_Pack-4.1.xxxx.vbox-extpack 


and it will install properly, you should get the following back.


0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
Successfully installed "Oracle VM VirtualBox Extension Pack".

Free up space on your hard drive.

ext2/ext3 and ext4, file systems automatically reserve space for themselves. (5% by default)
This is necessary for your root partition, so that  if you fill up the hard drive, Linux will still have space to write to the log files and to allow privileged processes to run so that they can avoid file system fragmentation.
However, if your hard disk is say a 650GB or bigger hard drive, that 5% amounts to a significant amount of disk space, and is a total overkill.
Additionally, you do not need this reserved space on hard drives that are only used for storage (ie are not part of your root partition)
so, how do we take back this valuable hard disk real estate ?
We use tune2fs.


so as an example,  type


tune2fs -m 1 /dev/sda2
to change the 5% to 1% on /dev/sda2


if /dev/sda was a 650GB hard drive this would give you an additional 26 GB Free!


tune2fs -m 0 /dev/sda2
will  reduce the 5% to 0%


to add reserved space for privileged processes back to a  drive
type
tune2fs -r 20000 /dev/sda2
will give back 20000 blocks, which should be more than sufficient


you can run tune2fs on  Logical volumes as well.


tune2fs -m 1 /dev/mapper/vg-lv_home 
will reclaim space from your logical volume


Just change /dev/mapper/vg/-lv_home to the name of your logical volume.
you can see all your volumes and partitions by typing df -h

Simple Webserver

python -m SimpleHTTPServer

Will serve your current Directory tree at
http://IP_of_machine_you_ran_the_command_on:8000

Serve current directory tree at http://$HOSTNAME:8000/

Check your spelling

yum install aspell

or apt-get install aspell for Ubuntu systems

then in future  when ever  you need to know how to spell a word simply type

aspell -a <<< 'word'

save man pages as pdf

man -t ls | ps2pdf - ls.pdf


Will save the man pages for ls to ls.pdf


substitute ls for the programme man pages you want to save as a pdf

Script Terminal Session

script -f /tmp/filename

will place all output of the terminal, including carriage returns, to a file (/tmp/filename)

So then on another terminal session type

tail -f /tmp/filename

 This file can be tail -f by one or more terminals to display Live the information of the main terminal.

Great  way to share your screen on short notice.

to Stop scripting type
 <Cntrl> D

Ascii Digital Clock

install banner

yum install banner
then type


watch -n1 'banner `date +%T`'

How To Add a start up script to be Run at Boot time in Ubuntu

First Save your script in

  /etc/init.d/

then type:

sudo update-rc.d script_name defaults

This script will now run each time you boot up.

sort the contents of a text file in place

This will sort the contents of a file without the need to pipe it into a second file.

great for cron jobs



sort -g name_of_file_to_sort.txt -o $_

Dropbox Free 2GB account

Always have your stuff when you need it with Dropbox.
2GB account is free!


Click Here To open an account

Dropbox will allow you to share folders across multiple computers.

Removing old unused Kernels from your Fedora system

Old unused Kernels can take up a fair amount of Disk Space.
to install old ones.

Install yum utils
yum install yum-utils

package-cleanup --oldkernels --count=2

will remove all old kernels except for the last 2.

 Make Amount of Installed Kernels Permanent
Edit /etc/yum.conf and set installonly_limit

 
installonly_limit=2
 

Remove empty directories or folders

find -depth -type d -empty -exec rmdir {} \;

Integrate google contacts into your Mutt address Book

Goobook will alow you to interact with your gmail contacts from the command line and also enable mutt to access them

install goobook
type


easy-install -U goobook

Once installed create .netrc  file in your home folder with the credentials to your google account
Vim ~/.netrc


inside .netrc put the following

machine google.com
login yourgmailaddress@gmail.com
password yourpassword

save the file

to test if it is working type

goobook dump_contacts

this will dump all your contact information from gmail to stn out

to search for a string from your gmail contacts type

goobook query query

eg to search for clive type

goobook query clive

if you want to use goobook from mutt

edit your .muttrc file and add in the following line:

set query_command="goobook query '%s'"

to query the address book from inside mutt use the "Q" key



If you want to be able to use to complete email addresses instead of Ctrl-t add this:

bind editor complete-query

To add email addresses (with "a" key normally bound to create-alias command) add the following line:

macro index,pager A "goobook add" "add the sender address to Google contacts"

If you want to add an email's sender to Contacts, press "a" while it's selected in the index or pager.

Rename image files according to EXIF date

This will rename all of your pictures in a given folder and prefix the date and time that the picture was taken in front of the file name.

Useful if your camera screws up your naming convention of your pictures, or if you want to simply organize all your pictures by date

yum install exiv2

cd to the folder with all your pictures that you want to rename

and type:

exiv2 -r'%Y%m%d-%H%M_:basename:' rename $(ls)

will rename to

20110929-2005_DSC_3782.JPG

Install Oracle 11G 32bit on 64bit Rhel 6

 

  

Install the following prerequisites


yum install gnome-icon-theme-2.28.0-2.el6.noarch sgml-common-0.6.3-32.el6.noarch dmz-cursor-themes-0.4-4.el6.noarch libstdc++-devel-4.4.4-13.el6.x86_64 kernel-headers-2.6.32-71.el6.x86_64 elfutils-libelf-devel-0.148-1.el6.x86_64 libgcc-4.4.4-13.el6.i686 nss-softokn-freebl-3.12.7-1.1.el6.i686 glibc-2.12-1.7.el6.i686 mpfr-2.4.1-6.el6.x86_64 libXt-1.0.7-1.el6.x86_64 libXmu-1.0.5-1.el6.x86_64 libXxf86misc-1.0.2-1.el6.x86_64 libXxf86vm-1.1.0-1.el6.x86_64 libaio-0.3.107-10.el6.i686 libstdc++-4.4.4-13.el6.i686 ncurses-libs-5.7-3.20090208.el6.i686 readline-6.0-3.el6.i686 libICE-1.0.6-1.el6.i686 xorg-x11-xauth-1.0.2-7.1.el6.x86_64 cpp-4.4.4-13.el6.x86_64 libtool-ltdl-2.2.6-15.5.el6.x86_64 unixODBC-2.2.14-11.el6.x86_64 ppl-0.10.2-11.el6.x86_64 cloog-ppl-0.15.7-1.2.el6.x86_64 libmcpp-2.7.2-4.1.el6.x86_64 mcpp-2.7.2-4.1.el6.x86_64 xorg-x11-server-utils-7.4-15.el6.x86_64 compat-db42-4.2.52-15.el6.x86_64 compat-db43-4.3.29-15.el6.x86_64 libdmx-1.1.0-1.el6.x86_64 libXxf86dga-1.1.1-1.el6.x86_64 libXv-1.0.5-1.el6.x86_64 libIDL-0.8.13-2.1.el6.x86_64 ORBit2-2.14.17-3.1.el6.x86_64 GConf2-2.28.0-6.el6.x86_64 libbonobo-2.24.2-4.el6.x86_64 gtk2-engines-2.18.4-5.el6.x86_64 shared-mime-info-0.70-4.el6.x86_64 libdaemon-0.14-1.el6.x86_64 avahi-0.6.25-8.el6.x86_64 avahi-glib-0.6.25-8.el6.x86_64 gnome-vfs2-2.24.2-6.el6.x86_64 libtool-ltdl-2.2.6-15.5.el6.i686 unixODBC-2.2.14-11.el6.i686 libuuid-2.17.2-6.el6.i686 libSM-1.1.0-7.1.el6.i686 libXau-1.0.5-1.el6.i686 xorg-x11-utils-7.4-8.el6.x86_64 compat-libstdc++-33-3.2.3-69.el6.x86_64 celt051-0.5.1.3-0.el6.x86_64 libXp-1.0.0-15.1.el6.x86_64 libxcb-1.5-1.el6.i686 libX11-1.3-2.el6.i686 libXext-1.1-3.el6.i686 ConsoleKit-x11-0.4.1-3.el6.x86_64 libXi-1.3-3.el6.i686 xorg-x11-xinit-1.0.9-13.el6.x86_64 libXtst-1.0.99.2-3.el6.i686 libXt-1.0.7-1.el6.i686 compat-libstdc++-33-3.2.3-69.el6.i686 glibc-headers-2.12-1.7.el6.x86_64 glibc-devel-2.12-1.7.el6.x86_64 gcc-4.4.4-13.el6.x86_64 compat-gcc-34-3.4.6-19.el6.x86_64 gnome-themes-2.28.1-6.el6.noarch system-icon-theme-6.0.0-2.el6.noarch system-gnome-theme-60.0.2-1.el6.noarch ncurses-devel-5.7-3.20090208.el6.x86_64 libgnome-2.28.0-11.el6.x86_64 gcc-c++-4.4.4-13.el6.x86_64 readline-devel-6.0-3.el6.x86_64 glibc-devel-2.12-1.7.el6.i686 compat-db-4.6.21-15.el6.x86_64 unixODBC-devel-2.2.14-11.el6.i686 unixODBC-devel-2.2.14-11.el6.x86_64 libaio-devel-0.3.107-10.el6.i686 libaio-devel-0.3.107-10.el6.x86_64 compat-gcc-34-c++-3.4.6-19.el6.x86_64

next you must install the 32 bit version of the Glib libraries

yum install glib-devel.i686

connect to the server with
ssh -X oracle@serverip address

./runInstaller -ignoresysprereq

the Oracle Xwindow will open on your desktop,
follow instructions to complete the installation.