Command line shortcuts

Clear screen
cntrl l 

ssh connection to unreachable host through a reachable host
ssh -t reachable_host ssh unreachable_host 

set an audible alarm when machine comes online
ping -i 60 -a IP_address

Display top 10 running processes sorted by memory usage
ps aux | sort -nk +4 | tail

save your previous command as a script
echo "!!" > foo.sh

what is my my public ipadress ?
curl ifconfig.me

Enable Logging for SFTP sessions

To enable logging of your sftp sessions

Replace the susbsystem line in your /etc/ssh/sshd_config with
Subsystem    sftp    /usr/libexec/openssh/sftp-server -f LOCAL5 -l INFO
Add the following to /etc/syslog.conf or  /etc/rsyslog.conf
#sftp logging
local5.*                        /var/log/sftpd.log
Restart the sshd and syslog/rsylog services,
sftp sessions should now be logged to /var/log/sftpd.log

setting persistant system wide environment variables

The folder /etc/profile.d/ is the recommended place to add customizations to the system profile.
do not edit /etc/profile  rather add files in the /etc/profile.d folder

For example, when installing the oracle JDK, you might need to set the JAVA_HOME and JRE_HOME environment variables.

Create a new file called java.sh
vim /etc/profile.d/java.sh

Within this file, initialize the necessary environment variables
export JRE_HOME=/usr/java/jdk1.7/jre
export PATH=$PATH:$JRE_HOME/bin

export JAVA_HOME=/usr/java/jdk1.7
export JAVA_PATH=$JAVA_HOME

export PATH=$PATH:$JAVA_HOME/bin

save the file.

every time you reboot the environment variable will be loaded system wide..

Undeleting Files that were accidentallly deleted

How to undelete files from ext3/ext4 partition
When you accidentally delete a file or files or an entire directory extundelete can recover them for you.

yum install extundelete

The first step should be to  unmount the partition that your lost files are on, as soon as possible.
If you know the path and the name of the file or directory  (let's assume it's /home/cgerada/Music/ and you accidentally deleted all your music files .
sudo to root
sudo -i or su - root and go to a partition with enough free space to store the deleted files. Then:
type

extundelete --restore-files /home/cgerada/Music/ /dev/sda3

you should get the following
NOTICE: Extended attributes are not restored.
WARNING: EXT3_FEATURE_INCOMPAT_RECOVER is set.
The partition should be unmounted to undelete any files without further data loss.
If the partition is not currently mounted, this message indicates 
it was improperly unmounted, and you should run fsck before continuing.
If you decide to continue, extundelete may overwrite some of the deleted
files and make recovering those files impossible.  You should unmount the
file system and check it with fsck before using extundelete.
Would you like to continue? (y/n) 
type y
y
Loading filesystem metadata ... 3679 groups loaded.
Loading journal descriptors ... 31276 descriptors loaded.

As soon as extundelete is  finished, you will  find the recovered files  in the folder you were in when you ran the command  /RECOVERED_FILES/

If you deleted  a  directory itself, you can use --restore-directory


There are some other  useful options such as  --restore-all , --restore-file, --after 'dtime' or --before 'dtime'

type extundelete --help  to see exactly what the other options do.

Installing with yum from a text file.

To install a list of specific  packages that are installed on one server to another server .

rpm -qa > installed.txt

will create a text file with a list of all installed packages

copy installed.txt from server1 using rsync to server2, like this:

rsync installed.txt  server2:

then on server2  type

 yum -y install $(cat installed.txt)

This will now install all the packages listed in installed.txt on server2.

Disallowing programs through Sudo

You want to grant user cgerada root privelages to all programs except one, lets use tcpdump in this example.
ie we want to prevent cgerada from running  tcpdump,  but he must still be able to run all other commands as root using sudo. Further ,you do not want cgerada to have the ability to sudo -i
which effectively changes cgerada to the root user.

Normally with sudo you list the programs that the user is allowed to run with root privelages.
in this example you want to list and implement a program that is not allowed..

To edit the sudoers config file
type visudo  [enter]
which will bring up the sudoers file in vi ready to edit..

add the following line

under the section were the Cmnd_Alias is commented out
add the following alias

Cmnd_Alias DISALLOWED = /user/tcpdump, /bin/bash

You can separate with commas all the commands that you want to disallow.

Im also disallowing /bin/bash simply because when a user types sudo -i a new bash session is started as root. by disallowing this my user will not be able to sudo -i.

Further down in the sudoers file were you see
root   ALL=(ALL)    ALL

add the following underneath

cgerada ALL=ALL, !DISALLOWED

The !(Bang) means the opposite  ie without the !(bang) the user will have access to those programs.
by putting in a !(bang) in front the opposite is true.

save the file and exit by typing :x [enter]

Now look what happens if the user cgerada tries to run tcpdump


sudo tcpdump -n port 25
[sudo] password for cgerada: 
Sorry, user cgerada is not allowed to execute '/usr/sbin/tcpdump -n port 25' as root on server.

now look what happens if the user tries to sudo -i

sudo -i
[sudo] password for cgerada: 
Sorry, user cgerada is not allowed to execute '/bin/bash' as root on server

Continuously keep trying a connection

To send continuous packets to a port on a server
useful for when your are tracing packets to troubleshoot a VPN or connection problem.

The following will keep retrying

 while true; do nc <ip address of server> <port>;done 

eg

 while true; do nc 192.168.0.1 8080;done 
or if you prefer telnet over netcat

while true; do telnet 192.168.0.1 8080;done 

can also be used to keep retrying your ssh connection until it connects.
eg
while true; do ssh user@192.168.0.1 ;done 

rdesktop tips

When connecting to Windows servers using Linux rdesktop
use the following command to connect to the windows server
rdesktop

eg rdesktop 192.168.2.100

This will open up a remote desktop session to the server

rdesktop -r disk:name=path  

eg rdesktop -r disk:home=/home/cgerada 192.168.2.100
will make your local path available under "my computer" so that you can copy files from client to server

rdesktop -g 1024x768

eg rdesktop -g 1024x768 192.168.2.100
will set your screen resolution to 1024x768

more examples


rdesktop -d domainname -u cgerada -p passw0rd  -k en-gb -a 16 -g 1024x768 -r disk:home=/home/cgerada 192.168.2.100

-d = domain name
-u = username
-p = password
-k = keyboard layout eg en-us for a us keyboard layout or en-gb for a british one
-a = amount of colours in the pallet

Make Ubuntu boot into run Level 3

Edit /etc/default/grub with your favorite editor,

sudo vim  /etc/default/grub
Find this line:

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash”
Change it to:

GRUB_CMDLINE_LINUX_DEFAULT=”text”

Update Grub:
sudo update-grub

Done, Next time you boot it will be into run level 3

Show how old your Linux installation is.

To find out when your Root partition was created.

type

sudo tune2fs -l $(df -h / |(read; awk '{print $1; exit}')) | grep -i created 

Convert MP4 to MKV

My Blue Ray Player does not play .mp4 files (x264)

To convert .mp4 files  to .mkv using ffmpeg
sudo yum install ffmpeg    (To install ffmpeg)

Then use the following command

ffmpeg -i filename.mp4 -vcodec ffv1 -acodec pcm_s16le filename.mkv

Upgrading Java

When ever you upgrade Java, the old version is always left on the server and is still in use. You will have to do the following to activate and use the new version.
in this example I am upgrading from Java 1.4 to 1.6
if java is available in your repository type 
yum update java or if you have the rpm
type rpm -Uvh java-version_of_yourJava.i386.rpm 
Although upgrade option is used in both instances, java is not actually upgraded. Just the new version is  installed alongside your current version.

You need to use the alternatives system to use the new version. here's how. type alternatives --config java 
The alternatives system maintains symbolic links determining default commands. Our new version of java is installed under
 /usr/java/jdk1.6.0_26 (so the path of java binary is /usr/java/jdk1.6.0_26/bin/java. I’ll add this as the default for Java:

type 

alternatives --config java 
You should receive output similar to the following:


There is 1 program which provide 'java'.

  Selection    Command
-----------------------------------------------
*  1           /usr/lib/jvm/jre-1.4.2-gcj/bin/java

Enter to keep the current selection[+], or type selection number: 


As you can see the new version of Java is not only not being used, but there is no mention of it in the alternatives system.
So we need to add it to the alternatives system to be able to use it. heres how. type 
alternatives --install /usr/bin/java java /usr/java/jdk1.6.0_43/bin/java 1 

The syntax of alternatives is as following 
-- install /path_to_symlink program_name /path_to_program priority

Once done if you type
alternatives --config java 
You should now get the following 


There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
*  1           /usr/lib/jvm/jre-1.4.2-gcj/bin/java
 + 2           /usr/java/jdk1.6.0_43/bin/java

Enter to keep the current selection[+], or type selection number: 

Simply select the version that you want to use as the default version.
Select 2 to use the new 1.6 version.
You can switch between versions this way and change back to the old version if you need to.

2 Way Synchronization with Unison

2 Way directory Synchronization

I found unison is a better option than rsync if the files in both locations frequently change, or if you want to synchronise between more than 2 locations. and you need to keep all locations synchronised.

yum install unison 
on all machines that you want to synchronise between.

for password-less sync make sure you setup ssh private/public key
as described in this previous post ssh public/private key

create a file sync.sh

vim sync.sh

copy and paste the following into your file


#!/bin/bash
# set paths / dirs
_paths="/home/cgerada/directory_to_sync"

# binary file name
_unison=/usr/bin/unison

# server names 
# sync local +server1 with server2 and server3
_rserver="server1.clive.com server2.clive.com server3.clive.com"

# sync it
for r in ${_rserver}
do
        for p in ${_paths}
        do
                ${_unison} -batch -force newer -times "${p}"  "ssh://${r}/${p}"
        done
done

save the file and give it execute rights

chmod + x sync.sh

to run the script on a cronjob every half an hour and output details into a log file

crontab -e

and add the following

*/30 * * * * /path/to/sync.sh &>/var/log/sync.sh.log

save and you are done.

~                                                                          
~                                                  

Chrooted SFTP

This will chroot (restrict)
all sftp users to their home directory

on your SFTP server type

group add sftpusers

vim /etc/ssh/sshd-config

comment out

#Subsystem       sftp    /usr/libexec/openssh/sftp-server

add

Subsystem       sftp    internal-sftp

You want to put only certain users (i.e users who belongs to sftpusers group) in the chroot jail environment. Add the following lines at the end of /etc/ssh/sshd_config

Match Group sftpusers

        ChrootDirectory %h

        ForceCommand internal-sftp

Match Group sftpusers – This indicates that the following lines will be matched only for users who belong to group sftpusers

ChrootDirectory /sftp/%h – This is the path that will be used for chroot after the user is authenticated. %h indicates the users home directory. So, for john, this will be /home/john.

ForceCommand internal-sftp – This forces the execution of the internal-sftp and ignores any command that are mentioned in the ~/.ssh/rc file.

next either add new users to your system or you can add existing users to the system

user add john mary clive

Add all sftp users to the sftp group by editing your 

/etc/group file  

sftpusers:x:501:john,mary,clive

Make sure users cannot login using ssh, do this by editing /etc/passwd

vim /etc/passwd

and changing /bin/bash to /bin/nologin of each SFTP user

From

john:x:500:500::/home/john:/bin/bash

To

john:x:500:500::/home/john:/bin/nologin

next 

chmod -R 755 /home/john

then you must set the following ownership to the users home directory

chown -R root:sftpusers /home/john

restart sshd

/etc/init.d/sshd restart

you can now sftp into your server and the sftp users will be restricted to their /home folder only.

                   

                                                                                                                                                

~                                                                                                                                                                 

Encrypting existin Swap Redhat / CentOS

yum install cryptsetup

Switch off swap

swapon -a

comment out existing swap partition is /etc/fstab

#/dev/mapper/VolGroup00-swap swap  

Wipe swap partition

dd if=/dev/zero of=/dev/mapper/VolGroup00-swap

add the swap partition to /etc/crypttab

If it is not already created, create the /etc/crypttab file. Add an entry to /etc/crypttab file. .


swap /dev/mapper/VolGroup00-swap /dev/urandom swap



Add the following entry to  /etc/fstab file.


/dev/mapper/swap none swap defaults 0 0


The next time you boot the system and the /etc/rs.sysinit script executes, it creates a raw dm-crypt device with a random key and formats it as a swap device. During /etc/fstab processing, the swap device is activated.
Reboot the system.
Verify that the swap space is encrypted.
swapon -s
You should see a new entry for the added swap file system. You can see it listed below in the second entry, in our example.
swapon -s


Filename Type Size Used Priority
/dev/dm-2                               partition 2064376 580 -1


Voila. your swap partition has been encrypted

mount remote directories over SSH using SSHFS

When you need to mount a remote directory securely
use SSHFS which is a much easier quicker option than trying to tunnel NFS over an ssh tunnel.

SSHS is quick , easy and secure.

yum install fuse-sshfs

If not done already you will wan't to create your private and public encryption keys and put your public key on the server who's directory you want to mount, so that you will have a password less connection
ssh-keygen to create the keys

leave passphrase blank

then to copy your public key to the server type
ssh-copy-id -i .ssh/id_rsa.pub user@remoteserver

Now, lets say there is some directory /mnt/dir/ on the remote system user@remoteserver and we want to mount it on our /localfolder directory. This is how we do it using sshfs.

type
sudo sshfs user@remoteserver:/mnt/dir /localfolder

Thats it. done.

and to unmount type

fusermount -u /localfolder/

If you want the directory to be available after a reboot

You could just put sudo sshfs user@remote:/mnt/dir /localfolder
in to your /etc/rc.local file

or if you prefer to use /etc/fstab then add the following line to your /etc/fstab file

sshfs#user@remoteserver:/mnt/dir /localfolder fuse    comment=sshfs,noauto,users,exec,uid=1000,gid=1000,allow_other,reconnect,transform_symlinks,BatchMode=yes

Dealing with Vcard meeting requests in Mutt

Receiving Vcard Meeting requests that have been generated in Microsoft exchange or MS outlook
arrives in to your Mutt inbox, as an illegible mess of text that is difficult to make heads or tails out of

To configure your mutt to play nicely with Vcard meeting requests do the following.
.
First install the following (If they are not already installed)

yum install perl
yum install perl-devel
yum install perl-Data-ICal
yum install perl-Text-Autoformat

or use apt-get install if your distribution is Debian based

Then edit your .muttrc and add in the following lines

alternative_order text/calendar
This tells Mutt to display the text/calendar part in preference to the text/plain part.

color index black yellow "~b text/calendar"
this shows all meeting requests as black on yellow
change the colours to which ever you would prefer

The final step is to decode the vCalendar text into something that’s a bit more readable.

To do this we use the following perl script
http://notes.asd.me.uk/wp-content/uploads/2012/08/vcal2text.txt

click on the link then

you can copy and paste the text into your own local file

name the file vcal2text

and save it in /usr/local/bin

Give the script execute permissions

chmod +x /usr/local/bin/vcal2text

Start up Mutt and all Vcard meeting requests will be Legible

Printing with Mutt

By default, when you press the p key to print a message in mutt, you will not be prompted to choose a printer. Mutt will just print to the printer defined in your PRINTER environment variable.

To change the printer mutt uses , from within mutt, type in the following:

:set print_command="/usr/bin/lp.cups"
Make sure you type in the colon first. If you do not type in the colon first, the rest of what you type will be interpreted by mutt as  commands (for example, the 's' from the word 'set' will try to save the message).

To see what your current printer command is, type in:

:set print_command
If you are using Gnome 3 and you would like to use your Default cups printer from within mutt, you can set your printer command as follows:

:set print_command="/usr/bin/lp.cups"
To make this setting permanent

edit your .muttrc file and put

set print_command="/usr/bin/lp.cups"

at the end of the file  like so

vim .muttrc
and this time without the :

set print_command="/usr/bin/lp.cups"

Install Gnome 3.4 weather extention on Fedora 17

su - yum install gnome-common gtk3-devel glib2-devel intltool automake autoconf vala wget gnome-tweak-tool


wget https://github.com/simon04/gnome-shell-extension-weather/zipball/gnome3.4
unzip gnome3.4
mv simon04-gnome-shell-extension-weather-* weather
cd weather
./autogen.sh --prefix=/usr
make 
make install
Restart Gnome [Alt] + [F2] r
Click on top right hand corner of desktop, Then click on advanced settings (gnome-tweak-tool)
Click on
Shell Extensions and turn on the weather indicator extension.
Next you need to set your area, open up your web browser and goto this site http://edg3.co.uk/
Enter your closest City to get your woeid eg my city is Valletta and the code is mtxx0001
In a non root terminal type the following to set your city
gsettings set org.gnome.shell.extensions.weather woeid mtxx0001
Substituting mtxx0001 for your own cities woeid.
You can also change the name of your City by typing the following would change the city name to "Mosta" which is my actual village gsettings set org.gnome.shell.extensions.weather city Mosta
To set the units to Fahrenheit or celcius, type one of the following.
gsettings set org.gnome.shell.extensions.weather unit celsius
gsettings set org.gnome.shell.extensions.weather unit fahrenheit
The position of the GNOME Shell extension in the panel can be configured to either 'left', 'center' or 'right' (requires restart of GNOME Shell). type one of the following
gsettings set org.gnome.shell.extensions.weather position-in-panel center
gsettings set org.gnome.shell.extensions.weather position-in-panel left
gsettings set org.gnome.shell.extensions.weather position-in-panel right

rc.local on suse

Suse does not have rc.local enabled by default.

which means it is difficult to have a program automatically start up, after your system has been booted.

Suse does have a file called /etc/init.d/boot.local.

However it is not the same as rc.local
Inputting paths to files to run in the boot.local file
executes them before going to the first run level.
Which is a problem if you need your application to run after the system has completely booted.

rc.local to the rescue.

simply create your own rclocal file like so.
I use vim but you can use any file editor program like nano or gedit
vim /etc/rc.d/rclocal

then inside the file type the following (between the -----)
--------------------------------------------------------------------------
#! /bin/sh
## This script simulates redhat's rc.local (Add commands at the end)
### BEGIN INIT INFO
# Provides: rclocal
# Required-Start: $local_fs $remote_fs $network
# X-UnitedLinux-Should-Start: $ALL
# Required-Stop:
# X-UnitedLinux-Should-Stop:
# Default-Start: 3 5
# Default-Stop: 0 1 2 6
# Short-Description: Simulates rc.local
# Description: Simulates redhat's rc.local: contains
# commands to execute after system has booted (all services are already
# available)
### END INIT INFO
## Execute ony when service is started
case "$1" in
start)
## commands will be executed
;;
*)
exit 0
;;
esac


#  Add your commands bellow this line

--------------------------------------------------------------------
Save the file.
Make the file executable by typing the following: chmod +x rclocal
Create symlink to make it easy to find:  ln -s rclocal rc.local
Next, you need to enable the rc.local simulation in yast.
Type
yast2
then scroll to
System > system services (Run Level)
then scroll down to
> rclocal   simulates rc.local
and enable it
 > Enable

Save your settings, and you are done.
you now have a rc.local that behaves exactly like the redhat/fedora  rc.local
You can add/remove commands to /etc/rc.d/rc.local anytime
by simply editing the rclocal file and adding your commands you wish to execute at the bottom of the file.