Playing with X(X11)

Virtual Terminals


Linux, FreeBSD, and many other modern Unix kernels support a virtual terminal.(VT) (or virtual console ) capability, which provides independent virtual video cards. The monitor, keyboard, mouse, and physical video card are associated with only one VT at a time, and each virtual video card can be in a different display mode—some may be in character mode while others are in graphical mode. This enables multiple X servers and nongraphical sessions to be active at the same time.

When you are connected to a virtual terminal that isn’t running an X server, you can use Alt-LeftArrow to go to the previous VT and use Alt-RightArrow to switch to the next VT. FreeBSD provides a very similar VT capability, except that the VTs are numbered starting at zero, and the key combination to switch VTs when in character mode is Alt-Fx .

NOTE: Although most kernels support more than 12 virtual terminals, this capability is rarely used because you can’t usually use the keyboard to go directly to higher-numbered Vts.


Starting a Raw X Server Manually
1. The simplest way to start an X server is also the least-used technique: simply type the name of the server at a shell prompt:

$ X

You must enter “X” as a capital letter.



2.If an X server is already running on display :0 , you will get an error message, because the network port will already be in use. In that case, you can give the new X server a different display number:


$ X :1


3 .By default, the X server will start on the first unused VT (usually VT8). You can
request a specific VT by specifying it on the command line:


$ X :1 vt10

4. You can also specify that a particular configuration file should be used, or a particular ServerLayout within a configuration file:


$ X :1 -config configFile


$ X :1 -layout layoutName



NOTE: The downside to starting the X server this way is that no clients are started. Until you start some manually, you’ll be left staring at a blank screen with only a mouse pointer to amuse yourself.

4.You can start the X server and a client at the same time like this:

$ X :1 -terminate & sleep 2 ; DISPLAY=:1 xterm

Using a Display Manager to Start the X
Server


5 .Three display managers are in common use. The biggest difference between them is the toolkit upon which they are built:

• GDM: GNOME Display Manager (built on GTK)
• KDM: KDE Display Manager (Qt)
• XDM: X Display Manager (Xt)

6.You may be able to recognize the display manager used on your system by its appearance, since each toolkit has a distinctive look. Alternately, you can search the process table to see what’s running, using the following:

$ ps -e | grep '[gkx]dm'


7. When you boot into any runlevel that does not start X automatically, you can start
the display manager manually by typing the command name at a root shell prompt:


# gdm

NOTE: By default, Debian-based systems (including Ubuntu) start the display
manager in all runlevels. You can easily disable the startup of the display
manager in runlevel 3 by executing these commands:



# update-rc.d -f gdm remove
# update-rc.d gdm start 31 2 4 5 . stop 31 1 3 .



Started Directly by init


In some Linux distributions, the display manager is directly started by init . For example, in Redhat based systems /etc/inittab, you will find this entry:


# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon

The script /etc/X11/prefdm will execute /usr/sbin/autologin to automatically log in one user if that feature has been set up. Otherwise, it will start one of the display managers (GDM, KDM, or XDM) depending on the specification in /etc/sysconfig/desktop . If that file does not exist, then the first display manager found in alphabetical order will be used.

Since init has been set up to respawn the display manager automatically, it is relatively easy to load and test changes to the display manager configuration file—just kill the display manager! If you’re using XDM or KDM, you can kill the display manager by name:


# killall xdm

NOTE: Killing the display manager will also kill all the display manager’s child processes, including X serversso if you do this through the graphical interface, expect your session to disappear!


GDM is a wrapper script for gdm-binary, so if your system uses GDM , you’d have to kill the display manager with the following:

# killall gdm-binary


You can restart GDM immediately using its restart script:

# gdm-restart


you can specify that a restart should take place as soon as everyone is logged out:


# gdm-safe-restart

On a SUSE system, the display manager is started by

/etc/rc.d/rc5.d/S17xdm
(which is a symbolic link to /etc/rc.d/xdm ).


Similar to the prefdm script used by Fedora, this script finds your preferred display
manager using a configuration file—in this case,

/etc/sysconfig/displaymanager
(or it uses XDM if that file is missing.)

Since this is a regular init script, it is executed only once at startup; when the display manager terminates, it will not be restarted. After editing the display manager configuration file, you can reinvoke the XDM init script using the restart option to put your changes into effect:

# /etc/X11/xdm restart

Or you can use the SUSE shortcut:

# rcxdm restart

Starting Multiple X Servers Using a Display
Manager

Starting Multiple X Servers Using XDM

XDM and older versions of KDM (pre-3.4) use the Xservers file to configure the number of servers started by the display manager.

Open /etc/X11/xdm/Xservers, /opt/kde3/share/config/kdm/Xservers

To start additional X servers, simply add lines at the bottom of this file:


:0 local /usr/bin/X // This is the default line.

Add the lines

:1 local /usr/bin/X :1 vt8
:2 local /usr/bin/X :2 vt9




If you wish to specify a different configuration file for one of the X servers, you can
add a -config argument to the command:

:3 local /usr/bin/X -config configgile :3 vt10

Starting Multiple X Servers Using KDM

If you’re using KDE 3.4 or higher, the local X server configuration is controlled by
the kdmrc file

# /usr/share/config/kdm/kdmrc


In the [General] section of that file, you can specify a list of local displays to be started by adding a StaticServers key:

StaticServers=:0,:1,:2

If this line is missing, the default is to start only display :0 .


Starting Multiple X Servers Using GDM

GDM is configured using two files; the first specifies default values, which may be
overwritten when GDM is updated, and the second provides local values, which are
never overwritten.

/usr/share/gdm/defaults.conf - Defaults

/etc/gdm/custom.conf – Local Values


# vi /usr/share/gdm/defaults.conf

Go to the section

[servers]
0=Standard
1=Standard // Thsi will start second X in

If you wish to use a different configuration for a specific display, you can add a new
configuration section to the local configuration file:
[server-LowRes]
name=Low-Resolution Server
command=/usr/bin/X -config /etc/X11/xorg.conf-lowres
flexible=false


Then specify that configuration for one of your displays:

[servers]
0=Standard
1=Standard
2=Standard
3=LowRes

Recent versions of both GDM and KDM are capable of starting additional X servers
on demand. This is useful when you occasionally want to use multiple X servers but
don’t want the extra overhead when a single X server only is in use. The GNOME
developers call these additional servers flexible servers; the KDE folks call them
reserve servers.


$ gdmflexiserver

gdmflexiserver can also start a nested X server (using Xnest) and present a session
login prompt there:


$ gdmflexiserver -n


Starting Additional X Servers Using KDM

To start multiple KDE desktop on boot open kdmrc file and enter the following.

ReserveServers=:3,:4,:5


The xinit utility can be used to start an X server with specified clients, but the startx wrapper script provides a friendlier interface. After logging in at a character-based login prompt, simply execute:

$ startx

You can explicitly specify a client to be started:

startx /usr/bin/xterm -bg yellow -geometry 180x50

Switching VTs from the Shell Prompt

xdpyinfo
We can switch the virtual terminals using one of the following command.

$ switchto 7
Or:
$ chvt 7

We can also use this command Remotely.




Starting X Within X

To start Xnest on the current display, use the following:


$ Xnest :1

To start Xnest with a particular client, you can use the startx script:

$ startx /usr/bin/startkde -- /usr/bin/Xnest :1

To start Xnest with two screens of 600 * 400 pixels, use the following:

$ Xnest -scrns 2 -geometry 600x400 :1

For many applications it’s desirable to have the X server exit when the last client disconnects. This is configured by adding the -terminate option to the X command line:

$ X -terminate

Let the X Server Configure Itself

The X.org server can, in most cases, probe, guess, and assume enough about the display configuration to start without a configuration file. Even better, it can generate a basic configuration file, if you specify the -configure option on the server command line:

# X -configure

If you’re already running the X server, you can specify an alternate display number
(such as :1 ) on the command line:

# X -configure :1

The X server will gather as much information as possible by probing the hardware,
and will then write the configuration file to /root/xorg.conf.new .
You can test the configuration file by manually specifying it on the command line:

# X -config /root/xorg.conf.new


If the server appears to start and then immediately exits, while displaying
the message Fatal server error: failed to initialize core devices, then
your configuration may be fine except for the pointer device. Try telling
the X server to continue even if the pointer cannot be opened:


# X -config /root/xorg.conf.new -allowMouseOpenFail

Clearing Logs in linux

# cd /var/log

# cat /dev/null > messages

# cat /dev/null > wtmp

LInux Advanced Routing

# ip link list // List al our local interfaces.

# ip address show // Shows our all Local interfaces

# ip route show // List all our routes.

# ip neigh show // To lsit current ARP cache

# ip neigh delete 192.168.0.229 dev eth0 // To delete an entry from arp cache.

# ping -c 1 192.168.0.229 // To add 192.168.0.229 to ARP cache.

#

ATTACK

A quick and useful command for checking if a server is under ddos:
netstat -anp |grep ‘tcp\|udp’ | awk ‘{print $5}’ | cut -d: -f1 | sort | uniq -c | sort -n

That will list the IPs taking the most amounts of connections to a server. It is important to remember that ddos is becoming more sophisticated and they are using fewer connections with more attacking ips. If this is the case you will still get low number of connections even while you are under a DDOS.

Another very important thing to look at is how many active connections your server is currently processing.

netstat -n | grep :80 |wc -l

netstat -n | grep :80 | grep SYN |wc -l

The first command will show the number of active connections that are open to your server. Many of the attacks typically seen work by starting a connection to the server and then not sending any reply making the server wait for it to time out. The number of active connections from the first command is going to vary widely but if you are much above 500 you are probably having problems. If the second command is over 100 you are having trouble with a syn attack.

To Block a certain IP address that on server .Please use following commands

—————–command——————————

route add ipaddress reject

for example route add 192.168.0.168 reject

You can check whether given IP is blocked on server by using following command

route -n |grep IPaddress

—————–command——————————

OR

use follwoing command to block a ip with iptables on server
—————–command——————————
iptables -A INPUT 1 -s IPADRESS -j DROP/REJECT

service iptables restart

service iptables save

—————–command——————————

Then KILL all httpd connection and restarted httpd service by using following command

killall -KILL httpd

service httpd startssl


additionally you can check the connection ports here


lsof | grep ESTABLISHED
lsof | grep LISTEN

lsof -p PID

POSTGRESQL ERROR

IF you get an error given below

FATAL 1: IDENT authentication failed for user "postgres"'

Do the following to fix it.

# vi /var/lib/pgsql/data/pg_hba.conf


Add the line

host all 127.0.0.0 255.255.255.255 trust

:wq // save the file


The /var/lib/pgsql/data/pg_hba.conf will look like this.

# TYPE DATABASE USER CIDR-ADDRESS METHOD

#local all all ident sameuser
host all all 127.0.0.1/32 trust




# service postgresql restart

INSTALLING MAVEN

# cd /opt


# wget -c http://www.eng.lsu.edu/mirrors/apache//maven/binaries/apache-maven-3.0-bin.tar.gz

# tar xvzf apache-maven-3.0-bin.tar.gz

# vi /etc/profile

Add the following lines to the end of the file

M2_HOME=/opt/apache-maven-3.0
export M2_HOME
PATH=$PATH:$M2_HOME/bin

:wq // save the file


# source /etc/profile

Apache maven is installed and ready to use.

Tux blog: INSTALLING OPENNMS

Tux blog: INSTALLING OPENNMS: "OpenNMS is the world's first enterprise-grade network management system developed under the open source model. As with any complex and power..."

INSTALLING OPENNMS

OpenNMS is the world's first enterprise-grade network management system developed under the open source model. As with any complex and powerful system, getting it installed and configured can take a little effort.

Minimum Requirements
--------------------

* A 1 GHz Pentium III (or equivalent processor) or better. OpenNMS can also take advantage of multiple processors.

* A minimum of 256 MB of RAM, although 512 MB is strongly recommended. The OpenNMS Java Virtual Machine benefits from large amounts of memory, up to 2 GB, and more if using a 64-bit processor.

* OpenNMS requires about 200 MB of disk space for the program files. In addition, each data variable collected requires, by default, a little under 300 KB of disk space.


Configure RPM-based Distributions with Yum
-------------------------------------------

[root@localhost ~]# yum install yum-fastestmirror


Install the OpenNMS Repository RPM
-----------------------------------

rpm -Uvh http://yum.opennms.org/repofiles/opennms-repo-snapshot-fc7.noarch.rpm

Or, to install the latest unstable release on CentOS or RHEL 5, you would run:

rpm -Uvh http://yum.opennms.org/repofiles/opennms-repo-unstable-rhel5.noarch.rpm

Installing Java on RPM-based Distributions Using Yum
----------------------------------------------------

[root@localhost ~]# yum install jdk


Installing PostgreSQL on RPM-Based Distributions Using Yum
----------------------------------------------------------

[root@localhost ~]# yum -y install postgresql-server


Configure PostgreSQL
--------------------

Locate the Postgres "data" directory. Often this is /var/lib/pgsql/data. You should then find the two files we need to modify in that directory.

First we need to make sure PostgreSQL is listening on an IP socket, and not just a local unix socket.


Edit postgresql.conf File and add the following.

listen_addresses = 'localhost'

max_connections = 256

max_connections = 256



Customizing the pg_hba.conf File
--------------------------------

Add the below lines.

# TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD
local all all trust
host all all 127.0.0.1 255.255.255.255 trust
host all all ::1 ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff trust


Creating the PostgreSQL Database
---------------------------------


# /etc/init.d/potgresql start


Installing JICMP on RPM-Based Distributions Using YUM
-----------------------------------------------------


[root@localhost ~]# yum install jicmp



Installing OpenNMS
------------------
------------------


[root@localhost ~]# yum install opennms-*

Configure Java for OpenNMS
--------------------------

[root@localhost ~]# /opt/opennms//bin/runjava -s


The desired outpu is given below:


runjava: Looking for an appropriate JRE...
runjava: Checking for an appropriate JRE in JAVA_HOME...
runjava: skipping... JAVA_HOME not set
which: no java in (/usr/lib/qt-3.3/bin:/usr/kerberos/sbin:/usr/kerberos/bin:/usr/lib/ccache:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/opt/opennms/bin:/root/bin)
runjava: did not find a JRE in user's path
runjava: searching for a good JRE...
runjava: found a good JRE in "/usr/java/jdk1.5.0_18/bin/java"
runjava: value of "/usr/java/jdk1.5.0_18/bin/java" stored in configuration file
You have new mail in /var/spool/mail/root


Configure a specific JRE
-------------------------


If you need to configure specific JRE do the following:

[root@localhost]# /opt/opennms/bin/runjava -S


Run the OpenNMS Installer Application
-------------------------------------

[root@localhost ~]# /opt/opennms/bin/install -l /usr/local/lib -dis




Login to the Web Application
-----------------------------

By default, OpenNMS's built-in web server listens on port 8980, so point your browser at http://:8980/opennms/


The initial user name is "admin" and the password is "admin".

Enjoyyyy...............


If you need any further assistance. Ping me

Email: vasanth462@gmail.com

To Speed up the installation using YUM

You may want to install the yum-fastestmirror RPM if your distro supports it. This can often speed up downloads of large packages. See the CentOS Wiki

# yum install yum-fastestmirror

SVN ADMINISTRATION

http://artis.imag.fr/~Xavier.Decoret/resources/svn/index.html

DANSGUARDIAN,SQUID,IPTABLES

If you want to filter a net browsing in a linux gateway server using iptables,squid and Dansguardian follow my steps

etho=Internet ipaddress
eth1=192.168.0.229

Do the necessary steps to make Linux machine as router and gateway


# yum install squid

Open the configuration file of the squid.


# vi /etc/squid/squid.conf


Enter the following line

http_port 3128 transparent

Add the Acls



acl home_network src 192.168.0.0/24
http_access allow home_network

# service squid start


# iptables -A INPUT -m tcp -p tcp -s ! 127.0.0.1 --dport 3128 -j DROP
# service iptables save
# service iptables restart

This Will block your employess from connecting to squid directly.








1 . Install Dansguardian from the source or RPM

I am using RPM here



The files are installed in /etc/dansguardian. Open Main configuration file of dansguardian. Enter the following details.


# vi /etc/dansguadian/dansguardian.conf

proxyip = 192.168.0.229


proxyport = 3128


filterport = 8080


save the file.


Run the following redirect

# iptables -A PREROUTING -s 192.168.0.0/24 -p tcp -m tcp --dport 80 -j REDIRECT --to-ports 8080



In the clients set the gateway as 192.168.0.229(in my case)

Shell script to start Authdeamon

#! /bin/sh

case "$1" in
start)
echo "Initializing authdaemon. (Courier)"
/usr/local/sbin/authdaemond start
;;
stop)
echo "Shutting down authdaemon:"
/usr/local/sbin/authdaemond stop
;;
restart|reload)
$0 stop && $0 start
;;
*)
echo "Usage: $0 {start|stop|restart|reload}"
exit 1
esac
exit 0


~

Installing Courier in a Postfix Server

Coming Soon............................

YUM THROUGH PROXY

If your internal network is protected with a proxy server and firewall use the following settings to use yum

1. Open a shell

2. export http_proxy=http://proxyhost:port number

Eg: http_proxy=http://192.168.0.229:3128

3. yum list


Enjoyyyy

OPENVZ COMMANDS

OpenVZ is an Operating System-level server virtualization solution, built on Linux. OpenVZ creates isolated, secure virtual environments.

FILES

/etc/vz/vz.conf
/etc/vz/conf/veid.conf
/proc/vz/veinfo
/proc/vz/vzquota
/proc/user_beancounters
/proc/fairsched

Log file /var/log/vzctl.log

vzctl Commands

Usage: vzctl [options] [parameters]

Help : vzctl --help


1. stop a VE (start/stop/restart) -

#vzctl stop VEID

2. to stop a VE in fast mode -

#vzctl stop VEID --fast

3. to see all the VE's -

#vzlist -a

4. to enter a VE -

#vzctl enter VEID

5. to see the uptime of a VE - run this from the node -

#vzctl exec VEID uptime

6. to see all the running process in a VE from the node -

#vzctl exec VEID ps aux

7. list the load of each VE -

#for vps in `vzlist -1`; do echo "$vps: `vzctl exec2 $vps uptime`"; done

8. when you think it is a RAM issue (Out Of Memory)-

#less /var/log/messages|grep OOM|grep VEID|wc -l

9. Reinstall a VE - all data will be lost and a fresh install will be there -

#vzctl reinstall VEID

10. number of running VE's in the node - 

#vzlist|grep running|wc -l

11. To find the status of a VC:

#vzctl status VEID

12. You can execute commands inside a VC from the node itself

#vzctl exec VEID COMMAND

13. Check inodevalue

#df -i

14. Set inodevalue

#vzctl set VEID --diskinodes 2000000:2000000 --save

15. Check numiptent value

#egrep numiptent /proc/user_beancounters
numiptent 336 336 2147483647 2147483647 0

16. Set numiptent value

#vzctl set VEID --numiptent 2000000:2000000 --save

17. To permanently remove this VE:

#vzctl destroy VE_ID

Configuration Commands


1) vzctl set VEID –-hostname vps.domain.com -–save : To set the Hostname of a VPS.


2) vzctl set VEID –-ipadd 1.2.3.4 –-save : To add a new IP to the hosting VPS.


3) vzctl set VEID –-ipdel 1.2.3.4 –-save : To delete the IP from VPS.


4) vzctl set VEID –-userpasswd root:new_password -–save : To reset root password of a VPS.


5) vzctl set VEID -–nameserver 1.2.3.4 -–save : To add the nameserver IP’s to the VPS.


6) vzctl exec VEID command : To run any command on a VPS from Node.


7) vzyum VEID install package_name : To install any package/Software on a VPS from Node.

PERMENETLY MOUNTING THE REMOTE WINDOWS SHARE USING /etc/fstab

To permanently mount the Windows share to Linux enter the following entry to the /etc/fstab and run



//192.168.1.21/D /mnt cifs defaults,credentials=/root/samba_credentials 0 0


:wq

# mount -a

PRIVATE READ WRITE SHARE

Private write share.

Create a share like below in /etc/samba/smb.conf


security = share

[privatewrite]

path = /private

writable = yes

create mask = 0765

valid users = vasanth



# smbpasswd -a vasanth

# smbpasswd -e vasanth

MAPPING LINUX FOLDER TO WINDOWS

MAPPING LINUX FOLDER TO WINDOWS

In winbox open cmd

Type trhe following command

> net use * \192.168.1.12\privatewrite /user:vasanth

It will prompt for password. Give it the remote Linux folder is mapper to my computer as drive Z: in windox

> net use // this command will display the current connections to the our windows server

To disconnect the drive

right click >> disconnect

or

> net use z: /delete

TO MAKE A HIDDEN SHARE IN WINDOWS

Enter the share in smb.conf

[privatewrite]

path = /private

writable = yes

create mask = 0765

valid users = vasanth

browseable = no
//this line cause the share to became invisible.



The above entry in the smb.conf make the share hidden but . It is still accessible using unc path.

On windows network places address bar please type

\\192.168.1.12\privatewrite

# smbclient -L server1

TO FIND OUT THE STATUS OF A FILE IN LINUX

# stat smb.conf

OUTPUT:

File: `smb.conf'

Size: 10041 Blocks: 24 IO Block: 4096 regular file

Device: 803h/2051d Inode: 1901530 Links: 1

Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)

Access: 2010-06-17 07:12:01.000000000 +0530

Modify: 2010-06-17 07:09:52.000000000 +0530

Change: 2010-06-17 07:09:52.000000000 +0530