How to write init script to start your own application

All the scripts are stored in /etc/rc.d/init.d or /etc/init.d directory. The scripts can be accessed by
/etc/init.d/httpd start or service httpd start
So, if you have a task to run 3(three) mongod at different port, and you want to run them using service, you will have to write the script in those directory mentioned above.

example:

#!/bin/bash
#description: Mongo Arbiter Servers
#Get function from functions library
. /etc/init.d/functions

prog="mongod arbiter servers"
#Start the service
start(){
initlog -c "echo -n Starting Mongo Arbiter Servers: "
/usr/bin/mongod --rest --replSet kdbsearch1 --dbpath /dbs/data1 --fork --logpath /var/log/mongodb1 --port 10001 &
/usr/bin/mongod --rest --replSet kdbsearch2 --dbpath /dbs/data2 --fork --logpath /var/log/mongodb2 --port 10002 &
/usr/bin/mongod --rest --replSet kdbsearch3 --dbpath /dbs/data3 --fork --logpath /var/log/mongodb3 --port 10003 &
#create the lock file
touch /var/lock/subsys/mongod
success $"mongo arbiter servers startup"
echo
}

stop(){
#initlog -c "echo -n Stopping mongo arbiter servers: "

echo -n $"Shutting down $prog: "
killproc mongod
#now, delete the lock file#
rm -f /var/lock/subsys/mongod
echo
}

case "$1" in
start)
start
;;
stop)
stop
;;
status)
status mongod
;;
esac
exit 0

"service" is replaced with "systemctl" in fedora 16

sysvinit Command	systemd Command	Notes
service frobozz start	systemctl start frobozz.service	Used to start a service (not reboot persistent)
service frobozz stop	systemctl stop frobozz.service	Used to stop a service (not reboot persistent)
service frobozz restart	systemctl restart frobozz.service	Used to stop and then start a service
service frobozz reload	systemctl reload frobozz.service	When supported, reloads the config file without interrupting pending operations.
service frobozz condrestart	systemctl condrestart frobozz.service	Restarts if the service is already running.
service frobozz status	systemctl status frobozz.service	Tells whether a service is currently running.
ls /etc/rc.d/init.d/	ls /lib/systemd/system/*.service /etc/systemd/system/*.service systemctl list-units --all	Used to list the services that can be started or stopped Used to list all the services and other units
chkconfig frobozz on	systemctl enable frobozz.service	Turn the service on, for start at next boot, or other trigger.
chkconfig frobozz off	systemctl disable frobozz.service	Turn the service off for the next reboot, or any other trigger.
chkconfig frobozz	systemctl is-enabled frobozz.service	Used to check whether a service is configured to start or not in the current environment.
chkconfig frobozz --list	ls /etc/systemd/system/*.wants/frobozz.service	Used to list what levels this service is configured on or off
chkconfig frobozz --add	systemctl daemon-reload	Used when you create a new service file or modify any configuration

How to compile libhdfs

gcc sample.c -I${HADOOP_HOME}/src/c++/libhdfs -L${HADOOP_HOME}/c++/Linux-amd64-64/lib -lhdfs -o sample

at your .bashrc


export LD_LIBRARY_PATH=/usr/lib/jvm/java-6-sun/jre/lib/amd64/server:/usr/lib/jvm/java-6-sun/jre/lib/amd64/server/libjvm.so:/usr/local/hadoop/c++/Linux-amd64-64/lib

export CLASSPATH=/usr/local/hadoop/lib:/usr/local/hadoop

Shared Library

To run a program linked with the shared version of the library the operating system must be able to locate the corresponding .so file at runtime. If the library cannot be found, the following error will occur:

     $ ./a.out      ./a.out: error while loading shared libraries:      libgsl.so.0: cannot open shared object file: No such      file or directory 

To avoid this error, either modify the system dynamic linker configuration¹ or define the shell variable LD_LIBRARY_PATH to include the directory where the library is installed.

For example, in the Bourne shell (/bin/sh or /bin/bash), the library search path can be set with the following commands:

     $ LD_LIBRARY_PATH=/usr/local/lib      $ export LD_LIBRARY_PATH      $ ./example 

In the C-shell (/bin/csh or /bin/tcsh) the equivalent command is,

     % setenv LD_LIBRARY_PATH /usr/local/lib 

The standard prompt for the C-shell in the example above is the percent character ‘%’, and should not be typed as part of the command.

To save retyping these commands each session they can be placed in an individual or system-wide login file.

To compile a statically linked version of the program, use the -static flag in gcc,

     $ gcc -static example.o -lgsl -lgslcblas -lm 

Dell system won't boot after ubuntu maverick server installation

The system thrown you out to initramfs, saying there is something wrong with root delay. What you need to do is to go to recovery mode, and edit grub.cfg (/boot/grub/grub.cfg). ADD rootdelay=90.

### BEGIN /etc/grub.d/10_linux ### menuentry 'Ubuntu, with Linux 2.6.32-21-generic' --class ubuntu --class gnu-linux --class gnu --class os {     recordfail     insmod ext2     set root='(hd0,1)'     search --no-floppy --fs-uuid --set c00fadde-f7e8-45e7-a4da-0235c605f756     linux   /boot/vmlinuz-2.6.32-21-generic root=UUID=c00fadde-f7e8-45e7-a4da-0235c605f756 ro rootdelay=90
    initrd  /boot/initrd.img-2.6.32-21-generic } 

Set Up NTP Server and Client

Setting Up NTP Server

Since servers in the data center is not able to synchronize with any external time server, we have to set up our standalone time server.

192.168.37.183 as Time Server

a. Make sure ntpd server is installed.

sudo apt-get install ntp

b. Since we are not going to synchronize with any external server. Edit /etc/ntp.conf:

# You do need to talk to an NTP server or two (or three).

server 127.127.1.0

fudge 127.127.1.0 stratum 10

c. Permit access for other servers in 192.168.37.0 network to synchronize

restrict 192.168.37.0 mask 255.255.255.0 nomodify notrap

broadcast 192.168.37.255

d. Star the ntp:

sudo service ntp start

At Client

a. Get ntpd server installed.

b. Synchronize to 192.168.37.183

#You do need to talk to an NTP server or two (or three).

server 192.168.37.183 iburst

c. Start the ntp:

sudo service ntp start

d. Command to check the ntp activity:

tail –f /var/log/syslog

ntpq –c lpeer

ntpd –q 192.168.37.183

ParaView in Ubuntu

Before launching paraview, do this:

tux@remote:~$ export LIBGL_ALWAYS_INDIRECT=y