How to find out which process is listening upon a port?

How to find out which process is listening upon a port (say 6000) ?

$ lsof -i :6000

Alternatively, you can use following command:

$ fuser -v -n tcp 6000

Find Command : A Swiss Army Knife

Find is a very useful and powerful utility. It is often used by system administration and in shell scripts. Here are 6 commands that might be useful:

$ find / -perm -4000 -print

This command will find every file on the system that is suid. This means that when you run it you will be running it as an other user. For example, traceroute is a utility that needs to be run as root. To allow users to run it, systems administrators will set it suid root so it will be run as root even if a user starts it. This can be useful, but can also be a big security risk if the utility has a security hole in it.

Here is another interesting command:

$ find / -atime +10 -print

This command will find all the files accessed more than 10 days ago. Commands like this one can be useful to find old files that need to be backuped or erased.

Find links that point to nothing

$ find / -type l -print | perl -nle '-e || print';

List zero-length files

$ find . -empty -exec ls {} \;

Finding files which contains a given pattern:

$ find . -type f -exec grep "pattern" /dev/null {} \;

Finding large files (>= 100 MB) in your home directory:

$find ~/ -size +100M

Creating Bootable USB from System Rescue CD

Creating Bootable USB from System Rescue CD

In order to create bootable USB stick from CD image (ISO file)
of System Rescue Linux, generally we follow steps given
in this link. After following instructions given, I have created
a small shell script to create bootable rescue USB.

The contents of the script create_rescue_usb.sh are:
$ cat create_rescue_usb.sh
#!/bin/bash

if [[ $# < 4 ]]

then
  echo "Usage: $0 CDROM_Device CDROM_mount USB_Device USB_mount"
  exit
fi

CDROM_Device=$1
CDROM_mount=$2
USB_Device=$3
USB_mount=$4

if [[ -e $CDROM_Device ]]
then
  echo "$CDROM_Device is present."
else
  echo "$0: $CDROM_Device is not present."
  exit
fi

if [[ -e $USB_Device ]]
then
  echo "$USB_Device is present."
else
  echo "$0: $USB_Device is not present."
  exit
fi

echo "Mounting..."
mount -o loop $CDROM_Device $CDROM_mount

if [ $? -ne 0 ]
then
  echo "$0: cannot mount $CDROM_Device on $CDROM_mount."
  exit
fi

mount $USB_Device $USB_mount

if [ $? -ne 0 ]
then
  echo "$0: cannot mount $USB_Device on $USB_mount."
  umount $CDROM_mount
  exit
fi

echo "Copying Files..."
cp $CDROM_mount/syslinux/syslinux.cfg $USB_mount/
cp -r $CDROM_mount/isolinux/* $USB_mount/
cp -r $CDROM_mount/bootdisk/* $USB_mount/
cp $CDROM_mount/sysrcd.dat $USB_mount/

echo "Unmounting..."
umount $USB_mount
umount $CDROM_mount

echo "Making $USB_Device bootable..."
syslinux $USB_Device
sync

echo "$USB_Device is now ready to serve as bootable Linux USB."
#end of script


Now, you can make it executable.
$ chmod u+x create_rescue_usb.sh

Sample execution of above script (Please run as root user):
# ./create_rescue_cd.sh /path/of/system-rescue-cd.iso /mnt/cdrom /dev/sdb /mnt/usb

Where,
a. /path/of/system-rescue-cd.iso -- ISO image of the CD can be created as given in blog Creation of ISO Image of CD/DVD.
b. /mnt/cdrom -- directory, where you want to mount above ISO.
c. /dev/sdb -- or /dev/sdb1, your usb-stick device. May differ
according to your system configuration
d. /mnt/usb -- directory, where you want to mount usb-stick.

Now, your usb stick is ready to serve as bootable rescue USB.
You can test it. At the time of BIOS boot, please select USB device
as first boot device in BIOS. then save and reboot with the usb-stick
plugged in one USB port.