Interactive Tape Backups using TAR and Linux

I sometimes want to run an on-demand backup of either a particular directory or file system.  I wrote an interactive script to do this and thought I would share it.
Assumptions:
1.  You have a tape device attached to your Computer or Server.
2.  You know what device your tape drive is.  Example: /dev/st0
3.  You have the mt-st package installed to manage the tape device.
4.  The tape you are using will be overwritten.
5.  You copy the contents of the script below in to a utility like notepad and check the contents.  Then copy from there in to a script called (whatever you want).
6.  Pay close attention to the command that starts like this:  TAPECHK=$(mt  It show up correctly in this post but if you cut and past the script in to notepad the lines do not match.  Edit it so it looks like it does here in the post.
7.  You make the script executable.
8.  I placed the script in /usr/local/sbin but you can put it where ever it make sense to you.

Here is the script:

#!/bin/bash
#
# SCRIPT: Interactive_2_tape.bash
# AUTHOR: Bob
# DATE: 02/24/2010
# REV:
#
# PURPOSE: This script is used to backup files
# from $SOURCE to $TAPEDEV
#
# set -x # Uncomment to debug this script
#
# set -n # Uncomment to check the script.s syntax
#        # without any execution. Do not forget to
#        # recomment this line!
#
####################
# Define Variables #
####################

# Capture the shell script file name
THIS_SCRIPT=$(basename $0)

# Define the start time of the script
STARTTIME=`date +%T`

# Define current directory to return to at end of script
CURRENTDIR=$PWD

# Ask for the source of the backup
echo "What directory or filesystem do you want to backup?"
echo "Type the directory in this format /dir1/dir2 followed by [ENTER]:"
read SOURCE
echo "Using $SOURCE as the source directory you want to backup."

# Ask for tape device
TAPEDEV="/dev/st0"
echo "I assume your tape device is $TAPEDEV"
read -p "Am I correct? yes/no: "
if [ "$REPLY" = "no" ]; then
     echo "What is your tape device? "
     read TAPEDEV
     echo "Using $TAPEDEV as your tape device."
else
     echo "Using $TAPEDEV as your tape device."
fi


################
# Main Section #
################

# Verify there is a tape in the
# drive and rewind the tape
TAPECHK=$(mt -f $TAPEDEV rewind 2>&1 1>/dev/null)
# If there is no tape tell me and exit out
#  If the mt command return any data then there is an error
#  Check the results of the mt command
if [ "$TAPECHK" != "" ]; then
     echo $TAPECHK
     echo "Check to see if there is a tape in the drive or if the device you entered is valid."
     exit
fi

# If we made it here, there is a tape in the drive and it has rewinded.
# Change to the directory to be backed up
cd $SOURCE
echo "Changing to the $SOURCE directory."

# Back up data
tar cvf $TAPEDEV .

# Rewind the tape again
mt -f $TAPEDEV rewind

# Change back to the directory from where you came
cd $CURRENTDIR
echo "Changing back to the directory you started from: $CURRENTDIR"
# Define the end time of this script
ENDTIME=`date +%T`

# Display the start and end time of this script
echo "$THIS_SCRIPT began at $STARTTIME and finished at $ENDTIME"

exit
#################
# End of Script #
#################

I hope this helps others out there trying to do the same thing.

Using tar to Copy a Large File into a Tight Space

I do a lot of work with virtual machine images.  I ran in to a situation where I wanted to copy a file called System.img from one server to another and even though I knew I had enough room to do it, I would get messages stating that there was not enough space.  What in the world was going on?  The file system I wanted to copy the file to was 33G in size.  The file was just under 33G in size.  I knew it should fit.  I knew this because the file system this file is coming from is also 33GB in size (same identical size).  When it was all said and done I should of had about 150M of free space according to the source.

I tried FTP, SCP, and various other mechanisms to copy the file from the one server to the other.  No joy.
So I copied the file to the destination server but to a different and larger file system.  That obviously was successful, but I still wanted it on my 33G file system.  So I tried copying the file locally from the larger file system to the 33G file system.  No joy again... I got a message after a few minutes stating there was not enough space, and the process errored out.

I found a solution!  Now, to be honest, I do not know why it works, but it does.

Assumptions: You are in the directory the System.img file is located.  The file resides on the same server you are copying to.  You have done the math and according to the calculator the file will fit on the destination file system.

Run this command with the appropriate path of your destination.

Note:  The following command is all on one line.
# tar cvf - System.img | ( cd /destination file system/destination folder/;tar xvf - )

Works like a charm.  I have used this little gem a dozen times in the past few months.

This should be obvious but...  Remember, you can not copy/place a file that is larger than the space available on the destination.  Hope this helps others out there.