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.

Filesystem Replication Using rsync and SHH

There are many reasons you may need to replicate a file system.  My reason was for DR purposes.  In a previous post I set up Passwordless SSH sessions between two systems.  This is a requirement if you want to sync file systems on an automated schedule.  I looked on the web for a script that would do what I wanted and I could not find something that met my needs.  So I wrote the script below.  To give credit where credit is due, I borrowed from some ideas and code from Randal K. Michael, author of Mastering UNIX Shell Scripting.  I placed the script below in /usr/local/bin directory on the "source" node and called it fsrsync.bash.  This script will replicated a designated filesystem from a source node to two different nodes after confirming they are "alive".  I used rsync because after the initial sync, future replications are much faster since only update and/or changes are sent and not the entire filesystem.

Here is the script below.  Highlight the contents and select copy.
Note:  When you grab the test here and paste it, do a sanity check on the text to verify the formatting has not changed.
Edit/create /usr/local/bin/fsrsync.bash and paste in the contents.
# vi /usr/local/bin/fsrsync.bash

Script starts below.

#!/bin/bash
#
# SCRIPT: fsrsync.bash
# AUTHOR:
# DATE:
# REV:
#
# PURPOSE: This script is used to replicate the
# /somedir/test filesystem from Node A to Node B and C
#
# 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 FILES AND GLOBAL VARIABLES HERE
##############################################

# Define the target machines to copy data to.
# To specify more than one host enclose the
# hostnames in double quotes and put at least
# one space between each hostname
#
# EXAMPLE: MACHINE_LIST="fred yogi booboo"

MACHINE_LIST="nodeB nodeC"

# Capture the shell script file name

THIS_SCRIPT=$(basename $0)

# The FS_PATTERN variable defines the regular expression
# matching the filesystems we want to replicate with rsync.
# Example:  FS_PATTERN="/home"

FS_PATTERN="/somedir/test"

# Query the system for the hostname

THIS_HOST=$(hostname)

##############################################
# BEGINNING OF MAIN
##############################################

# Comfirm the nodes are alive and replicate
# the filesystems.
echo -e "\n####################################################\n"
echo -e "$THIS_SCRIPT started execution $(date)\n"
echo -e "Verifying the node is alive..."

for M in $MACHINE_LIST
do
    echo "Pinging $M..."
    ping -c1 $M >/dev/null 2>&1
    if (( $? != 0 ))
    then
        echo -e "ERROR: $M host is not pingable...cannot continue..."
        echo -e "...EXITING...\n"
        echo -e "####################################################"
        exit 2
    else
        echo -e "$M is alive... Starting rsync process!\n"
        echo -e "Replicating $FS_PATTERN/ from $THIS_HOST to $M\n"
        #The rsync command is all on one line although it doesn't appear so here.  This comment can be removed.
        rsync -aqz --delete -e ssh $FS_PATTERN/ root@$M:$FS_PATTERN
    fi
echo -e "$THIS_SCRIPT finished execution $(date)\n"
echo -e "####################################################"
done

###############################################
# END OF SCRIPT
###############################################

Make sure you make the file executable.
# chmod 754 /usr/local/bin/fsrsync.bash

You can manually run the file by simply running this command as a user with the appropriate rights.
# /usr/local/bin/fsrsync.bash

Do you want to schedule this script to replicate the file system every 5 minutes and log results?  Add the following entry to the crontab.
# crontab -e
0,5,10,15,20,25,30,35,40,45,50,55 * * * *     /usr/local/bin/fsrsync.bash 2>&1 >> /var/log/fsrsync.log


Do you want to rotate your log file (assuming you use logrotate)?  If so create a file in /etc/logrotate.d/ called fsrsync.
# vi /etc/logrotate.d/fsrsync

The contents of the file should look like this:
/var/log/fsrsync.log {
        weekly
        rotate 4
        nocompress
        missingok
}

I hope this helps someone out there.

PS:  If you want to test logrotate without having to wait a week you can do the following.
# /usr/sbin/logrotate -v /etc/logrotate.d/fsrsync
This will give you details on what it will do and rotate the log if needed.  If you want to force a log rotation, do the following.
# /usr/sbin/logrotate -f /etc/logrotate.d/fsrsync