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Painless Thumbdrive Backups

Issue 154

From Issue #154
February 2007

Feb 01, 2007  By Andrew Fabbro
 in
Exploit udev rules to back up your Flash drive daily or every time you insert it.
Set Up the Backup Script

backup-thumb.sh is the engine that backs up your thumbdrive. Our rule calls it, giving the name of the device (the SYMLINK) as its only argument. Everything else is configured in the CONFIG section. The backup script is shown in Listing 1.

Listing 1. Backup Script

#!/bin/bash

# Thumbdrive backup script from <citetitle>Linux Journal</citetitle>

# ##############################################
# CONFIG section

# where you want the backups to be kept
BACKUP_DIR=/backups/thumb

# how many old backups to keep
GENERATIONS=7

# backup only once a day
# set to 0 if you want a backup run every time
# you insert your thumbdrive
BACKUP_ONCE_DAY=1

# completion sound to play when backup is done
SOUND=/usr/share/sounds/KDE_Beep_ClockChime.wav

# END CONFIG
# ##############################################

# main program

# wait for device to settle
sleep 10

# make sure no one will be able to copy our backups
umask 077

# check the directory
DEVICE=$1
if [ ! -d ${BACKUP_DIR} ] ; then
        mkdir -p ${BACKUP_DIR}
fi

# only backup once per day
if [ ${BACKUP_ONCE_DAY} -gt 0 ] ; then
        DIDTODAY=${BACKUP_DIR}/${DEVICE}.did_today
        find ${BACKUP_DIR} -name ${DEVICE}.did_today -a -mtime +1 -delete
        if [ -f ${DIDTODAY} ] ; then
                exit
        else
                touch ${DIDTODAY}
        fi
fi

# rotate backups
cd ${BACKUP_DIR}
let GENERATIONS=${GENERATIONS}-1
while [ ${GENERATIONS} -ge 0 ] ; do
  let NEWFILE=${GENERATIONS}+1
        if [ -f ${DEVICE}.backup.${GENERATIONS} ] ; then
          mv -f ${DEVICE}.backup.${GENERATIONS}
${DEVICE}.backup.${NEWFILE}
        fi
  let GENERATIONS=${GENERATIONS}-1
done

# do the backup
dd if=/dev/${DEVICE} of=${BACKUP_DIR}/${DEVICE}.backup.0 > /dev/null 2>&1

# notify that we're done
aplay ${SOUND} > /dev/null 2>&1

Put this script in /usr/local/bin/backup-thumb.sh, and remember to chmod +x it. Next, edit the CONFIG section—the parameters are as follows:

  • BACKUP_DIR: where you want the backups to go.

  • GENERATIONS: how many days of backups to keep. Backups will be numbered 0 (most recent) to the limit you enter (oldest). Keep in mind that you need to have enough storage space for this many backups. If you are backing up a 1GB fob and set GENERATIONS to 7, backups will consume 7GB of space.

  • BACKUP_ONCE_DAY: if you plug and unplug your fob multiple times a day, you probably won't want to back it up each time. backup-thumb.sh uses a tag file so that it backs up only once per day. If you want to change this so it runs a backup every time you plug in a thumbdrive, set BACKUP_ONCE_DAY to 0.

  • SOUND: in this example, I've chosen a sound from the KDE distribution, but any WAV file will work. You easily can modify the script to use madplay instead of aplay and use an MP3 file as your completion sound.

How It Works

backup-thumb.sh sleeps for ten seconds on startup, because it must wait for the kernel to finish scanning the thumbdrive. If you plug in a thumbdrive and type dmesg, you'll see a “waiting for device to settle” message while this happens. Ten seconds for the kernel scan should be sufficient even for older machines.

Next, backup-thumb.sh sets permissions tightly so that only root can read the backups. Otherwise, some nefarious person could copy your backup to a different machine and mount it there.

The script executes a simple dd (bit-for-bit copy) of your thumbdrive to a backup file. This works whether the device is encrypted or not. When it's finished, it plays a noise you will hear on your computer's speakers. On a USB 2.0 port, backing up a 1GB thumbdrive takes about one minute.

How to Recover

If you lose your thumbdrive and want to restore your backup to its replacement, simply dd the backup image to the new thumbdrive, like so:

dd if=corsair_drive.backup.0 of=/dev/corsair_drive

Or, if you want to grab only some files from the backup, do the following:

mkdir /mnt/thumb
mount -o loop corsair_drive.backup.0 /mnt/thumb

You now can copy the files from /mnt/thumb.

If you're using TrueCrypt to encrypt your thumbdrive, you can mount the backup image in much the same way:

truecrypt corsair_drive.backup.0 /mnt/thumb/

That's about as painless as we can make thumbdrive backups. If you're too lazy to plug your drive in and come back when it beeps...well, stay away from laundromats!

______________________

Andrew Fabbro is a senior technologist living in the Portland, Oregon, area. He's used Linux since Slackware came on floppies and presently works for Con-way, a Fortune 500 transportation company.

Comments

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Please see my question above

Benjamin Cathey's picture
Submitted by Benjamin Cathey (not verified) on Wed, 09/24/2008 - 06:36.

Please see my question above - no one ever responded with any help. I thought it was because no one read this - but there have been posts since.

Automatically backup any USB storage device

Thomas Damgaard's picture
Submitted by Thomas Damgaard (not verified) on Wed, 09/03/2008 - 01:22.

Hi

I have a server that only serves as backup server.
I've been trying to make a udev rule that would automatically backup any USB storage device connected.
This way, I can just plug in my USB devices to my server, and it is automatically backed up.

However, what I have made so far does not work. I hope you can help me.

Here is my udev rule:

BUS=="scsi"
KERNEL=="sd?1"
SUBSYSTEM=="block"
ATTRS{removable}=="1"
ACTION=="add"
RUN+="/usr/local/bin/copy-drive.sh %k"

I hope you can help.

Cannot get this script working

Benjamin Cathey's picture
Submitted by Benjamin Cathey (not verified) on Thu, 07/03/2008 - 08:40.

I read you magazine regularly and was glad when I found this article. However I cannot get it working at all --

I am running Ubuntu 8.04

For starters, when I run the udev check I do not get any values that speficy SYSFS, they are all ATTRS (although there is a line for serial and model) - also there is no BUS line at all.

I tried writing the rule using ATTRS and nothing, I also tried writing the rule using SYSFS (even though that parameter did not appear) and nothing -

They symlink is not even created.

HELP please

So I never heard back on this???

Benjamin Cathey's picture
Submitted by Benjamin Cathey (not verified) on Wed, 09/24/2008 - 06:35.

Well, I asked for help and I never heard back on this - the output of udevinfo -a -p $(udevinfo -q path -n /dev/sdf) does not result in anything similar to what you are suggesting. There is no sysctl line or bus line - i see similar values in here but they are labelled attrs and the udev script just won't work

This is what I ended up making

root@lighthouse:/etc/udev/rules.d# cat 96-backuphome.rules
BUS=="usb", SYSFS{serial}=="0010101640150EE9W", SYMLINK=="tosh_ext", RUN+="/home/benito/scripts/homebackuponplugin.sh tosh_ext"
root@lighthouse:/etc/udev/rules.d#

Although usb is listed as

SUBSYSTEMS=="usb"
DRIVERS=="usb"

NOT the BUS (although I know that it is) ... and serial looks like ATTRS{serial}== not SYSFS{serial}== as suggested in this article. I figured the reason I hadn't heard back is that no one read this. I read your magazine monthly - maybe I shouldn't bother if I can't get a reply?

Thanks,

Benjamin

How to recover

Derk Tattersall's picture
Submitted by Derk Tattersall (not verified) on Sun, 01/07/2007 - 17:47.

At the end of your article, you state that you can recover files from the image usong mount like so:

mkdir /mnt/thumb
mount -o loop corsair_drive.backup.0 /mnt/thumb

My own thumb drive (and most such drives, I think) has the data partition on a partition within the drive. You have to use a different mount command:

mount -o loop, offset=xxxxx corsair_drive.backup.0 /mnt/thumb

Determining the value of the offset is a pain. I found a script at http://www.number.ch/wiki/index.php/PartitionRecovery that makes it much easier:

#/bin/sh
offset=$1; shift
limit=$1; shift
while [ $offset -le $limit ]
do if mount -o ro,loop,offset=$offset $* 2> /dev/null
then echo " Successfully mounted starting from offset $offset."
exit 0
fi
offset=$(($offset+1))
[ $(($offset % 1000)) == 0 ] && echo -n . # Progress indicator
done
echo "No filesystem found up to $offset."
exit 1

I found the article very useful. Thanks.

Derek Tattersall

usb key partitions

Jeff Pipkins's picture
Submitted by Jeff Pipkins (not verified) on Fri, 02/16/2007 - 12:18.

I found it instructive to write the run rule like this:
RUN+="/usr/local/bin/usbkey.sh myserialnum %k"

Then in the script I added echo $0 $@ >>/tmp/log.txt
I found that the script was called several times, with different device names. Then I removed the echo and added an if [ "$2" = "sdb2" ]
so I could mount only the partition I wanted.

I added a mount line in /etc/fstab and used the uid= and gid= to set myself as the owner. I have the script mount the drive, and luckily enough, when I remove the key, the mount goes away.

BTW, I don't use the key for backup, but I've found that the "unison" utility is very useful for syncing the data on the key with the data on either of two systems.

What I'd really like to do is to pop up a window, like gnome-terminal or xterm or something, and then execute an optionally interactive script. Anybody know how to do that? I tried sudo -u jpipkins gnome-terminal, but that didn't work.

Correction/Diff that worked for me

will's picture
Submitted by will on Sun, 01/07/2007 - 11:57.

Great article. This is something I've had to manually do and now I'm free of that task. Yahooo!

I struggled a little at first because it just didn't work straight away. I'm running Ubuntu Edgy. Then I followed the link to Daniel Drake's "Writing udev Rules" and noticed that his examples all used "==" instead of "=". Each declaration in the udev rule seems to need 2 math symbols. They should be "==" or "+=". Here is my rule and it worked great. Oh the joy!

BUS=="usb", SYSFS{serial}=="00176F962D19E", SYMLINK=="cruzer", RUN+="/usr/local/bin/backup-thumb.sh cruzer "

Now I just need new laptop with USB2.0 as a gig thumbdrive takes 30 mins to backup.

rsync

Luis Sismeiro's picture
Submitted by Luis Sismeiro (not verified) on Thu, 03/01/2007 - 11:57.

Why not use rsync to backup only the modified files? It isn't difficult if the flash isn't encryped.

Regards,
Luis Sismeiro

generations

Bill Arlofski's picture
Submitted by Bill Arlofski (not verified) on Wed, 03/21/2007 - 08:50.

Rsync is a great solution for keeping files and/or directories in sync, and is much faster than copying the whole thing each time.

But, rsync is not so great if you sync, then realize that you need a specific version of a file from 2 days ago.

--
Bill Arlofski
Reverse Polarity

rsync snapshots

Chris's picture
Submitted by Chris (not verified) on Wed, 03/21/2007 - 10:29.

You can get the best of both worlds though (speed of rsync + multiple versions), with the added bonus of consuming less space than multiple full copies.

http://www.mikerubel.org/computers/rsync_snapshots/

The solution described there gives the illusion of multiple full copies, while only requiring the space of one copy plus the sum of the deltas.

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