Restore canary file from backup

Thu, 17 Dec 2020 11:19:37 +0000

Why Link to heading

To ensure you can successfully restore a file from a tar backup. A sha256sum only checks the integrity of the created archive, not it’s restorability.

Prerequisites Link to heading

Create a playground:

mkdir archive-test
cd archive-test

Create some content:

mkdir content
echo content1 >> content/file1
echo content2 >> content/file2
echo content3 >> content/file3

Back up your content:

tar -cf backup1.tar content

Canary Link to heading

Generate a random id:

export CANARY_ID=$(tr -dc "a-zA-Z0-9" < /dev/urandom | head -c 32)

Save that id to a file:

echo $CANARY_ID > canary

Add it to your archive:

tar -rf backup1.tar canary

Rename your archive to contain the id:

mv backup1.tar backup1."$CANARY_ID".tar

Remove the unarchived canary file:

rm -f canary

Optionally compress/encrypt/checksum the archive with gzip, gpg, and sha256sum.

Restore Link to heading

Extract the canary id:

export RESTORE_ID=$(ls backup1.$CANARY_ID.tar | cut -d '.' -f 2)

Extract the canary file:

tar -xf backup1."$CANARY_ID".tar canary

Compare the two values:

[ "$CANARY_ID" == "$RESTORE_ID" ] && echo "Match!" || echo "Fail!" && false

Cleanup Link to heading

Don’t forget to remove your test files after playing with this:

Backup on Codrut Constantin Gusoi

Restore canary file from backup

Why Link to heading

Prerequisites Link to heading

Canary Link to heading

Restore Link to heading

Cleanup Link to heading