Files management


Everyone has personal data that nothing could recreate (pictures, emails, creations, …), or global data and configuration that it would take a lot of time to recreate. However you can lose some of them or all of them in several situations: hard drive crash, hard drive corruption, computer theft, computer destruction (fire…).

My advice:

  • partition your hard drive to have a separate partition for system and data
  • put important application data on the data partition (configuration, emails, …)
  • do a full mirror backup of the data partition regularly (eg with rsync or a deduplicate software such as Attic) on an external hard drive or a network drive. Try to keep at least one copy somewhere else from your home (network drive, or one at home and one at work).
  • take precautions to put the odds on your side in case of problem: make copies of your disks MBR (output of command p of fdisk), of your encrypted partitions headers, etc.

Digital Will

The goal is threefold:

  • No one non-authorized can ever access to your data
  • The trusted persons can only access to your data in some conditions (deceased, coma, …)
  • You are alerted when your data is accessed by the trusted persons (in case the access was not legitimate)

Different approaches:

  1. A service that gives your data to designated persons when they provide a death certificate for you (Wishbook, …)
    • Cons: sending a fake document, does not work for coma, service needs to remain available, price, incomplete control.
    • Variants: store it directly in a vault at the bank, or at the notary.
  2. A service that regularly checks that you are alive by requesting a connection with your private credentials (period can be adapted to the situations), and gives your data when you fail to do it, after warning emails (can be self-hosted).
    • Cons: there will be some delay between when you stop pinging and when your data becomes available, service needs to remain available, and if you host it yourself there is still a risk that your server crashes at the wrong time.
  3. A service that waits for a request to reveal your data with a personal password, sends you one or several emails to warn you that this request has been made, and in the absence of opposition from you in some delay (that can be adapted to the situation) sends your data (can be self-hosted).
    • Cons: there will be some delay between when you stop pinging and when your data becomes available, service needs to remain available, or if you host it yourself there is still a risk that your server crashes at the wrong time (but if the service is associated to your password manager for instance, then the availability is not a problem anymore…)
  4. Split the secret between several people (cf Shamir's secret, implemented for instance in ssss or libgfshare), so that X out of Y need to agree to obtain your data.
    • Cons: people need to remain accessible (and not loose the information), compromise between robustness and risk of conspiracy, what data can each person access
  5. Store your key on a piece of opaque paper (eg visit card), with you (eg in your smartphone), wrapped in a unique piece of paper (eg journal paper) that is glued. The goal is that it is impossible to read the key (eg through light) without removing the wrapping paper, impossible to remove it without tearing it apart, impossible to replace it without you noticing quickly. This base key then has to be derived a large number of times, so that it takes several days with a classical computer to derive the final key, which the designated persons then can use to decrypt their personal message. In case of unauthorized attempt, you can change the password. A better solution could be to use a proper TLP (Time Lock Problem) / TLE (Time Lock Encryption) / VDF (Verifiable Delay Function) / Delayed encryption, which would have the big advantage of fast generation, but it doesn't seem to exist standard implementations, even of seminal Rivest & Shamir proposal.
    • Cons: need to actively monitor the integrity of your artifact, doesn't work if you have an accident that destroys the artifact, need to revoke the information in case of unauthorized attempt (thus only revokable information is protected, such as passwords protecting data for which it is impossible to make an unauthorized copy beforehand), need to revoke the information in case of upgrade of the derivation scheme in order to follow hardware improvements.
    • Variant: it seems that it is possible to make “paint to scratch” with dishwashing soap and gouache, thus it can be an alternate way to hide while allowing to detect unauthorized access. Even if there is a tentative of reconstructing the paint layer, if a complex color mix was chosen, with approximate random borders, and even random color gradients, it would be very difficult to replicate accurately enough so that it goes unnoticed (especially if the color changes while drying).

Different methods could be combined, for instance 2 or 3 plus 4. But 3 managed by the password manager is probably unbeatable.

Ideally, for increased safety, the data to be obtained is always encrypted with a key that the designated persons possess.

What to transmit?

  • Passwords (master password of your password manager, computer, encrypted data partitions, phone, …)
  • Instructions about what data you have


  • Different levels of amount of information for your spouse, children, other family, friends?
  • How to transmit data (such as pictures) to a child? Probably has to go through a tutor.

File Systems

ext3, ext4

Reserved blocks

By default ext3 reserves 5% of disk space to super-user. The intent is to let to critical applications the ability to write to the disk when it is full, but it has no use for a data partition, you just waste 5% of your partition.

You can check and remove these reserved blocks with the following commands:

tune2fs -l /dev/sda1 | grep Reserved
tune2fs -r 0 /dev/sda1


  • geekie for images (fork of gqview)
  • fdupes
  • fslint

Secure delete

  • secure-delete (srm, sfill, sswap, smem)
    • -l option to be a lot faster: 2 passes instead of 38 (or -ll for only 1 pass), enough to prevent the use of consumer tools like photorec, but not for specialized companies and governments ;-)
  • shred (less advanced but more common)

Data recovery

First unmount your partition and remount it read-only.

  • extundelete –restore-file Documents/file.dat /dev/sda4 : the easiest solution if there are only a few files and you know their name. Accepts not unmounting the partition, works generally ok if you do it immediately after removing the files.
  • testdisk (photorec) is great to recover files on a mobile storage device because it works with any filesystem (finds signatures in data so no need of journal), and find all deleted files on the partition.
  • ext3grep
    ext3grep <partition> --restore-file <filename> # filename => file ; works great, but only for one file at a time...
    ext3grep <partition> --restore-all --deleted --after=1270639550 # dates -> files
    ext3grep <partition> --histogram=dtime --deleted --after=1270639000 --before=1270640000 # => dates
    ext3grep <partition> --ls --inode 2 # filenames => inodes (navigating in directories with inodes)
    ext3grep <partition> --search Libs/jafar/modules/ # filename,dates -> blocks
    ext3grep <partition> --restore-inode <inode> # inodes => files

    Notes: “restore-all” failed while building stage2 cache with error “ext3grep: void init_directories(): Assertion `lost_plus_found_directory_iter != all_directories.end()' failed.”. However doing a “ls inode” created this stage2 cache, and afterwards “restore-all” worked… but just restored everything on the disk even not deleted files/dirs, not taking into account the “after” option… But manually editing the stage2 cache to only keep files/dirs you want to restore then “restore-all” worked perfectly!

  • ext4magic
  • others: debugfs, foremost, unrm, ext3undel

Disk Recovery

In case the MBR/partition table of you disk is damaged.

Make a backup before

You should always keep a backup of your partition table !

The first way is to store the output of p command of fdisk.

You can also do a dump of the MBR and EBR:

dd if=/dev/sda of=sda.dd bs=512 count=1 # full MBR dump
sfdisk -d /dev/sda > sda.sfdisk         # MBR and EBR partition tables

Out of curiosity, the file command is able to interpret the content of your MBR dump:

file sda.dd

Restore with a backup

If you have the output of the p command of fdisk, then you can manually recreate the partition table with fdisk with the same information. As long as you don't mount or format, modifying the partition table with fdisk doesn't modify the partitions data.

If you have a full dump of MBR and EBR, you can automatically restore it:

dd if=sda.dd of=/dev/sda
sfdisk /dev/sda < sda.sfdisk

To restore the MBR without the partition table:

dd if=sda.dd of=/dev/sda bs=446 count=1

To restore only the partition table:

dd if=sda.dd of=/dev/sda bs=1 skip=446 count=66

Restore without a backup

If you don't have a copy of your partition info, don't panic, some software can recover them by searching for the partitions in the disk content (but it has to be formatted as a standard filesystem, ie not encrypted):

  • testdisk (very good) howto
  • gpart (didn't work very well for me, only found the NTFS partition) howto

Performance optimization

  • verynice
software/files.txt · Last modified: 2022/12/24 00:07 by cyril
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