Creating

dd if=/dev/zero of=file.img bs=1 count=0 seek=512M

Copy

cp --sparse=always new_file.img recovered_file.img

Growing

dd if=/dev/zero of=file.img bs=1 count=0 seek=1G

This will increase its size to 1 Gb, and leave its information intact.

cryptsetup …

Doing it manually

Since I can’t use the tool provided by Seagate, the workaround is:

• find the firmware in the ISO
• apply it manually to both disks

> sudo mount -o loop ./Downloads/BarracudaLP-ALL-CC35.iso /home/fabien/plop/

Dockerfile

FROM gentoo/portage:latest as portage
FROM gentoo/stage3-amd64:latest

COPY --from=portage /var/db/repos/gentoo /var/db/repos/gentoo

ENV ACCEPT_KEYWORDS="~amd64" \
    EMERGE_DEFAULT_OPTS="--jobs=4 --quiet" \
    FEATURES="-sandbox -usersandbox -ipc-sandbox -network-sandbox -mount-sandbox -pid-sandbox" \
    MAKEOPTS="-j4" \
    USE=""

RUN emerge dev-vcs/git app-portage/repoman dev-util/pkgcheck \
 && rm -rf /var …

concat

FFmpeg has three concat methods.

ffmpeg -i 'concat:input1|input2' -codec copy output

ffmpeg -i opening.mkv -i episode.mkv -i ending.mkv \
  -filter_complex '[0:0] [0:1] [1:0] [1:1] [2:0] [2:1] concat=n=3:v=1:a=1 [v …

Shrink a vdi VirtualBox disk image

• Run defrag in the guest (Windows only)
• Nullify free space:

With a Linux Guest run this:

cat /dev/zero > zero.fill;sync;sleep 1;sync;rm -f zero.fill

With a Windows Guest, download SDelete from Sysinternals and run this:

sdelete.exe c: -z …

clean up git

git reflog expire --expire=1.minute refs/heads/master
git fsck --unreachable
git prune
git gc

A simple way to create git repository on a server machine connecting via ssh

Boot Kernel Command Line

On boot systemd activates (by default), the target unit default.target whose job is to activate services and other units by pulling them in via dependencies.

To override the unit to activate, systemd parses its own kernel command line arguments via the systemd.unit= command line …

replace symlinks

for i in *; do link=$(readlink $i) && rm $i && mv $link $i; done

permissions

find /home/user -type d -print0 | xargs -0 chmod 0775
find /home/user -type f -print0 | xargs -0 chmod 0664

clean up dconf

For a single key:

dconf reset "/path/to/the/key"

Must …

pdfimages

pdfimages -j foo.pdf  bar

This will extract all images from foo.pdf and save them in JPEG format (option -j) to bar-000.jpg, bar-001.jpg, bar-002.jpg, etc.

delete metadata

exiftool -exif:all= *.jpg
exiftool -xmp:all= *.jpg

or use MAT: Metadata Anonymisation Toolkit https://0xacab.org/jvoisin …

Warning

The instructions below will irretrievably destroy data. Moreover, as the hdparm manpage explains, "these switches are DANGEROUS to experiment with, and might not work with every kernel. USE AT YOUR OWN RISK."

Explanation

According to National Institute of Standards and Technology (NIST) Special Publication 800-88: Guidelines for Media Sanitization …

shrink lvm

# Unmount the filesystem and check its' LV
umount /mnt/foo
e2fsck -f /dev/mapper/vg0-foo

# Shrink ext4 and then the LV to the desired size
resize2fs -p /dev/mapper/vg0-foo 40G
lvreduce -L 40G /dev/mapper/vg0-foo

# Before continuing, run e2fsck. If it bails because the partition
# is …

Systemd

CONFIG_UTS_NS=y
CONFIG_IPC_NS=y
CONFIG_USER_NS=y
CONFIG_PID_NS=y
CONFIG_NET_NS=y
CONFIG_DEVPTS_MULTIPLE_INSTANCES=y

mkdir /var/lib/machines/gentoo-stage3-amd64 && cd /var/lib/machines/gentoo-stage3-amd64
wget https://gentoo.osuosl.org/releases/amd64/autobuilds/current-stage3-amd64 …

Get the track information

mkvmerge -i /path/to/matroska.file.mkv

Sample output

Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_DTS)

This means that the matroska.file.mkv contains two tracks, a video track with id 1 and a DTS track with id 2.

Extract the …

calibration

This is the command to start the calibrator:

dispcal -v -y l -g 2.2 -t 6500 -q h target

There are a few options that can be set in this command by changing the values after the option flags (the dash followed by a letter):

Monitor type: -y …

cdparanoia

cdparanoia -B -- "-3"

flac

for i in *.flac; do flac -d "$i"; done

split cue

shnsplit -o flac -f FILE.cue -t %n.%t FILE.flac

mp3

for i in *.wav; do lame -vbr-new -V 0 "$i" "${i%.wav}.mp3"; done

coverart

eyeD3 --add-image=./cover.jpg:FRONT_COVER ./*.mp3

scan …