====== Remote Backup ======

If your intent is to backup a remote computer's HDD A via SSH to a single file that's on your local computer's HDD, you could do one of the following.
Examples

* run from remote computer

  $ dd if=/dev/sda | gzip -1 - | ssh user@local dd of=image.gz

* run from local computer

  $ ssh user@remote "dd if=/dev/sda | gzip -1 -" | dd of=image.gz
====== Backup mit restic ======
Backup einer remotemaschine auf meinen rechner hinter NAT.
  $ ssh -R 20022:127.0.0.1:22 <remoteserver>  "sudo restic -r 'sftp:<user>@127.0.0.1:<restic/repo>' -p /root/.resticpw backup -x /"
====== Add apt-key (the new way) ======

* from a webserver in armor format (mostly):
  $ curl <https://example.com/key/repo-key.gpg> | gpg --dearmor > /usr/share/keyrings/<myrepository>-archive-keyring.gpg

* from a webserver not in armor:
  $ wget -O /usr/share/keyrings/<myrepository-archive-keyring.gpg> <https://example.com/key/repo-key.gpg>
  
* from gpg key server:
  $ gpg --no-default-keyring --keyring /usr/share/keyrings/<myrepository>-archive-keyring.gpg --keyserver <hkp://keyserver.ubuntu.com:80> --recv-keys <fingerprint>

* in /etc/apt/sources.list.d muss dann das signed-by:
  deb [signed-by=/usr/share/keyrings/<myrepository>-archive-keyring.gpg] <https://repository.example.com/debian/ stable main>

====== Lösche leere Verzeichnisse rekursiv ======

  $ find . -type d -empty -delete

====== Ändere recursiv die Rechte aller Verzeichnisse ======

  $ find . -mindepth 1 -type d -exec chmod 775 {} \;

====== IP forwarding ======

  $ echo "1" >/proc/sys/net/ipv4/ip_forward
  $ iptables --table nat --append POSTROUTING --out-interface eth0 -j MASQUERADE
  $ iptables --append FORWARD --in-interface eth1 -j ACCEPT

====== Festplatte testen ======
  $ smartctl --all /dev/sda
  $ smartctl -t long /dev/sda

  ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  5   Reallocated_Sector_Ct   0x0033   100   100   036    Pre-fail  Always       -       48
  197 Current_Pending_Sector  0x0012   100   100   000    Old_age   Always       -       2

  * Reallocated_Sector_Ct = wie viele Blöcke wurden durch Reseveblöcke ersetzt
  * Current_Pending_Sector = verdächtige Sektoren

  $ badblocks -s -v -v -n -c 262144 /dev/sda

  * Bei großen Platten

  $ sudo -n blockdev --getbsz /dev/sdX # <- für blocksize
  $ sudo badblocks -t random -w -s -b {blocksize} /dev/sdX
  
====== Starte über ssh ein Program in einer Wayland session ======
  $ ssh <maschine>
  $ export DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/$UID/bus
  $ systemd-run --user firefox --new-tab --url 'https://palava.tv'

====== Lösche alle configs von remove'ten Paketen ======

  $ aptitude purge ?config-files
  
====== Ändere bookworm zu trixie ======

  $ sed -i 's/bookworm/trixie/g' /etc/apt/sources.list