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# Linux commands
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# User management
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#### create a New Group
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If you want to create a new group on your system, use the groupadd command following command, replacing new_group with the name of the group you want to create.
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> sudo groupadd mynewgroup
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#### add an existing user account to a group
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To add an existing user account to a group on your system, use the usermod command, replacing examplegroup with the name of the group you want to add the user to and example username with the name of the user you want to add.
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> sudo usermod -a -G examplegroup exampleusername
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For example, to add the user geek to the group sudo , use the following command:
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> sudo usermod -a -G sudo geek
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remove a user from a group
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> sudo gpasswd -d user group
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Change user
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> su backups
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Voer een comando uit als een andere user
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> sudo -u user commando
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#### ownership
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(recursive in folder)
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> sudo chown -R syncthing:syncthing Muziek/
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#### change permissions CHMOD
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chmod ...
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Alle folders naar 770
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> sudo find Muziek/ -type d -exec chmod 770 {} \;
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Alle bestanden naar 660
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> sudo find Muziek/ -type f -exec chmod 660 {} \;
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recursief verwijderen (niet lege) directories
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>rm -R /path-to-dir
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##### copy
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You can copy the content of a folder /source to another existing folder /dest with the command
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cp -a /source/. /dest/
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The -a option is an improved recursive option, that preserve all file attributes, and also preserve symlinks.
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The . at end of the source path is a specific cp syntax that allow to copy all files and folders, included hidden ones.
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##### find
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vinden bestand (recursief):
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sudo find -iname “naam.bestand”
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grootte directory
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##### disk use
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du -hs /dir
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sudo du -hc --max-depth=1
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##### mounten
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usb stick mounten
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sudo fdisk -l
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sudo mkdir /mnt/usb-stick/
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sudo mount /dev/sdb1 /mnt/usb-stick/
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##### formateren
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formateren
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sudo umount /dev/sdb1
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sudo mkfs.ext4 /dev/sdb1
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#### rsync
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backup met permissies:
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sudo rsync -auvh --progress <sourceDir>/ <destDir>
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sudo rsync -auh /mnt/usb-stick/ /home
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Overzicht en gebruik partities
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sudo df -h
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Filesystem Size Used Avail Use% Mounted on
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udev 3.9G 0 3.9G 0% /dev
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tmpfs 786M 11M 776M 2% /run
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/dev/sde2 9.9G 1.9G 7.5G 20% /
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tmpfs 3.9G 4.0K 3.9G 1% /dev/shm
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tmpfs 5.0M 0 5.0M 0% /run/lock
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tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
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/dev/sde1 511M 3.3M 508M 1% /boot/efi
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/dev/sde6 27G 9.3G 16G 38% /home
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/dev/sde3 14G 6.0G 6.5G 49% /var
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/dev/sde5 682M 1.5M 631M 1% /tmp
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/dev/sdb1 688G 356G 298G 55% /mnt/e03b13e7-2b23-4bad-8aed-d42606a60487
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/dev/sda1 1.8T 743G 1.1T 41% /mnt/9f553b41-1144-4d23-9cef-f0722fc76bde
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/dev/sdc1 2.7T 1.4T 1.2T 55% /mnt/a8966e82-2455-4fc5-bf9a-4cfcaa44277d
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/dev/sdd1 688G 183G 506G 27% /mnt/b8827aaf-3ead-4856-a73b-2d0e4e9f7e47
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Overzicht grootte directories
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sudo du -sh *
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137M allusers
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8.8G backups
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161M joris
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16K lost+found
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203M syncthing
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Computer info
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hostnamectl
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Static hostname: rpi4
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Icon name: computer
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Machine ID: ce513f1a44ff4c9dbd382eb66e08c51e
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Boot ID: 2f7cbe4f653c4865989fd402b50861dc
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Operating System: Raspbian GNU/Linux 11 (bullseye)
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Kernel: Linux 5.15.32-v7l+
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Architecture: arm
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Ssh key less login
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@zon
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ssh-keygen
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@thrush
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(id_rsa.pub plakken in authorized keys)
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sudo nano /etc/ssh/sshd_config
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line 57: PasswordAuthentication yes
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sudo service ssh restart
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@zon
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ssh-copy-id -p 22226 joris@thrush.minded.net
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@thrush
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sudo nano /etc/ssh/sshd_config
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line 57: PasswordAuthentication no
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sudo service ssh restart
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@zon
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ssh joris@thrush.minded.net -p 22226
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How to find out top Directories and files in Linux
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Type the following command at the shell prompt to find out top 10 largest file/directories:
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# du -a /var | sort -n -r | head -n 10
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Nano commands
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Delete line Ctrl + k
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Journalctl
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• Logs van de huidige boot: journalctl -b.
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• Filteren op service: journalctl -u nginx.service
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• Filteren op tijd: journalctl --since "1 hour ago" of journalctl --since yesterday.
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• Prioriteit (fouten): journalctl -p err (toon alleen meldingen met prioriteit 'error' of hoger).
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• Kernellogs: journalctl -k.
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cron -N
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Running 'cron -N' triggers a cron tick, causing all job definitions
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to be processed immediately, and then exits. This is useful for
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testing changes in crontabs.