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Usefull Commands

Interfaces
lsusb Liste les périphériques USB
dmesg | grep tty Trouver le nom du périphérique série qui vient d’être branché
lsblk List devices with mount points
sudo iw wlan0 scan Scan available wifi networks

Files
sudo chown pi mydb.db Le propriétaire du fichier mydb.db devient l’utilisateur “pi”
chmod a+x run.py rend le fichier exécutable (change les permissions)
stat -c "%a %n" file.txt to see file permission in octal (777..)
lsof file.txt to see what processes are currently reading/writing the file

processus
ps auxf List all processes
kill -9 $(lsof -ti tcp:5007) socket.error: [Errno 98] Address already in use. tue le processus serveur qui écoute le port 5007
killall -9 chromium-browse Kill a process by name
sudo ss -ltnp port listening (socket statistics)
sudo ss -ltnp | grep :port kill -9 port listening and killing zombie thread server

server / ports
sudo ss -tulpn Show servers and port listenning (socket statistics)

disk usage
Trier par taille, plus grand en premier:
sudo du -shc /var/* | sort -rh dossiers
ls -lh --sort=size fichiers
du -kx | egrep -v "\./.+/" | sort -nr fichiers et dossiers

du -xksh ./* | sort -n Espace utilisé
du -hs
df -h
cat /proc/meminfo : affiche l’état d’utilisation de la mémoire

Partitions
lsblk liste les partitions (attention: ne montre pas l'ordre réelle sur le disque)
blkid UUID des partitions
sudo fdisk -l liste les partitions (avec secteurs de début/fin)

Mounts
findmnt --fstab --evaluate show fstab content with options mount show devices currently mounted

copy / moove
cp -r source/ dest/ copie le répertoir “source” et son contenu dans le répertoire “dest”. résultat: il existe un chemin dest/source/file.txt
cp -p fstab fstab.old copie de sauvegarde conservant les permissions/mode/propriétaire
mv foo/ bar/ Déplace le répertoir foo et son contenu dans le répertoire bar. résultat: il existe un chemin bar/foo/file.txt
mv foo bar Renomme le répertoir ou le fichier foo en bar
rm -r dir/ supprime le répertoire dir et son contenu

console
tree Tree representation
tree -d Tree representation, directories only

commandes d'administration
supprimer les snaps inutiles snap list --all | awk '/désactivé|disabled/{print $1, $3}' | while read snapname revision; do sudo snap remove "$snapname" --revision="$revision"; done

Files permissions

User, Group, Others
0 No permission 
1 Execute permission 
2 Write permission 
3 Execute and write permission: 1 (execute) + 2 (write) = 3 
4 Read permission 
5 Read and execute permission: 4 (read) + 1 (execute) = 5 
6 Read and write permission: 4 (read) + 2 (write) = 6 
7 All permissions: 4 (read) + 2 (write) + 1 (execute) = 7

default permission
files 644
directory 755 (execute means ability to cd into the directory)

To change all the directories to 755 (drwxr-xr-x):
find /opt/lampp/htdocs -type d -exec chmod 755 {} \;
To change all the files to 644 (-rw-r--r--):
find /opt/lampp/htdocs -type f -exec chmod 644 {} \;

File Sharing

NFS

NFS debug

After updating /etc/exports on server, run 

exportfs -r

check if export is actually exported from server

exportfs -av
exportfs -sv
showmount -e

from client

showmount -e server_name # Check if server is providing some exports
df                       # Check if nfs export is actually mounted
cat /etc/mtab | grep nfs # Show nfs currently mounted and nfs version used

NFS options

no_root_squash

Problem: normal user can write but root cannot. Explanation: NFS was designed with the idea that user and group ids would be the same on all machines across the network. For ordinary users, that works ok. But root's UID is always 0, and just because you have root on one box, it doesn't mean that you should have root access to every machine on the network. Therefore, NFS treats root specially. By default, root is mapped to the nobody user, which normally has no write access. The no_root_squash option allows you to change how root is handled. This option must be used for rsnapshot/rsync (to preserve ownership)

https://help.ubuntu.com/community/SettingUpNFSHowTo

Mount NFS drive (synology) from linux (NFSV4 client)

sudo mkdir /media/nas
sudo mount -t nfs -o proto=tcp,port=2049 192.168.1.52:/volume1/hpsrv-backup /media/nas
sudo chmod xxx /media/nas

To do this on startup, edit /etc/fstab: 

<nfs-server-IP>:/   /mnt   nfs    auto  0  0

Samba

turn-your-raspberry-pi-into-a-nas-box/
share a directory

sudo apt-get install samba samba-common-bin
sudo nano /etc/samba/smb.conf

Guest account (no password) To add at the end of smb.conf :

[public]
comment = Partage Samba sur Raspberry Pi
path = /home/pi/partage
writable = yes
guest ok = yes
guest only = yes
;create mode = 0777
;directory mode = 0777
share modes = yes
force user = pi
force group = pi

Private account

Create user 'pi' with the following command: sudo smbpasswd -a pi

[private]
comment = Dev_chaudiere
path = /home/pi/private
writable = yes
create mode = 0777
directory mode = 0777
public = no

Restart service
sudo systemctl restart smbd.service

From Windows PC
\\server_ip\samba_share_name

Security

Firewall (UFW)

Do not enable if webmin is active on the system

sudo ufw status verbose

https://www.tecmint.com/setup-ufw-firewall-on-ubuntu-and-debian/

fail2ban

sudo apt-get install fail2ban

Log

main log files

  • /var/log/syslog - main log file for all services
  • /var/log/message - whole systems log file
  • /var/log/auth.log - all authentication attempts are logged here

usefull commands

  • journalctl -u motioneye > motioneye.log Export log to a file
  • journalctl -n 20 Show last 20 lines of system log
  • journalctl -f show live log
  • tail -f my_log_file.log show live log of custom file
  • tail -f log/* show live log of all files in log/ directory