Overview

Debian is a free and open source operating system based on linux kernel. Many OS are based on the Debian including: Ubuntu, Mint & Raspbian.

Hardware

Check processor architecture

dpkg --print-architecture

Date & Time

date
date "+%H:%M:%S"

Timezone

# set in 
/etc/timezone

Debian version

cat /etc/os-release
cat /etc/debian_version

Manage User & Group

Find a user’s UID or GID

id <username>
# id
id -u <username>

# gid
id -g <username>

# all the groups a user belongs to
id -G <username>

# find all
cat /etc/passwd
cat /etc/group

Modify user account

# add user to group
usermod <username> -aG <groupname>

Add user

# add user and create the home directory for the user
# group with the same name also created
useradd -m <username>
useradd -m <username> -p <password>

# add user with group; so that group of the same name NOT created
useradd -m <username> -g <groupname>

# add user BUT not create home directory, and not allowed to login
useradd -M -L <username>

# add user with a specific id; a group of SAME "name and id" is also created 
useradd -M <username> -u 1883

Add group

groupadd <groupname>
cat /etc/group

Delete user and group

# delete user from a group
deluser <username> <groupname>

# delete user with no home directory, no login
userdel <username>

# delete regular user with password, home dir, login, files, etc. 
passwd -l <username>
tar -zcvf /nas/backup/account/deleted/v/<username>.$uid.$now.tar.gz /home/<username/

pgrep -u <username>
ps -fp $(pgrep -u <username>)
killall -KILL -u <username>
find /var/spool/at/ -name "[^.]*" -type f -user <username> -delete
crontab -r -u <username>
lprm <username>
find / -user <username> -print
find / -user <username> -exec chown newUserName:newGroupName {} \;
userdel -r <username>

# delete group
groupdel <groupname>

chmod and chown

- Make shell file executable:

chmod +x <filename>

- Change owner user of file:

chown <userName> <filename>

- Change owner group of file:

chown :<groupName> <filename>

- Change both owner user and group of file:

chown <userName>:<groupName> <filename>
chown -R <userName>:<groupName> <foldename>

Package Management

apt is debian package management.

Debian maintains a list of links to repository that apt- or apt-get can download from. The list(s) is stored in a file /etc/apt/sources.list, and in a directory containing the list files. These files are merged at runtime to form the complete list. Therefore, the content format of these files are exactly the same.

The benefits for allowing list of files in the sources.list.d folder are: ease of configuration and automation. For example, to disable a repository that is listed on a file, you can just remove the file instead of manipulating the main list (i.e. sources.list).

Also see:

- List of apt repositories

grep ^[^#] /etc/apt/sources.list /etc/apt/sources.list.d/*

Example of the default content of /etc/apt/sources.list for raspbian

deb http://raspbian.raspberrypi.org/raspbian/ stretch main contrib non-free rpi
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://raspbian.raspberrypi.org/raspbian/ stretch main contrib non-free rpi

and /etc/apt/sources.list.d/debian.list

deb http://archive.raspberrypi.org/debian/ stretch main ui
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
#deb-src http://archive.raspberrypi.org/debian/ stretch main ui

Also see:

- List of installed packages

dpkg -l

dpkg --get-selections | grep python3-picamera

# list where package install files
dpkg -L <packageName>

- Web-based tool to search apt packages

  • https://www.debian.org/distrib/packages

  • https://aur.archlinux.org/packages/

  • https://tracker.debian.org/

- Install package

apt-get install <packageName> --no-install-recommends

Notes:

  • Do not consider recommended packages as a dependency for installing
  • during package search, gathers the list required packages, recommended packages, and suggested packages
  • The required packages are dependencies so their installation is mandatory
  • The recommended packages will be installed by default unless the --no-install-recommends is specified or turned off in the /etc/apt/apt.conf
  • The suggested packages is not installed by default.

- References

  • https://www.howtoforge.com/linux-dpkg-command/
    • additional dpkg features & how-to

How-to

Setting Environment vars

export K3S_URL="https://rpik3ssvr:6443"
  • Preset environment variables 
    echo $HOME

Configure program to run at boot

Old school mechanism for starting python program, svc.py at boot:

  • add it to /etc/rc.local
  • make sure rc.local runs at boot time
  • must be setup as root.

setup commands:

sudo chmod 755 /etc/rc.local
sudo nano /etc/rc.local

# in the editor; scroll to the bottom & add one line

ifup eth0
 
/usr/bin/python /home/svc.py &
  
exit 0

# exit nano editor CTL-X

sudo /etc/rc.local

Setup SSH for putty and winscp

  • https://devops.ionos.com/tutorials/use-ssh-keys-with-putty-on-windows/

/etc

apt Repository list

/etc/apt/sources.list
/etc/apt/sources.list.d/*

File System Table - fstab

/etc/fstab

Add entry in the fstab file to persist mount point across reboot

Hosts

/etc/hosts

rc.local

/etc/rc.local

Example - setup startup program

Timezone

/etc/timezone

Example - Setting Timezone

References

Tags:
os
linux
debian