Add User:
useradd -m -g [group] -G [additional_group] [username]
The
-mflag creates /home directory for user
Expire User:
usermod --expiredate [YYYY-MM-DD] [username]
If user try to login, he or she will get the following message:
Your account has expired; please contact your system administrator Authentication failure
Adding .desktop files:
sudo vim /usr/share/applications/program-name.desktop
Adding .deb source:
sudo vim /etc/apt/sources.list.d/name-of-program.list
Import PGP key:
gpg2 --import /path/to/key/name.pgp
Revieve PGP Key:
gpg2 --recv [key]
Export PGP Key:
gpg2 --export [key] | apt-key add -
List system package version:
dpkg -l | grep [packagename]
Create Symlink:
ln -sfv /path/to/file /path/to/symlink
Read Symlink Destination:
readlink /path/to/symlink
Remove Symlink:
unlink /path/to/symlink