Users and permissions

Read rwx bits, use chmod and chown, and stay off root when you can.

Every file has an owner, a group, and a permission triplet for user, group, and others. ls -l shows that line. r is read, w is write, x is execute (or traverse, on a directory).

ls -l /usr/bin/python3
chmod 755 backup.sh
chown sam:sam backup.sh

Prefer a sudo user over working as root in a daily shell. Use sudo -l to see what you are allowed to run. When a service needs a dedicated account, create one instead of sharing root.