Boring Sysadmin task, only do if absolutely necessary. It will demotivate you.

Check file or folder permissions

{bash} ls -l

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let's explain the second line in more details (7thProblem.py)

-rw-r--r--: file permission string:

-: first character - indicates the type of file. A minus for regular files, d for folder
rw-: next three characters are the owners permissions, rwx, "read, write, execute". Here the owner (philipp) is only allowed to read and write, not to execute the file.
r--: The group permissions: read, not write, not execute.
r--: The permissions for everyone else.

1: The number indicates the amount of hard links towards that file.

philipp: Owner of the file/directory
staff: Group name that owns the file/directory
591: Size of the file in Bytes.
Apr 15 15:48: Date the file was last modified
7thProblem.py: File name

Modify owners

{shell}chown stands for "change owner"

modify the owner of a file

{shell} chown userName fileName

modify the group that owns a file

{shell} chown :groupName filename

You can modify both at the same time

{shell} chown userName:groupName fileName

For a folder, add -R to apply it to every subfolder and file

{shell} chown -R userName:groupName folderName

Modify permissions

{shell} chmod permissions resource-name

example:
{shell} chmod 740 fileName

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You simply add the numbers together to give permissions. 4: read, 6: read + write, 7: read + write and execute

If this is too complex you can also use this:

{shell} chmod u=rwx,g=r,o-rwx fileName

Other:

List all users and their groups:

{shell} less /etc/passwd