Permessi e proprietà dei file con chmod e chown

Now that you can create users and groups, the next step is controlling what each user can do with files. Linux enforces this through file permissions and ownership.

ls -l shows a permission string like -rwxr-xr--. The first char is the file type; the next three triples are permissions for owner, group, and others.

• r (read) = 4
• w (write) = 2
• x (execute) = 1

Add them per triple to get an octal digit. rwx = 7, r-x = 5, r-- = 4.

chmod 754 file sets owner rwx, group r-x, others r--.

You can also add or remove specific bits: u=user, g=group, o=others, a=all.

A very common task: give a newly written script execute permission so you can run it directly.

chown user:group file reassigns who owns a file. This ties directly into the user/group management you already learned.

You can change just the group with chgrp or with the :group form of chown.

The -R flag applies changes to a directory and everything inside it. Use carefully.

New files get default permissions masked by umask. A umask of 022 removes write for group and others, producing 644 files and 755 directories.

When sharing a project directory with a team: set the group, grant group read/write, and keep others restricted.

What octal value represents rwxr-xr--?

You now control access to files:

• Permissions split into owner/group/others with r(4)/w(2)/x(1)
• chmod sets modes via octal or symbols
• chown/chgrp reassign ownership
• -R applies recursively; umask sets defaults