In this manual, we will learn to change the permissions of any file in a GNU/Linux operating system through the command line.
However, before mentioning any type of command, we must learn about the operation of the permissions system in GNU/Linux operating systems. We show it to you:
In particular there are three types of permissions that a file or directory in Linux can have assigned.
The three types of permissions listed below can be activated or deactivated in each file/directory for any of the three types of users mentioned below:
As we have explained in the previous section, these three types of users and these three types of permits can be freely assigned.
For example, the owner of the file/directory can have read, write, and execute permissions while other users of the system can only have read permissions. Any combination of these three permits and three users is possible, providing a total of 512 possible combinations.
Finally, to assign these permissions we will use the "chmod" command.
Important: To be able to change the permissions of a file or directory you must be an owner or user with administrative privileges. Only the owner or users of type 'root' can change the permissions of a file/directory.
The chmod command has the following syntax:
chmod [permission to assign or remove] nombredearchivo
The symbols used to describe a permission are the following:
Permissions: r: reading w: writing x: execution
Users: u: owner g: group or: others a: all of the above
Thus the abbreviation "u+w" would indicate that you want to assign write permission to the owner. Other examples and combinations:
Knowing these abbreviations, we can now use the "chmod" command as follows:
chmod u+x nombredearchivo
This command would grant execution permission to the file "nombredearchivo" to the owner of the file.
Multiple permissions can be granted to multiple users at the same time in this way:
chmod ug+wrx nombredearchivo
This command would grant read, write, and execute permissions (full permissions) to both the owner and the group members to the file " nombredearchivo ".
Finally, it is worth highlighting the usefulness of the "-R" option that applies these permissions recursively to any file that is inside a directory. For example:
chmod -R u+wx nombrededirectorio
This command applies the write and execute permissions for the owner to any file or directory contained within "nombrededirectorio", including files/directories contained in lower levels.
Note: the "chmod" command has a so-called "octal mod" that allows assigning permissions through the use of numbers. This information will be detailed in another user manual.