Using special permissions

As we've seen in the previous section, there are special permissions that could be applied to files and directories. Let's start by reviewing Set-UID (or suid) and Set-GUID (or sgid).

Understanding and applying Set-UID

Let's review how Set-UID applies to files and directories:

• Set-UID permission applied to a file: When applied to an executable file, this file will run as if the owner of the file was running it, applying the permissions.
• Set-UID permission applied to a directory: No effect.

Let's check a file with Set-UID:

[root@rhel8 ~]# ls -l /usr/bin/passwd 
-rwsr-xr-x. 1 root root 33544 dic 13  2019 /usr/bin/passwd

The passwd command requires root permissions to change hashes in the /etc/shadow file.

To apply this permission, we can use the chmod command, applying u+s permissions:

[root@rhel8 ~]# touch testsuid
[root@rhel8 ~]# ls -l testsuid 
-rw-r--r--. 1 root root 0 ene 28 05:16 testsuid...