If a user does not have sudo privileges, can he/she create a file or modify any file outside of his/her home directory, and outside of any external media devices he/she might have connected to the system? Let's assume he/she has not been explicitly given access to any other directory. I'm trying to back up the files of someone who cannot be reached. The system is RHEL, but I'm interested in knowing the answer for Ubuntu (and CentOS too, but I assume the answer for CentOS would be similar to RHEL.)
Can non-sudoer modify anything outside of home directory
permissions
Yes, he/she can write files on /tmp for instance. Regarding modification of files, that depends on the file's permissions. If all users are allowed to modify that file he/she will be able to modify that file or if he/she belongs to the other user's group and that group has permissions to do that.In the end it all depends on the permissions, so take a look at the file system, use ls -l or find and discover by yourself where he/she can or can not write or modify.