chmod 755 all directories,
644 to all files, and made sure directories such as
/usr/bin/ all have +x bit, but I am not the most knowledgeable about the file system structure, how do I make sure everything is correct? (I accidentally
chmod 644 / my entire system before this and that's how I messed it up initially)
The only sure method is to re-install. If you make a backup you could do a re-install without formatting /. That would overwrite all system files with their correct permissions.
I just chmod 755 all directories, 644 to all files
That is not correct for all the files on your system. It might make your system use able though.
- /tmp/ needs 777 and sticky bit set.
- Logfiles in /var/log/, some should be 640 (like
syslog) to prevent "others" looking at your log files.