mjhjmtu

I understand that creating/removing a file from a directory with sticky bit set requires one of the followings

• you are root


• you are the owner of the file


• you are the owner of the directory

and you must also have +w on the directory.

The problem is with +x on the directory. I understand that if sticky bit of the directory is not set, +x is needed to create/remove files in it. However, my prof says that if the sticky bit is set, +x is not needed.

I tried it on Ubuntu 16.04, and it seems that +x is still needed even when the sticky bit is set.

Bob@david-VirtualBox:/home/Alice$ ls -ld InBox/
drwx----wT 2 Alice Alice 4096 十一 7 01:09 InBox/
Bob@david-VirtualBox:/home/Alice$ touch InBox/some_file
touch: cannot touch 'InBox/some_file': Permission denied
Bob@david-VirtualBox:/home/Alice$ rm InBox/link
rm: cannot remove 'InBox/link': Permission denied
Bob@david-VirtualBox:/home/Alice$ su Alice
Password: 
Alice@david-VirtualBox:~$ chmod 1703 InBox/
Alice@david-VirtualBox:~$ su Bob
Password: 
Bob@david-VirtualBox:/home/Alice$ touch InBox/some_file
Bob@david-VirtualBox:/home/Alice$ rm InBox/link
Bob@david-VirtualBox:/home/Alice$ 

My problem

1. Is this behavior consistent across different distributions or described in some standard?


2. I tried to google, but most resources about sticky bit on directory emphasize the 3 points mentioned above. I'd like to know if there is some (historical?) reason why my prof says so.

In case somebody asks, I would have asked my prof directly if he replies my email :(

Thank you in advance.

Your professor is wrong:

If you like to remove something from a directory you need the so called "search permission" and this is granted by the x bit on the directory.

If you don't have the x bit, you are not allowed to verify whether the file to be removed is present.