From: Joerg Bruehe
Date: January 20 2011 11:53am
Subject: Re: Can't read dir of '.' (errno: 13)
List-Archive: http://lists.mysql.com/mysql/224125
Message-Id: <4D38223C.3020702@oracle.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-15
Content-Transfer-Encoding: quoted-printable

Hi!


Jerry Schwartz wrote:
> [[...]]
>=20
>> [[...]]
>>
> [JS] Sorry, that still doesn't make sense to em. To authenticate the us=
er,=20
> mysqld needs to read the mysql database. That is also where the databas=
es are=20
> listed (in `mysql`.`db`). If the daemon can read `mysql`.`user`, why ca=
n't it=20
> read `mysql`.`db`? It's a MyISAM database, so everything is in the same=
 file.

Now I understand how your question was meant - sorry to explain a
completely different issue first.

About reading files: MyISAM is stored file-per-table, so the table
"mysql.user" is stored in the three files "mysql/user.{frm,MYD,MYI}";
table "mysql.db" is stored in other files which might have got different
permissions. (This would be a handling error, obviously.)

>=20
> What am I missing? Does SHOW DATABASES do something other than pull the=
=20
> database names out of `mysql`.`db`?

AIUI, there are operations for which the server wants to read the
directory, and "show databases" seems to be one of them.
For examples, see these bug reports:
  http://bugs.mysql.com/bug.php?id=3D22615
  http://bugs.mysql.com/bug.php?id=3D42676
  http://bugs.mysql.com/bug.php?id=3D51399
Sorry - I would tell you more details, if I knew them for sure.

Now, consider a case like this:
  drwx--x--x   user-A group-B   .
  -rw-rw-rw-   user-A group-B   file

In this case, "file" would be readable (and even writable) for everybody
knowing the name, but a "ls ." would fail for everybody but "user-A":
There is no "read" permission on the directory for anybody but the owner.=



Regards,
J=F6rg

--=20
Joerg Bruehe,  MySQL Build Team,  joerg.bruehe@stripped
ORACLE Deutschland B.V. & Co. KG,   Komturstrasse 18a,   D-12099 Berlin
Geschaeftsfuehrer: Juergen Kunz, Marcel v.d. Molen, Alexander v.d. Ven
Amtsgericht Muenchen: HRA 95603