Paul Howarth írta:
On Sun, 2006-05-28 at 22:14 +0200, Zoltan Boszormenyi wrote:
> Paul Howarth írta:
>
>> On Sun, 2006-05-28 at 20:33 +0200, Zoltan Boszormenyi wrote:
>>
>>
>>> Paul Howarth írta:
>>>
>>>
>>>> On Sun, 2006-05-28 at 17:13 +0200, Zoltan Boszormenyi wrote:
>>>>
>>>>
>>>>
>>>>> Hi,
>>>>>
>>>>> answering to myself. :-)
>>>>>
>>>>> Zoltan Boszormenyi írta:
>>>>>
>>>>>
>>>>>
>>>>>> So, how can I fix the current situation and include /home1/pgsql
in
>>>>>> the postgresql context/domain? I would like to relabel it to
recover
>>>>>> the context...
>>>>>>
>>>>>> BTW the same principle would apply if one would like to create
>>>>>> another tablespace for postgresql under another mount point...
>>>>>>
>>>>>>
>>>>>>
>>>>> After some more RTFM, it would seem simple:
>>>>>
>>>>> semanage fcontext -a -t postgresql_db_t
'/home1/pgsql/data(/.*)?'
>>>>> semanage fcontext -a -t postgresql_log_t
'/home1/pgsql/pgstartup.log'
>>>>> fixfiles relabel /home1/pgsql
>>>>>
>>>>> But it was not enough. Starting it with "service postgresql
start" fails.
>>>>> I had to modify the rc script, too. I had to replace /var/lib/pgsql
with
>>>>> /home1/pgsql everywhere despite the /var/lib/pgsql -> /home1/pgsql
symlink.
>>>>>
>>>>>
>>>>>
>>>> This will be failing because SELinux is blocking access to reading the
>>>> symlink. You should find an avc denial for the lnk_file in your logs.
>>>>
>>>>
>>>>
>>> I haven't found any. :-(
>>>
>>>
>> Perhaps you won't find any now because it's never trying to
>> access /var/lib/pgsql since you changed the configs to get around the
>> problem? Are there none from first attempt?
>>
>>
> Sorry, I expected the audit messages in /var/log/messages.
> Yes, I have such messages in audit.log:
>
You must have auditd running (probably a system upgraded from FC4 rather
than a clean FC5 install).
Actually, no. I was a clean install over my previous FC3.
I installed and set auditd to run.
> type=AVC msg=audit(1148827118.909:2493): avc: denied { read }
\
> for pid=29719 comm="postmaster" name="pgsql" dev=hdb3 \
> ino=1010804 scontext=user_u:system_r:postgresql_t:s0 \
> tcontext=user_u:object_r:var_lib_t:s0 tclass=lnk_file
> type=PATH msg=audit(1148827118.909:2493): item=0 \
> name="/var/lib/pgsql/data/postgresql.conf" flags=101
>
...
>> The existence of the symlink itself is probably the problem, rather than
>> its context. Applications have to have specific permission to be able to
>> read (and hence follow) symlinks in SELinux.
>>
>>
> So, how can I tweak the policy so postgres can follow just this one symlink?
>
Set yourself up for making local policy modules:
# yum install checkpolicy
# cd /root
# mkdir selinux.local
# cd selinux.local
# chcon -R -t usr_t .
# ln -s /usr/share/selinux/devel/Makefile .
Make a local policy module for this issue, in this directory:
1. Create a file postgres.te with this content:
module postgres 0.1;
require {
class lnk_file read;
type postgresql_t;
type var_lib_t;
};
# Allow postgres to read /var/lib/pgsql -> /home1/pgsql symlink
allow postgresql_t var_lib_t:lnk_file read;
2. Create a file postgres.fc with this content:
/home1/pgsql[^/]*/data(/.*)?
gen_context(system_u:object_r:postgresql_db_t,s0)
/home1/pgsql[^/]*/pgstartup.log --
gen_context(system_u:object_r:postgresql_log_t,s0)
(that's two long lines)
3. Create an empty postgres.if file:
# touch postgres.if
4. Build the policy module
# make
Next, remove any file context objects you added for this issue using
semanage (contexts will now be managed using your local policy module):
# semanage fcontext -d -t postgresql_db_t '/home1/pgsql/data(/.*)?'
# semanage fcontext -d -t postgresql_log_t '/home1/pgsql/pgstartup.log'
# semanage fcontext -d -t postgresql_db_t '/home1/pgsql2/data(/.*)?'
Finally, install your new policy module:
# semodule -i postgres.pp
Thanks, it almost worked. After doing these above,
I still got avc denied { search } messages like this below:
type=AVC msg=audit(1148979521.381:10): avc: denied { search } for
pid=2666 comm="postmaster" name="/" dev=sda1 ino=2
scontext=system_u:system_r:postgresql_t:s0
tcontext=system_u:object_r:default_t:s0 tclass=dir
As it turned out, /home1 was default_t and postgresql is not enabled to
search
and read files in default_t context. It made it working:
# semanage fcontext -a -t var_lib_t -f -d '/home1'
# fixfiles relabel /home1
What puzzled me is starting postgresql failed at boot
but not the manual "service postgresql start" after bootup.
(Maybe different contexts are applied to the logged-in root
and the init program?)
The two lines above made it working again.
>>>> An easier way is to bind mount /home/pgsql on
/var/lib/pgsql etc. and do
>>>> a restorecon -R on the "new" /var/lib/pgsql. That achieves the
same
>>>> effect without the symlink.
>>>>
Actually I missed the "bind mount" part. That would have been much easier.
But the crash course in SELinux was most fruitful, thank you.
>>> I know, but the disk I install will be (or already is)
used for both my
>>> databases
>>> and for extending /home. I created only one partition on that disk, so...
>>> The system is my home/devel machine and the disk is SATA and fast enough.
>>> Although for a high performance production machine, I would always give
>>> PostgreSQL it's own disks to separate WAL, table and index spaces.
>>>
>>>
>> Perhaps you'll use LVM next time :-)
>>
>>
> Well, how can you merge two disks with LVM and still
> be able to record from the BTTV card to only one of them?
> Having a separate disk dedicates the disk speed to this task
> while another program can write under /home. Maybe
> my knowledge is a bit outdated, so enlightenment is welcome. :-)
>
You could create two partitions on the additional disk, one for
extending the space on /home and one dedicated to BTTV. Create an LVM
physical volume on each partition. Add the first physical volume to the
volume group used for /home, then extend the logical volume for /home
and resize up the partition. Create a new volume group for BTTV purposes
and add the second physical volume to it. Create a new logical volume
for BTTV, and create a new filesystem on that logical volume. Since it's
in a separate volume group, it will be allocated space only from the
fast new drive.
Thanks for this info. Next time I reinstall my machine (FC6?)
I will do a similar scheme.
Sorry for the late answer, yesterday I donated my blood
and had to hit the bed earlier that my usual.
Best regards,
Zoltán Böszörményi