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.\" $Header: /usr/local/cvsroot/postgres95-support/doc/man/unix.1,v 1.1 1996/08/18 22:14:28 scrappy Exp scrappy $
.TH INTRODUCTION UNIX 11/05/95 Postgres95 Postgres95
.SP INFORMATION UNIX 11/05/95
.BH "SECTION 2 \(em Unix COMMANDS (Unix)"
.SH "OVERVIEW"
This section outlines the interaction between Postgres and
the operating system.  In particular, this section describes 
the Postgres support programs that are executable as Unix
commands.
.SH TERMINOLOGY
In the following documentation, the term
.IR site
may be interpreted as the host machine on which Postgres is installed.
Since it is possible to install more than one set of Postgres
databases on a single host, this term more precisely denotes any
particular set of installed Postgres binaries and databases.
.PP
The 
.IR "Postgres super-user"
is the user named \*(lqpostgres\*(rq who owns the Postgres
binaries and database files.  As the database super-user, all
protection mechanisms may be bypassed and any data accessed
arbitrarily.  In addition, the Postgres super-user is allowed to execute
some support programs which are generally not available to all users.
Note that the Postgres super-user is
.IR not
the same as the Unix super-user,
.IR root ,
and should have a non-zero userid for security reasons.
.PP
The
.IR "database base administrator"
or DBA, is the person who is responsible for installing Postgres to
enforce a security policy for a site.  The DBA can add new users by
the method described below 
and maintain a set of template databases for use by
.IR createdb (1).
.PP
The
.IR postmaster
is the process that acts as a clearing-house for requests to the Postgres
system.
Frontend applications connect to the 
.IR postmaster ,
which keeps tracks of any system errors and communication between the
backend processes.  The
.IR postmaster
can take several command-line arguments to tune its behavior.
However,
supplying arguments is necessary only if you intend to run multiple
sites or a non-default site.  See
.IR postmaster (1)
for details.
.PP
The
.IR "Postgres backend"
(the actual executable program called "postgres") may be executed
directly from the user shell by the 
Postgres super-user (with the database name as an argument).  However,
doing this bypasses the shared buffer pool and lock table associated
with a postmaster/site, therefore this is not recommended in a multiuser
site.
.SH NOTATION
\*(lq.../\*(rq at the front of a file name is used to represent the
path to the Postgres super-user's home directory.  Anything in brackets
(\*(lq[\*(rq and \*(lq]\*(rq) is optional.  Anything in braces
(\*(lq{\*(rq and \*(lq}\*(rq) can be repeated 0 or more times.
Parentheses (\*(lq(\*(rq and \*(lq)\*(rq ) are used to group boolean
expressions.  \*(lq|\*(rq is the boolean operator
.SM OR .
.SH "USING Postgres FROM Unix"
All Postgres commands that are executed directly from a Unix shell are
found in the directory \*(lq.../bin\*(rq.  Including this directory in
your search path will make executing the commands easier.
.PP
A collection of system catalogs exist at each site.  These include a
class (\*(lqpg_user\*(rq) that contains an instance for each valid
Postgres user.  The instance specifies a set of Postgres privileges, such as
the ability to act as Postgres super-user, the ability to create/destroy
databases, and the ability to update the system catalogs.  A Unix
user cannot do anything with Postgres until an appropriate instance is
installed in this class.  Further information on the system catalogs
is available by running queries on the appropriate classes.
.SH "Security"
.SP SECURITY UNIX 03/12/94
.SH "USER AUTHENTICATION"
.IR Authentication
is the process by which the backend server and 
.IR postmaster
ensure that the user requesting access to data is in fact who he/she
claims to be.  All users who invoke Postgres are checked against the
contents of the \*(lqpg_user\*(rq class to ensure that they are
authorized to do so.  However, verification of the user's actual
identity is performed in a variety of ways.
.SS "From the user shell"
A backend server started from a user shell notes the user's (effective)
user-id before performing a 
.IR setuid (3)
to the user-id of user \*(lqpostgres\*(rq.  The effective user-id is used
as the basis for access control checks.  No other authentication is
conducted.
.SS "From the network"
If the Postgres system is built as distributed, access to the Internet
TCP port of the
.IR postmaster
process is available to anyone.  However, Postgres offers optional
host-based authentication where only access from certain hosts are
allowed.  Of course, host-based authentication is not fool-proof in
Unix, either. It is possible for determined intruders to also
masquerade the origination host. Those security issues are beyond the
scope of Postgres.
.PP
If greater security is desired, Postgres and its clients may be
modified to use a network authentication system.  For example, the
.IR postmaster ,
.IR psql
and the
.IR libpq
library have already been configured to use either Version 4 or Version 5 of
the
.IR Kerberos
authentication system from the Massachusetts Institute of Technology.
For more information on using
.IR Kerberos
with Postgres, see the appendix below.
.SH "ACCESS CONTROL"
Postgres provides mechanisms to allow users to limit the access to
their data that is provided to other users.
.SS "Database superusers"
Database super-users (i.e., users who have \*(lqpg_user.usesuper\*(rq
set) silently bypass all of the access controls described below with
two exceptions: manual system catalog updates are not permitted if the
user does not have \*(lqpg_user.usecatupd\*(rq set, and destruction of
system catalogs (or modification of their schemas) is never allowed.
.SS "Access Privilege
The use of access privilege to limit reading, writing and setting
of rules on classes is covered in
.IR "grant/revoke" (l).
.SS "Class removal and schema modification"
Commands that destroy or modify the structure of an existing class,
such as
.IR "alter" ,
.IR "drop table" ,
and
.IR "drop index" ,
only operate for the owner of the class.  As mentioned above, these
operations are
.BR never
permitted on system catalogs.
.SH "FUNCTIONS AND RULES"
Functions and rules allow users to insert code into the backend server
that other users may execute without knowing it.  Hence, both
mechanisms permit users to
.BR "trojan horse"
others with relative impunity.  The only real protection is tight
control over who can define functions (e.g., write to relations with
SQL fields) and rules.  Audit trails and alerters on
\*(lqpg_class\*(rq, \*(lqpg_user\*(rq and \*(lqpg_group\*(rq are also
recommended.
.SS "Functions"
Functions written in any language except SQL 
run inside the backend server
process with the permissions of the user \*(lqpostgres\*(rq (the
backend server runs with its real and effective user-id set to
\*(lqpostgres\*(rq).  It is possible for users to change the server's
internal data structures from inside of trusted functions.  Hence,
among many other things, such functions can circumvent any system
access controls.  This is an inherent problem with user-defined C functions.
.SS "Rules"
Like SQL functions, rules always run with the identity and
permissions of the user who invoked the backend server.
.SH "SEE ALSO"
postmaster(1),
alter(l),
insert(l),
grant/revoke(l),
copy(l),
create(l),
delete(l),
drop table(l),
drop index(l),
drop rule(l),
update(l),
select(l),
kerberos(1),
kinit(1),
kerberos(3)
.SH CAVEATS 
.PP
There are no plans to explicitly support encrypted data inside of
Postgres (though there is nothing to prevent users from encrypting
data within user-defined functions).  There are no plans to explicitly
support encrypted network connections, either, pending a total rewrite
of the frontend/backend protocol.
.PP
User names, group names and associated system identifiers (e.g., the
contents of \*(lqpg_user.usesysid\*(rq) are assumed to be unique
throughout a database.  Unpredictable results may occur if they are
not.
.SH "APPENDIX: USING KERBEROS"
.SS "Availability"
The
.IR Kerberos
authentication system is not distributed with Postgres, nor is it
available from the University of California at Berkeley.  Versions of
.IR Kerberos
are typically available as optional software from operating system
vendors.  In addition, a source code distribution may be obtained
through MIT Project Athena by anonymous FTP from ATHENA-DIST.MIT.EDU
(18.71.0.38).  (You may wish to obtain the MIT version even if your
vendor provides a version, since some vendor ports have been
deliberately crippled or rendered non-interoperable with the MIT
version.)  Users located outside the United States of America and
Canada are warned that distribution of the actual encryption code in
.IR Kerberos
is restricted by U. S. government export regulations.
.PP
Any additional inquiries should be directed to your vendor or MIT
Project Athena (\*(lqinfo-kerberos@@ATHENA.MIT.EDU\*(rq).  Note that FAQLs
(Frequently-Asked Questions Lists) are periodically posted to the
.IR Kerberos
mailing list, \*(lqkerberos@@ATHENA.MIT.EDU\*(rq (send mail to
\*(lqkerberos-request@@ATHENA.MIT.EDU\*(rq to subscribe), and USENET
news group, \*(lqcomp.protocols.kerberos\*(rq.
.SS "Installation"
Installation of 
.IR Kerberos
itself is covered in detail in the 
.IR "Kerberos Installation Notes" .
Make sure that the server key file (the
.IR srvtab
or
.IR keytab )
is somehow readable by user \*(lqpostgres\*(rq.
.PP
Postgres and its clients can be compiled to use either Version 4 or
Version 5 of the MIT
.IR Kerberos
protocols by setting the 
.SM KRBVERS
variable in the file \*(lq.../src/Makefile.global\*(rq to the
appropriate value.  You can also change the location where Postgres
expects to find the associated libraries, header files and its own
server key file.
.PP
After compilation is complete, Postgres must be registered as a
.IR Kerberos
service.  See the
.IR "Kerberos Operations Notes"
and related manual pages for more details on registering services.
.SS "Operation"
After initial installation, Postgres should operate in all ways as a
normal
.IR Kerberos
service.  For details on the use of authentication, see the manual
pages for 
.IR postmaster (1)
and 
.IR psql (1).
.PP
In the 
.IR Kerberos
Version 5 hooks, the following assumptions are made about user
and service naming: (1) user principal names (anames) are assumed to
contain the actual Unix/Postgres user name in the first component; (2)
the Postgres service is assumed to be have two components, the service
name and a hostname, canonicalized as in Version 4 (i.e., all domain
suffixes removed).
.PP
.nf
user example: frew@@S2K.ORG
user example: aoki/HOST=miyu.S2K.Berkeley.EDU@@S2K.ORG
host example: postgres_dbms/ucbvax@@S2K.ORG
.fi
.PP
Support for Version 4 will disappear sometime after the production
release of Version 5 by MIT.
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