pam-linux, /etc/shadow : HOW-TO

note: i'm no sysad, nor do i even pretend to understand pam, the linux kernel,
or postgresql, but this setup is a safe, working, postgresql/linux/pam setup.

0) configure postgresql for pam, for example

      [root@omega tmp]# grep pam /usr/local/pgsql/data/pg_hba.conf
      host    all         all          137.75.0.0        255.255.0.0       pam

1) create a /etc/pam.d/postgresql entry, here's how i did mine

      [root@omega tmp]# cp /etc/pam.d/passwd /etc/pam.d/postgresql

  i don't know if it's the best setup, but it works!  mine looks like this

      [root@omega tmp]# cat /etc/pam.d/postgresql
      #%PAM-1.0
      auth       required     /lib/security/pam_stack.so service=system-auth
      account    required     /lib/security/pam_stack.so service=system-auth
      password   required     /lib/security/pam_stack.so service=system-auth

2) create a shadow group which will be used for user's needing read-access to
/etc/shadow, and add postgres (or whatever user the postmaster runs as) to
this entry.  i used vi to add this entry to /etc/group

      [root@omega tmp]# grep shadow /etc/group
      shadow:*:4002:root,postgres

  root probably does not *need* to be added.

  note the '*' v.s. an 'x' in the password field.  if you place an 'x' there
  you will also have to set up /etc/gshadow - i did not want to do this.  if
  you don't set up /etc/gshadow pam will NOT work if an 'x' is in the password
  field - at least with my linux system.

3) make /etc/shadow group shadow

      [root@omega tmp]# chgrp shadow /etc/shadow

4) chmod 0440 /etc/shadow


essentially, pam will not work with postgres since the daemon needs at some
point, no matter how many library calls deep, to open and read /etc/shadow
(assuming this is how your system is using pam).  you must have some solution
which allows postgres, but not everyone, to read /etc/shadow.  others probably
exist.

-a

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  ====================================
  | Ara Howard
  | NOAA Forecast Systems Laboratory
  | Information and Technology Services
  | Data Systems Group
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