The link between sudo and LDAP.

Aaron Spangler aaron at
Mon Mar 1 21:52:47 EST 2004

On Monday 01 March 2004 08:48 am, Leadbeter, Jim wrote:
> 1) where can I find documentation on the web that details the link between
> sudo and LDAP.

Attached is the README.LDAP text file from the CVS Repository.

Also for information about how to download the sudo source from CVS, follow 
this hyperlink.

Please let me know if you have problems compiling it.  I would be glad to 

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This file explains how to use the optional LDAP functionality of SUDO to
store /etc/sudoers information.  This feature is separate from LDAP passwords.

LDAP philosophy
As times change and servers become cheap, an enterprise can easily have 500+
UNIX servers.  Using LDAP to synchronize Users, Groups, Hosts, Mounts, and
others across an enterprise can greatly reduce the administrative overhead.

Sudo in the past has only used a single local configuration file /etc/sudoers.
Some have attempted to workaround this by synchronizing changes via
RCS/CVS/RSYNC/RDIST/RCP/SCP and even NFS.  Many have asked for a Hesiod, NIS,
or LDAP patch for sudo, so here is my attempt at LDAP'izing sudo.

Many times the word 'Directory' is used in the document to refer to the LDAP
server, structure and contents.

Many times 'options' are used in this document to refer to sudoer 'defaults'.
They are on in the same.

Design Features

  * Sudo no longer needs to read all sudoers.  Parsing of /etc/sudoers requires
      the entire file to be read.  The LDAP feature of sudo uses two
      (sometimes three) LDAP queries per invocation.  It never reads the
      all the sudoer entries in the LDAP store.  This makes it
      especially fast and particularly usable in LDAP environments.
      The first query is to parse default options (see below).  The second
      is to match against the username or groups a user belongs to.
      (The special ALL tag is matched in this query too.)
      If not match is against the username, the third query pulls the entries
      that match against user netgroups to compare back to the user.

  * Sudo no longer blows up if there is a typo.  Parsing of /etc/sudoers can
      still blow up when sudo is invoked.  However when using the LDAP feature
      of sudo, LDAP syntax rules are applied before the data is uploaded into
      the LDAP server, so proper syntax is always guaranteed!
      One can of course still insert a bogus hostname or username,
      but sudo will not care.

  * Options inside of entries now override global default options.
      /etc/sudoers allowed for only default options and limited options
      associated with user/host/command aliases.  The syntax can be difficult
      for the newbie.  The LDAP feature attempts to simplify this and yet
      still provide maximum flexibility.

      Sudo first looks for an entry called 'cn=default' in the SUDOers
      container.  If found, the multi-valued sudoOption attribute is parsed
      the same way the global 'Defaults' line in /etc/sudoers is parsed.

      If on the second or third query, a response containing a sudoRole
      which matches against the user, host, and command, then the matched
      object is scanned for a additional options to override the top-level
      defaults.  See the Example LDAP content below for more information.

  * Visudo is no longer needed.  Visudo provides locking and syntax checking
      against the /etc/sudoers file.  Since LDAP updates are atomic, locking
      is no longer necessary.  Because syntax is checked when the data is
      inserted into LDAP, the sudoers syntax check becomes unnecessary.

  * Aliases are no longer needed.  User, Host, and Command Aliases were setup
      to allow simplification and readability of the sudoers files.  Since the
      LDAP sudoer entry allows multiple values for each of its attributes and
      since most LDAP browsers are graphical and easy to work with, original
      aliases are no longer needed.

      If you want to specify lots of users into an entry or want to have
      similar entries with identical users, then use either groups or user
      netgroups.  Thats what groups and netgroups are for and Sudo handles
      this well.  Or just paste them all into the LDAP record.

      If you want to specify lots of hosts into an entry, use netgroups or
      IP address matches (  Thats what netgroups are
      for and Sudo handles this well.  Or just past them all into the LDAP

      If you want to specify lots of commands, use directories or wildcards,
      or just paste them all into LDAP.  That's what it's for.

  * The /etc/sudoers file can be disabled.  Paranoid security administrators
      can now disallow parsing of any local /etc/sudoers file by an LDAP
      sudoOption '!local_sudoers'.  This way all sudoers can be controlled
      and audited in one place because local entries are not allowed.
      In the future, this file may not be present.

  * The sudo binary compiled with LDAP support should be totally
      backward compatible and be syntactically and source code equivalent
      to its non LDAP-enabled build.

Build instructions
The most simplest way to build sudo with LDAP support is to include the
'--with-ldap' option.  I recommend including the '--with-pam' option on those
system with PAM so that if you decide to use LDAP for authentication, you won't
need to recompile sudo.

  $ ./configure --with-ldap --with-pam

If your ldap libraries and headers are in a non standard place, you will need
to specify them at configure time.

  $ CPPFLAGS="-I/usr/local/ldapsdk/include" \
  > LDFLAGS="-L/usr/local/ldapsdk/lib" \
  > ./configure --with-ldap --with-pam

In early revs of sudo where the '--with-ldap' option is not available, you
need to manually append '#define HAVE_LDAP 1' to config.h and set
LIBS='-lldap' in Makefile.

Sudo by default builds against OpenLDAP's libraries.  For others LDAP
libraries such as Netscape, iPlanet, Mozilla, SecureWay, add these lines
to config.h before running make:

  #define HAVE_LBER_H

You might have to also include '-llber' or '-lldif' in your LIBS.

Your Mileage may vary.  Please let Aaron Spangler <aaron at>
know what combinations worked best for your OS & LDAP Combinations so
we can improve sudo.

Schema Changes
Add the following schema to your LDAP server so that it may contain sudoer
content.  In OpenLDAP, simply place this into a new file and 'include' it
in your slapd.conf and restart slapd.  For other LDAP servers, provide this
to your LDAP Administrator.  Make sure to index the attribute 'sudoUser'.

  #  schema file for sudo

  attributetype (
        NAME 'sudoUser'
        DESC 'User(s) who may  run sudo'
        EQUALITY caseExactIA5Match
        SUBSTR caseExactIA5SubstringsMatch
        SYNTAX )

  attributetype (
        NAME 'sudoHost'
        DESC 'Host(s) who may run sudo'
        EQUALITY caseExactIA5Match
        SUBSTR caseExactIA5SubstringsMatch
        SYNTAX )

  attributetype (
        NAME 'sudoCommand'
        DESC 'Command(s) to be executed by sudo'
        EQUALITY caseExactIA5Match
        SYNTAX )

  attributetype (
        NAME 'sudoRunAs'
        DESC 'User(s) impersonated by sudo'
        EQUALITY caseExactIA5Match
        SYNTAX )

  attributetype (
        NAME 'sudoOption'
        DESC 'Options(s) followed by sudo'
        EQUALITY caseExactIA5Match
        SYNTAX )

  objectclass ( NAME 'sudoRole' SUP top STRUCTURAL
        DESC 'Sudoer Entries'
        MUST ( cn )
        MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoOption $
              description )

Importing /etc/sudoers to LDAP
Importing is a two step process.

Step 1:
Ask your LDAP Administrator where to create the ou=SUDOers container.
(An example location is shown below).  Then use the provided script to convert
your sudoers file into LDIF format.  The script will also convert any default

  # SUDOERS_BASE=ou=SUDOers,dc=example,dc=com
  # export SUDOERS_BASE
  # ./sudoers2ldif /etc/sudoers > /tmp/sudoers.ldif

Step 2:
Import into your directory server.  If you are using OpenLDAP, do the following
if you are using another directory, provide the LDIF file to your LDAP
Administrator.  An example is shown below.

  # ldapadd -f /tmp/sudoers.ldif -h ldapserver \
  > -D cn=Manager,dc=example,dc=com -W -x

Example sudoers Entries in LDAP
The equivalent of a sudoer in LDAP is a 'sudoRole'.  It contains sudoUser(s),
sudoHost, sudoCommand and optional sudoOption(s) and sudoRunAs(s).
<put an example here>

Managing LDAP entries
Doing a one-time bulk load of your ldap entries is fine.  However what if you
need to make minor changes on a daily basis?  It doesn't make sense to delete
and re-add objects.  (You can, but this is tedious).

I recommend using any of the following LDAP browsers to administer your SUDOers.
  * GQ - The gentleman's LDAP client - Open Source - I use this a lot on
         Linux and since it is Schema aware, I don't need to create a sudoRole

  * LDAP Browser/Editor - by Jarek Gawor - I use this a lot on Windows
    and Solaris.  It runs anywhere in a Java Virtual Machine including
    web pages.  You have to make a template from an existing sudoRole entry.

  There are dozens of others, some open source, some free, some not.

Configure your /etc/ldap.conf
The /etc/ldap.conf file is meant to be shared between sudo, pam_ldap, nss_ldap
and other ldap applications and modules.  IBM Secureway unfortunately uses
the same filename but has a different syntax.  If you need to rename where
this file is stored, recompile SUDO with the -DLDAP_CONFIG compile option.

Make sure you sudoers_base matches exactly with the location you specified
when you imported the sudoers.  Below is an example /etc/ldap.conf

  # Either specify a uri or host & port
  #host          ldapserver
  #port          389
  uri            ldap://ldapserver
  # must be set or sudo will ignore LDAP
  sudoers_base   ou=SUDOers,dc=example,dc=com
  # verbose sudoers matching from ldap
  #sudoers_debug 2
  # optional proxy credentials
  #binddn        <who to search as>
  #bindpw        <password>
  # LDAP Protocol Version defaults to 3
  #ldap_version 3

Debugging your LDAP configuration
Enable debugging if you think sudo is not parsing LDAP the way you think it
it should.  A value of 1 shows moderate debugging.  A value of 2 shows the
results of the matches themselves.  Make sure to set the value back to zero
so that other users don't get confused by the debugging messages.  This value
is 'sudoers_debug' in the /etc/ldap.conf.

Configure your /etc/nsswitch.conf
At the time of this writing, sudo does not consult nsswitch.conf for the
search order.  But if it did, it would look like this:
This might be implemented in the future.  For now just skip this step.

  sudoers: files ldap

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