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LDAP

Introduction

The Lightweight Directory Access Protocol accesses a directory service over a network. We currently use OpenLDAP to store information about accounts (except password hashes which are in Kerberos).

Definition of an OCF account

Attributes that define an OCF account (group or individual). Some of these attributes cannot be seen without the proper permissions, such as mail:

  • dn: distinguished name; primary key for the entry. Should be in the form uid=[uid],ou=People,dc=OCF,dc=Berkeley,dc=EDU, where uid is the user's username.
  • objectClass: account, ocfAccount, and posixAccount for accounts.
  • cn: common name; full name for users, group name for group accounts
  • uid: username
  • uidNumber: POSIX user ID number (sequentially-assigned starting at 1000)
  • gidNumber: primary POSIX group ID number (For example, 1000 if in group ocf, or 2390 for group sorry)
  • homeDirectory: location of home directory
  • loginShell: shell (usually /bin/bash)
  • mail: Email address. Usually a @berkeley.edu email, but any email address works. Some OCF staff have @g.ocf.berkeley.edu emails (Google Apps)
  • calnetUid: CalNet ID number (for individuals)
  • callinkOid: CalLink organization ID number (for student groups)
  • userPassword: Not actually a password, this is only used for pass-through authentication with Kerberos, so that the LDAP server can be authenticated with directly for things that don't support Kerberos.
  • creationTime: Account creation time in ISO 8601 format

Definition of a POSIX group

Attributes that define a POSIX group:

  • dn: distinguished name; primary key for the entry. Should be in the form cn=[gid],ou=Group,dc=OCF,dc=Berkeley,dc=EDU, where gid is the group's name.
  • objectClass: posixGroup for groups
  • cn: common name; full name
  • description: description of the group
  • gidNumber: POSIX group ID number (greater than 1000, less than 1000 is reserved for system groups)
  • memberUid: A member of the group (will often have multiple memberUid attributes)

Utilities

ldapsearch

For most staff, their primary interface to LDAP will be ldapsearch. ldapsearch is a powerful program that allows queries of the LDAP database. For most usage, you want to type in -x, which skips authentication. After that you provide a search filter (in this case UID).

Searching for an account:

$ ldapsearch -x uid=sanjayk
dn: uid=sanjayk,ou=People,dc=OCF,dc=Berkeley,dc=EDU
objectClass: ocfAccount
objectClass: account
objectClass: posixAccount
cn: Sanjay Krishnan
uid: sanjayk
uidNumber: 18298
gidNumber: 20
homeDirectory: /home/s/sa/sanjayk
gecos: Sanjay Krishnan
loginShell: /bin/tcsh
calnetUid: 646431

Searching for an account in a group:

$ ldapsearch -x memberUid=sanjayk | grep cn:
cn: ocfstaff
cn: admin

Searching for all accounts created after a certain time:

$ ldapsearch -x '(creationTime>=20160101000000Z)'
<many lines of output>

ldapvi

ldapvi is a "text editor" for LDAP which can generate LDIF change records to pass to ldapadd (or modify directly if you have the proper permissions). The easiest way to edit a single record with ldapvi is to just run kinit [username]/admin ldapvi [record], which will authenticate with Kerberos and then run ldapvi all in one step.

$ ldapvi uid=daradib
0 uid=daradib,ou=People,dc=OCF,dc=Berkeley,dc=EDU
objectClass: ocfAccount
objectClass: account
objectClass: posixAccount
cn: Dara Adib
uid: daradib
uidNumber: 19892
gidNumber: 20
homeDirectory: /home/d/da/daradib
loginShell: /bin/bash
calnetUid: 872544

Now if you make changes to some attributes (say, change the shell to tcsh) and try to save the temporary file which has been opened in a text editor:

      1 entry read
add: 0, rename: 0, modify: 1, delete: 0
Action? [yYqQvVebB*rsf+?]

You can enter v to view the LDIF change record (or ? for help).

dn: uid=daradib,ou=People,dc=OCF,dc=Berkeley,dc=EDU
changetype: modify
replace: loginShell
loginShell: /bin/tcsh

You can enter y to apply changes, q to save the LDIF change record as a file in your current directory, or Q to discard.

ldapadd

ldapadd is a utility to add entries to the LDAP directory if you have the proper permissions.

To add an account, first create a file (we call it user_file):

dn: uid=asdf,ou=People,dc=OCF,dc=Berkeley,dc=EDU
objectClass: ocfAccount
objectClass: account
objectClass: posixAccount
cn: asdf
uid: asdf
uidNumber: 25444
gidNumber: 20
homeDirectory: /home/a/as/asdf
loginShell: /bin/bash
calnetUid: 758472

Then authenticate with Kerberos:

$ kinit myusername/admin

Finally run ldapadd:

$ ldapadd < user_file

This also works on lists of entries to add separated by empty newlines.