How To Configure Sudoers
In addition to the standard sudoers file, sudo may be configured via LDAP. This can be especially useful for synchronizing sudoers in a large, distributed environment.
Using LDAP for sudoers has several benefits:
â€¢ sudo no longer needs to read sudoers in its entirety. When LDAP isused, there are only two or three LDAP queries per invocation. Thismakes it especially fast and particularly usable in LDAPenvironments.
â€¢ sudo no longer exits if there is a typo in sudoers. It is not possible to load LDAP data into the server that does not conform to the sudoers schema, so proper syntax is guaranteed. It is still possible to have typos in a user or host name, but this will not prevent sudo from running. â€¢ It is possible to specify per-entry options that override the global default options. /etc/sudoers only supports default options and limited options associated with user/host/commands/aliases. The syntax is complicated and can be difficult for users to understand. Placing the options directly in the entry is more natural.
â€¢ The visudo program is no longer needed. visudo provides locking and syntax checking of 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, there is no need for a specialized tool to check syntax.
Another major difference between LDAP and file-based sudoers is that in LDAP, sudo-specific Aliases are not supported.
For the most part, there is really no need for sudo-specific Aliases. Unix groups or user netgroups can be used in place of User_Aliases and Runas_Aliases. Host netgroups can be used in place of Host_Aliases. Since Unix groups and netgroups can also be stored in LDAP there is no real need for sudo-specific aliases.
Cmnd_Aliases are not really required either since it is possible to have multiple users listed in a sudoRole. Instead of defining a Cmnd_Alias that is referenced by multiple users, one can create a sudoRole that contains the commands and assign multiple users to it.
SUDOers LDAP container The sudoers configuration is contained in the ou=SUDOers LDAP container.
Sudo first looks for the cn=default entry in the SUDOers container. If found, the multi-valued sudoOption attribute is parsed in the same manner as a global Defaults line in /etc/sudoers. In the following example, the SSH_AUTH_SOCK variable will be preserved in the environment for all users.
dn: cn=defaults,ou=SUDOers,dc=example,dc=com objectClass: top objectClass: sudoRole cn: defaults description: Default sudoOption’s go here sudoOption: env_keep+=SSH_AUTH_SOCK
The equivalent of a sudoer in LDAP is a sudoRole. It consists of the following attributes:
A user name, user ID (prefixed with ‘#’), Unix group (prefixed with ‘%’), Unix group ID (prefixed with ‘%#’), or user netgroup (prefixed with ‘+’). sudoHost A host name, IP address, IP network, or host netgroup (prefixed with a ‘+’). The special value ALL will match any host.
sudoCommand A Unix command with optional command line arguments, potentially including globbing characters (aka wild cards). The special value ALL will match any command. If a command is prefixed with an exclamation point ‘!’, the user will be prohibited from running that command.
sudoOption Identical in function to the global options described above, but specific to the sudoRole in which it resides.
sudoRunAsUser A user name or uid (prefixed with ‘#’) that commands may be run as or a Unix group (prefixed with a ‘%’) or user netgroup (prefixed with a ‘+’) that contains a list of users that commands may be run as. The special value ALL will match any user.
The sudoRunAsUser attribute is only available in sudo versions 1.7.0 and higher. Older versions of sudo use the sudoRunAs attribute instead.
sudoRunAsGroup A Unix group or gid (prefixed with ‘#’) that commands may be run as. The special value ALL will match any group.
The sudoRunAsGroup attribute is only available in sudo versions 1.7.0 and higher.
sudoNotBefore A timestamp in the form yyyymmddHHMMSSZ that can be used to provide a start date/time for when the sudoRole will be valid. If multiple sudoNotBefore entries are present, the earliest is used. Note that timestamps must be in Coordinated Universal Time (UTC), not the local timezone. The minute and seconds portions are optional, but some LDAP servers require that they be present (contrary to the RFC).
The sudoNotBefore attribute is only available in sudo versions 1.7.5 and higher and must be explicitly enabled via the SUDOERS_TIMED option in /etc/sudo-ldap.conf.
sudoNotAfter A timestamp in the form yyyymmddHHMMSSZ that indicates an expiration date/time, after which the sudoRole will no longer be valid. If multiple sudoNotBefore entries are present, the last one is used. Note that timestamps must be in Coordinated Universal Time (UTC), not the local timezone. The minute and seconds portions are optional, but some LDAP servers require that they be present (contrary to the RFC).
The sudoNotAfter attribute is only available in sudo versions 1.7.5 and higher and must be explicitly enabled via the SUDOERS_TIMED option in /etc/sudo-ldap.conf.
sudoOrder The sudoRole entries retrieved from the LDAP directory have no inherent order. The sudoOrder attribute is an integer (or floating point value for LDAP servers that support it) that is used to sort the matching entries. This allows LDAP-based sudoers entries to more closely mimic the behaviour of the sudoers file, where the of the entries influences the result. If multiple entries match, the entry with the highest sudoOrder attribute is chosen. This corresponds to the ‘’last match’’ behavior of the sudoers file. If the sudoOrder attribute is not present, a value of 0 is assumed.
The sudoOrder attribute is only available in sudo versions 1.7.5 and higher.
Each attribute listed above should contain a single value, but there may be multiple instances of each attribute type. A sudoRole must contain at least one sudoUser, sudoHost and sudoCommand.
The following example allows users in group wheel to run any command on any host via sudo:
dn: cn=%wheel,ou=SUDOers,dc=example,dc=com objectClass: top objectClass: sudoRole cn: %wheel sudoUser: %wheel sudoHost: ALL sudoCommand: ALL
Anatomy of LDAP sudoers lookup
When looking up a sudoer using LDAP there are only two or three LDAP queries per invocation. The first query is to parse the global options. The second is to match against the user’s name and the groups that the user belongs to. (The special ALL tag is matched in this query too.) If no match is returned for the user’s name and groups, a third query returns all entries containing user netgroups and checks to see if the user belongs to any of them. If timed entries are enabled with the SUDOERS_TIMED configuration directive, the LDAP queries include a subfilter that limits retrieval to entries that satisfy the time constraints, if any.
Differences between LDAP and non-LDAP sudoers
There are some subtle differences in the way sudoers is handled once in LDAP. Probably the biggest is that according to the RFC, LDAP ordering is arbitrary and you cannot expect that Attributes and Entries are returned in any specific order. The order in which different entries are applied can be controlled using the sudoOrder attribute, but there is no way to guarantee the order of attributes within a specific entry. If there are conflicting command rules in an entry, the negative takes precedence. This is called paranoid behavior (not necessarily the most specific match).
Here is an example:
Allow all commands except shell
johnny ALL=(root) ALL,!/bin/sh # Always allows all commands because ALL is matched last puddles ALL=(root) !/bin/sh,ALL
LDAP equivalent of johnny
Allows all commands except shell
dn: cn=role1,ou=Sudoers,dc=my-domain,dc=com objectClass: sudoRole objectClass: top cn: role1 sudoUser: johnny sudoHost: ALL sudoCommand: ALL sudoCommand: !/bin/sh
LDAP equivalent of puddles
Notice that even though ALL comes last, it still behaves like
role1 since the LDAP code assumes the more paranoid configuration
dn: cn=role2,ou=Sudoers,dc=my-domain,dc=com objectClass: sudoRole objectClass: top cn: role2 sudoUser: puddles sudoHost: ALL sudoCommand: !/bin/sh sudoCommand: ALL Another difference is that negations on the Host, User or Runas are currently ignored. For example, the following attributes do not behave the way one might expect. # does not match all but joe # rather, does not match anyone sudoUser: !joe
does not match all but joe
rather, matches everyone including Joe
sudoUser: ALL sudoUser: !joe
does not match all but web01
rather, matches all hosts including web01
sudoHost: ALL sudoHost: !web01 Sudoers schema
In order to use sudo’s LDAP support, the sudo schema must be installed on your LDAP server. In addition, be sure to index the sudoUser attribute. Three versions of the schema: one for OpenLDAP servers (schema.OpenLDAP), one for Netscape-derived servers (schema.iPlanet), and one for Microsoft Active Directory (schema.ActiveDirectory) may be found in the sudo distribution.
The schema for sudo in OpenLDAP form is also included in the EXAMPLES section.
Sudo reads the /etc/sudo-ldap.conf file for LDAP-specific configuration. Typically, this file is shared amongst different LDAP-aware clients. As such, most of the settings are not sudo-specific. Note that sudo parses /etc/sudo-ldap.conf itself and may support options that differ from those described in the system’s ldap.conf(8) manual. Also note that on systems using the OpenLDAP libraries, default values specified in /etc/openldap/ldap.conf or the user’s .ldaprc files are not used.
Only those options explicitly listed in /etc/sudo-ldap.conf as being supported by sudo are honored. Configuration options are listed below in upper case but are parsed in a case-independent manner.
URI ldap[s]://[hostname[:port]] ...
Specifies a whitespace-delimited list of one or more URIs describing the LDAP server(s) to connect to. The protocol may be either ldap ldaps, the latter being for servers that support TLS (SSL) encryption. If no port is specified, the default is port 389 for ldap:// or port 636 for ldaps://. If no hostname is specified, sudo will connect to localhost. Multiple URI lines are treated identically to a URI line containing multiple entries. Only systems using the OpenSSL libraries support the mixing of ldap:// and ldaps:// URIs. Both the Netscape-derived and Tivoli LDAP libraries used on most commercial versions of Unix are only capable of supporting one or the other. Host
name[:port] … If no URI is specified, the HOST parameter specifies a whitespace-delimited list of LDAP servers to connect to. Each host may include an optional port separated by a colon (‘:’). The HOST parameter is deprecated in favor of the URI specification and is included for backwards compatibility. Port port_number If no URI is specified, the PORT parameter specifies the default port to connect to on the LDAP server if a HOST parameter does not specify the port itself. If no PORT parameter is used, the default is port 389 for LDAP and port 636 for LDAP over TLS (SSL). The PORT parameter is deprecated in favor of the URI specification and is included for backwards compatibility. BIND_TIMELIMIT seconds The BIND_TIMELIMIT parameter specifies the amount of time, in seconds, to wait while trying to connect to an LDAP server. If multiple URIs or HOSTs are specified, this is the amount of time to wait before trying the next one in the list.
NETWORK_TIMEOUT seconds An alias for BIND_TIMELIMIT for OpenLDAP compatibility.
Timelimit seconds The TIMELIMIT parameter specifies the amount of time, in seconds, to wait for a response to an LDAP query. Timeout seconds The TIMEOUT parameter specifies the amount of time, in seconds, to wait for a response from the various LDAP APIs. SUDOERS_BASE base The base DN to use when performing sudo LDAP queries. Typically this is of the form ou=SUDOers,dc=example,dc=com for the domain example.com. Multiple SUDOERS_BASE lines may be specified, in which case they are queried in the order specified.
SUDOERS_SEARCH_FILTER ldap_filter An LDAP filter which is used to restrict the set of records returned when performing a sudo LDAP query. Typically, this is of the form attribute=value or (&(attribute=value)(attribute2=value2)).
SUDOERS_TIMED on/true/yes/off/false/no Whether or not to evaluate the sudoNotBefore and sudoNotAfter attributes that implement time-dependent sudoers entries.
SUDOERS_DEBUG debug_level This sets the debug level for sudo LDAP queries. Debugging information is printed to the standard error. A value of 1 results in a moderate amount of debugging information. A value of 2 shows the results of the matches themselves. This parameter should not be set in a production environment as the extra information is likely to confuse users.
Binddn DN The BINDDN parameter specifies the identity, in the form of a Distinguished Name (DN), to use when performing LDAP operations. If not specified, LDAP operations are performed with an anonymous identity. By default, most LDAP servers will allow anonymous access. Bindpw secret The BINDPW parameter specifies the password to use when performing LDAP operations. This is typically used in conjunction with the BINDDN parameter. Rootbinddn DN The ROOTBINDDN parameter specifies the identity, in the form of a Distinguished Name (DN), to use when performing privileged LDAP operations, such as sudoers queries. The password corresponding to the identity should be stored in /etc/ldap.secret. If not specified, the BINDDN identity is used (if any). LDAP_VERSION number The version of the LDAP protocol to use when connecting to the server. The default value is protocol version 3.
Ssl on/true/yes/off/false/no If the SSL parameter is set to on, true or yes, TLS (SSL) encryption is always used when communicating with the LDAP server. Typically, this involves connecting to the server on port 636 (ldaps). Ssl start_tls If the SSL parameter is set to start_tls, the LDAP server connection is initiated normally and TLS encryption is begun before the bind credentials are sent. This has the advantage of not requiring a dedicated port for encrypted communications. This parameter is only supported by LDAP servers that honor the start_tls extension, such as the OpenLDAP and Tivoli Directory servers. TLS_CHECKPEER on/true/yes/off/false/no If enabled, TLS_CHECKPEER will cause the LDAP server’s TLS certificated to be verified. If the server’s TLS certificate cannot be verified (usually because it is signed by an unknown certificate authority), sudo will be unable to connect to it. If TLS_CHECKPEER is disabled, no check is made. Note that disabling the check creates an opportunity for man-in-the-middle attacks since the server’s identity will not be authenticated. If possible, the CA’s certificate should be installed locally so it can be verified. This option is not supported by the Tivoli Directory Server LDAP libraries.
TLS_CACERT file name An alias for TLS_CACERTFILE for OpenLDAP compatibility.
TLS_CACERTFILE file name The path to a certificate authority bundle which contains the certificates for all the Certificate Authorities the client knows to be valid, e.g. /etc/ssl/ca-bundle.pem. This option is only supported by the OpenLDAP libraries. Netscape-derived LDAP libraries use the same certificate database for CA and client certificates (see TLS_CERT).
TLS_CACERTDIR directory Similar to TLS_CACERTFILE but instead of a file, it is a directory containing individual Certificate Authority certificates, e.g. /etc/ssl/certs. The directory specified by TLS_CACERTDIR is checked after TLS_CACERTFILE. This option is only supported by the OpenLDAP libraries.
TLS_CERT file name The path to a file containing the client certificate which can be used to authenticate the client to the LDAP server. The certificate type depends on the LDAP libraries used.
OpenLDAP: tls_cert /etc/ssl/client_cert.pem
Netscape-derived: tls_cert /var/ldap/cert7.db
Tivoli Directory Server: Unused, the key database specified by TLS_KEY contains both keys and certificates.
When using Netscape-derived libraries, this file may also contain Certificate Authority certificates.
TLS_KEY file name The path to a file containing the private key which matches the certificate specified by TLS_CERT. The private key must not be password-protected. The key type depends on the LDAP libraries used.
OpenLDAP: tls_key /etc/ssl/client_key.pem
Netscape-derived: tls_key /var/ldap/key3.db
Tivoli Directory Server: tls_cert /usr/ldap/ldapkey.kdb When using Tivoli LDAP libraries, this file may also contain Certificate Authority and client certificates and may be encrypted.
TLS_KEYPW secret The TLS_KEYPW contains the password used to decrypt the key database on clients using the Tivoli Directory Server LDAP library. If no TLS_KEYPW is specified, a stash file will be used if it exists. The stash file must have the same path as the file specified by TLS_KEY, but use a .sth file extension instead of .kdb, e.g. ldapkey.sth. The default ldapkey.kdb that ships with Tivoli Directory Server is encrypted with the password ssl_password. This option is only supported by the Tivoli LDAP libraries.
TLS_RANDFILE file name The TLS_RANDFILE parameter specifies the path to an entropy source for systems that lack a random device. It is generally used in conjunction with prngd or egd. This option is only supported by the OpenLDAP libraries.
TLS_CIPHERS cipher list The TLS_CIPHERS parameter allows the administer to restrict which encryption algorithms may be used for TLS (SSL) connections. See the OpenLDAP or Tivoli Directory Server manual for a list of valid ciphers. This option is not supported by Netscape-derived libraries.
USE_SASL on/true/yes/off/false/no Enable USE_SASL for LDAP servers that support SASL authentication.
SASL_AUTH_ID identity The SASL user name to use when connecting to the LDAP server. By default, sudo will use an anonymous connection.
ROOTUSE_SASL on/true/yes/off/false/no Enable ROOTUSE_SASL to enable SASL authentication when connecting to an LDAP server from a privileged process, such as sudo.
ROOTSASL_AUTH_ID identity The SASL user name to use when ROOTUSE_SASL is enabled.
SASL_SECPROPS none/properties SASL security properties or none for no properties. See the SASL programmer’s manual for details.
KRB5_CCNAME file name The path to the Kerberos 5 credential cache to use when authenticating with the remote server.
Deref never/searching/finding/always How alias dereferencing is to be performed when searching. See the ldap.conf(8) manual for a full description of this option. See the ldap.conf entry in the EXAMPLES section.
Configuring nsswitch.conf Unless it is disabled at build time, sudo consults the Name Service Switch file, /etc/nsswitch.conf, to specify the sudoers search order. Sudo looks for a line beginning with sudoers: and uses this to determine the search order. Note that sudo does not stop searching after the first match and later matches take precedence over earlier ones. The following sources are recognized:
files’ read sudoers from /etc/sudoers ldap’ read sudoers from LDAP
In addition, the entry [NOTFOUND=return] will short-circuit the search if the user was not found in the preceding source.
To consult LDAP first followed by the local sudoers file (if it exists), use:
sudoers: ldap files
The local sudoers file can be ignored completely by using:
sudoers: ldap If the /etc/nsswitch.conf file is not present or there is no sudoers line, the following default is assumed: sudoers: files Note that /etc/nsswitch.conf is supported even when the underlying operating system does not use an nsswitch.conf file, except on AIX (see below). Configuring netsvc.conf
On AIX systems, the /etc/netsvc.conf file is consulted instead of /etc/nsswitch.conf. sudo simply treats netsvc.conf as a variant of nsswitch.conf; information in the previous section unrelated to the file format itself still applies. To consult LDAP first followed by the local sudoers file (if it exists), use:
sudoers = ldap, files The local sudoers file can be ignored completely by using: sudoers = ldap To treat LDAP as authoratative and only use the local sudoers file if the user is not present in LDAP, use: sudoers = ldap = auth, files Note that in the above example, the auth qualfier only affects user lookups; both LDAP and sudoers will be queried for Defaults entries. If the /etc/netsvc.conf file is not present or there is no sudoers line, the following default is assumed:
sudoers = files Files /etc/sudo-ldap.conf’ LDAP configuration file /etc/nsswitch.conf’ determines sudoers source order /etc/netsvc.conf’ determines sudoers source order on AIX
Examples Example ldap.conf
Either specify one or more URIs or one or more host:port pairs.
If neither is specified sudo will default to localhost, port 389.
#host ldapserver #host ldapserver1 ldapserver2:390 # # Default port
if host is specified without one, defaults to 389. #port 389 # # URI
will override the host and port settings. uri ldap://ldapserver #uri
ldaps://secureldapserver #uri ldaps://secureldapserver ldap://ldapserver
# # The amount of time, in seconds, to wait while trying to connect to #
an LDAP server. bind_timelimit 30 # # The amount of time, in seconds, to
wait while performing an LDAP query. timelimit 30 # # Must be set or
sudo will ignore LDAP; may be specified multiple times. sudoers_base
ou=SUDOers,dc=example,dc=com # # verbose sudoers matching from ldap
#sudoers_debug 2 # # Enable support for time-based entries in sudoers.
#sudoers_timed yes # # optional proxy credentials #binddn
attributetype ( 126.96.36.199.4.1.159188.8.131.52 NAME ‘sudoUser’ DESC ‘User(s) who may run sudo’ EQUALITY caseExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 184.108.40.206.4.1.14220.127.116.11.26 )
attributetype ( 18.104.22.168.4.1.15922.214.171.124 NAME ‘sudoHost’ DESC ‘Host(s) who may run sudo’ EQUALITY caseExactIA5Match SUBSTR caseExactIA5SubstringsMatch SYNTAX 126.96.36.199.4.1.14188.8.131.52.26 )
attributetype ( 184.108.40.206.4.1.159220.127.116.11 NAME ‘sudoCommand’ DESC ‘Command(s) to be executed by sudo’ EQUALITY caseExactIA5Match SYNTAX 18.104.22.168.4.1.1422.214.171.124.26 )
attributetype ( 126.96.36.199.4.1.159188.8.131.52 NAME ‘sudoRunAs’ DESC ‘User(s) impersonated by sudo’ EQUALITY caseExactIA5Match SYNTAX 184.108.40.206.4.1.14220.127.116.11.26 )
attributetype ( 18.104.22.168.4.1.15922.214.171.124 NAME ‘sudoOption’ DESC ‘Options(s) followed by sudo’ EQUALITY caseExactIA5Match SYNTAX 126.96.36.199.4.1.14188.8.131.52.26 )
attributetype ( 184.108.40.206.4.1.159220.127.116.11 NAME ‘sudoRunAsUser’ DESC ‘User(s) impersonated by sudo’ EQUALITY caseExactIA5Match SYNTAX 18.104.22.168.4.1.1422.214.171.124.26 )
attributetype ( 126.96.36.199.4.1.159188.8.131.52 NAME ‘sudoRunAsGroup’ DESC ‘Group(s) impersonated by sudo’ EQUALITY caseExactIA5Match SYNTAX 184.108.40.206.4.1.14220.127.116.11.26 )
attributetype ( 18.104.22.168.4.1.15922.214.171.124 NAME ‘sudoNotBefore’ DESC ‘Start of time interval for which the entry is valid’ EQUALITY generalizedTimeMatch ORDERING generalizedTimeOrderingMatch SYNTAX 126.96.36.199.4.1.14188.8.131.52.24 )
attributetype ( 184.108.40.206.4.1.159220.127.116.11 NAME ‘sudoNotAfter’ DESC ‘End of time interval for which the entry is valid’ EQUALITY generalizedTimeMatch ORDERING generalizedTimeOrderingMatch SYNTAX 18.104.22.168.4.1.1422.214.171.124.24 )
attributeTypes ( 126.96.36.199.4.1.159188.8.131.52 NAME ‘sudoOrder’ DESC ‘an integer to order the sudoRole entries’ EQUALITY integerMatch ORDERING integerOrderingMatch SYNTAX 184.108.40.206.4.1.14220.127.116.11.27 )
objectclass ( 18.104.22.168.4.1.15922.214.171.124 NAME ‘sudoRole’ SUP top STRUCTURAL DESC ‘Sudoer Entries’ MUST ( cn ) MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoRunAsUser $ sudoRunAsGroup $ sudoOption $ sudoNotBefore $ sudoNotAfter $ sudoOrder $ description )