SNMPUSM(1)                                                  Net-SNMP                                                  SNMPUSM(1)



NAME
       snmpusm - creates and maintains SNMPv3 users on a network entity

SYNOPSIS
       snmpusm [COMMON OPTIONS] create USER [CLONEFROM-USER]
       snmpusm [COMMON OPTIONS] delete USER
       snmpusm [COMMON OPTIONS] cloneFrom USER CLONEFROM-USER
       snmpusm [COMMON OPTIONS] [-Ca] [-Cx] passwd OLD-PASSPHRASE NEW-PASSPHRASE [USER]
       snmpusm [COMMON OPTIONS] <-Ca | -Cx> -Ck passwd OLD-KEY-OR-PASSPHRASE NEW-KEY-OR-PASSPHRASE [USER]
       snmpusm [COMMON OPTIONS] [-Ca] [-Cx] changekey [USER]


DESCRIPTION
       snmpusm  is an SNMP application that can be used to do simple maintenance on the users known to an SNMP agent, by manipu-
       lating the agent's User-based Security Module (USM) table.  The user needs write access to the  usmUserTable  MIB  table.
       This tool can be used to create, delete, clone, and change the passphrase of users configured on a running SNMP agent.


OPTIONS
       Common options for all snmpusm commands:

       -CE ENGINE-ID
              Set  usmUserEngineID  to  be used as part of the index of the usmUserTable.  Default is to use the contextEngineID
              (set via -E or probed) as the usmUserEngineID.

       -Cp STRING
              Set the usmUserPublic value of the (new) user to the specified STRING.

       Options for the passwd and changekey commands:

       -Ca    Change the authentication key.

       -Cx    Change the privacy key.

       -Ck    Allows to use localized key (must start with 0x) instead of passphrase.  When this option is used, either the  -Ca
              or -Cx option (but not both) must also be used.


CREATING USERS
       An unauthenticated SNMPv3 user can be created using the command

              snmpusm [OPTIONS] create USER

       This  constructs an (inactive) entry in the usmUserTable, with no authentication or privacy settings.  In principle, this
       user should be useable for 'noAuthNoPriv' requests, but in practise the Net-SNMP agent will not allow such an entry to be
       made active.


       In order to activate this entry, it is necessary to "clone" an existing user, using the command

              snmpusm [OPTIONS] cloneFrom USER CLONEFROM-USER

       The USER entry then inherits the same authentication and privacy settings (including pass phrases) as the CLONEFROM user.


       These two steps can be combined into one, by using the command

              snmpusm [OPTIONS] create USER CLONEFROM-USER


       The  two  forms of the create sub-command require that the user being created does not already exist.  The cloneFrom sub-
       command requires that the user being cloned to does already exist.


       Cloning is the only way to specify which authentication and privacy protocols to use for a given user,  and  it  is  only
       possible to do this once.  Subsequent attempts to reclone onto the same user will appear to succeed, but will be silently
       ignored.  This (somewhat unexpected) behaviour is mandated by the SNMPv3 USM specifications (RFC 3414).   To  change  the
       authentication and privacy settings for a given user, it is necessary to delete and recreate the user entry.  This is not
       necessary for simply changing the pass phrases (see below).  This means that the agent must be initialized with at  least
       one  user for each combination of authentication and privacy protocols.  See the snmpd.conf(5) manual page for details of
       the createUser configuration directive.


DELETING USERS
       A user can be deleted from the usmUserTable using the command

              snmpusm [OPTIONS] delete USER


CHANGING PASS PHRASES
       User profiles contain private keys that are never transmitted over the wire in clear  text  (regardless  of  whether  the
       administration  requests  are  encrypted  or  not).   To change the secret key for a user, it is necessary to specify the
       user's old passphrase as well as the new one.  This uses the command

              snmpusm [OPTIONS] [-Ca] [-Cx] passwd OLD-PASSPHRASE NEW-PASSPHRASE [USER]


       After cloning a new user entry from the appropriate template, you should immediately change the new user's passphrase.


       If USER is not specified, this command will change the passphrase of the (SNMPv3) user issuing the command.  If  the  -Ca
       or  -Cx options are specified, then only the authentication or privacy keys are changed.  If these options are not speci-
       fied, then both the authentication and privacy keys are changed.


              snmpusm [OPTIONS] [-Ca] [-Cx] changekey [USER]


       This command changes the key in a perfect-forward-secrecy compliant way through a  diffie-helman  exchange.   The  remote
       agent  must  support the SNMP-USM-DH-OBJECTS-MIB for this command to work.  The resulting keys are printed to the console
       and may be then set in future command invocations using the --defAuthLocalizedKey and --defPrivLocalizedKey options or in
       your snmp.conf file using the defAuthLocalizedKey and defPrivLocalizedKey keywords.


       Note  that  since  these keys are randomly generated based on a diffie helman exchange, they are no longer derived from a
       more easily typed password.  They are, however, much more secure.


       To change from a localized key back to a password, the following variant of the passwd sub-command is used:


              snmpusm [OPTIONS] <-Ca | -Cx> -Ck passwd OLD-KEY-OR-PASSPHRASE NEW-KEY-OR-PASSPHRASE [USER]


       Either the -Ca or the -Cx option must be specified.  The OLD-KEY-OR-PASSPHRASE and/or NEW-KEY-OR-PASSPHRASE arguments can
       either be a passphrase or a localized key starting with "0x", e.g. as printed out by the changekey sub-command.


EXAMPLES
       Let's assume for our examples that the following VACM and USM configurations lines were in the snmpd.conf file for a Net-
       SNMP agent.  These lines set up a default user called "initial" with the authentication passphrase "setup_passphrase"  so
       that we can perform the initial setup of an agent:

              # VACM configuration entries
              rwuser initial
              # lets add the new user we'll create too:
              rwuser wes
              # USM configuration entries
              createUser initial MD5 setup_passphrase DES

       Note: the "initial" user's setup should be removed after creating a real user that you grant administrative privileges to
       (like the user "wes" we'll be creating in this example.

       Note: passphrases must be 8 characters minimum in length.

   Create a new user
       snmpusm -v3 -u initial -n "" -l authNoPriv -a MD5 -A setup_passphrase localhost create wes initial

              Creates a new user, here named "wes" using the user "initial" to do it.  "wes" is cloned  from  "initial"  in  the
              process, so he inherits that user's passphrase ("setup_passphrase").

   Change the user's passphrase
       snmpusm -v 3 -u wes -n "" -l authNoPriv -a MD5 -A setup_passphrase localhost passwd setup_passphrase new_passphrase

              After creating the user "wes" with the same passphrase as the "initial" user, we need to change his passphrase for
              him.  The above command changes it from  "setup_passphrase",  which  was  inherited  from  the  initial  user,  to
              "new_passphrase".

   Test the new user
       snmpget -v 3 -u wes -n "" -l authNoPriv -a MD5 -A new_passphrase localhost sysUpTime.0

              If  the  above  commands  were successful, this command should have properly performed an authenticated SNMPv3 GET
              request to the agent.

       Now, go remove the vacm "group" snmpd.conf entry for the "initial" user and you have a valid user 'wes' that you can  use
       for future transactions instead of initial.


WARNING
       Manipulating the usmUserTable using this command can only be done using SNMPv3.  This command will not work with the com-
       munity-based versions, even if they have write access to the table.


SEE ALSO
       snmpd.conf(5), snmp.conf(5), RFC 3414



4th Berkeley Distribution                                  22 Oct 2005                                                SNMPUSM(1)