SNMPUSM(1)                         Net-SNMP                         SNMPUSM(1)


       snmpusm - creates and maintains SNMPv3 users on a network entity


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


       snmpusm  is  an  SNMP application that can be used to do simple mainte-
       nance on the users known to an SNMP agent, by manipulating 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


       -Ca    Change the authentication key.

       -Cx    Change the privacy key.

       -Ck    Use old localized key instead  of  old  passphrase.   When  this
              option is used, either the -Ca or -Cx (but not both) option must
              also be used.


       An unauthenticated SNMPv3 user can be created using the command

              snmpusm 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 cloneFrom USER CLONEFROM-USER

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

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

              snmpusm 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 2474).  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.


       A user can be deleted from the usmUserTable using the command

              snmpusm delete USER


       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 nec-
       essary to specify the user’s old passphrase as well  as  the  new  one.
       This uses the command

              snmpusm [-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 specified, then both the authentication and
       privacy keys are changed.

              snmpusm [-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 invo-
       cations  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  vari-
       ant of the passwd sub-command is used:

              snmpusm  <-Ca | -Cx> -Ck passwd OLD-LOCALIZED-KEY NEW-PASSPHRASE

       Either the -Ca or the -Cx option must be specified.  The OLD-LOCALIZED-
       KEY  parameter  is  the  localized  key  that  was  printed  out by the
       changekey sub-command.


       Let’s assume for our examples that the following VACM and USM  configu-
       rations  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 users 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 local-
       host sysUpTime.0

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

       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 transac-
       tions instead of initial.


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


       snmpd.conf(5), snmp.conf(5), RFC 2574

4th Berkeley Distribution         08 Feb 2002                       SNMPUSM(1)

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