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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 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 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  contex-
              tEngineID (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  prin-
       ciple,  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 clone-
       From 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  specifica-
       tions  (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 neces-
       sary 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 specified, 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 --def-
       PrivLocalizedKey options or in your snmp.conf file using the defAuthLocalizedKey and  defPrivLocalizedKey  key-
       words.


       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 community-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)