Quick ?s
Cheat Sheets
Man Pages
The Lynx
SNMPUSM(1)			   Net-SNMP			    SNMPUSM(1)

       snmpusm - creates and maintains SNMPv3 users on a network entity

       snmpusm [COMMON OPTIONS] [-CE ENGINE-ID] delete USER
       snmpusm	[COMMON  OPTIONS]  [-CE  ENGINE-ID]  [-Ca]  [-Cx]  passwd OLD-
       snmpusm [COMMON OPTIONS] [-CE ENGINE-ID] <-Ca | -Cx>  -Ck  passwd  OLD-
       snmpusm [COMMON OPTIONS] [-CE ENGINE-ID] [-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  agents
       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

       -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.

       -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
	      (but not both) option must also be used.

       An unauthenticated SNMPv3 user can be created using the command

	      snmpusm [-CE ENGINE-ID] 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 [-CE ENGINE-ID] 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 [-CE ENGINE-ID] 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.

       A user can be deleted from the usmUserTable using the command

	      snmpusm [-CE ENGINE-ID] 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 users old passphrase as well  as  the  new  one.
       This uses the command

	      snmpusm  [-CE  ENGINE-ID] [-Ca] [-Cx] passwd OLD-PASSPHRASE NEW-

       After cloning a new user  entry	from  the  appropriate	template,  you
       should immediately change the new users 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 [-CE ENGINE-ID] [-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 [-CE ENGINE-ID]  <-Ca  |	-Cx>  -Ck  passwd  OLD-KEY-OR-

       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.

       Lets 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 well create too:
	      rwuser wes
	      # USM configuration entries
	      createUser initial MD5 setup_passphrase DES

       Note: the "initial" users setup should be  removed  after  creating  a
       real  user  that  you grant administrative privileges to (like the user
       "wes" well 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 users 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 3414

4th Berkeley Distribution	  22 Oct 2005			    SNMPUSM(1)

Yals.net is © 1999-2009 Crescendo Communications
Sharing tech info on the web for more than a decade!
This page was generated Thu Apr 30 17:05:22 2009