Go to main content

man pages section 5: File Formats

Exit Print View

Updated: Wednesday, July 27, 2022

snmpd.examples (5)


snmpd.examples - SNMP agent


Please see following description for synopsis


SNMPD.EXAMPLES(5)                  Net-SNMP                  SNMPD.EXAMPLES(5)

       snmpd.examples - example configuration for the Net-SNMP agent

       The snmpd.conf(5) man page defines the syntax and behaviour of the var-
       ious configuration directives that can be used to control the operation
       of the Net-SNMP agent, and the management information it provides.

       This  companion  man  page  illustrates  these directives, showing some
       practical examples of how they might be used.

   Listening addresses
       The default agent behaviour (listing on the standard SNMP UDP  port  on
       all interfaces) is equivalent to the directive:
              agentaddress udp:161
       or simply
              agentaddress 161
       The  agent  can be configured to only accept requests sent to the local
       loopback interface (again listening on the SNMP UDP port), using:
              agentaddress localhost:161     # (udp implicit)
              agentaddress     # (udp and standard port implicit)
       It can be configured to accept both UDP and  TCP  requests  (over  both
       IPv4 and IPv6), using:
              agentaddress udp:161,tcp:161,udp6:161,tcp6:161
       Other combinations are also valid.

   Run-time privileges
       The agent can be configured to relinquish any privileged access once it
       has opened the initial listening ports.  Given a suitable "snmp"  group
       (defined in /etc/group), this could be done using the directives:
              agentuser  nobody
              agentgroup snmp
       A similar effect could be achieved using numeric UID and/or GID values:
              agentuser  #10
              agentgroup #10

   SNMPv3 Configuration
       Rather  than  being  generated  pseudo-randomly,  the engine ID for the
       agent could be calculated based on the MAC address of the  second  net-
       work interface (eth1), using the directives:
              engineIDType 3 engineIDNic  eth1
       or it could be calculated from the (first) IP address, using:
              engineIDType 1
       or it could be specified explicitly, using:
              engineID "XXX - WHAT FORMAT"

   SNMPv3 Users
       The following directives will create three users, all using exactly the
       same authentication and encryption settings:
              createUser me     MD5 "single pass phrase"
              createUser myself MD5 "single pass phrase" DES
              createUser andI   MD5 "single pass phrase" DES "single pass phrase"
       Note that this defines three distinct users, who could be granted  dif-
       ferent  levels of access.  Changing the passphrase for any one of these
       would not affect the other two.

       Separate pass phrases can be specified for authentication  and  encryp-
              createUser onering SHA "to rule them all" AES "to bind them"
       Remember  that  these  createUser  directives  should be defined in the
       /var/net-snmp/snmpd.conf file, rather than the usual location.

   Traditional Access Control
       The SNMPv3 users defined above can be granted access to  the  full  MIB
       tree using the directives:
              rouser me
              rwuser onering
       Or selective access to individual subtrees using:
              rouser myself   .
              rwuser andI     system

       Note that a combination repeating the same user, such as:
              rouser onering
              rwuser onering
       should  not  be  used. This would configure the user onering with read-
       only access (and ignore the rwuser entry altogether).  The  same  holds
       for the community-based directives.

       The directives:
              rocommunity public
              rwcommunity private
       would define the commonly-expected read and write community strings for
       SNMPv1 and SNMPv2c requests.   This  behaviour  is  not  configured  by
       default, and would need to be set up explicitly.

              Note:  It  would  also  be a very good idea to change private to
                     something a little less predictable!

       A slightly less vulnerable configuration might restrict  what  informa-
       tion could be retrieved:
              rocommunity public   default system
       or the management systems that settings could be manipulated from:
              rwcommunity private
       or a combination of the two.

   VACM Configuration
       This last pair of settings are equivalent to the full VACM definitions:
              #         sec.name  source        community
              com2sec   public    default       public
              com2sec   mynet private
              com2sec6  mynet     fec0::/64     private

              #                  sec.model  sec.name
              group  worldGroup  v1         public
              group  worldGroup  v2c        public
              group  myGroup     v1         mynet
              group  myGroup     v2c        mynet

              #              incl/excl   subtree     [mask]
              view   all     included    .1
              view   sysView included    system

              #              context model level   prefix  read    write  notify (unused)
              access  worldGroup  ""  any  noauth  exact   system  none   none
              access  myGroup     ""  any  noauth  exact   all     all    none

       There are several points to note in this example:

       The  group  directives  must  be  repeated  for both SNMPv1 and SNMPv2c

       The com2sec security name is distinct from the community string that is
       mapped   to   it.   They  can  be  the  same  ("public")  or  different
       ("mynet"/"private") - but what appears in the group  directive  is  the
       security name, regardless of the original community string.

       Both  of  the view directives are defining simple OID subtrees, so nei-
       ther of these require an explicit mask.  The same holds for  the  "com-
       bined  subtree2  view  defined  below.   In  fact, a mask field is only
       needed when defining row slices across a table (or similar views),  and
       can almost always be omitted.

       In  general,  it  is  advisible  not  to mix traditional and VACM-based
       access configuration settings, as these can  sometimes  interfere  with
       each  other  in  unexpected  ways.  Choose a particular style of access
       configuration, and stick to it.

   Typed-View Configuration
       A similar configuration could also be configured as follows:
              view   sys2View included    system
              view   sys2View included    .

              authcommunity read       public  default      -v sys2View
              authcommunity read,write private

       This mechanism allows multi-subtree (or other non-simple) views  to  be
       used with the one-line rocommunity style of configuration.

       It  would  also support configuring "write-only" access, should this be

   System Group
       The full contents of the 'system' group (with the exception  of  sysUp-
       Time) can be explicitly configured using:
              # Override 'uname -a' and hardcoded system OID - inherently read-only values
              sysDescr     Universal Turing Machine mk I
              sysObjectID  .

              # Override default values from 'configure' - makes these objects read-only
              sysContact   Alan.Turing@pre-cs.man.ac.uk
              sysName      tortoise.turing.com
              sysLocation  An idea in the mind of AT

              # Standard end-host behaviour
              sysServices  72

   Host Resources Group
       The  list  of devices probed for potential inclusion in the hrDiskStor-
       ageTable (and hrDeviceTable) can be amended using any of the  following
              ignoredisk /dev/rdsk/c0t2d0
       which prevents the device /dev/rdsk/c0t2d0 from being scanned,
              ignoredisk /dev/rdsk/c0t[!6]d0
              ignoredisk /dev/rdsk/c0t[0-57-9a-f]d0
       either   of   which   prevents  all  devices  /dev/rdsk/c0tXd0  (except
       .../c0t6d0) from being scanned,
              ignoredisk /dev/rdsk/c1*
       which prevents all devices whose device names start  with  /dev/rdsk/c1
       from being scanned, or
              ignoredisk /dev/rdsk/c?t0d0
       which  prevents  all  devices /dev/rdsk/cXt0d0 (where 'X' is any single
       character) from being scanned.

   Process Monitoring
       The list of services running on a system can be monitored  (and  provi-
       sion made for correcting any problems), using:
              # At least one web server process must be running at all times
              proc    httpd
              procfix httpd  /etc/rc.d/init.d/httpd restart

              # There should never be more than 10 mail processes running
              #    (more implies a probable mail storm, so shut down the mail system)
              proc    sendmail   10
              procfix sendmail  /etc/rc.d/init.d/sendmail stop

              # There should be a single network management agent running
              #   ("There can be only one")
              proc    snmpd    1  1
       Also see the "DisMan Event MIB" section later on.

   Disk Usage Monitoring
       The state of disk storage can be monitored using:
              includeAllDisks 10%
              disk /var 20%
              disk /usr  3%
              #  Keep 100 MB free for crash dumps
              disk /mnt/crash  100000

   System Load Monitoring
       A simple check for an overloaded system might be:
              load 10
       A  more  refined check (to allow brief periods of heavy use, but recog-
       nise sustained medium-heavy load) might be:
              load 30 10 5

   Log File Monitoring
              file FILE [MAXSIZE]
              logmatch NAME PATH CYCLETIME REGEX

   Notification Handling
       Configuring the agent to report invalid access attempts might  be  done
              authtrapenable 1
              trapcommunity  public
              trap2sink      localhost
       Alternatively,  the  second and third directives could be combined (and
       an acknowledgement requested) using:
              informsink     localhost  public
       A configuration with repeated sink destinations, such as:
              trapsink       localhost
              trap2sink      localhost
              informsink     localhost
       should NOT be used, as this will cause multiple copies of each trap  to
       be sent to the same trap receiver.

       TODO - discuss SNMPv3 traps
              trapsess  snmpv3 options  localhost:162

       TODO - mention trapd access configuration

   DisMan Event MIB
       The  simplest configuration for active self-monitoring of the agent, by
       the agent, for the agent, is probably:
              # Set up the credentials to retrieve monitored values
              createUser    _internal MD5 "the first sign of madness"
              iquerySecName _internal
              rouser        _internal

              # Active the standard monitoring entries
              defaultMonitors         yes
              linkUpDownNotifications yes

              # If there's a problem, then tell someone!
              trap2sink localhost

       The first block sets up a suitable user for retrieving the  information
       to by monitored, while the following pair of directives activates vari-
       ous built-in monitoring entries.

       Note that the  DisMan  directives  are  not  themselves  sufficient  to
       actively  report  problems - there also needs to be a suitable destina-
       tion configured to actually send the resulting notifications to.

       A more detailed monitor example is given by:
              monitor -u me -o  hrSWRunName  "high  process  memory"  hrSWRun-
              PerfMem > 10000

       This defines an explicit boolean monitor entry, looking for any process
       using more than 10MB of active memory.  Such processes will be reported
       using  the  (standard) DisMan trap mteTriggerFired, but adding an extra
       (wildcarded) varbind hrSWRunName.

       This entry also specifies an explicit user (me, as defined earlier) for
       retrieving the monitored values, and building the trap.

       Objects that could potentially fluctuate around the specified level are
       better monitored using a threshold monitor entry:
              monitor -D -r 10 "network traffic" ifInOctets 1000000 5000000

       This will send a mteTriggerRising trap whenever  the  incoming  traffic
       rises  above  (roughly) 500 kB/s on any network interface, and a corre-
       sponding mteTriggerFalling trap when it falls below 100 kB/s again.

       Note that this monitors the  deltas  between  successive  samples  (-D)
       rather than the actual sample values themselves.  The same effect could
       be obtained using:
              monitor -r 10 "network traffic" ifInOctets - - 1000000 5000000

       The linkUpDownNotifications directive above is broadly equivalent to:
              notificationEvent  linkUpTrap    linkUp   ifIndex ifAdminStatus ifOperStatus
              notificationEvent  linkDownTrap  linkDown ifIndex ifAdminStatus ifOperStatus

              monitor  -r 60 -e linkUpTrap   "Generate linkUp"   ifOperStatus != 2
              monitor  -r 60 -e linkDownTrap "Generate linkDown" ifOperStatus == 2

       This defines the  traps  to  be  sent  (using  notificationEvent),  and
       explicitly  references  the  relevant notification in the corresponding
       monitor entry (rather than using the default DisMan traps).

       The defaultMonitors directive above is equivalent to a series of (bool-
       ean) monitor entries:
              monitor   -o prNames      -o prErrMessage  "procTable" prErrorFlag   != 0
              monitor   -o memErrorName -o memSwapErrorMsg "memory"  memSwapError  != 0
              monitor   -o extNames     -o extOutput     "extTable"  extResult     != 0
              monitor   -o dskPath      -o dskErrorMsg   "dskTable"  dskErrorFlag  != 0
              monitor   -o laNames      -o laErrMessage  "laTable"   laErrorFlag   != 0
              monitor   -o fileName     -o fileErrorMsg  "fileTable" fileErrorFlag != 0
       and will send a trap whenever any of these entries indicate a problem.

       An  alternative  approach  would  be to automatically invoke the corre-
       sponding "fix" action:
              setEvent   prFixIt  prErrFix = 1
              monitor -e prFixIt "procTable" prErrorFlag   != 0
       (and similarly for any of the other defaultMonitor entries).

   DisMan Schedule MIB
       The agent could be configured to reload its configuration once an hour,
              repeat 3600 versionUpdateConfig.0 = 1

       Alternatively  this  could be configured to be run at specific times of
       day (perhaps following rotation of the logs):
              cron 10 0 * * * versionUpdateConfig.0 = 1

       The one-shot style of scheduling is rather less common, but the  secret
       SNMP  virus  could  be  activated  on the next occurance of Friday 13th
              at   13 13 13 * 5 snmpVirus.0 = 1

   Arbitrary Extension Commands
       Old Style
              exec [MIBOID] NAME PROG ARGS"
              sh   [MIBOID] NAME PROG ARGS"
              execfix NAME PROG ARGS"
       New Style
              extend [MIBOID] NAME PROG ARGS"
              extendfix [MIBOID] NAME PROG ARGS"

   MIB-Specific Extension Commands
              "pass [-p priority] MIBOID PROG"

              "pass_persist [-p priority] MIBOID PROG"

   Embedded Perl Support
       If embedded perl support is enabled in the agent, the default initiali-
       sation is equivalent to the directives:
              disablePerl  false
              perlInitFile /etc/net-snmp/snmp/snmp_perl.pl
       The  main  mechanism  for  defining  embedded  perl scripts is the perl
       directive.  A very simple (if somewhat pointless) MIB handler could  be
       registered using:
              perl use Data::Dumper;
              perl sub myroutine  { print "got called: ",Dumper(@_),"\n"; }
              perl $agent->register('mylink', '.', \&myroutine);

       This  relies  on the $agent object, defined in the example snmp_perl.pl

       A more realistic MIB handler might be:
              XXX - WHAT ???
       Alternatively, this code could be  stored  in  an  external  file,  and
       loaded using:
              perl 'do /etc/net-snmp/snmp/perl_example.pl';

   Dynamically Loadable Modules
              dlmod NAME PATH"

   Proxy Support
       A  configuration for acting as a simple proxy for two other SNMP agents
       (running on remote systems) might be:
              com2sec -Cn rem1context  rem1user default  remotehost1
              com2sec -Cn rem2context  rem2user default  remotehost2

              proxy -Cn rem1context  -v 1 -c public  remotehost1  .1.3
              proxy -Cn rem2context  -v 1 -c public  remotehost2  .1.3
       (plus suitable access control entries).

       The same proxy  directives  would  also  work  with  (incoming)  SNMPv3
       requests,  which  can specify a context directly.  It would probably be
       more sensible to use contexts of  remotehost1  and  remotehost2  -  the
       names above were chosen to indicate how these directives work together.

       Note that the administrative settings for the proxied request are spec-
       ified explicitly, and are independent of the settings from the incoming

       An  alternative  use for the proxy directive is to pass part of the OID
       tree to another agent (either on a remote host or listening on  a  dif-
       ferent port on the same system), while handling the rest internally:
              proxy -v 1 -c public  localhost:6161  .
       This mechanism can be used to link together two separate SNMP agents.

       A  less  usual  approach is to map one subtree into a different area of
       the overall MIB tree (either locally or on a remote system):
              # uses SNMPv3 to access the MIB tree . on 'remotehost'
              # and maps this to the local tree .
              proxy -v 3 -l noAuthNoPriv -u user remotehost . .

   SMUX Sub-Agents
              smuxpeer . ospf_pass

   AgentX Sub-Agents
       The Net-SNMP agent could be configured to operate as an  AgentX  master
       agent  (listening on a non-standard named socket, and running using the
       access privileges defined earlier), using:
              master agentx
              agentXSocket /tmp/agentx/master
              agentXPerms  0660 0550 nobody snmp
       A sub-agent wishing to connect to this master agent would need the same
       agentXSocket directive, or the equivalent code:
              netsnmp_ds_set_string(NETSNMP_DS_APPLICATION_ID, NETSNMP_DS_AGENT_X_SOCKET,

       A loopback networked AgentX configuration could be set up using:
              agentXSocket   tcp:localhost:705
              agentXTimeout  5
              agentXRetries  2
       on the master side, and:
              agentXSocket   tcp:localhost:705
              agentXTimeout  10
              agentXRetries  1
              agentXPingInterval 600
       on the client.

       Note  that the timeout and retry settings can be asymmetric for the two
       directions, and the sub-agent can poll  the  master  agent  at  regular
       intervals  (600s = every 10 minutes), to ensure the connection is still

              override sysDescr.0 octet_str "my own sysDescr"
              injectHandler stash_cache NAME table_iterator


       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |        ATTRIBUTE VALUE          |
       |Availability   | system/management/snmp/net-snmp |
       |Stability      | Volatile                        |

       snmpconf(1),  snmpd.conf(5),  snmp.conf(5),  snmp_config(5),  snmpd(8),
       EXAMPLE.conf, netsnmp_config_api(3).

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source   was   downloaded  from   https://sourceforge.net/projects/net-

       Further information about this software can be found on the open source
       community website at http://www.net-snmp.org/.

V5.8                              13 Oct 2006                SNMPD.EXAMPLES(5)