Provided by: libsnmp-base_5.4.3~dfsg-2.4ubuntu1_all bug

NAME

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

DESCRIPTION

       The  snmpd.conf(5)  man page defines the syntax and behaviour of the various 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.

AGENT BEHAVIOUR

   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)
       or
              agentaddress 127.0.0.1     # (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 network 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"

ACCESS CONTROL

   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 different 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 encryption:
              createUser onering SHA "to rule them all" AES "to bind them"
       Remember   that   these   createUser    directives    should    be    defined    in    the
       /var/lib/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   .1.3.6.1.2
              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  information  could  be
       retrieved:
              rocommunity public   default system
       or the management systems that settings could be manipulated from:
              rwcommunity private  10.10.10.0/24
       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     10.10.10.0/24 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 requests.

       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 neither of these require
       an explicit mask.  The same holds for the "combined 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    .1.3.6.1.2.1.25.1

              authcommunity read       public  default      -v sys2View
              authcommunity read,write private 10.10.10.0/8

       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 required.

SYSTEM INFORMATION

   System Group
       The  full  contents  of  the  'system'  group  (with  the  exception  of sysUpTime) can be
       explicitly configured using:
              # Override 'uname -a' and hardcoded system OID - inherently read-only values
              sysDescr     Universal Turing Machine mk I
              sysObjectID  .1.3.6.1.4.1.8072.3.2.1066

              # 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  hrDiskStorageTable  (and
       hrDeviceTable) can be amended using any of the following directives:
              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  provision  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 recognise sustained medium-
       heavy load) might be:
              load 30 10 5

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

ACTIVE MONITORING

   Notification Handling
       Configuring the agent to report invalid access attempts might be done by:
              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 various built-in monitoring entries.

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

       A more detailed monitor example is given by:
              monitor -u me -o hrSWRunName "high process memory" hrSWRunPerfMem > 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 corresponding 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 (boolean) 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 corresponding "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, using:
              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 using:
              at   13 13 13 * 5 snmpVirus.0 = 1

EXTENDING AGENT FUNCTIONALITY

   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
       One-Shot
              "pass [-p priority] MIBOID PROG"

              Persistent
              "pass_persist [-p priority] MIBOID PROG"

   Embedded Perl Support
       If embedded perl support is enabled in the agent, the default initialisation is equivalent
       to the directives:
              disablePerl  false
              perlInitFile /usr/share/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', '.1.3.6.1.8765', \&myroutine);

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

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

   Dynamically Loadable Modules
       TODO
              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  specified  explicitly,
       and are independent of the settings from the incoming request.

       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 different port on the same system), while
       handling the rest internally:
              proxy -v 1 -c public  localhost:6161  .1.3.6.1.4.1.99
       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 .1.3.6.1.2.1.1 on 'remotehost'
              # and maps this to the local tree .1.3.6.1.3.10
              proxy -v 3 -l noAuthNoPriv -u user remotehost .1.3.6.1.3.10 .1.3.6.1.2.1.1

   SMUX Sub-Agents
              smuxsocket 127.0.0.1
              smuxpeer .1.3.6.1.2.1.14 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,
                                    "/tmp/agentx/master");

       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 working.

OTHER CONFIGURATION

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

FILES

       /etc/snmp/snmpd.conf

SEE ALSO

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