Provided by:
snmpd_5.2.1.2-4ubuntu2_i386 
NAME
snmpd.conf - configuration file for the Net-SNMP SNMP agent
DESCRIPTION
snmpd.conf is the configuration file which defines how the Net-SNMP
SNMP agent operates. These files may contain any of the directives
found in the DIRECTIVES section below. If this file is not found (or
does not contain any access control directives), the agent will run but
will not respond to any requests.
PLEASE READ FIRST
First, make sure you have read the snmp_config(5) manual page that
describes how the Net-SNMP configuration files operate, where they are
located and how they all work together.
Also, you might consider looking into the snmpconf application (perl
script) which can help you build an snmpd.conf file by prompting you
for information. You should try it. Really. Go ahead. Right now.
Run:
snmpconf -g basic_setup
to get you started. See the snmpconf(1) manual page for more
information.
EXTENSIBLE-MIB
The Net-SNMP SNMP agent reports much of its information through queries
to the 1.3.6.1.4.1.2021 section of the MIB tree. Every MIB in this
section has the following table entries in it.
.1 -- index
This is the table’s index numbers for each of the DIRECTIVES
listed below.
.2 -- name
The name of the given table entry. This should be unique, but
is not required to be.
.100 -- errorFlag
This is a flag returning either the integer value 1 or 0 if an
error is detected for this table entry.
.101 -- errorMsg
This is a DISPLAY-STRING describing any error triggering the
errorFlag above.
.102 -- errorFix
If this entry is set to the integer value of 1 AND the errorFlag
defined above is indeed a 1, a program or script will get
executed with the table entry name from above as the argument.
The program to be executed is configured in the net-snmp-
config.h file at compile time.
Directives
proc NAME
proc NAME MAX
proc NAME MAX MIN
Checks to see if processes called NAME are running on the agent
machine. An error flag (1) and a description message are then
passed to the 1.3.6.1.4.1.2021.2.1.100 and
1.3.6.1.4.1.2021.2.1.101 MIB columns (respectively) if the
NAME’d program is not found in the process table as reported by
" -acx".
If MAX and MIN are not specified, MAX is assumed to be infinity
and MIN is assumed to be 1.
If MAX is specified but MIN is not specified, MIN is assumed to
be 0.
procfix NAME PROG ARGS
This registers a command that knows how to fix errors with the
given process NAME. When 1.3.6.1.4.1.2021.2.1.102 for a given
NAMEd program is set to the integer value of 1, this command
will be called. It defaults to a compiled value set using the
PROCFIXCMD definition in the net-snmp-config.h file.
exec NAME PROG ARGS
exec MIBNUM NAME PROG ARGS
If MIBNUM is not specified, the agent executes the named PROG
with arguments of ARGS and returns the exit status and the first
line of the STDOUT output of the PROG program to queries of the
1.3.6.1.4.1.2021.8.1.100 and 1.3.6.1.4.1.2021.8.1.101 mib
columns (respectively). All STDOUT output beyond the first line
is silently truncated.
If MIBNUM is specified, it acts as above but returns the exit
status to MIBNUM.100.0 and the entire STDOUT output to the table
MIBNUM.101 in a MIB table. In this case, the MIBNUM.101 mib
contains the entire STDOUT output, one MIB table entry per line
of output (ie, the first line is output as MIBNUM.101.1, the
second at MIBNUM.101.2, etc...).
Note: The MIBNUM must be specified in dotted-integer notation
and can not be specified as ".iso.org.dod.internet..."
(should instead be .1.3.6.1...).
Note: The agent caches the exit status and STDOUT of the
executed program for 30 seconds after the initial query.
This is to increase speed and maintain consistency of
information for consecutive table queries. The cache can
be flushed by a snmp-set request of integer(1) to
1.3.6.1.4.1.2021.100.VERCLEARCACHE.
extend NAME PROG ARGS
extend MIBNUM NAME PROG ARGS
This is similar to the ’exec’ directive, but uses a different
MIB output structure (for both forms) which covers multi-line
output as standard. See NET-SNMP-EXTEND-MIB for details.
Output is cached for each entry separately, controlled by the
NET-SNMP-AGENT-MIB::nsCacheTable.
execfix NAME PROG ARGS
This registers a command that knows how to fix errors with the
given exec or sh NAME. When 1.3.6.1.4.1.2021.8.1.102 for a
given NAMEd entry is set to the integer value of 1, this command
will be called. It defaults to a compiled value set using the
EXECFIXCMD definition in the net-snmp-config.h file.
disk PATH
disk PATH [ MINSPACE | MINPERCENT% ]
Checks the named disks mounted at PATH for available disk space.
If the disk space is less than MINSPACE (kB) if specified or
less than MINPERCENT (%) if a % sign is specified, or
DEFDISKMINIMUMSPACE (kB) if not specified, the associated entry
in the 1.3.6.1.4.1.2021.9.1.100 MIB table will be set to (1) and
a descriptive error message will be returned to queries of
1.3.6.1.4.1.2021.9.1.101.
includeAllDisks MINPERCENT%
Adds all the disks that can be found on the system using the
setmntent(3) and getmntent(3), or fopen(3) and getmntent(3), or
setfsent(3) and getfsent(3) system calls. If none of the above
system calls are available then it adds the root partition "/",
(which is assumed to exist on any UNIX based system) using the
statfs(2) system call.
There can only be one ’includeAllDisks’ directive in the config-
uration file. It can be used in conjunction with the ’disk’
directive. They may be used in any order. The ’disk’ directive
overrides the disk usage specified by the ’includeAllDisks’
directive, no matter in which order they are specified in the
configuration file.
The ’includeAllDisks’ directive only includes the disks that are
mounted when the snmpd daemon is started. It cannot include
disks that are dynamically loadable, such as with automount. So
the preferred way is to mount all the disks that will ever need
to be monitored before starting the snmpd daemon.
load MAX1
load MAX1 MAX5
load MAX1 MAX5 MAX15
Checks the load average of the machine and returns an error flag
(1), and an text-string error message to queries of
1.3.6.1.4.1.2021.10.1.100 and 1.3.6.1.4.1.2021.10.1.101
(respectively) when the 1-minute, 5-minute, or 15-minute
averages exceed the associated maximum values. If any of the
MAX1, MAX5, or MAX15 values are unspecified, they default to a
value of DEFMAXLOADAVE.
file FILE [MAXSIZE]
Monitors file sizes and makes sure they don’t grow beyond a
certain size (in kilobytes). MAXSIZE defaults to infinite if
not specified, and only monitors the size without reporting
errors about it. A maximum of 20 files can be monitored.
Errors
Any errors in obtaining the above information are reported via the
1.3.6.1.4.1.2021.101.1.100 flag and the 1.3.6.1.4.1.2021.101.1.101
text-string description.
AGENTX SUB-AGENTS
To enable AgentX support in the SNMP master agent, put the following
line in your snmpd.conf file:
master agentx
See README.agentx for further details.
AgentXSocket addr
This defines the address the master agent listens at. The
default is /var/agentx/master. By default the Unix Domain socket
is accessible only to subagents which have the same userid as
the agent. Another possibility is localhost:705
AgentXTimeout addr
Defines the timeout period for an AgentX request. Default is 1
second.
AgentXRetries addr
Defines the number of retries for an AgentX request. Default is
5 retries.
You can also put the following in your subagent.conf file (where
"subagent" is the name you used in your init_snmp("subagent") api call:
agentPingInterval NUM
This makes the subagent try and reconnect every NUM seconds to
the master if it ever becomes (or starts) disconnected.
SMUX SUB-AGENTS
To enable and SMUX based sub-agent, such as gated, use the smuxpeer
configuration entry
smuxpeer OID PASS
For gated a sensible entry might be smuxpeer .1.3.6.1.4.1.4.1.3
secret
DYNAMICALLY LOADABLE MODULES
If the agent is built with support for the UCD-DLMOD-MIB it is capable
of loading agent MIB modules dynamically at startup through the dlmod
directive and during runtime through use of the UCD-DLMOD-MIB. The
following directive loads the shared object module file PATH which uses
the module name prefix NAME.
dlmod NAME PATH
ACCESS CONTROL
snmpd supports the View-Based Access Control Model (VACM) as defined in
RFC 2575. To this end, it recognizes the following keywords in the
configuration file: com2sec, group, access, and view as well as some
easier-to-use wrapper directives: rocommunity, rwcommunity, rouser,
rwuser. If IPv6 support has been enabled, the rocommunity6 and
rwcommunity6 tokens will also be available. This section defines how
to configure the snmpd program to accept various types and levels of
access.
rouser USER [noauth|auth|priv [OID]]
rwuser USER [noauth|auth|priv [OID]]
Creates a SNMPv3 USM user in the VACM access configuration
tables. It is more efficient (and powerful) to use the combined
group, access, and view directives instead, but these wrapper
directives are much simpler.
The minimum level of authentication and privacy the user must
use is specified by the first token (which defaults to "auth").
The OID parameter restricts access for that user to everything
below the given OID.
rocommunity COMMUNITY [SOURCE [OID]]
rwcommunity COMMUNITY [SOURCE [OID]]
These create read-only and read-write communities that can be
used to access the agent. They are a quick wrapper around the
more complex and powerful com2sec, group, access, and view
directive lines. They are not as efficient either, as groups
aren’t created so the tables are possibly larger. In other
words: don’t use these if you have complex situations to set up.
If your setup is simple or you don’t mind a small performance
hit, use these directives.
The format of the SOURCE is token is described in the com2sec
directive section below. The OID token restricts access for
that community to everything below that given OID.
rocommunity6 COMMUNITY [SOURCE [OID]]
rwcommunity6 COMMUNITY [SOURCE [OID]]
They are the alternative directives to the rocommunity,
rwcommunity for the transport domain UDPIPv6. They are only
valid in specifing UDPIPv6 as transport domain.
The format of the SOURCE is token is described in the com2sec6
directive section below. The OID token restricts access for
that community to everything below that given OID.
com2sec [-Cn CONTEXT] NAME SOURCE COMMUNITY
This directive specifies the mapping from a source/community
pair to a security name. SOURCE can be a hostname, a subnet, or
the word "default". A subnet can be specified as IP/MASK or
IP/BITS. For example, given a directive "com2sec myLocal
10.10.10.0/24 public" then this would match requests from IP
addresses 10.10.10.0 through to 10.10.10.255, but not one from
10.10.11.1 or similar. The first source/community combination
that matches the incoming packet is selected. If a CONTEXT is
specified, the community name gets mapped to the SNMPv3 CONTEXT
of the same name, otherwise the default context ("") is used.
com2sec6 [-Cn CONTEXT] NAME SOURCE COMMUNITY
This directive is the IPv6 version of com2sec. A subnet can be
specified as IPv6/IPv6MASK or IPv6/BITS. It is only valid in
specifing UDPIPv6 as transport domain.
group NAME MODEL SECURITY
This directive defines the mapping from
securitymodel/securityname to group. MODEL is one of v1, v2c,
or usm.
access NAME CONTEXT MODEL LEVEL PREFX READ WRITE NOTIFY
The access directive maps from group/security model/security
level to a view. MODEL is one of any, v1, v2c, or usm. LEVEL
is one of noauth, auth, or priv. PREFX specifies how CONTEXT
should be matched against the context of the incoming pdu,
either exact or prefix. READ, WRITE and NOTIFY specifies the
view to be used for the corresponding access. For v1 or v2c
access, LEVEL will be noauth, and CONTEXT will be empty.
view NAME TYPE SUBTREE [MASK]
This defines the named view. TYPE is either included or
excluded. MASK is a list of hex octets, separated by ’.’ or
’:’. The MASK defaults to "ff" if not specified.
The reason for the mask is, that it allows you to control access
to one row in a table, in a relatively simple way. As an
example, as an ISP you might consider giving each customer
access to his or her own interface:
view cust1 included interfaces.ifTable.ifEntry.ifIndex.1 ff.a0
view cust2 included interfaces.ifTable.ifEntry.ifIndex.2 ff.a0
(interfaces.ifTable.ifEntry.ifIndex.1 == .1.3.6.1.2.1.2.2.1.1.1,
ff.a0 == 11111111.10100000. which nicely covers up and including
the row index, but lets the user vary the field of the row)
VACM Examples:
# sec.name source community
com2sec local localhost private
com2sec mynet 10.10.10.0/24 public
com2sec public default public
com2sec6 mynet fec0::/64 public
# sec.model sec.name
group mygroup v1 mynet
group mygroup v2c mynet
group mygroup usm mynet
group local v1 local
group local v2c local
group local usm local
group public v1 public
group public v2c public
group public usm public
# incl/excl subtree mask
view all included .1 80
view system included system fe
view mib2 included .iso.org.dod.internet.mgmt.mib-2 fc
# context sec.model sec.level prefix read write notify
access mygroup "" any noauth exact mib2 none none
access public "" any noauth exact system none none
access local "" any noauth exact all all all
Default VACM model
The default configuration of the agent, as shipped, is functionally
equivalent to the following entries:
com2sec public default public
group public v1 public
group public v2c public
group public usm public
view all included .1
access public "" any noauth exact all none none
SNMPv3 CONFIGURATION
engineID STRING
The snmpd agent needs to be configured with an engineID to be
able to respond to SNMPv3 messages. With this configuration
file line, the engineID will be configured from STRING. If this
directive is omitted, the default value of the engineID is built
from 2 fairly random elements: a random number and the current
time in seconds.
createUser [-e ENGINEID] username (MD5|SHA) authpassphrase [DES]
[privpassphrase]
MD5 and SHA are the authentication types to use. The only
privacy protocol currently supported is DES. If the privacy
passphrase is not specified, it is assumed to be the same as the
authentication passphrase. Note that the users created will be
useless unless they are also added to the VACM access control
tables described above.
SHA authentication and DES privacy require OpenSSL to be
installed and the agent to be built with OpenSSL support. MD5
authentication may be used without OpenSSL.
Warning: the minimum pass phrase length is 8 characters.
SNMPv3 users can be created at runtime using the snmpusm(1)
command.
Instead of figuring out how to use this directive and where to
put it (see below), just run "net-snmp-config --create-
snmpv3-user" instead, which will add one of these lines to the
right place.
This directive should be placed into the
/var/lib/snmp/snmpd.conf file instead of the other normal
locations. The reason is that the information is read from the
file and then the line is removed (eliminating the storage of
the master password for that user) and replaced with the key
that is derived from it. This key is a localized key, so that
if it is stolen it can not be used to access other agents. If
the password is stolen, however, it can be.
If you need to localize the user to a particular EngineID (this
is useful mostly in the similar snmptrapd.conf file), you can
use the -e argument to specify an EngineID as a hex value (EG,
"0x01020304").
If you want to generate either your master or localized keys
directly, replace the given password with a hexstring (preceeded
by a "0x") and precede the hex string by a -m or -l token
(respectively). EGs:
[these keys are *not* secure but are easy to visually parse for
counting purposes. Please generate random keys instead of using
these examples]
createUser myuser SHA -l 0x0001020304050607080900010203040506070809 AES -l 0x00010203040506070809000102030405
createUser myuser SHA -m 0x0001020304050607080900010203040506070809 AES -m 0x0001020304050607080900010203040506070809
Due to the way localization happens, localized privacy keys are
expected to be the length needed by the algorithm (128 bits for
all supported algorithms). Master encryption keys, though, need
to be the length required by the authentication algorithm not
the length required by the encrypting algorithm (MD5: 16 bytes,
SHA: 20 bytes).
SETTING SYSTEM INFORMATION
syslocation STRING
syscontact STRING
sysname STRING
Sets the system location, system contact or system name for the
agent. This information is reported in the ’system’ group the
mibII tree. Ordinarily these objects (sysLocation.0,
sysContact.0 and sysName.0) are read-write. However, specifying
the value for one of these objects by giving the appropriate
token makes the corresponding object read-only, and attempts to
set the value of the object will result in a notWritable error
response.
sysservices NUMBER
Sets the value of the system.sysServices.0 object. For a host,
a good value is 72.
sysdescr STRING
sysobjectid OID
Sets the system description or object ID for the agent.
Although these values are not SNMP-writable, it is conceivable
that a network administrator may wish to configure them to
something other than the default values.
agentaddress [<transport-specifier>:]<transport-address>[,...]
Makes the agent list on the specified comma-separated list of
listening addresses instead of the default behaviour, which is
to listen on UDP port 161 on all IPv4 interfaces. See the
section LISTENING ADDRESSES in the snmpd(8) manual page for more
information about the format of listening addresses. For
example, specifying agentaddress 161,tcp:161,localhost:9161 will
make the agent listen on UDP port 161 on all IPv4 interfaces,
TCP port 161 on all IPv4 interfaces and UDP port 9161 only on
the interface associated with the localhost address.
agentgroup groupid
Change to this gid after opening port. The groupid may refer to
a group by name or a number if the group number starts with ’#’.
For example, specifying agentgroup snmp will cause the agent to
run as the snmp group or agentgroup #10 will cause the agent to
run as the group with groupid 10.
agentuser uid
Change to this uid after opening port. The userid may refer to a
user by name or a number if the user number starts with ’#’. For
example, specifying agentuser snmp will cause the agent to run
as the snmp user or agentuser #10 will cause the agent to run as
the user with userid 10.
interface NAME TYPE SPEED
For interfaces where the agent fails to guess correctly on the
type and speed, this directive can supply additional
information. TYPE is a type value as given in the IANAifType-
MIB.
ignoredisk STRING
When scanning for available disk devices the agent might block
in trying to open all possible disk devices. This might lead to
a timeout when walking the device tree. Sometimes the next walk
will run without timeout, sometimes it will timeout every time
you try it.
If you experience such behaviour you might add this directive
and give all device names not to be checked (i.e. opened). You
might have more than one such directive in your configuration
file stating all devices not to be opened. You might also
specify those devices using wildcards similar to the syntax you
can use in a bourne shell (see examples below).
Note: For a list of devices scanned for every system please
consult the sources (host/hr_disk.c) and check for the
Add_HR_Disk_entry() calls relevant for your type of OS.
Examples:
ignoredisk /dev/rdsk/c0t2d0
This directive prevents the device /dev/rdsk/c0t2d0 from being
scanned.
ignoredisk /dev/rdsk/c0t[!6]d0
This directive prevents all devices /dev/rdsk/c0tXd0 except
.../c0t6d0 from being scanned. For most systems similar is the
following directive:
ignoredisk /dev/rdsk/c0t[0-57-9a-f]d0
ignoredisk /dev/rdsk/c1*
This directive prevents all devices whose device names start
with /dev/rdsk/c1 from being scanned.
ignoredisk /dev/rdsk/c?t0d0
This directive prevents all devices /dev/rdsk/cXt0d0 (’X’ might
be any char) from being scanned.
You might use more than one such wildcard expression in any such
directive.
storageUseNFS NUMBER
Setting storageUseNFS to 1 causes all NFS and NFS-like file
systems to be marked as ’Network Disks’ in the hrStorageTable.
This is according to RFC 2790. Not setting storageUseNFS or
setting it to 2 causes NFS and NFS-like file systems to be
marked as ’Fixed Disks’ as it has been in previous versions of
the ucd-snmp SNMP agent.
authtrapenable NUMBER
Setting authtrapenable to 1 enables generation of authentication
failure traps. The default value is disabled(2). Ordinarily
the corresponding object (snmpEnableAuthenTraps.0) is read-
write, but setting its value via this token makes the object
read-only, and attempts to set the value of the object will
result in a notWritable error response.
override [-rw] OID TYPE VALUE
This directive allows you to override a particular OID with a
different value (and possibly a different type of value). The
-rw flag will allow snmp SETs to modify it’s value as well.
(note that if you’re overriding original functionality, that
functionality will be entirely lost. Thus SETS will do nothing
more than modify the internal overridden value and will not
perform any of the original functionality intended to be
provided by the MIB object. It’s an emulation only.) An
example:
override sysDescr.0 octet_str "my own sysDescr"
That line will set the sysDescr.0 value to "my own sysDescr" as
well as make it modifiable with SNMP SETs as well (which is
actually illegal according to the MIB specifications).
Note that care must be taken when using this. For example, if
you try to override a property of the 3rd interface in the
ifTable with a new value and later the numbering within the
ifTable changes it’s index ordering you’ll end up with problems
and your modified value won’t appear in the right place in the
table.
Valid TYPEs are: integer, uinteger, octet_str, object_id,
counter, null (for gauge’s, use "uinteger"; for bit strings, use
"octet_str"). Note that setting an object to "null" effectively
delete’s it as being accessible. No VALUE needs to be given if
the object type is null.
More types should be available in the future.
SETTING UP TRAP AND/OR INFORM DESTINATIONS
trapcommunity STRING
This defines the default community string to be used when
sending traps. Note that this command must be used prior to any
of the following three commands that are intended use this
community string.
trapsink HOST [COMMUNITY [PORT]]
trap2sink HOST [COMMUNITY [PORT]]
informsink HOST [COMMUNITY [PORT]]
These commands define the hosts to receive traps (and/or inform
notifications). The daemon sends a Cold Start trap when it
starts up. If enabled, it also sends traps on authentication
failures. Multiple trapsink, trap2sink and informsink lines may
be specified to specify multiple destinations. Use trap2sink to
send SNMPv2 traps and informsink to send inform notifications.
If COMMUNITY is not specified, the string from a preceding
trapcommunity directive will be used. If PORT is not specified,
the well known SNMP trap port (162) will be used.
trapsess [SNMPCMD_ARGS] HOST
This is a more generic trap configuration token that allows any
type of trap destination to be specified with any version of
SNMP. See the snmpcmd(1) manual page for further details on the
arguments that can be passed as SNMPCMD ARGS . In addition to
the arguments listed there, the special argument -Ci specifies
that you want inform notifications to be used instead of
unacknowledged traps (this requires that you also specify a
version number of v2c or v3 as well).
PROXY SUPPORT
proxy [-Cn CONTEXTNAME] [SNMPCMD ARGS] HOST OID [REMOTEOID]
This token specifies that any incoming requests under OID should
be proxied on to another HOST instead. If a CONTEXTNAME is
specified, it assigns the proxied tree to a particular context
name within the local agent. This is the proper way to query
multiple agents through a single proxy. Assign each remote
agent to a different context name. Then you can use "snmpwalk
-n contextname1" to walk one remote proxied agent and "snmpwalk
-n contextname2" to walk another, assuming you are using SNMPv3
to talk to the proxy (snmpv1 and snmpv2c context mappings aren’t
currently supported but might be in the future). Optionally,
relocate the local OID tree to the new location at the
REMOTEOID. To authenticate to HOST you should use the
appropriate set of SNMPCMD ARGS. See the snmpcmd(1) manual page
for details.
Examples:
# assigns the entire mib tree on remotehost1 to the context of the
# same name:
proxy -Cn remotehost1 -v 1 -c public remotehost1 .1.3
# ditto, but for remotehost 2
proxy -Cn remotehost2 -v 1 -c public remotehost2 .1.3
# proxies only the ucdavis enterprises tree to the remote host using snmpv1
proxy -v 1 -c public remotehost .1.3.6.1.4.1.2021
# uses v3 to access remotehost and converts the remote .1.3.6.1.2.1.1
# oid to local .1.3.6.1.3.10 oid (another way to access mulitple hosts
# without using contexts)
proxy -v 3 -l noAuthNoPriv -u user remotehost .1.3.6.1.3.10 .1.3.6.1.2.1.1
PASS-THROUGH CONTROL
pass MIBOID EXEC
(If you’re writing perl scripts, please see the embedded perl
support information later in this manual page). Passes entire
control of MIBOID to the EXEC program. The EXEC program is
called in one of the following three ways:
EXEC -g MIBOID
EXEC -n MIBOID
These call lines match to SNMP get and getnext requests.
It is expected that the EXEC program will take the
arguments passed to it and return the appropriate
response through it’s stdout.
The first line of stdout should be the MIB OID of the
returning value. The second line should be the TYPE of
value returned, where TYPE is one of the text strings:
string, integer, unsigned, objectid, timeticks,
ipaddress, counter, or gauge. The third line of stdout
should be the VALUE corresponding with the returned TYPE.
For instance, if a script was to return the value integer
value "42" when a request for .1.3.6.1.4.100 was
requested, the script should return the following 3
lines:
.1.3.6.1.4.100
integer
42
To indicate that the script is unable to comply with the
request due to an end-of-mib condition or an invalid
request, simple exit and return no output to stdout at
all. An SNMP error will be generated corresponding to
the SNMP noSuchName response.
EXEC -s MIBOID TYPE VALUE
For SNMP set requests, the above call method is used.
The TYPE passed to the EXEC program is one of the text
strings: integer, counter, gauge, timeticks, ipaddress,
objid, or string, indicating the type of value passed in
the next argument.
Return nothing to stdout, and the set will assumed to
have been successful. Otherwise, return one of the
following error strings to signal an error: not-writable,
or wrong-type and the appropriate error response will be
generated instead.
Note: By default, the only community allowed to write
(ie snmpset) to your script will be the "private"
community,or community #2 if defined differently
by the "community" token discussed above. Which
communities are allowed write access are
controlled by the RWRITE definition in the
snmplib/snmp_impl.h source file.
Example (in snmpd.conf):
pass .1.3.6.1.4.1.2021.255 /path/to/local/passtest
pass_persist MIBOID EXEC
Passes entire control of MIBOID to the EXEC program. Similar to
pass, but the EXEC program continues to run after the initial
request is answered. Also, pass and pass_persist block till
they return.
Upon initialization, EXEC is passed the string "PING\n" in
stdin, and it should respond by printing "PONG\n" to stdout.
For get and getnext requests, EXEC program is passed two lines,
the command (get or getnext) and the MIB OID. It should return
three lines, the MIB OID, the TYPE of value returned, the VALUE
corresponding with the returned TYPE.
For example, if the value for .1.3.6.1.4.100 was requested, the
following 2 lines would be passed in to stdin:
get
.1.3.6.1.4.100
To return the value, say, 42, the script would write to stdout:
.1.3.6.1.4.100
integer
42
To indicate that the script is unable to comply with the request
due to an end-of-mib condition or an invalid request, print
"NONE\n" to stdout.
Example (in snmpd.conf):
pass_persist .1.3.6.1.4.1.2021.255
/path/to/local/pass_persisttest
EMBEDDED PERL SUPPORT
Warning: though embedded perl is working, not much functionality has
been implemented yet and thus writing mib module pieces for the agent
within perl is not trivial at this point. It should get better in
future releases.
The net-snmp package has ability to call perl scripts directly inside
the agent through embedded perl technology (similar to mod_perl for the
apache web server). This must be turned on at compile time by passing
--enable-embedded-perl to the configure script when the package is
built. To see if your package was built with embedded perl, run "net-
snmp-config --configure-options" and see if that flag was used.
If compiled in, it defines the following snmpd.conf configuration
directives:
disablePerl true
This will turn off perl support entirely. If the embedded perl
support stops working due to a change in perl, etc, this will
stop any calls to the perl core.
perlInitFile FILE
Use FILE as the initialization file. This file is normally
/usr/share/snmp/snmp_perl.pl but this token can override that
default. This file performs any in-perl initialization that is
needed before the rest of the perl directives (below) are
called. It is sourced once just before the first perl directive
is parsed. See the default file for an example of the
initialization it performs.
perl EXPRESSION
Calls perl to evaluate an expression. Normally you’d want to do
something like register a function to call when an OID is
requested, but you can really do anything perl related you want.
For example:
perl print "hello world\n";
is the most basic hello world example.
The init script by default initializes a $agent variable which
is a pointer to a NetSnmp::agent object through which you can
register callbacks when a section of the OID tree is hit:
perl use Data::Dumper;
perl sub myroutine { print "got called: ",Dumper(@_),"\n"; }
perl $agent->register(’mylink’, ’.1.3.6.1.8765’, \&myroutine);
Sourcing an external file:
perl ’do /path/to/file.pl’;
No better examples exist at the moment, unfortunately. Look for
improved support in future releases. Comments on how this looks
as an architecture are certainly appreciated now.
DISMAN-EVENT-MIB SUPPORT (READ: SENDING TRAPS ON ERRORS)
Warning: this implementation has not been extensively tested and is
additionally not known to be entirely complete. The concepts defined
here should function appropriately, however, but no promises are made
at this time.
If your agent was compiled with support for the DISMAN-EVENT-MIB (you
can enable this by running the net-snmp configure script with the
--with-mib-modules=disman/event-mib argument) you have support for
having the agent check its own data at regular intervals and to send
out traps when certain conditions occur. Traps are sent when
expressions are first noticed, not once per evaluation. Once a test
expression fires a trap, the test will have to fail again before a new
trap is sent. See the DISMAN-EVENT-MIB documentation for more details.
This can be configured either using the MIB tables themselves or by
using these special key words:
agentSecName NAME
The DISMAN-EVENT-MIB support requires a valid user name for
which to scan your agent with. This can either be specified
using the agentSecName token or by explicitly list one on the
"monitor" lines described below using the -u switch. Either
way, a "rouser" line (or equivalent access control settings)
must also be specified with the same security name name. If you
need an example, just do something like this:
agentSecName internal
rouser internal
And everything below should work just fine.
monitor [OPTIONS] NAME EXPRESSION
This token tells the agent to monitor itself for problems based
on EXPRESSION. Expression is a simple expression based on an
oid, a comparison operator (!=, ==, <, <=, >, >=) and an integer
value (see the examples below). NAME is merely an arbitrary
name of your choosing for administrative purposes only. OPTIONS
include the following possibilities:
-t Use a threshold monitor instead of a boolean monitor.
This means that expression should be a low and high
value. If the given OID passes beyond the high value, a
rising alarm will triggered. A falling alarm will then
be triggered after it falls below the low value.
-r FREQUENCY
Monitors the given expression every FREQUENCY seconds.
The default is 600 (10 minutes).
-u SECNAME
Use the SECNAME security name for scanning the local
host. Specifically, this SECNAME must then be given
access control rights via something like the "rouser"
snmpd.conf token for this expression to be valid at all.
If not specified, it uses the default security name
specified by the agentsecname snmpd.conf token. Either
the -u flag or a valid agentsecname token must be
specified (and that name must be given proper access
control rights via a "rouser" token).
-o OID Specifies additional object values to be delivered with
in the resulting trap in addition to the normal trap
objects. This is useful for obtaining other columns in
the table for the row that triggered the expression. See
the examples below for more details.
-e EVENTNAME
Specifies an event name that describes what to do when
the trigger is fired. Currently, this must be the name
of a notificationEvent event as described below.
The following example configuration checks the hrSWRunPerfTable
table (listing running processes) for any process which is
consuming > 10Mb of memory. It performs this check every 600
seconds (the default). For every process it finds exceeding the
limit, it will end out exactly one notification. In addition to
the normal hrSWRunPerfMem oid and value sent in the trap, the
hrSWRunName object will also be sent. Note that the hrSWRunName
object actually occurs in a different table, but since the
indexes to the two tables are the same this works out alright.
rouser me
monitor -u me -o sysUpTime.0 -o hrSWRunName "high process memory" hrSWRunPerfMem > 10000
The above line would produce a trap which, when formated by
snmptrapd, would look like:
2002-04-05 13:33:53 localhost.localdomain [udp:127.0.0.1:32931]:
sysUpTimeInstance = Timeticks: (1629) 0:00:16.29 snmpTrapOID.0 = OID: mteTriggerFired mteHotTrigger = high process memory mteHotTargetName = mteHotContextName = mteHotOID = OID: hrSWRunPerfMem.1968 mteHotValue = 28564 hrSWRunName.1968 = "xemacs"
This shows my xemacs process using 28Mb of resident memory.
Which, considering it’s xemacs, is not that surprising.
Threshold example:
monitor -t -r 15 -o prNames -o prErrMessage "process table" prErrorFlag 0 1
notificationEvent NAME NOTIFICATION [[-w] OID_OBJECT ...]
This will create a notification event, which can be fired by
attaching it to a monitor using a monitor’s -e switch and an
identical NAME field. The NOTIFICATION to be sent should be the
OID of a notification. Additional objects can be included, and
by default the suffix of the row/object being monitored will be
appended to the object identifier unless it’s told not to be a
wild-card object by prefixing it with the -w switch. EG, if
you’re monitoring the ifTable and you want your trap to include
the ifDescr object for the row that was discovered, don’t add
the -w switch and the .INDEX field will be appended. If the OID
is fully qualified (EG, "sysContact.0") and no instance suffix
should be appended to it then add a -w switch before it. See
the linkUpDownNotifications token below for example usage of
this token to send the linkUp and linkDown traps.
linkUpDownNotifications yes
This will make the DISMAN-EVENT-MIB support watch the ifTable to
determine when a network interface is taken up or down. When
this happens, a linkUp or linkDown notification will be
triggered. This is exactly equivalent to doing:
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
defaultMonitors yes
By default, the agent and the DISMAN-EVENT-MIB support do
nothing until configured. Typically people wish to watch a
bunch of tables within the UCD-SNMP-MIB which are designed
specifically for reporting problems. If the "defaultMonitors
yes" line is put into the snmpd.conf file (which must be
accompanied by an appropriate agentSecName line and a rouser
line), the following monitoring conditions will be installed:
monitor -o prNames -o prErrMessage "process table" 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
DEBUGGING AND OTHER EXTENSIBILITY NOTES
If you’re trying to figure out aspects of the various mib modules
(possibly some that you’ve added yourself), the following may help you
spit out some useful debugging information. First off, please read the
snmpd manual page on the -D flag. Then the following configuration
snmpd.conf token, combined with the -D flag, can produce useful output:
injectHandler HANDLER modulename
This will insert new handlers into the section of the mib tree
referenced by "modulename". The types of handlers available for
insertion are:
stash_cache - Caches information returned from the lower level. This
greatly help the performance of the agent, at the cost
of caching the data such that its no longer "live" for
30 seconds (in this future, this will be configurable).
Note that this means snmpd will use more memory as well
while the information is cached. Currently this only
works for handlers registered using the table_iterator
support, which is only a few mib tables. To use it,
you need to make sure to install it before the
table_iterator point in the chain, so to do this:
injectHandler stash_cache NAME table_iterator
If you want a table to play with, try walking the
nsModuleTable with and without this injected.
debug - Prints out lots of debugging information when
the -Dhelper:debug flag is passed to the snmpd
application.
read_only - Forces turning off write support for the given module.
serialize - If a module is failing to handle multiple requests
properly (using the new 5.0 module API), this will force
the module to only receive one request at a time.
bulk_to_next - If a module registers to handle getbulk support, but
for some reason is failing to implement it properly,
this module will convert all getbulk requests to
getnext requests before the final module receives it.
Figuring out module names
To figure out which modules you can inject things into, snmpwalk
the nsModuleTable which will give you a list of all named
modules registered within the agent.
EXAMPLE CONFIGURATION FILE
See the EXAMPLE.CONF file in the top level source directory for a more
detailed example of how the above information is used in real examples.
RE-READING snmpd.conf AND snmpd.local.conf
The Net-SNMP agent can be forced to re-read its configuration files.
It can be told to do so by one of two ways:
1. An snmpset of integer(1) to UCD-SNMP-MIB::versionUpdateConfig.0
(.1.3.6.1.4.1.2021.100.11.0)
2. A "kill -HUP" signal sent to the snmpd agent process.
FILES
/etc/snmp/snmpd.conf
SEE ALSO
snmpconf(1), snmpusm(1), snmp.conf(5), snmp_config(5), snmpd(8),
EXAMPLE.conf, read_config(3).