FAQ
FAQ Maintainer: Dave ShieldGENERAL ======= What is it? ---------- - Various tools relating to the Simple Network Management Protocol including: * An extensible agent * An SNMP library * tools to request or set information from SNMP agents * tools to generate and handle SNMP traps * a version of the unix 'netstat' command using SNMP * a graphical Perl/Tk/SNMP based mib browser This package is originally based on the Carnegie Mellon University SNMP implementation (version 2.1.2.1), but has developed significantly since then. Where can I get it? ------------------ Download: - http://www.net-snmp.org/download/ - ftp://ftp.net-snmp.org/pub/sourceforge/net-snmp/ Web page: - http://www.net-snmp.org/ Sourceforge Project page: - http://www.net-snmp.org/project/ Mirrors (note that sourceforge download servers are mirrored themselves): - US: ftp://ftp.freesnmp.com/mirrors/net-snmp/ - Greece: ftp://ftp.ntua.gr/pub/net/snmp/net-snmp/ What documentation is available? ------------------------------- This FAQ (!) README and individual READMEs for various platforms README.thread (discusses threading issues) INSTALL PORTING EXAMPLE.conf man pages for the individual tools, files and the API A guide for extending the agent Tutorials for both ucd-snmp v4 and net-snmp v5 at http://www.net-snmp.org/tutorial/ and http://www.net-snmp.org/tutorial-5/ respectively Most of this documentation (plus archives of the mailing lists) is also available on our web page: http://www.net-snmp.org/ There is also a Wiki (including a community-maintained version of this FAQ) at http://www.net-snmp.org/wiki/ Are there binaries available? ---------------------------- There are binaries for some versions/systems available under the "net-snmp binaries" package on the project download site. What's the difference between UCD-SNMP and Net-SNMP? --------------------------------------------------- Not a great deal, really. Although the project originally started at UC Davis (hence the name), and it has always been based there, most of the contributors have had little or no connection with this institution. The move to SourceForge was intended to provide a more flexible environment for the project, and to distribute the administrative workload more evenly. The change of name simply reflects this move, which was the last remaining link with UC Davis. The 4.2.x line saw the last releases made using the ucd-snmp name, and all releases on this line have been been bug-fixes only. Release 5.0 was the first version released under the Net-SNMP name, and all further development is being done on the 5.x code base. The 4.2.x code line is now almost completely dormant, and is due to be closed down altogether. Much of the work done for the various 5.x releases has involved some fairly significant changes to the code - in particular the architecture of the agent. However attempts have been made to retain backwards compatibility as much as possible, and most code written for earlier releases should continue to work. The most significant change from the 4.2.x ucd suite to the 5.x Net-SNMP releases was a restructuring of the header file organisation - not least a change from <ucd-snmp/xxx.h> to <net-snmp/yyy.h>. But given the maturity of the Net-SNMP code, this should be less of a consideration for most current SNMP development projects. What operating systems does it run on? ------------------------------------- Both the applications and the agent have been reported as running (at least in part) on the following operating systems: * Linux (kernels 2.6 to 1.3) * Solaris/SPARC (11 to 2.3), Solaris/Intel (10, 9) -- see README.solaris * HP-UX (10.20 to 9.01 and 11.23 to 11.0 -- see README.hpux11) * Mac OS X (10.4 to 10.1) -- see README.osX * NetBSD (2.0 to 1.0) * FreeBSD (6.1 to 2.2) * OpenBSD (4.0 to 2.6) * BSDi (4.0.1 to 2.1) * AIX (5.3, 5.2, 5.1, 4.3.3, 4.1.5, 3.2.5) -- see README.aix * IRIX (6.5 to 5.1) * OSF (4.0, 3.2 and Tru64 Unix 5.1B -- see README.tru64) * SunOS 4 (4.1.4 to 4.1.2) * Ultrix (4.5 to 4.2) * Dynix/PTX 4.4 * QNX 6.2.1A We have also been informed about a port to the Stratus VOS. See http://ftp.stratus.com/vos/network/network.html for details. See the next question for the status of Windows support. Certain systems fail to compile particular portions of the agent. These can usually be persuaded to compile (at the loss of some functionality) by omitting the modules affected. See the next question for more details. Also note that the presence of a particular configuration in this list does not imply a perfect or complete implementation. This is simply what various people have reported as seeming to work. (Or more frequently, the configurations people have reported problems which that we think we've fixed!) What happens if mine isn't listed? --------------------------------- It's probably worth trying to compile it anyway. Unless your system is significantly different to the supported configurations, most of the code (library, applications and the agent infrastructure) should probably compile with little or no difficulty. The most likely source of problems will be MIB modules within the agent, as this tends to be where the most system-specific code is found. If only a few modules fail to compile, try removing them from the agent by running "configure --with-out-mib-module=xxx,yyy", and re-compiling. If a large number of modules fail, then it might be easier to start from a relatively bare system, using "configure --enable-mini-agent --with-defaults". Then if this minimal agent compiles and runs successfully, try adding each of the missing mibgroups individually using the configure option '--with-mib-module'. If configure fails with "invalid configuration" messages, or you get completely stuck, contact the coders list for advice. Similarly, if you manage to get this working on a new system, please let us know of any code changes that you needed to make, together with details of the hardware you're using, and what versions of the operating system you've tried it on. The entry 'host' in the file 'config.status' should show this information. Oh, and congratulations! Does it run on Windows? ---------------------- The suite will compile and run on Win32 platforms, including the library, command-line tools and the basic agent framework. Note that the agent now includes support for the MIB-II module, but this requires Microsoft's Core Platform SDK. Instructions for how to install this are given in README.win32. Pre-compiled binaries are available from the Net-SNMP web site. As of Net-SNMP 5.4, the Net-SNMP agent is able to load the Windows SNMP service extension DLLs by using the Net-SNMP winExtDLL extension. Some Net-SNMP MIB modules, including the UCD pass-through extensions, do not currently work under Windows. Volunteers to assist in these missing modules are likely to welcomed with open arms :-) Further details of Windows support (currently Visual C++, MinGW and Cygnus cygwin32) is available in the file README.win32. How do I find out about new releases? ------------------------------------ There is a mailing list for these announcements net-snmp-announce@lists.sourceforge.net To be added to (or removed from) this list, visit http://www.net-snmp.org/lists/net-snmp-announce/. Or you can send a message to the address 'net-snmp-announce-request@lists.sourceforge.net' with a subject line of 'subscribe' (or 'unsubscribe' as appropriate). Major code revisions may be announced more widely (e.g. on the SNMP mailing lists, or comp.protocols.snmp) but this list is the most reliable way to keep in touch with the status of this package. Patches to fix known problems are also made available via the web site: http://www.net-snmp.org/patches/ How can I find out what other people are doing? ---------------------------------------------- There is a general purpose discussion list net-snmp-users@lists.sourceforge.net To be added to (or removed from) this list, visit http://www.net-snmp.org/lists/net-snmp-users. Or you can send a message to the address 'net-snmp-users-request@lists.sourceforge.net' with a subject line of 'subscribe' (or 'unsubscribe' as appropriate). To find out what the developers are doing, and to help them out, please read the PORTING file enclosed with the package. There is also an net-snmp IRC channel set up on the freenode.net IRC chat servers (you can use irc.freenode.net to connect and/or see http://www.freenode.net/ for getting started with irc). Several core developers hang out there on a regular basis. How do I submit a patch or bug report? ------------------------------------- The best way to submit a bug report is via the bug database through the interface found at http://www.net-snmp.org/bugs/. Be sure to include the version of the package that you've been working with, the output of the command 'uname -a', the precise configuration or command that triggers the problem and a copy of any output produced. All patches should be submitted to the patch manager at http://www.net-snmp.org/patches/. If possible, submit a bug report describing the patch as well (referencing it by its patch number) since the patch manager doesn't contain a decent description field. Questions about using the package should be directed at the net-snmp-users@lists.sourceforge.net mailing list. Note that this mailing list is relatively busy, and the people answering these questions are doing so out of the goodness of their hearts, and in addition to their main employment. Please note the following: - use plain text mail, rather than HTML - don't resend questions more than once (even if no-one answered immediately) - include full details of exact commands and error messages ("I've tried everything, and it doesn't work" isn't much use!) - do *NOT* send messages to -users and -coders mailing lists (most developers read both anyway) - don't mail the developers privately - keep everything on the list Remember that this is basically an unsupported package. Fundamentally it's Open Source, so you have the source code. If you need something fixing badly enough, it's up to you to do the work. We can't promise to be able to solve all problems, but we'll certainly try and help. But remember that this is basically an unsupported package. It's Open Source, so if you need something fixing badly enough, fundamentally it's up to you to do the work. Can I reuse the code in my commercial application? ------------------------------------------------- The details of the COPYRIGHTs on the package can be found in the COPYING file. You should have your lawyer read this file if you wish to use the code in your commercial application. We will not summarize here what is in the file, as we're not lawyers and are unqualified to do so. What's the difference between SNMPv1, SNMPv2 and SNMPv3? ------------------------------------------------------- What's the difference between SNMPv2 and SNMPv2c? ------------------------------------------------ A full description is probably beyond the scope of this FAQ. Very briefly, the original protocol and admin framework was described in RFCs 1155-1157, and is now known as SNMPv1. Practical experience showed up various problems and deficiencies with this, and a number of revised frameworks were developed to try and address these problems. Unfortunately, it proved difficult to achieve any sort of agreement - particularly over the details of the administrative framework to use. There was less disagreement over the proposed changes to the protocol operations. These included: * increasing the range of errors that could be reported * introducing "exception values" (so a single missing value didn't affect the other varbinds in the same request) * a new GETBULK operation (a supercharged GETNEXT) * new notification PDUs (closer in structure to the other request PDUs) Strictly speaking, it's this revised protocol (originally defined in RFC 1905, and most recently in RFC 3416) that is "SNMPv2". The only framework based on this protocol that saw a significant level of use was "Community-based SNMPv2" or "SNMPv2c" (defined in RFCs 1901-1908). This retained the same administrative framework as SNMPv1 (with all of the accompanying limitations), but using the new protocol operations. More recently, a new administrative framework has been developed, building on the various competing SNMPv2 proposals, and using the same SNMPv2 protocol operations. This is SNMPv3, which is defined in RFCs 3411-3418. It addresses some of the deficiencies of the community-based versions, including significant improvements to the security of SNMP requests (like it finally has some!). SNMPv3 is now a full IETF standard protocol. Strictly speaking, SNMPv3 just defines a fairly abstract framework, based around the idea of "Security Models" and "Access Control Models". It's this combination of SNMPv3 plus accompanying models that actually provides a working SNMP system. However, the only models in common use are the "User-based Security Model" (RFC 3414) and the "View-based Access Control Model" (RFC 3415). So "SNMPv3" is frequently used to mean the combination of the basic SNMPv3 framework with these two particular models. This is also sometimes described as "SNMPv3/USM". So in brief: - SNMPv2c updated the protocol operations but left the administrative framework unchanged. - SNMPv3 updated the administrative framework but left the protocol operations unchanged. Which versions of SNMP are supported in this package? ---------------------------------------------------- This package currently supports the original SNMPv1, Community-based SNMPv2 (i.e. RFCs 1901-1908), and SNMPv3 (i.e. RFCs 3411-3418). The agent will respond to requests using any of these protocols, and all the tools take a command-line option to determine which version to use. Support for SNMPv2 classic (a.k.a. "SNMPv2 historic" - RFCs 1441-1452) was dropped with the 4.0 release of the UCD-snmp package. Can I use SNMPv1 requests with an SNMPv2 MIB (or vice versa)? ------------------------------------------------------------ Yes. The syntax used to specify a MIB file (better referred to as SMIv1 or SMIv2) is purely concerned with how to define the characteristics of various management objects. This is (almost) completely unrelated to the versions of the protocol used to operate on these values. So it is quite reasonable to use SNMPv1 requests on objects defined using SMIv2, or SNMPv2 (or SNMPv3) requests on objects defined using SMIv1. The one exception is objects of syntax Counter64, which are only accessible using SNMPv2 or higher. SNMPv1 requests will either treat such objects as an error, or skip them completely. Where can I find more information about network management? ---------------------------------------------------------- There are a number of sites with network management information on the World Wide Web. A couple of the most useful are http://www.simpleweb.org/ http://www.snmplink.org/ http://www.mibdepot.com/ There are two Usenet newsgroups which are relevant. 'comp.dcom.net-management' which discusses general issues relating to network management 'comp.protocols.snmp' which is specifically concerned with use of SNMP in particular (though there is a large overlap between these two groups). The SNMP group also has an FAQ (split into two parts) which discusses more general issues related to SNMP, including books, software, other sites, how to get an enterprise number, etc, etc. This is available from ftp://rtfm.mit.edu/pub/usenet/comp.protocols.snmp/ or via any of the Web sites above. Is Net-SNMP thread safe? ----------------------- Strictly speaking, no. However, it should be possible to use the library in a thread-safe manner. This is covered in detail in the file README.thread (shipped with the standard distribution), but can be summarised as follows: - Call 'snmp_sess_init()' prior to activating any threads. This reads in and parses MIB information (which isn't thread-safe) as well as preparing a session structure for subsequent use. - Open an SNMP session using 'snmp_sess_open()' which returns an opaque session handle, which is essentially independent of any other sessions (regardless of thread). - Resource locking is not handled within the library, and is the responsibility of the main application. The applications and the agent have not been designed for threaded use. It should be safe to use the agent library to embed a subagent within a threaded application as long as *all* SNMP-related activity (including generating traps, and parsing MIBs) is handled within a single thread. Unfortunately, the SNMPv3 support was added about the same time as the thread support and since they occurred in parallel the SNMPv3 support was never checked for multi-threading correctness. It is most likely that it is not thread-safe at this time. APPLICATIONS ============ How do I add a MIB? ------------------ This is actually two separate questions, depending on whether you are referring to the tools, or the agent (or both). See the next question or the next section respectively. How do I add a MIB to the tools? ------------------------------- Adding a MIB to the client-side tools has two main effects: - it allows you to refer to MIB objects by name (rather than having to use the numeric OIDs) - it allows the results to be displayed in a more immediately meaningful fashion. Not just giving the object names, but also showing named enumeration values, and interpreting table indexes properly (particularly for string and OID index values). Most of the tools (apart from 'snmptable') will work quite happily without any MIB files at all - although the results won't be displayed in quite the same way. The same holds true for the agent - see the AGENT section for details. There are two steps required to add a new MIB file to the tools. Firstly, copy the MIB file into the appropiate location: cp MY-MIB.txt /usr/local/share/snmp/mibs (which makes it available to everyone on the system) or mkdir $HOME/.snmp mkdir $HOME/.snmp/mibs cp MY-MIB.txt $HOME/.snmp/mibs (which makes it available to you only) Note that the location of the shared MIB directory may be different from that given here - particularly if you're working with a vendor supplied distribution. See where the MIBs are currently installed, and copy the new MIB to the same place. Secondly, tell the tools to load this MIB: export MIBS=+MY-MIB (load it for this session only) or echo "mibs +MY-MIB" >> $HOME/.snmp/snmp.conf (load it every time) This will add the new MIB to the list of MIBs loaded by default. Omitting the '+' will *replace* the list of MIBs to be loaded by the specified (colon-separated) list - together with any MIBs that they explicitly rely on. Note that the value for this variable is the name of the MIB module, *not* the name of the MIB file. These are typically the same (apart from the .txt suffix), but if in doubt, check the contents of the file. The value to use is the token immediately before the word DEFINITIONS at the start of the file. If you prefer to have the tools load all available MIBs (which may slow them down), then set the MIBS environmental variable (or the snmp.conf token "mibs") to the special value "ALL". Note that you need *both* steps. Why can't I see anything from the agent? --------------------------------------- There are two main general causes of problems retrieving information from the agent. Either the client tool may not like the request (and refuse to send it at all), or the agent may not respond with anything useful. The simplest way to distinguish between the two is to run the command with the command-line option '-d'. If this doesn't display a hex dump of the raw outgoing packet, then it's the client side which is dropping the request. Hopefully you should see some form of error message, to help identify what's wrong. If this displays one or more outgoing dumps (but nothing coming back), then the request is failing at the agent end. See the next entry for more details. If you see dumps of both the outgoing request, and a response, but no results are displayed, then either there may be a problem with decoding the response (in which case you should see an error message), or the agent may simply not support the requested information (and the response is being discarded as irrelevant). Why doesn't the agent respond? ----------------------------- Assuming that the agent is actually sending the request (see the previous entry), there are two main likely causes for the agent not to respond. Either it doesn't receive the request (e.g. it's being blocked by a firewall or packet filtering), or it receives it, but is unwilling (or unable) to process it. If the remote system is running the Net-SNMP agent, then the easiest way to check what's going wrong is to shut down the agent, and re-start it using the options: -f -Le -d This will display raw dumps of packets seen (or sent) by the agent, just as the '-d' flag did for the client side in the previous entry. Restart the agent with these flags, and send the same query as before. If the agent doesn't display anything in response to this request, then it's probably some form of firewall settings, which are preventing the agent from ever seeing the request. If the agent displays a dump of the incoming request, but nothing going out, then the most likely cause is access control settings. See the relevant entries in the AGENT section for details. A third possibility is that the agent *is* responding to the request, but only after a long delay. This would be indicated by a series of incoming packet dumps (showing various retries from the client side), followed by several outgoing dumps - possibly long after the client tool has given up in disgust. See the entry The agent worked for a while, then stopped responding. Why? later in this section. The same basic causes could also affect other vendors' SNMP agents. Please consult the relevant documentation for how to investigate and address such problems. I can see the system group, but nothing else. Why? -------------------------------------------------- This is almost definitely due to the access configuration of the agent. Many pre-configured systems (such as most Linux distributions) will only allow access to the system group by default, and need to be configured to enable more general access. The easiest way to test this is to try a GETNEXT request that ought to return the entry of interest. e.g. snmpgetnext -v1 -c public localhost UCD-SNMP-MIB::versionTag instead of snmpget -v1 -c public localhost UCD-SNMP-MIB::versionTag.0 If the agent responds with "end of MIB" or a different object, then either the agent doesn't implement that particular object at all, or the access control won't allow you access to it. See the entries on access control in the AGENT section for how to configure the Net-SNMP agent, or consult the agent's own documentation. Why can't I see values in the <INSERT ENTERPRISE HERE> tree? ----------------------------------------------------------- If you're walking a specific tree, but failing to see anything in it, then the most likely cause is that the agent simply does not implement those particular MIB objects. Or if it does, that the access control or other configuration settings mean that there's nothing for you to see there. However, if you're trying a basic "snmpwalk" with no explicit OID specified, then this would also explain why you're not seeing any enterprise-specific results. By default, unless given an explicit starting OID, then the 'snmpwalk' command will display the contents of the 'mib-2' tree, containing most of the IETF-standard management information supported by the agent. When the agent reaches the end of this tree, it will return the first enterprise-specific value, and 'snmpwalk' will recognise that this marks the end of the (implicitly) request tree, and stop. No enterprise-specific information will be displayed. To walk the whole tree, and see *all* the information that the agent supports, specify a starting point of '.iso' or '.1'. To walk a specific enterprise subtree, specify the root of this tree as the starting point - e.g: snmpwalk -v1 -c public localhost UCD-SNMP-MIB::ucdavis There is more information about particular UCD-specific subtrees in the AGENT section. The agent worked for a while, then stopped responding. Why? ----------------------------------------------------------- There are three basic possibilities: - the agent has crashed - it is hanging - it is temporarily overloaded Detecting whether the agent has crashed should be fairly straighforward. If you can reliably reproduce this crash (e.g. by sending a particular SNMP request), then contact the coders list for advice. It's the other two cases that are probably more significant. To tell the difference between these two, try leaving the agent undisturbed for a while, and then probe it using a single 'snmpget' request, specifying a longer timeout (e.g. '-t 120'). If it now responds, then something was probably sending requests (including duplicate retries) faster than the agent could process them, and it was building up a backlog. Try adjusting the timeout period and retry frequency of these client requests, or look at improving the efficiency of the implementation of the relevant MIB objects. If the agent remains unresponsive (particularly if the load on the system is steadily climbing), then it's probably hanging, and all you can really do is restart the agent. If you can identify what causes this to happen, then contact the coders list for advice. Requesting an object fails with "Unknown Object Identifier" Why? ---------------------------------------------------------------- If a general snmpwalk shows a particular entry, but asking for it more specifically gives a "sub-identifier not found:" or "Unknown Object Identifier" error, then that's a problem with the tool, rather than the agent. Firstly, make sure that you're asking for the object by the right name. Object descriptors are case-sensitive, so asking for 'sysuptime' will not be recognised, but 'sysUpTime' will. Alternatively, the object may be defined in a MIB that hasn't been loaded. Try loading in all the MIB files: snmpget -m ALL -v1 -c public localhost sysUpTime.0 or specify the name of the appropriate MIB explicitly: snmpget -v1 -c public myhost SNMPv2-MIB::sysUpTime.0 Note that this uses the name of the *module*, not the name of the file. See the second entry in this section for the distinction. However, if 'snmpwalk' displays the object by name, this is unlikely to be the cause, and you should look closely at the exact object name you are using. Why do I get "noSuchName" when asking for "sysUpTime" (or similar)? ------------------------------------------------------------------ Assuming that you do have access to this object, the most likely cause is forgetting the "instance subidentifier". If you try walking the 'system' group, you should notice that all of the results have a number after the MIB object name. This is the "instance subidentifier" of that particular MIB instance. For values from the sysORTable, this basically provides an index into the table, and should be very familiar. But the other values in the system group also have an instance number displayed. For non-table objects ("scalars"), this instance subidentifier will always be '0', and it *must* be included when making a GET request. Compare the following: $ snmpget -v1 -c public localhost sysUpTime Error in packet Reason: (noSuchName) There is no such variable name in this MIB. This name doesn't exist: system.sysUpTime $ snmpget -v1 -c public localhost sysUpTime.0 system.sysUpTime.0 = Timeticks: (69189271) 8 days, 0:11:32.71 This is a little less obscure when using SNMPv2c or v3 requests: $ snmpget -v 2c -c public localhost sysUpTime system.sysUpTime = No Such Instance currently exists Why do I sometimes get "End of MIB" when walking a tree, and sometimes not? -------------------------------------------------------------------------- This depends on which MIB modules are supported by the agent you are querying and exactly what you're asking for. Note that a tree is walked by repeatedly asking for "the next entry" until all the values under that tree have been retrieved. However, the agent has no idea that this is what's happening - all it sees is a request for "the next entry after X". If the object X happens to be the last entry in a sub-tree, the agent will provide the next object supported (as requested) even though this will be in a different subtree. It's up to the querying tool to recognise that this last result lies outside the area of interest, and simply discard it. If the object X happens to be the last entry supported by the agent, it doesn't have another object to provide, so returns an "end of MIB" indication. The Net-SNMP tools report this with the message above. But in either case, the actual information provided will be the same. How do I use SNMPv3? ------------------- The simplest form of SNMPv3 request (unauthenticated, unencrypted) would be something like: snmpget -v 3 -l noAuthNoPriv localhost sysUpTime.0 An authenticated request would specify a username and pass phrase: snmpget -v 3 -l authNoPriv -u dave -A "Open the Door" localhost sysUpTime.0 A fully secure request would also specify the privacy pass phrase: snmpget -v 3 -l authPriv -u dave -A "Open the Door" -X "Bet you can't see me" localhost sysUpTime.0 In practise, most of these would probably be set via configuration directives in a personal $HOME/.snmp/snmp.conf file (note, *not* the agent's snmpd.conf file). The equivalent settings for the third example would be: defSecurityName dave defSecurityLevel authPriv defAuthPassphrase "Open the Door" defPrivPassphrase "Bet you can't see me" If the AuthPassphrase and the PrivPassphrase are the same, then you can use the single setting defPassphrase "Open the Door and see me" instead. See the AGENT section for how to configure the agent for SNMPv3 access. I cannot set any variables in the MIB. ------------------------------------- There are three possible reasons for this: Many MIB objects are defined as "read-only" and inherently cannot be changed via SET requests. Attempts to do so will typically be dropped by the 'snmpset' command without ever being sent to the agent. Of those objects that can in principle be changed, the agent may not include the code necessary to support SET requests. (GET and GETNEXT are much easier to handle - particularly for objects relating to the internals of the underlying operating system). Even if SET support has been implemented, the agent may not be configured to allow write access to this object. Ready-installed distributions (such as those shipped with Linux) tend to be configured with read-only access to part of the mib tree (typically just the system group) and no write access at all. To change this, you will need to set up the agent's access control configuration. See the AGENT section for more details. Note that neither the community string "public" nor "private" can be used to set variables in a typical default configuration. Variables seem to disappear when I try to set them. Why? -------------------------------------------------------- This is actually the same as the previous question - it just isn't particularly obvious, particularly when using SNMPv1. A typical example of this effect would be $ snmpget -v1 -c public localhost system.sysLocation.0 system.sysLocation.0 = somewhere nearby $ snmpset -v1 -c public localhost system.sysLocation.0 s "right here" Error in packet. Reason: (noSuchName) There is no such variable name in this MIB. This name doesn't exist: system.sysLocation.0 Trying the same request using SNMPv2 or above is somewhat more informative: $ snmpset -v 2c -c public localhost system.sysLocation.0 s "right here" Error in packet. Reason: notWritable The SNMPv1 error 'noSuchName' actually means: "You can't do that to this variable" rather than "this variable doesn't exist". It may be the case that it doesn't exist at all. It may exist but you don't have access to it (although someone else with different administrative credentials might do). Or it may exist, but you simply can't perform that particular operation (e.g. changing it). Similarly, the SNMPv2 error 'notWritable' means "not writable in this particular case" rather than "not writable under any circumstances". If you are sure that the object is writable (and has been implemented as such), then you probably need to look at the agent access control. See the AGENT section for more details. Why can't I change sysLocation (or sysContact)? ---------------------------------------------- Assuming that the access control settings should allow this, another possibility for the 'sysLocation' and 'sysContact' objects is that you've got a configuration option in the 'snmpd.conf' file which already sets the corresponding value there. Earlier versions of the Net-SNMP agent would allow you to write to these objects, but the new value would be forgotten the next time the agent was re-started. More recent versions of the agent reject such write requests if there's a value configured via the 'snmpd.conf' file. If there isn't such a config setting, then the write request will succeed (assuming suitable access control settings), and the new value will be retained the next time the agent restarts. I get an error when trying to set a negative value - why? -------------------------------------------------------- This is a different problem. What's happening here is that the routine that parses the arguments to the 'snmpset' command is seeing the '-' of the new value, and treating it as a command-line option. This normally generates an error (since digits typically aren't valid command line options). The easiest way to solve this is include the "end-of-option" indicator '--' in the command line, somewhere before the new value (but after all of the options, obviously). For example: snmpset -v 2c -c public localhost -- versionRestartAgent.0 i -1 (This will also fail, since -1 isn't an acceptable value for this particular object, but that's not the point here!) I get an error when trying to get a string-indexed table value - why? -------------------------------------------------------------------- This is probably due to the shell swallowing the quotes, before they ever get to the SNMP command's OID parser. Try escaping them: snmpget ..... vacmGroupName.3.\"wes\" or snmpget ..... 'vacmGroupName.3."wes"' How do I send traps and notifications? --------------------------------------- Traps and notifications can be sent using the command 'snmptrap'. The following examples generate the generic trap 'coldStart' and a (dummy) enterprise specific trap '99' respectively: snmptrap -v 1 -c public localhost "" "" 0 0 "" snmptrap -v 1 -c public localhost "" "" 6 99 "" The empty parameters "" will use suitable defaults for the relevant values (enterprise OID, address of sender and current sysUptime). An SNMPv2 or SNMPv3 notification (either trap or inform) takes the OID of the trap to send: snmptrap -v 2c -c public localhost "" UCD-SNMP-MIB::ucdStart snmptrap -v 2c -c public localhost "" .1.3.6.1.4.1.2021.251.1 (These two are equivalent ways of specifying the same trap). Any of these commands can be followed by one or more varbinds, using the same (OID/type/value) syntax as for 'snmpset': snmptrap -v 2c -c public localhost "" ucdStart sysContact.0 s "Dave" Generating traps from within the agent is covered in the AGENT and CODING sections. You should also read the snmptrap tutorial at http://www.net-snmp.org/tutorial-5/commands/snmptrap.html which will help you understand everything you need to know about traps. How do I handle traps and notifications? --------------------------------------- Handling received traps is done using the tool 'snmptrapd'. This can log these traps via the syslog mechanism: snmptrapd -Ls 7 (log to 'LOCAL7') printed to standard output snmptrapd -f -Lo or pass them to an external command. This last approach uses a 'traphandle' directive in the configuration file 'snmptrapd.conf'. A typical file might look something like: traphandle .1.3.6.1.6.3.1.5.1 page_me up traphandle .1.3.6.1.4.1.2021.251.1 page_me up traphandle .1.3.6.1.4.1.2021.251.2 page_me down traphandle default log_it where 'page_me' and 'log_it' are the command to be run. (You probably need to specify full pathnames, to ensure that the commands will be found. They're just short here for readability). Note that the first entry uses the OID corresponding to the SNMPv1 'coldStart' trap. See the co-existence RFC (RFC 2576) for details of mapping SNMPv1 traps to SNMPv2 OIDs. Starting with net-snmp 5.3, snmptrapd will no longer automatically accept all incoming traps. It must be configured with authorized SNMPv1/v2c community strings and/or SNMPv3 users. Non-authorized traps/informs will be dropped. Please refer to the snmptrapd.conf(5) manual page for details. There's a tutorial with more details on the web site at http://www.net-snmp.org/tutorial-5/commands/snmptrap.html My traphandler script doesn't work when run like this - why not? --------------------------------------------------------------- If a traphandler script works fine when run manually from the command line, but fails or generates an error when triggered by an incoming notification, then there are two likely causes. Firstly, the interactive shell environment may not be precisely the same as that for programs executed by the snmptrapd daemon. In particular, it's quite possible that the PATH environmental variable may not include all the additional directories that are commonly set up for a personal login configuration. To avoid this problem (particularly for traphandler shell scripts), it's worth giving the full path to all programs used within the script. Secondly, the snmptrapd daemon may not always recognise the appropriate interpreter to use for a particular trap handler. If this is the case, then you can specify this interpreter explicitly as part of the trap handle directive: traphandle default /usr/bin/perl /usr/local/bin/log_it In this case, it's almost certain that you'll also need to give the full path to the traphandle script (as shown) How big can an SNMP request (or reply) be? ----------------------------------------- The protocol definition specifies a "minimum maximum" packet size (484 bytes for UDP), which all systems must support, but does not attempt to define an upper bound for this maximum size. This is left to each individual implementation. The UCD software used a fixed size buffer of 1472 bytes to hold the encoded packet, so all requests and responses had to fit within this. The Net-SNMP releases handle packet buffers rather differently, and are not subject to the same fixed restrictions. How can I monitor my systems (disk, memory, etc)? ------------------------------------------------ In general, the Net-SNMP suite consists of relatively low-level tools, and there is nothing included that is designed for high-level, long-term monitoring of trends in network traffic, disk or memory usage, etc. There are a number of packages available that are designed for this purpose. Two of the most widely used are MRTG (http://www.mrtg.org/) and RRDtool (http://oss.oetiker.ch/rrdtool/). There are also several frontends built on top of RRDtool, including Cacti (http://www.cacti.net/) and Cricket (http://cricket.sourceforge.net/). There are details of how to set up Cricket to monitor some of the UCD extensions at http://www.afn.org/~jam/software/cricket/ We have also set up a page that describes in detail how MRTG can be set up to monitor disk, memory and cpu activity at http://www.net-snmp.org/tutorial-5/mrtg/index.html There is also a web-based network configuration system "Net-Policy", based upon SNMP. This is not strictly connected to the Net-SNMP project, but a number of the core developers are also involved with that system. See http://net-policy.sourceforge.net for more details. Applications complain about entries in your example 'snmp.conf' file. Why? -------------------------------------------------------------------------- There *is* no example 'snmp.conf' shipped with the standard distribution. The configuration file 'EXAMPLE.conf' is designed as a config for the agent, and should be installed as 'snmpd.conf' (note the 'd'). The file 'snmp.conf' is intended for general configuration options, applicable to all applications (via the SNMP library). Rename (or merge) the 'snmp.conf' file to 'snmpd.conf', and this should fix the problem. OK, what should I put in snmp.conf? ---------------------------------- This is used to set common configuration values for most of the applications, to avoid having to specify them every time. Examples are the SNMPv3 settings mentioned above, defaults for which MIBs to load and where from (see the second entry in the APPLICATIONS section), and the default SNMP version, port and (if appropriate) community string to use. Some of these (such as the MIB file location), might be best put in a shared snmp.conf file (typically /usr/local/share/snmp/snmp.conf or /etc/snmp/snmp.conf) to apply to all users of the system. Others (particularly the SNMPv3 security settings), are more likely to refer to a particular user, and should go in a personal snmp.conf file (typically $HOME/.snmp/snmp.conf). See 'snmpget -H' and/or the snmp.conf(5) man page for more details. You can also use the "snmpconf" command to help you generate your snmp.conf configuration file (just run it and answer its questions). PERL ==== Where can I get the Perl SNMP package? ------------------------------------- Joe Marzot's excellent Perl 'SNMP' module, is included in the Net-SNMP source releases. It can be found located in the perl/SNMP subdirectory of the source tree. This is accompanied by a number of Perl modules grouped together under the NetSNMP namespace. The basic SNMP module (though not the NetSNMP additions), can also be found at any Comprehensive Perl Archive Network (CPAN) mirror site, under modules/by-module/SNMP. To find the CPAN site nearest you, please see http://www.cpan.org/SITES.html. These Perl modules need to be used in conjunction with a compatible version of the Net-SNMP library. Consult the README file in the SNMP Perl distribution to find out which version of the library it needs. How do I install the Perl SNMP modules? -------------------------------------- Assuming you have a reasonably new (and properly configured) Perl system, this should be simply: cd perl perl Makefile.PL (press RETURN when prompted for host and community) make make test make install (probably as root) It might be possible to install the basic module using perl -MCPAN -e shell ; "install SNMP" but this has not been reliably tested, and very much relies on having the correct version of the Net-SNMP library. There may also be appropriate pre-compiled versions of the Perl modules available from the Net-SNMP project website, or your O/S vendor. But compiling this fails! Why? ----------------------------- The Perl module tends to delve quite deeply into the internals of the main Net-SNMP library, and so is quite sensitive to changes within the library. It's important to use the correct version of the module, that corresponds to the version of the library you have installed. If you're working with a Net-SNMP source distribution, the appropriate version of the Perl modules are shipped as part of the source code, but you *must* have run "make install" on the main Net-SNMP distribution *first*. If you're working with a ready-installed version of the library, make sure you obtain a compatible version of the Perl module. Note that the Perl modules will be compiled using the compiler (and compiler settings) used for compiling the original perl binary, *not* those used for compiling the Net-SNMP (or UCD) library. If these are different (e.g. 'gcc' used for one and 'cc' for the other) then this may well cause problems. It's much safer to use a consistent environment for both. This issue is discussed in greater detail in the README.solaris file. Also note that the v5 Net-SNMP suite *must* be configured to provide shared libraries in order for the Perl modules to work correctly. This is not necessary with the v4 UCD-SNMP libraries. Compiling the Perl module works OK, but 'make test' fails. Why? -------------------------------------------------------------- That's difficult to answer in general. Some of the Perl tests are rather picky, so this may simply be some minor inconsistency between your precise setup, and the expectations of the test environment. Check that you are working with the Perl distribution that matches the SNMP libraries (use the 'perl/SNMP' in preference to CPAN), and that you have installed the main libraries successfully (uninstall any old versions if you're having trouble). If all this looks OK, and if most of the tests pass, then it's probably safe to run 'make install' anyway. Probably. I'm trying to use mib2c (or tkmib) and it can't locate SNMP.pm? ------------------------------------------------------------ That's probably because the SNMP perl module hasn't been installed. It's not part of the standard perl distribution, nor is it installed by default in many vendor distributions. You'll need to install it. See the previous questions. I'm trying to use mib2c (or tkmib) and it can't load SNMP.so? ------------------------------------------------------------ This is probably the same problem. Either the SNMP module hasn't been installed, or it's the wrong version. See the previous questions. I'm trying to use tkmib and it can't locate Tk.pm? ------------------------------------------------- Tk.pm is another Perl package that needs to be installed before tkmib will run. It's also available on Perl CPAN. We suggest using version "Tk800.011" or later. It can be installed by issuing the command: perl -MCPAN -e shell ; "install Tk" I'm trying to install your RPM, but it complains about missing Perl modules. Why? -------------------------------------------------------------------------------- This has been particularly noted on RedHat 9, complaining about the module "perl(Term::ReadKey)" - even if this is actually present (e.g. having been installed directly from CPAN). In fact, this is not specific to Perl modules - the same issue can potentially arise with other RPM dependencies. The problem is that the RPM mechanism keeps a local database of what software packages have been installed, and checks this for any other features that this RPM requires. If software is installed "manually" rather than via rpm packages, then it will not appear in this database. Attempting to install another RPM that rely on this functionality will then complain about the "missing" package, because the RPM system doesn't know that's it's actually available. The ideal solution is to *always* install software using a consistent mechanism (which may involve building RPMs locally, or looking for a suitable pre-built version). Failing this, it's possible to tell the "rpm" command to ignore such dependencies, and install the package anyway. Try: rpm -i --nodeps {package} In this situation, it's then up to you to make sure that any other necessary packages *are* actually present on the system. I've got a problem with the Net-SNMP module. Can you help? ---------------------------------------------------------- Sorry, despite the similar-sounding name, the Net-SNMP (or Net::SNMP) module is nothing to do with this package, or the NetSNMP modules. Net::SNMP is a "pure-perl" implementation of SNMP support, developed by David Town. The developers of the (C-based) Net-SNMP suite do not have any significant experience in using this particular module, and you'll probably be better off asking for help via CPAN or some other perl-related forum. MIBS ==== Where can I find a MIB compiler? ------------------------------- That depends what you mean by a "MIB compiler". There are at least two types of tool that are commonly referred to by this name. The first is a tool to check MIB files for validity. This functionality is mostly integrated within the MIB parser (part of the Net-SNMP library) and hence included in all the applications. The tool 'snmptranslate' is probably the most appropriate for this purpose. Note that the parser is fairly forgiving (see 'What ASN.1 parser is used' below), so this should not be regarded as a stamp of approval. The second type of tool is one to turn a MIB specification into C code, specifically one designed to aid agent implementation. The command 'mib2c' is an example of such a tool for the Net-SNMP agent. See the CODING section for more information. Why aren't my mib files being read in? ------------------------------------- The Net-SNMP library only loads a specific subset of MIB files by default. This list is set at when the suite is first configured and compiled, and basically corresponds to the list of modules that the agent supports. (This is a simplification, but is a reasonable first approximation). You can override this by using the command-line option '-m', the environmental variable 'MIBS' or the snmp.conf directive 'mibs'. Each of these take a (colon-separated) list of MIB module names to load. Starting the list with a '+' character will add them to the default list - otherwise it replaces the defaults. Using the special value 'ALL' will load all the MIB files that the library can find. Alternatively, the tools may be looking in the wrong place. The default location for the mib files is /usr/local/share/snmp/mibs. Again, this is set when the suite is first configured and compiled. This can be changed using the environmental variable 'MIBDIRS' or the snmp.conf directive 'mibdirs'. Note that this may very well affect you if you've installed a new version of the suite manually, replacing one provided by the supplier (which typically would use a more 'central' location). Finally, are you sure that you've installed the MIB files? If you've compiled the suite from scratch, you need to run "make install" at least once, before the tools will be able to find the MIB files. This is unlikely to be a problem if you've been working with the tools for a while, but can bite those working with a fresh installation. I'm getting answers, but they're all numbers. Why? ------------------------------------------------- This is related to the previous question. The results that you receive do not depend on which MIBs are loaded - just on how the agent was compiled and configured. Because the tools don't read in every MIB module they can find (and the relevant MIB file may not be installed anyway), it is quite possible for results from an agent to refer to modules that have not been loaded (particularly with GETNEXT requests, or when walking a tree). The results will be reported quite correctly, but won't be translated to use named identifiers or enumerations. To fix this, use the environmental variables MIBS or MIBFILES (or the '-m' and '-M' flags) to read in the relevant module files (assuming these are available). What does "Cannot find module (XXX-MIB)" mean? --------------------------------------------- If this error is only generated for one or two modules, then it's likely that the named modules are not being found - perhaps they're not installed in the correct location, are not readable, or the name being used is incorrect. Note that the name reported is the name of the MIB module, which is not necessarily the same as the name of the file. See the question 'How do I add a MIB to the tools?' for more details on this. If there are a large number of such errors, then it's more likely that either the MIB files haven't been installed at all, or the library is looking in the wrong place for them. Try running "snmptranslate -Dparse-mibs" to see where the MIB files are expected to be found. What about "unlinked OID"? ------------------------- This means that the library has been able to find the MIB module, and parse the individual objects defined in it, but is having problems linking them together into a consistent tree. In particular, it can't find an object corresponding to the name within the braces (i.e. the 'xxx' in '{xxx 99}'). This is probably due either to a typo in this name (remember that names are case sensitive, so a reference to 'xxx' will *not* match a definition of 'Xxx'), or else the name is defined in another MIB file, and this dependency is missing from the IMPORT clause of this MIB file. The parser doesn't handle comments properly. Why not? ---------------------------------------------------- The most likely reason is that the line in question contains two (or more) sequences of pairs of dashes. This is often used to try and "comment out" an unwanted line that already contains a comment: -- broken ::= { myMIB 1 } -- This isn't working yet The assumption here is that a comment continues to the end of the line. Unfortunately, this is not correct. A comment will continue either to the end of the line, *or* the next occurance of a pair of dashes. Thus in this case, the definition of "broken" is commented out (as intended) but the following text is treated as an active part of the MIB, and will generate an error. A similar effect can be obtained when a line of dashes has been used to try and mark separate parts of a MIB file. Most of the applications have a command-line option (-Pc) which will work around this problem by treating the whole line as a comment. But this is not strictly legal, and the offending MIB file should really be corrected. How can I get more information about problems with MIB files? ------------------------------------------------------------ The command 'snmptranslate' is used to translate between numeric and symbolic forms of OIDs. It uses the same MIB parsing routines as the commands that actually communicate with a network management agent, but can be used standalone. As such, it is a useful tool for identifying problems with reading in MIB files. In particular, the following options may be useful in identifying problems: -Pw warns about conflicting symbols -PW prints more verbose warnings about other problems as well (in both cases, ignore the 'xmalloc' reports) -T provides sub-options for various views of these entries There are other '-P' options to control various aspects of MIB parsing. See the 'snmptranslate(1)' and 'snmpcmd(1)' man pages for more details, or the tutorial at http://www.net-snmp.org/tutorial-5/commands/snmptranslate.html What's this about "too many imported symbols"? --------------------------------------------- Any MIB file starts with an (optional) list of identifiers that it "imports" from other files. The parser handles this using a fixed size buffer to hold the import information. There are two circumstances in which this can result in the error message shown above. Firstly, if the MIB file refers to an unusually large number of external identifiers. Handling this case requires a (trivial) patch to the parsing code. Contact the coders list for advice. (This is extremely rare - the only example that we've come across is the Cabletron Trap MIB). Much more common is a syntax error in the IMPORTS clause of the MIB file in question. In particular, check that this section ends in a semicolon, before going on to the main MIB object definitions. Do I actually need the MIB files? -------------------------------- Probably not. The MIB files play two main roles - they are used to translate between numeric OIDs and the corresponding textual names, and they define the structure and syntax of the relevant MIB objects. This second role is perhaps best thought of in terms of a design document. It's vital while developing an application (typically the MIB module or handler within the agent), since it defines what the application (MIB) must actually do. But once the code has been written, the design document becomes redundent. The agent then has the same information hardcoded into it (literally!), and no longer needs the MIB file. The translation task is not strictly necessary - SNMP will operate fine without any MIB files at all, as long as you're happy to work with numeric OIDs throughout, and know which MIB objects you're interested in. But it's much easier to work with the (hopefully) meaningful names, enumeration tags and the like, and to view the description of a particular object. This requires having the relevant MIB files installed and loaded. AGENT ===== What MIBs are supported? ----------------------- The following MIBs are supported (at least in part and on some systems): - MIB-2 General network statistics (RFC 1213 and subsequent revisions) - Host Resources (RFC 1514 and 2790) - SNMPv3 framework (RFCs 2571-5, 3411-3418) (including USM, VACM, Target and Notification MIBs) - DisMan Event and Schedule MIBs - MTA-MIB (sendmail) - private UCD/Net-SNMP agent extensions (monitor specified processes and disks, memory, CPU, load average, plus extend the agent using shell commands) See README.agent-mibs for details. Not all MIB modules are included by default on all systems, and some of these may need to be explicitly requested when the software is first configured and built. From Net-SNMP 5.3 and above, this primarily applies to the MTA-MIB of those listed above. There are a few other MIB implementations distributed as part of the source tarball, but these are basically unsupported and most of the core developers have little or no experience with using them. What protocols are supported? ---------------------------- The agent supports all three current versions of SNMP (v1, v2c and v3), over both UDP and TCP transports, as well as acting as a SMUX (RFC 1227) master agent, AgentX (RFC 2741) in both master and subagent roles, and SNMP proxying. How do I configure the agent? ---------------------------- That depends on what you want it to do, and what stage of the process you have in mind. There are actually two very distinct ways you can configure the agent. Firstly, you can determine what capabilities and defaults are included within the library and agent, at the time that the software is first built. This uses suitable flags to the 'configure' script, before compiling the source. As far as the agent is concerned, the most significant option is '--with-mib-modules' (or '--with-out-mib-modules') to control which MIBs will be supported by the agent. See the next few entries for details. You can also control various aspects of the agent behaviour (and the information it returns) at run time, via the 'snmpd.conf' configuration file. Various aspects of this are touched on throughout this FAQ. Or see the snmpd.conf(5) manual page for full details. The "snmpconf" script can help in creating this config file. Start off with 'snmpconf -g basic_setup' to get you going. How do I remove a MIB from the agent? ------------------------------------ Deleting the text file for a MIB does not affect the agent (other than to prevent it from recognising MIB object names in the config files). It's necessary to tell the agent not to activate the relevant code that actually implements these objects. There are three ways to do this: 1) re-run 'configure' to exclude the given MIB module(s) from the build configuration, recompile, and reinstall: ./configure --with-out-mib-modules=host .... make make install 2) use access control to exclude the mib from the view used to query the agent: com2sec public default public group public v1 public group public v2c public view ourmib included system view ourmib included printmib view ourmib excluded host view ourmib included privatemib access public "" any noauth exact ourmib none none With v5.3 and above, this can also be done by supplying the relevant view name to the "rocommunity" or similar directive: rocommunity public default -V ourmib 3) disable the MIB at runtime snmpd -I -hr_system,hr_storage,hr_device,hr_other,.... Note that this relies on knowing which modules are used to implement the relevant MIB objects. If you're not sure, you can check which MIB modules are loaded by getting the agent to report them as they are initialised: snmpd -Dmib_init -H Hopefully it should then be fairly obvious which ones to turn off. I've installed a new MIB file. Why can't I query it? ---------------------------------------------------- Similarly, installing a new MIB file isn't sufficient for the agent to automatically support this MIB. It's necessary to have some form of code which can provide the corresponding information. The next few entries, and the following section (CODING) address this issue in some detail. How do I add a MIB to the agent? ------------------------------- As indicated above, this basically involves writing some code to implement the objects defined in the new MIB. There are three basic approaches that can be used to do this: - The agent can invoke an external command or shell script to return the necessary information. There are several possible variations on this approach - see the next entry for details. - The agent can pass the request off to another (sub-)agent, which already implements the required MIB. Again, there are several ways of doing this - including AgentX, SMUX and proxied SNMP. See the next entry but one for details. - You can write code to implement the new MIB objects, and include this within the agent. This is most commonly C (or C++) code, although the agent can also support MIB modules implemented in perl or (from 5.4) python. See the next section (CODING) for more details. Note that there is no visible difference between external commands, subagents, and modules implemented within the main agent itself. Tools querying the agent will see a single MIB structure. What's the difference between 'exec', 'sh', 'extend' and 'pass'? --------------------------------------------------------------- 'exec' will fork off the specified command and return the exit status and/or the output. Any arguments are passed directly to the command. 'sh' is similar, but invokes a shell to run the command line given. This means that quoted arguments will be recognised as such, and also allows redirection, and other similar shell interpretation. The results are returned in exactly the same way. 'extend' is also similar, but provides a richer and more flexible MIB framework - both for configuring the exact command to be run, and for displaying the results. None of these mechanisms require the command to have any knowledge of the fact that they are being used in this manner. But the output is returned in a fixed format, and it is up to the receiving application to interpret this appropriately. 'pass' is a more general mechanism for implementing arbitrary MIB objects. The specified command will be invoked for any request within the named MIB subtree, and should return the information relevant to the requested OID. 'pass-persist' is similar, but the command will continue running even after the initial request has been answered. All of these mechanisms are described in the 'snmpd.conf(5)' man page, in the section entitled "Extending Agent Functionality". What's the difference between AgentX, SMUX and proxied SNMP? ----------------------------------------------------------- All three are protocols that can be used to make two or more agents appear as one to the querying application. In each case, one agent takes the role of "master", and delegates requests to one of the others as and where this is appropriate. The differences between them mainly relate to how data is represented, and the mechanisms for communication between master and subagents. SMUX and proxy SNMP both essentially use the standard SNMP packet format. The main difference is that a proxy SNMP subagent need not be aware that it is acting in such a role. It typically listens on a non-standard port, and simply receives requests as usual, forwarded from the master agent. The main issue to be aware of is that such requests will appear to come from the local host, and this may affect how the access control mechanisms need to be set up. SMUX uses a similar packet format, but the subagent "registers" with the master agent, providing a suitable password. The Net-SNMP (and UCD) agent includes the possibility of acting as a SMUX master agent, but the suite does not include a subagent API. Note that the SMUX protocol has essentially been superceded by AgentX, but is still provided in order to support existing SMUX subagents. However the core developers have little experience (and even less interest!) in this code, so assistance with SMUX-related problems is likely to be somewhat limited. See the file 'agent/mibgroup/README.smux' for details. AgentX uses a more compact (and simpler) packet format, with a richer range of administrative commands, and provides a more flexible and reliable extension mechanism. The Net-SNMP agent can be used in both master and subagent roles, and the agent library can also be used to embed an AgentX subagent within another application. See the file 'README.agentx' for details. Note that support for SMUX is not configured in by default. You will need to run configure with the option --with-mib-modules=smux AgentX support is included by default, but needs to be explicitly activated in the master agent. Do this by adding the line master agentx to the snmpd.conf file before starting the agent. What about 'dlmod' - what's that about? -------------------------------------- The choice of which C-coded modules to include within an agent (or subagent) is usually made when the agent is first built. Adding new MIB modules would therefore require re-compiling the agent. This is not always convenient - particularly when working with a production system, and/or pre-installed binaries. Dynamically loaded modules are a means of including a MIB implementation module within the main SNMP agent (or an AgentX subagent) without needing to re-compile and re-link the agent binary. Instead, details of the module(s) to load are specified in the configuration file, and the agent locates the files listed, and merges them in at run time. See http://www.net-snmp.org/tutorial-5/toolkit/dlmod/ for more information. Which should I use? ------------------ That's not easy to answer in general. If there's an existing agent that already implements the desired new MIB, then it makes sense to re-use that, via whatever extension protocol it might support. Ideally, this would be an AgentX sub-agent, since the AgentX protocol is deliberately designed for this purpose, and provides a fuller and more reliable mechanism than either SMUX or proxied SNMP. But if the target subagent only supports SMUX or basic SNMP, then that would dictate the extension protocol to use. Implementing the module directly within the main agent (or via dlmod) is probably the most efficient and reliable (since there's minimal overheads between the code implementing the MIB module, and the agent framework). But it does assume that there's a suitable mechanism for retrieving the necessary information. If the new MIB is monitoring or managing some other subsystem, external to the agent, then it may be necessary to embed a subagent within the subsystem itself - particularly if there's no suitable public API to retrieve the necessary information. In this case, AgentX is probably the most appropriate way forward. Unless you prefer to implement the missing public management API, and develop a module within the main agent instead. In terms of writing C code for the Net-SNMP agent, the way that the (sub-)agent receives the request is more or less irrelevant. The MIB module API was deliberately designed to be independent of any extension mechanism being used - so the exact same module code could be included as part of a pure-SNMP master agent, or an AgentX subagent, either compiled in or dynamically loaded. No modifications should be needed to the MIB module code itself - just to how it's compiled into the appropriate application. Can I use AgentX when running under Windows? ------------------------------------------- Yes, but there are a couple of things to be aware of. Firstly, by default the AgentX master listens on the Unix domain socket '/var/agentx/master', which doesn't work under Windows. You'll need to tell it to listen on a TCP port, either by using the command-line option "-x localhost:705", or by adding the directive "agentxSocket localhost:705" to the snmpd.conf file. Secondly, be aware that the security of AgentX connectivity is not particularly strong. The examples given here would allow any process running on the local machine to register as an AgentX subagent. The more obvious settings "-x 705" or "agentxSocket 705" would allow a system *anywhere* on the network (or even from remote networks) to register as an AgentX subagent. This could potentially be used to hijack the agent, or provide false information. Can I use AgentX (or an embedded SNMP agent) in a threaded application? ----------------------------------------------------------------------- With care. As mentioned in the earlier "thread-safe" FAQ entry, the Net-SNMP agent (including the AgentX subagent) has not been designed for threaded operation. In particular, it makes use of various global variables without attempting to protect them against simultaneous use. This means that it is *NOT* safe to have SNMP or AgentX related processing in two separate threads. This also applies to handling GET (and SET) processing in one thread, and generating traps in another. This is still vulnerable to the usual threading problems. However, as long as *all* of the SNMP-related activity is limited to the one thread, then there should be no reason why this cannot safely communicate with other threads within the same application, using private (thread-safe) mechanisms. But in terms of the Net-SNMP-provided code, the agent (and AgentX subagent) should *not* be regarded as thread-safe. How can I run AgentX with a different socket address? ---------------------------------------------------- There are two sides to an AgentX connection, and they need to agree about which socket address to use. So if you want to use a different socket, you need to configure both parties accordingly. The socket that the Net-SNMP master agent uses to listen for AgentX registrations (and send appropriate requests) can be specified using the option '-x'. The command "snmpd -x localhost:705 ...." would start the agent listening on the TCP port 705 for connections from the local system. The same effect can also be obtained by adding the line agentxsocket localhost:705 to the file 'snmpd.conf'. The same option can be used with the Net-SNMP agent when running in "subagent" mode, to specify the socket to register with (and receive requests from). So a subagent might connect to the master agent above (both running on the same host), using: "snmpd -X -x localhost:705 ...." A subagent running embedded within some other application will typically not understand the same command-line options, so would need to set the same configuration programmatically: netsnmp_ds_set_string(NETSNMP_DS_APPLICATION_ID, NETSNMP_DS_AGENT_X_SOCKET, "localhost:705"); With the example subagent code from the Net-SNMP tutorial, this line would be added immediately before the 'init_agent' call. The same approach can also be used to listen on a different named socket, using: agentxsocket /tmp/agentx agentxperms 777 777 myuser mygroup or snmpd -x /tmp/agentx .... or netsnmp_ds_set_string(NETSNMP_DS_APPLICATION_ID, NETSNMP_DS_AGENT_X_SOCKET, "/tmp/agentx"); as appropriate. But also see the mention of AgentX security (or the lack of it!) in the earlier entry. How can I turn off SMUX support? ------------------------------- Normally, you would use the command-line option '-I -{module}' to disable the initialisation of a particular MIB module within the agent. Unfortunately, it's not currently possible to turn off SMUX support this way. The safest approach is to re-run configure with the option "--with-out-mib-modules=smux", and recompile the agent. If this is not possible, an alternative workaround might be to have the agent bind to an invalid IP address. If you put a line such as smuxsocket 1.0.0.0 in the snmpd.conf file, the agent will whinge at startup, but won't accept any incoming SMUX requests. If the agent complains about not recognising the "smuxsocket" token, then you're out of luck. You'll either have to recompile from source, or use local firewall rules to block connections to port 199. How can I combine two copies of the 'mib2' tree from separate subagents? ----------------------------------------------------------------------- This is the purpose of the SNMPv3 'context' field. Register the MIB module a second time in a non-default context (see the relevant entry in the CODING section for details), and specify this context when querying the agent. The MIB module can use this context information to determine which set of information to report. Or you could register two completely different handlers for the same OID (using different contexts), and the agent will invoke the appropriate code. This holds for both MIB modules implemented within the main agent, or AgentX subagents - the same approach will work for both. Contexts can also be used with proxied SNMP requests - just specify the option '-Cn {context}' as part of the "proxy" entry. See the 'snmpd.conf(5)' man page for details. It's currently not possible to support parallel MIB trees when using SNMPv1 or SNMPv2c. In principle, it should be possible to use the community string in a similar way, but this has not (yet) been implemented. This mechanism is only available with the v5 Net-SNMP agent. The v4 UCD agent does not support contexts at all. Sorry about that. Another way to handle this would be to tweak one of the subagents to use a different set of (non-standard) OID assignments - perhaps by relocating the whole of the subtree to another (private) OID. This is not ideal, but should work with all configurations. What traps are sent by the agent? -------------------------------- The agent sends a 'coldStart(0)' trap when it first starts up, and an enterprise-specific trap 'nsNotifyShutdown' (or 'ucdShutdown') when it stops. It can also be configured to send an 'authenticationFailure(4)' trap when it receives an SNMPv1 request using an unknown community name. The Net-SNMP agent generates an enterprise-specific trap 'nsNotifyRestart' (rather than the standard 'coldStart(0)' or 'warmStart(1)' traps) on receiving a HUP signal - typically after being re-configured. The agent does not send 'linkUp' or 'linkDown' traps by default. The Net-SNMP agent can be configured to do this using the config directive 'linkUpDownNotifications'. See the 'snmpd.conf(5)' man page (under ACTIVE MONITORING) for details. Similarly, it does not generate traps by default when one of the monitored characteristics (disk usage, running processes, etc) enters or leaves an error state. This can be configured using the 'defaultMonitors' config directive (also documented under ACTIVE MONITORING). Note that these facilities are only available with the v5 Net-SNMP agent, and are not supported by the v4 UCD agent. Where are these traps sent to? ----------------------------- With all these alerts, the agent needs to be told where to send them, specifying the type of notification (v1 or v2 trap, or v2 inform) and the community name to use. This uses the snmpd.conf directives 'trapsink', 'trap2sink' and 'informsink' for the destination type, and 'trapcommunity' for the community name. SNMPv3 destinations can be configured using the directive 'trapsess'. See the 'snmpd.conf(5)' man page for details. Note that the type of trap generated is totally determined by these directives - irrespective of which API call was used to trigger sending the trap. See the trap-related entries in the CODING section for details. A configuration block such as trapsink localhost trap2sink localhost informsink localhost will result in *three* notifications being sent for each call to 'send_easy_trap' (or 'send_v2trap'). Probably not what was wanted! How can I send a particular trap to selected destinations? ---------------------------------------------------------- This is not currently possible. All notifications will be sent to all configured destinations. The agent does not (currently) support notification filtering. There is a preliminary implementation of the snmpNotifyFilterTable which is designed to allow this sort of selective trap direction. However this is not currently active. (The tables are present and can be manipulated and updated, but the information is not consulted) Documentation on how to use this facility will appear once the functionality is working properly. When I run the agent it runs and then quits without staying around. Why? ----------------------------------------------------------------------- Firstly, are you certain that this is what is happening? The normal operation of the agent is to 'fork' itself into the background, detaching itself so that it will continue running even when you log out, and freeing the command line for subsequent use. This looks at first sight as if the agent has died, but using 'ps' to show all processes should reveal that the agent is still running. To prevent this behaviour (such as when attempting to debug the agent), you can start it with the '-f' flag. This suppresses the fork, and the agent will run as a 'normal' command. It's also often useful to use the '-Le' (or '-L') flag, to log messages to stderr. On the other hand, if 'ps' shows that the agent is not running, then this is an error, and probably show that something went wrong in starting the agent up. Check the agent log file for any error messages, or run it with '-f -Le' and see what it reports. Another possible cause might be an existing agent (or some other process) that's already listening on the SNMP port. Trying to start a second agent will fail with an error about "opening the specified endpoint". If you're starting the agent as a non-root user, then this may also fail with the very same error. By default, the agent (and trap handler) will attempt to listen on the standard SNMP port 161 (or 162 for the trap handler). These are defined as "privileged ports", and processes will need to be running as root in order to open them. One way to tackle this is to start the agent as root, but use the -u option to switch to run as another user once the port has been opened. Alternatively, you can specify a different port to use instead. Anything greater than 1024 is available to non-root users. In this case, you'll also need to specify the same port when issuing client commands. After a while the agent stops responding, and starts eating CPU time. Why? -------------------------------------------------------------------------- This is basically the same problem described in the APPLICATIONS section, in the entry The agent worked for a while, then stopped responding. Why? See that entry for details. How can I stop other people getting at my agent? ----------------------------------------------- Firstly, are you concerned with read access or write access? As far as changing things on the agent is concerned, there is relatively little that can actually be altered (see the answer to " I cannot set any variables in the MIB" above). If you are using the example config file, this is set up to allow read access from your local network, and write access only from the system itself (accessed as 'localhost'), both using the community name specified. You will need to set appropriate values for both NETWORK and COMMUNITY in this file before using it. This mechanism can also be used to control access much more precisely. (see the next few questions for details) Other options include: - Blocking access to port 161 from outside your organisation (using filters on network routers) - Using kernel-level network filtering on the system itself (such as IPTables) - Configuring TCP wrapper support ("--with-libwrap") This uses the TCP 'libwrap' library (available separately) to allow/deny access via /etc/hosts.{allow,deny} For strict security you should use only SNMPv3, which is the secure form of the protocol. However, note that the agent access control mechanisms does not restrict SNMPv3 traffic by location - an SNMPv3 request will be accepted or rejected based purely on the user authentication, irrespective of where it originated. Source-based restrictions on SNMPv3 requests would need to use one of the "external" mechanisms listed above. How can I listen on just one particular interface? ------------------------------------------------- Normally, the agent will bind to the specified port on all interfaces on the system, and accept requests received from any of them. However, if a particular port (or ports) is specified when the agent is first started, then it will only listen for requests on these particular ports. For example: snmpd 127.0.0.1:161 would listen (on the standard port) on the loopback interface only, and: snmpd 10.0.0.1:6161 will listen on port 6161, on the (internal network) interface with address 10.0.0.1. To listen on both of these interfaces (and no others) provide a list of all the desired addresses: snmpd 127.0.0.1:161 127.0.0.1:6161 The AgentX port option ('-x') works in much the same way. How do I configure access control? --------------------------------- The simplest way is to use the configure directives: rocommunity public (for SNMPv1/2c) rwcommunity private or rouser user1 (for SNMPv3) rwuser user2 These specify the community names or security names to accept for read-only and read-write access to the whole of the supported MIB tree. (Obviously you should change these names to match your requirements - which is a particularly good idea in the case of 'rwcommunity'!) Note that you should *not* specify the same community name for both rocommunity and rwcommunity directives. The rwcommunity setting automatically provides read access, and having both lines (with the same community name) may result in unexpected behaviour. Only use both settings when specifying *different* community names. The same holds true for rouser and rwuser. The two community directives can be restricted to allow requests from particular sources, and all four can be restricted to a particular subtrees or (from v5.3) a named view. See 'snmpd.conf(5)' for details. These directives are effectively wrappers round the core access control mechanism, which uses the four directives 'com2sec', 'group', 'view' and 'access' to provide a more efficient and flexible control over who can access which portions of the tree. See the next question for the gory details. I don't understand the new access control stuff - what does it mean? ------------------------------------------------------------------- The idea behind the new access control model is to give a more flexible way of specifying who can see and do what within the MIB tree. It's more complicated to understand than the simple example above, but that's because it can do a whole lot more. There are four configuration keywords in the new scheme: 'com2sec', 'group', 'view', and 'access' We'll consider these one at a time, starting with 'access'. (Because I feel like starting with the last one, that's why - OK?) The "access" keyword has the job of specifying who has access to which bits of the MIB tree. This has eight parameters, so can look rather offputting. Most of these can be safely left with default values in most cases (so don't you worry your pretty little head about them). The syntax is access {group} "" any noauth exact {read-tree} {write-tree} {notify-tree} where the entries in braces need to be defined elsewhere (I'm coming to that - be patient!), and the rest can be left as shown here. [ If you really want to know, the 'sec.model' field can be used to have an access line that's only relevant to specific versions of SNMP (such v1 or v2c) rather than "any" version, and the 'sec.level' field to ensure that the request must be authenticated or encrypted. The context and prefix fields can be used to distinguish between parallel versions of the same overall OID tree ] The "view" keyword is used to define particular bits of the MIB tree, for use in the last three fields of the access entry. This has the syntax view {name} included/excluded {subtree} {mask} where {name} is the identifier to be used for this view (i.e. what should appear in the access entry), and {subtree} is the portion of the MIB tree that this name refers to (in either numeric or named form). Note that the name of the view does not have to have anything to do with the MIB sub-identifier names - it's purely an identifying tag for use within the config file (though choosing a meaningful name is, as always, a very good idea). The {mask} field can be used to control which elements of the OID subtree should be regarded as relevant when determining which view an OID is in. This is most relevant when defining "unusual" views, such as a single row of a table. In most cases, this field should be omitted. The third field can be used to include or exclude particular portions of the MIB from the named view. A single view can be built up using several 'view' lines (with the same view name), including or excluding OID subtrees as appropriate. The three view fields in the access line are used to control which portions of the MIB tree a particular {group} can see (GET et al), alter (SET), or request NOTIFYs on. That's dealt with the "what" - now for the "who". This is the role of the "group" and "com2sec" entries. The "group" keyword gives general control, by mapping between a "security name" (for a particular protocol version), and the internal name used in the access line. Note that the token "any" is no longer acceptable for the security model - the original support for this was due due to a misreading of the RFC. You should replace any such line with separate versions for each of the desired security models ('v1', 'v2c' & 'usm'). For SNMPv1 and SNMPv2c, the group line is just an intermediate step between the "access" line and the "com2sec" line, which is the last bit of the jigsaw. The "com2sec" entry is used to determine a "security name" from the traditional community string, taking into account where the request has come from. Thus the same community string can give access to different portions of the tree, depending on where the request is sent from. For example, in an earlier version of the example config file, there were two com2sec lines with the community string "public" - one was valid from anywhere (with the security name "public") and one was only valid from the local network (using the security name "mynet"). The group lines converted these security names into the groups "public" and "mygroup" respectively, and the access lines gave these two groups the ability to GET values in the 'system' sub-tree (from anywhere) or the 'mib-2' sub-tree (from the local network). Neither of these could SET any values though, (since the write-tree was "none" in both cases). Someone on the local machine, using the community string "private", had the security name "local" and the group name "local", and hence had full access (both GET and SET, as well as NOTIFY) to the whole of the MIB tree (or at least everything under .1, which covers most things!) Note that the three occurrences of "public", as community string, security name and group name, were three totally separate things. You can't use a community string in a security name field, or either of these as a group name (or vice versa), unless you set up suitable entries to map one name onto the other. With SNMPv3, the security name is part of the basic protocol (or near enough), and can be used directly in a group definition. And here concludes our tour of the view-based access control mechanism. Phew! How do I configure SNMPv3 users? ------------------------------- There are three ways to configure SNMPv3 users: 1) Stop the agent, and create a file /var/net-snmp/snmpd.conf, containing the line createUser {myUser} MD5 {myPassword} DES (where {myUser} and {myPassword} are the appropriate values, _without_ the braces!). Then re-start the snmpd agent. 2) Stop the agent, run the command net-snmp-config --create-snmpv3-user and follow the instructions. This will create an entry in the /var/net-snmp/snmpd.conf file similar to the above. Then re-start the snmpd agent. 3) Make sure the agent is running, and will respond to a suitable existing SNMPv3 user (with the same Authentication and Encryption protocols as required for the new user). Then use the 'snmpusm' command to clone this template user, and change the password. See the access control entries above and the file 'README.snmpv3' for more details about how to use SNMPv3 users, Note that simply having a 'rouser' or 'rwuser' line does *not* automatically create the corresponding user. You will need the above 'createUser' line (or an equivalent 'usmUser') as well. The 'createUser' line disappears when I start the agent. Why? ------------------------------------------------------------- That's deliberate. The agent removes the (human-readable) 'createUser' directive, and replaces it with an equivalent 'usmUser' entry. This contains the same information, but in a form that's only meaningful internally. Not only is the passphrase no longer visible in the config file, it has actually been converted to a key that is only valid on the local machine. If someone stole the new usmUser line from this system, they could not use that information to access any of your other agents (even if the usernames and passwords were the same). What's the difference between /var/net-snmp and /usr/local/share/snmp? --------------------------------------------------------------------- The /var/net-snmp location is primarily used for information set during the running of the agent, which needs to be persistent between one run of the agent and the next. Apart from "createUser" (see the previous entry), you shouldn't need to touch this file. All other user-provided configuration should go in the traditional location (typically /usr/local/share/snmp/snmpd.conf or /etc/snmp). My new agent is ignoring the old snmpd.conf file. Why? ----------------------------------------------------- The most likely explanation is that the new version of the agent is looking in a different location than the previous one. This is commonly experienced when replacing a ready-installed version (e.g. from a vendor distribution), with the current release installed from the source. The default location for this file with the basic distribution is /usr/local/share/snmp/snmpd.conf (or PREFIX/share/snmp/snmpd.conf). Ready-installed versions often look for the file as /etc/snmpd.conf, or /etc/snmp/snmpd.conf. Try moving the old config file to the new location, and restart the agent. With release 5.0, the name of the package changed from "ucd-snmp" to "net-snmp", and this change was reflected in the name of the persistent /var directory. So a v5 Net-SNMP agent will not look in /var/ucd-snmp/snmpd.conf for settings from a v4 UCD agent. Why am I getting "Connection refused"? ------------------------------------- This is actually nothing to do with the access control mechanism (though that's an understandable mistake). This is the result of the TCP wrapper mechanism using the files 'hosts.allow' and 'hosts.deny' to control access to the service. Some distributions may come with this enabled automatically - otherwise you need to explicitly activate this by configuring using '--with-libwrap'. If TCP wrappers are enabled, and both hosts.allow and hosts.deny are empty, then all requests will be rejected (with "Connection refused"). The simplest way to avoid this problem and allow incoming requests is to add the line snmpd: ALL to the file /etc/hosts.allow (or wherever this file is on your system). Though be aware that doing this removes one level of protection and allows anyone to try and query your agent (though the agent's own access control mechanisms can still be used to restrict what - if anything - they can see). If you do wish to use the TCP wrappers to restrict access, it's sensible to have an explicit entry: snmpd: ALL in the file /etc/hosts.deny, which makes it crystal clear that access to the SNMP agent has been denied. This mechanism can also be used to restrict access to specific management hosts, using a hosts.deny entry such as: snmpd: ALL EXCEPT 127. which will allow connections from localhost, and nothing else. Note that personal firewalls (such as Linux' ipchains or iptables mechanism) may have a similar effect (though typically this won't be logged). See the earlier entry Requests always seem to timeout, and don't give me anything back. Why? Why can't I see values in the UCDavis 'extensible' or 'disk' trees? ------------------------------------------------------------------ Both these trees are designed to report things you ask it to report on. If you don't declare anything in the snmpd.conf file for it to monitor, it will not report anything. See the snmpd.conf manual page and the EXAMPLE.conf file for details on configuring the agent. Optionally, run snmpconf -g monitoring to help you set up this section of the snmpd.conf file. Why can't I see values in the UCDavis 'memory' or 'vmstat' trees? ---------------------------------------------------------------- These mib modules are not supported on all operating systems, and will not be included on any other system. Currently, they are only supported on Linux, HP-UX (memory only), Solaris, BSDi (vmstat on BSDi4 only), Dynix, FreeBSD, NetBSD and OpenBSD. If you want to help port it to other systems, let us know. Note that these subtrees only report the current usage when explicitly queried. They do *not* automatically generate traps when the usage strays outside the configured bounds. See the earlier FAQ entry What traps are sent by the agent? for more information. What do the CPU statistics mean - is this the load average? ---------------------------------------------------------- No. Unfortunately, the original definition of the various CPU statistics was a little vague. It referred to a "percentage", without specifying what period this should be calculated over. It was therefore implemented slightly differently on different architectures. The 5.4 release has clarified the situation, and standardised on calculating these percentages over a minute. The relevant MIB descriptions have been updated to make the desired behaviour more explicit. The Net-SNMP agent also includes "raw counters", which can be used to calculate the percentage usage over any desired period. This is the "right" way to handle things in the SNMP model. The original percentage objects have been deprecated, and may possibly be removed in a future release of the agent. Note that this is different from the Unix load average, which is available via the loadTable, and is supported on all architectures. How do I get percentage CPU utilization using ssCpuRawIdle? ----------------------------------------------------------- This one of the "raw counters" mentioned in the previous entry. You need to take two readings of this object and look at the difference between them. That difference divided by the total number of 'ticks' between the two readings (where one tick is probably 0.01 seconds) will give you the percentage utilization over that period. What about multi-processor systems? ---------------------------------- The CPU objects (both percentages and raw counters) were designed to monitor the overall CPU activity of a system, and typically reflect whatever the underlying operating system reports for the (single) CPU statistics information. How these are handled for a multi-CPU system will probably differ from one O/S to another, and will need to be investigated for each system individually. The htProcessorTable was designed to handle monitoring multi-CPU machines, but the Net-SNMP implementation has up to now treated most systems (with the honourable exception of Solaris, and more recently Linux) as implicitly single-CPU. With the 5.4 release, there is now a cleaner framework for reporting on multi-CPU equipment, and it is hoped that an increasing number of systems will be able to report suitable processor information. Also with the 5.4 release, for the first time the agent will report the hrProcessorLoad value properly, which should provide some simple per-CPU statistics. T