opConfig Concepts

The main concepts to bear in mind are nodes, credential sets, commands, changes and revisions:

  • NODES:

    • Nodes are devices/computers that opConfig knows about, and which it is configured to run commands for.

    • As opConfig needs to connect to the node in question and execute commands on that node, the node needs to be configured with access credentials. In opConfig these are stored independent from the nodes in what opConfig calls credential sets.


    • Credential sets are a combination of usernames, passwords, privileged passwords etc. allowing access to the devices CLI.
    • Once the credential set has been used to create a working CLI access then "commands" can be issued and the results recorded.

    • Commands are normally command line constructs which will be executed on the node in question. 

      • (Some are "passive commands" like "audit-import" which are not actually run on the node but the result is associated with node.

      • Commands can be grouped and collected into what opConfig calls a "command set". Command sets are configured to apply only to particular OS and maybe versions or platforms.

    • The command output is captured and stored by opConfig.

    •  Command outputs are compared against the previous revision, and if different it's saved as a new revision in opConfig.  It could also be a one-shot command which is not analyzed in great detail (e.g. a process listing or some other diagnostic command)

    • A command can be marked for change detection in which case more detailed analysis occurs for changes.


    • Revisions are the command outputs as collected over time.
    • opConfig lets you distinguish between "very dynamic" and "mostly static" commands in an efficient flexible fashion:
      • Static commands should be marked for detailed change detection.
        In this case, a new revision is created if and only if there are (relevant) differences between the most recent state and the new  command output.
      • Dynamic commands should not be marked for change detection.
        Every time such a command is run, the output will be saved as a new revision - regardless of whether there were any differences between historic and current state.

Using current command sets on current nmis devices

General Node management from the Command Line

The tool opnode_admin.pl lets you list, export, create, modify or delete nodes from the command line. Editing operations involve an export to a JSON file, which you then modify using an editor or other tool of choice, followed by an update of the node using that JSON file. The opnode_admin.pl tool is pretty self-explanatory and documented on this page.

Managing Command Sets

As mentioned above opConfig lets you organize whatever commands you'd like it to run into an arbitrary number of groups which we call command sets.

Command sets are stored in the single file conf/command_sets.nmis in opConfig before 2.2.4.

Since 2.2.4 opConfig supports this and individual command set files in conf/command_sets.d/ and the files are now .json rather than .nmis.

It is recommended that you use individual files (as that makes things easier to maintain and more robust, e.g. should one file have syntactical problems). For backwards compatibility the old single file is consulted first, then any individual ones. opConfig loads a command set when it's seen for the first time, and any subsequent occurrences of a clashing config set (i.e. same name) will be ignored but logged.

A command set definition consists of these types of information:

  • meta-information like the command set's name (which can be used in CRON to determine when / how often this command set is run),
  • optional control information like scheduling constraints and an expiration policy for the commands in that set,
  • filters for selecting which devices/nodes the command set should apply to. These are discussed in more detail below.
  • and finally the list of the actual commands to be run (which may also have certain modifiers and meta-data attached to them).

Here is an excerpt from the default command set that ships with opConfig (in .nmis, pre 2.2.4 format).

  'IOS_HOURLY' => {
    'os_info' => {
      'version' => '/12.2|12.4|15.\d+/',
      'os' => 'IOS'
        'purging_policy' => {
            'keep_last' => 1000,
            'purge_older_than' => 2592000, # 30 days
            'autoprotect_first_revision' => 'true', 
        'scheduling_info' => {
      'run_commands_on_separate_connection' => 'false',
    'commands' => [
        'multipage' => 'true',
        'privileged' => 'false',
        'command' => 'show interfaces',
        'tags' => [ 'HOURLY', 'performance', 'interfaces' ],
        'multipage' => 'true',
        'privileged' => 'false',
        'command' => 'show ip interface',
        'tags' => [ 'HOURLY', 'detect-change', 'configuration' ],
... and lots more

Below is much the same, but in the post 2.2.4, json format.

   "IOS_HOURLY" : {
      "scheduling_info" : {
         "run_commands_on_separate_connection" : "false",
         "attempt_timeout_recovery" : 1
      "purging_policy" : {
         "purge_older_than" : 2592000,
         "keep_last" : 1000,
         "autoprotect_first_revision" : "true"
      "commands" : [
            "command" : "show interfaces",
            "privileged" : "false",
            "tags" : [
            "multipage" : "true"

Defining which nodes a command set applies to

This is normally done by filtering by OS info, but not necessarily limited to OS info only:

# Filter using both regular expression and string equality checks:
'os_info' => {
 'version' => '/12.2|12.4|15.0/',
 'os' => 'IOS'
# Or just the specific os family/type and that's all:
'os_info' => { 
 'os' => '/(Linux|CentOS|Ubuntu)/'

The examples above specify that the node in question must have an os_info property set, with sub-properties os and version in the first example and just os in the second.

Plain string values indicate string comparison, but regular expressions can be given too. A node is only considered for this particular command set if all filtering expressions match. You can filter on any node property, not just properties from os_info (but the default command sets only use os_info).

Prior to version 3.1.1, opConfig considered command sets without filter blocks as disabled; for these versions you may want a 'wildcard' filter matching anything whatsoever,  which can be achieved by adding an os_info filter block with a 'match-everything' regular expression for os, e.g 'os' => '/.*/'.

From opConfig 3.1.1 onwards a command set without filter is interpreted as to apply to all nodes without any restriction.

Controlling how the command output is stored

By default opConfig stores all command outputs in its MongoDB database, and only there.

In recent versions two new options let you fine-tune the behaviour and make use of on-disk storage where desired:

  • Shadowing outputs on disk is controlled by the option shadow_file,
  • and the choice between database storage and disk storage is made via the option store_internal.

Disk or Database?

If you set  the store_internal option to "true" or omit  it altogether, then all command outputs are stored in the database.
With this option set to false, opConfig creates a separate file on disk for each revision of the command.

The storage location for such files is configured with the config option opconfig_external_store (default /usr/local/omk/var/opconfig/external).
The actual  files are then stored in the directory <opconfig_external_store>/<node name>/<command name>/<revision>.
In version 3.1.1 and newer, an additional symbolic link latest that points to the most recent revision is maintained in that directory.

For externally stored data the visible 'command output' in the GUI is made up from the size and the SHA256 checksum of the contents, and change detection (and the GUI) uses this data instead of the (possibly binary or huge) file contents. This produces much more coarse change detection, but works with binary files. In the GUI you'll see the made up 'command output', and a button to download the actual contents.

All other opConfig capabilities work normally for externally stored data; e.g. scheduling, tags, purging of old revisions, revision creation itself and so on.

Please note that in versions before 3.1.1 store_internal is only supported for Tracking Files.

Commands or Files that cannot fit into the Database?

MongoDB doesn't support documents greater than 16 megabytes. In opConfig 3.1.1 and newer, any command output that is larger than this limit is automatically reconfigured for storage on disk, i.e. store_internal is overridden and set to "false" for just this one revision.

Both Disk and Database?

In opConfig 3.1.1 an option for shadowing command output on disk was added: if you set the property shadow_file to true (in the command's block, or in the command set's scheduling_policy section), then opConfig will store the data both in the database and also on disk (in the same place as externally stored command outputs).

Please note that shadow_file has no effect for commands that have been configured for disk storage.

Large Command Outputs 

opConfig can handle Large Command Outputs, but there are some things to take into account: 

  • Memory usedFiles under 16mb did not use much perl memory, but for a 1.5GB file, the perl process could use up to twice that in memory, depending on how it was being handled. 
  • StorageMongoDB doesn't support documents greater than 16 megabytes. So command outputs larger than that size will be stored in the path specified in opconfig_external_store configuration option ("<omk_var>/opconfig/external" by default).
  • Time: The file has to be transferred over the network, so it will be dependant on the transfer rate. 

For example, a file up to 100 MB can be obtained with a cat command, but there are more efficient ways to track the file content. Using a command output will be done with ssh, but opConfig can use scp for that purpose (See below section - Tracking Files). Choosing the right protocol can make a difference. 

Tracking Files

opConfig version 3.0.3 introduces a new capability: Arbitrary files can now be downloaded from a node (with SCP), stored and tracked by opConfig.
Here is an snippet from the example command set named file_store.nmis that ships with opConfig:

# ...other command set structure
scheduling_info => 
  # indicates work to be performed by and on the opConfig host
  run_local => 'true',        
commands => [
    command => '_download_file_ scp:///var/log/secure', 
    store_internal => 'false',
    tags => [ 'detect-change', 'other', 'custom', 'tags' ], 
    command => '_download_file_ scp://file_in_user_homedir',
    store_internal => 'true', # is the default,
    tags => [ 'detect-change' ],

To instruct opConfig to track one or more files, you have to

  1. set up a command set with the scheduling property run_local set to true,
  2. and add a separate special _download_file_ command for every file you want  to track.
  3. If the file data is binary or larger than 16 megabytes, set store_internal to false.

The run_local option indicates that all commands in this command set are to be run on the opConfig server, instead of on the node in question.

The special/pseudo-command _download_file_ requires an scp URI to be given. Note that the first two "/" characters in scp:///some/abs/path.txt belong to the URI, and the path in question is /some/abs/path.txt. In the second example above, the path is a plain relative file_in_user_homedir which means scp will look for this file in the user's home directory.

The store_internal option works as described in the previous section.

Grouping commands into sessions

By default all commands for a node will be run sequentially, one after another within the same session/connection to that device.  This can save time as connecting to the device (and authenticating) often takes longer than running all the commands one by one. 

But this is not always the case, some devices have weird shell command processors which don't take well to this kind of scripted remote control; and then there are certain commands that do run for a longer period of time (for example system statistics gatherers like vmstat or top).  These commands would cause long delays in a sequential run, and opConfig lets you adjust this behaviour to your liking.

Separate sessions for some commands

You can specify which commands should have their own separate connections. Separate connections can be opened in parallel, if opconfig-cli.pl is run with mthread=true.

If you would like to change the default behavior and have opConfig run all commands in all command set in separate session/connection, simply modify opCommon.nmis like this:

# to run each command in it's own session, change this to true
 'opconfig_run_commands_on_separate_connection' => 'false',

It makes a lot more sense to tell opConfig to run a set of commands on their own or, in most cases, just a single command on its own.  Here is how to make a command or command set have their own sessions/connections:

# for all commands in a set, define this in the command set - note the S in run_commandS_...!
'scheduling_info' => {
 'run_commands_on_separate_connection' => 'true'

# for just a specific command, set this for the command in question - no S in run_command_...!
commands => [
 'command' => 'show version',
 'run_command_on_separate_connection' => 'true',

Dealing with particular slow commands: Recovering from timeouts

opConfig doesn't block indefinitely if a command on a device doesn't return a response; instead the session times out after a configurable period (see config  item opconfig_command_timeout, default 20 seconds) and the command is marked as failed.

From version 3.0.7 onwards, opConfig handles timeouts in long-lived sessions robustly; earlier versions could, under certain circumstances, get confused into associating the wrong outputs with commands if a timeout had occurred earlier during that session.

Version 3.0.7 lets you decide how to react to a command timing out:

  • If your command set activates the  attempt_timeout_recovery option, then opConfig  will attempt to re-synchronise the session state for a little while longer.
    It does so by looking for your device's prompt for a little while. If none is forthcoming (ie. the problematic command is still blocking progress), then opConfig will send a newline to "wake" the device. This is repeated a few times, unless a prompt is found.
  • If that option is off or the resynchronisation is unsuccessful, then opConfig will close the session (and open a new one, if further commands are to be run for this node).

The value of the attempt_timeout_recovery option must be a nonnegative integer; it defines how many wait-and-wake-up cycles opConfig should perform. Each such cycle takes up to opconfig_command_timeout seconds.

You may set the attempt_timeout_recovery for all commands belonging to a set or for individual commands. Individual commands' setting override the ones for the set. The default if neither are given is zero, i.e. no extra recovery grace period.

Here is an example config set snippet, whose commands all get one extra timeout cycle for recovery, except  some_brittle_command gets up to five extra timeout periods.

%hash = (  
  'my_first_config_set' =>  {
    'os_info' =>  {   
	# ...node conditions
    # add one extra timeout period for all commands
    'scheduling_info' => {
       'attempt_timeout_recovery' => 1,
    'commands' => [
       { 'command' => "uptime" },
	   # any number of commands, treated equal wrt. timeouts
       # but the following command is more prone to timing out, so we give it up to 5 x timeout
       { 'command' => 'some_brittle_command',
          'attempt_timeout_recovery' => 5,

Dealing with slow nodes: using Device Presets

opConfig cannot let one misbehaving device block progress for all others; therefore all interactions with remote devices are subject to a timeout (configuration item opconfig_command_timeout, default: 20 seconds). This timeout is shared by all nodes.

From version 3.0.7 onwards, opConfig  offers Device Presets: a more fine-grained mechanism for adjusting the timing for each node.
Device presets are configured in conf/opCommon.nmis, under the key opconfig_device_presets. Here is the default setting as shipped with opConfig 3.0.7:

'opconfig_device_presets' => {
  'normal' => { wake_up => 0, settling_time => 0, timeout_factor => 1 },
  'slow' => { wake_up => 2, settling_time => 5, timeout_factor => 1.25 },

A device preset can provide adjustments using the following three properties:

  • wake_up controls whether a slow login process (that has timed out) should be 'revived' by sending an 'enter' keystroke to wake the device.
    The default is 0, or no extra 'wake up' keystrokes and if the login times out,  the connection is terminated.
    With a positive value N for wake_up, opConfig  will send a wake up keystroke, then wait for a prompt up to the configured timeout, and retry this sequence up to N times.
    If no prompt is detected during that sequence, the connection is terminated.
    Please note that the default for versions before 3.0.7 for wake_up was 1, ie. one login retry. Under certain circumstances and with devices responding excessively slowly this could lead to misinterpreted command outputs and data corruption.
  • settling_time controls whether opConfig should wait an extra N seconds for stray output after the login is done but before issuing the first command.
    This setting is meant for compensating for overly slow and/or complex logins with extra banners and the like, which can cause opConfig to mis-trigger on a premature, undesirable prompt if the device in question responds overly slowly. Any output that arrives between the login and the end of the settling period is consumed and discarded. The default values is 0, or no extra compensation delay.
  • timeout_factor allows the setup of a longer or shorter interaction timeout for particular devices.
    This option accepts positive values, and the configured opconfig_command_timeout is scaled by that factor for any device that uses this device preset.
    The default value is 1, i.e. no scaling. In the example above and with the default opconfig_command_timeout of 20 seconds, devices marked with the "slow" preset would get a timeout of 25 seconds.

In the GUI, assigning a device preset to a device is done on the Edit Node page, on the Connection tab.
On the command line  you can use opnode_admin.pl act=set node=<somenode> entry.connection_info.device_preset=<presetname> to select a preset for a node.

A node without preset  is subject to the default values.

Privileged Mode

Many types of devices distinguish between a normal and a privileged/superuser/elevated mode, and allow certain commands only in privileged mode. opConfig needs to know whether that applies to your device and which commands are affected.

In opConfig 3.0.2 and newer, every credential set indicates whether it grants direct and permanent access to privileged mode (always_privileged true), or whether opConfig needs to switch between normal and privileged mode (possibly repeatedly). Older versions only support the dual, mode-switching setup.

Commands affected by this distinction need to be marked with the privileged property, in which case opConfig will attempt to gain elevated/superuser privileges before attempting to run the command.
When connected to a device in always privileged mode, opConfig ignores the privileged property.

Non-interactive commands

Before version 3.0.3 opConfig would always open an interactive session to the device, then issue commands one by one. Amongst other things this requires a working phrasebook for the type of device, and imposes certain constraints - but when it works it's very efficient.

Recently we've run into a few devices (types and versions), where remote controlling  the shell processor is unreliable - which can cause opConfig to fail to properly communicate with the device, e.g. if the prompt cannot be determined reliably.

Version 3.0.3 introduces an alternative, but for SSH only, which bypasses the shell/cli command processor on the device as much as possible.

You can adjust this behavior for a whole command set (or an individual command) with the command set property run_commands_noninteractively. Default is false; if set to true, opConfig will issue every single command 'blindly' and independently in a new SSH connection just for this command. For transport type Telnet this property is ignored.

This option is similar to what run_commands_on_separate_connection does, except interactive prompts and the like are not relevant here: opConfig starts a new ssh client for each command, and each ssh client terminates after returning the output of the command execution on the node.

  • The advantage here is that opConfig doesn't have to interact with the node's command processor in a command-response-prompt-command-response... cycle; As such it's more robust.
  • The disadvantage is that a new SSH connection must be opened for every single command, which is a relatively costly operation in terms of processing.
    Furthermore this cannot work with Telnet (which is interactive by design).

Dealing with devices without or insufficient command-line interface

opConfig version 3.1.1 has introduced a new plugin mechanism for collecting configuration data, which can help with devices whose command-line interface is found lacking for any reason; Please consult this separate document for information about how Plugins in opConfig work.

How long should revisions (and their captured command output) be kept

opConfig 2.2. (and newer) have a flexible purging subsystem which is described in detail on a separate page here. The example above shows roughly how it's controlled: a command or command set can have a  section called purging_policy which controls whether and when a revision should be removed from the database.

What constitutes a change, and when should opConfig create new revisions

Not all output is worthy of change detection; configuration information generally is while performance information generally is not. The configuration for a router, for example, is - but the usage counters on an interface likely are not. As mentioned above, opConfig can deal with both of these types of commands, the "one-shot" ones as well as the change-indicating ones.

In a command set you tell opConfig which commands belong to what class by setting (or omitting) the tag detect-change.

If the tag is present, then change detection is run on this command's output: If and only if  the output is different from the previously stored revision, a new revision is stored along with detailed information of what the changes were. If the tag is not defined, then a new revision is created if the output is different - but no detailed changes are tracked, and the opConfig GUI will only report the command's revision in the list of "commands" but not in the list of "configuration changes".

'tags' => ['detect-change'],

Related to this is the question of what changes that were found should be considered important or relevant.  opConfig can "ignore" unimportant differences in a command's output if you provide it with a set of command filters for a command:

'privileged' => 'false',
'command' => 'ifconfig -a',
'tags' => [ 'DAILY', 'configuration', 'detect-change' ],
  'command_filters' => [
    '/RX packets/',
    '/TX packets/',
    '/RX bytes/',
    '/TX bytes/'

In the example above, the output of the "ifconfig -a" command would be checked and any changed lines that match TX/RX packets or TX/RX bytes (i.e. the interface counters) are ignored. Any other changes that remain after applying the filters are used to figure out whether to create a new revision or not.

Please note that command filters are possible for both one-shot commands and commands with change-detect enabled,  and behave the same for both.

In opConfig 3.1.1, support for post-processing plugins was added which provides facilities for more flexible filtering (e.g. whole blocks of data may be excluded programatically). The Plugins in opConfig page describes how to make use of this new functionality.

Raising Events when changes are detected

opConfig 2.2 and newer can raise an event with NMIS if a change was detected for a node and a particular command. The event name is "Node Configuration Change Detected" and includes details of the change which has been detected.  To activate this feature you have to  give the command in question both the tags detect-change and report-change. You may also give a fixed event severity (values as defined in NMIS), like in this example:

'privileged' => 'false',
'command' => 'chkconfig',
'tags' => [ 'DAILY', 'configuration', 'detect-change', 'report-change' ],
'report_level' => 'Minor',

To enable or disable this feature in general edit /usr/local/nmis8/conf/Config.nmis. 

    'log_node_configuration_events' => 'true',

If set to true the feature is enabled; if set to false the feature is disabled.

In this case, the Redhat/Centos command chkconfig (= list of system services to automatically start on boot) will be checked for changes, and if any are found then a "Node Configuration Change" event with the context node in question, the element "chkconfig" and the serverity "Minor" will be raised in the local NMIS.

If you want a more dynamic event severity, then you can use report_level_min_changes which selects a severity based on the number of changes that were found:

 'privileged' => 'true',
 'command' => 'vgdisplay',
 'tags' => [ 'DAILY', 'configuration', 'detect-change', 'report-change' ],
 'report_level_min_changes' => {
   1 => "Normal",
   3 => "Minor",
   10 => "Major" },

In this example, changes in the vgdisplay command output would result in an event of severity Normal if there are 1 or 2 changes, Minor for 3 to 9 changes, and Major for 10 or more.

How to categorize command sets (and why)

As seen in the examples above, commands can have a number of pre-defined tags like detect-change or report-change; but you are encouraged to set your own custom tags to characterize the commands according to your preferences.

The default command set shipped with opConfig uses two primary tags for categorization, DAILY and HOURLY.These are used in the example cron invocations of "opconfig-cli.pl act=run_command_sets" so that all commands with tag DAILY are run only once a day, whereas the HOURLY ones run once an hour. Commands with neither tag will not run periodically, for example there are numerous commands tagged with troubleshooting which will only be run in reaction to an event detected in opEvents.

Using tags in this fashion for categorization is much more convenient than having to tell opconfig-cli.pl which command sets to run by name (which is also possible).

General Usage of opconfig-cli.pl


Information on what commands are supported is printed when no options are specified.  All options support debug=true for debug output and debug=9 for extremely verbose output.  

Listed below are the possible options for the act=X argument:



This option is only available from versions < 4.0.0. From opConfig 4.0.0, the data is shared between applications. 

Grabs one or more nodes from NMIS. Identical in function to "Refresh" or "Import Nodes from NMIS" in the GUI.

Automatically Setting a Nodes opConfig attributes

When a device is imported we automatically set a number of the devices opConfig attributes such as "connection_info.personality" "os_info.os" etc.

The matching of NMIS device attributes and the subsequent setting of opConfig attributes is controlled via omk/conf/OS_Rules.nmis

You can extend this file to automatically set all sorts of opConfig device attributes when an import is done, e.g you might set all cisco devices to use ssh by setting 'connection.transport' => 'SSH',

For more information see Create an OS Rule and OS Rules Help Text


Tests a single given node (argument node=nodeX) and attempts to determine its Transport and Credential Set configuration. The node must already have a Personality set.


opconfig-cli can be used to test connections to help debug situations that don't make any sense. 

An example of how it can be used:

bin/opconfig-cli.pl act=test_connect host= transport=Telnet personality=ios username=testuser password=testpass

The options for transport and personality are given above.

It is also possible to test an existing connection from the connections.nmis file by specifying node=node_name , if any options are specified on the command line along with the node they will override the settings loaded from the connections.nmis file.

command="some command" can also be specified to test the output of a specific command.

run_command_sets, Running commands on devices

This command will run all applicable command sets for all nodes (by default).


  • nodes=node1,node2,etc -- only command sets that apply to the specified nodes will be run.
  • names=command_set1,command_set2,etc – only run the specified command sets (and of course only for nodes matching the command sets' criteria)
  • tags=tag1,tag2,etc –  The candidate commands are filtered by the tags specified. If one or more tags given on the command line is present in the list of a command's tags, then the command will be run.

get_command_output, Get the last output from a command for a node

Requries node=node_name command="command name" and returns output collected from the last run of this command

diff_command_outputs, Diff two revisions 

Shows the diff from the output of 2 revisions of stored output (does not run them, only queries).  The command line would look similar to get_command_output with the edition of revision_1= and revision_2=

eg. act=diff_command_outputs node=node1 command="show run" revision_1=10 revision_2=13


This action imports audit information from Open-AudIT Enterprise, for all devices known to Open-AudIT.

This requires a licensed Version 1.4 of Open-AudIT Enterprise or newer. The audit information will show up in opConfig as command "audit", and the command output  will be the full audit data set in JSON format. Nodes will be consolidated as much as possible with your currently existing node definitions.

To enable this functionality, set the necessary options in conf/opCommon.nmis and run opconfig-cli.pl act=import_audit periodically or as a one-off. The required config settings are as follows:

'opconfig_audit_import' => 1, # to enable this altogether
'opconfig_audit_import_url_base' => "http://my.oae.system.com/omk/oae/",
'opconfig_audit_import_user' => "nmis",         # needs ro-access
'opconfig_audit_import_password' => "somepassword",

list_policies, import_policy, export_policy; update_config_status, export_config_status  and check_compliance

These operations are documented on the separate page about Compliance Management.