PRTG Manual: SNMP Linux Disk Free Sensor

The SNMP Linux Disk Free sensor monitors free space on disks of a Linux/Unix system using Simple Network Management Protocol (SNMP).

It shows the following:

  • Free total disk space in bytes
  • Free space in bytes for every mounted partition
  • Free space in percent for every mounted partition
  • Free inodes in percent for every mounted partition

icon-book-bulbThe free space returned by this sensor type shows the disk space that is not yet used. Not all of this space may be available for use, as a part of this space can be reserved by the system, for example, for redundancy purposes. For details, see the Knowledge Base: Why do SSH Disk Free and SNMP Linux Disk Free show different values for my target Linux system?

SNMP Linux Disk Free Sensor
SNMP Linux Disk Free Sensor

Sensor in Other Languages

Dutch: SNMP Linux vrije schijf ruimte, French: Espace disque libre SNMP Linux, German: SNMP Linux Plattenplatz, Japanese: SNMP Linuxディスク空き容量, Portuguese: Disco livre Linux SNMP, Russian: Свободное пространство диска в Linux по SNMP, Simplified Chinese: SNMP Linux 磁盘可用空间, Spanish: SNMP disco libre Linux

Remarks

Add Sensor

The Add Sensor dialog appears when you manually add a new sensor to a device. It only shows the setting fields that are required for creating the sensor. Therefore, you will not see all setting fields in this dialog. You can change (nearly) all settings in the sensor's Settings tab later.

Sensor Settings

On the details page of a sensor, click the Settings tab to change its settings.

icon-i-roundUsually, a sensor connects to the IP Address or DNS Name of the parent device where you created this sensor. See the Device Settings for details. For some sensor types, you can define the monitoring target explicitly in the sensor settings. Please see below for details on available settings.

Basic Sensor Settings

Sensor Name

Enter a meaningful name to identify the sensor. By default, PRTG shows this name in the device tree, as well as in alarms, logs, notifications, reports, maps, libraries, and tickets.

Parent Tags

Shows Tags that this sensor inherits from its parent device, group, and probe. This setting is shown for your information only and cannot be changed here.

Tags

Enter one or more Tags, separated by spaces or commas. You can use tags to group sensors and use tag–filtered views later on. Tags are not case sensitive. We recommend that you use the default value.

You can add additional tags to the sensor if you like. Other tags are automatically inherited from objects further up in the device tree. These are visible above as Parent Tags.

icon-i-roundIt is not possible to enter tags with a leading plus (+) or minus (-) sign, nor tags with round parentheses (()) or angle brackets (<>).

Priority

Select a priority for the sensor. This setting determines where the sensor is placed in sensor lists. Top priority is at the top of a list. Choose from one star (low priority) to five stars (top priority).

Set limits checked against ALL disks

In this section you can set limits that are valid for all channels and all drives. By entering limits, you can define when the sensor will enter a Warning or Down status, depending on the data provided by all drives that this sensor monitors. If you want to individually define limits for separate channels, please use the limit settings in the Sensor Channels Settings.

icon-i-round-redAll limits that you define here are valid in addition to the limits defined in the particular Channel settings! The limits are valid simultaneously, so the first limit that is breached applies.

Percentage Limit Check

Enable or disable a limit check for the free space in percentage channels of all drives. By default, percentage limits are enabled with lower warning and lower error limit. Choose between:

  • Only use the limits in the settings of the percentage channels: Do not define sensor limits that are valid for all percentage channels. The sensor only uses limits that you define in the settings of the particular "free space in percent" channels to determine the status.
  • Use the limits of both the sensor and the channel settings: Define limits for the sensor that are valid for all drives (percentage channels). Additional fields appear below. The sensor enters a Warning or Down status when free space limits are undercut or overrun.

Upper Error Limit

This field is only visible if you enable percentage limit check above. Specify an upper limit in percent for a Down status. If the free disk space of one of your drives overruns this percent value, the sensor switches to Down. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Upper Warning Limit

This field is only visible if you enable percentage limit check above. Specify an upper limit in percent for a Warning status. If the free disk space of one of your drives overruns this percent value, the sensor switches to Warning. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Lower Warning Limit

This field is only visible if you enable percentage limit check above. Specify a lower limit in percent for a Warning status. If the free disk space of one of your drives undercuts this percent value, the sensor switches to warning. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Lower Error Limit

This field is only visible if you enable percentage limit check above. Specify a lower limit in percent for a Down status. If the free disk space of one of your drives undercuts this percent value, the sensor switches to Down. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Size Limit Check

Enable or disable a limit check for the free bytes channels of all drives. By default, byte size limits are not enabled for drives. Choose between:

  • Only use the limits in the settings of the byte size channels: Do not define sensor limits that are valid for all byte size channels. The sensor only uses limits that you define in the settings of the particular free space in bytes channels to determine the status.
  • Use the limits of both the sensor and the channel settings: Define limits for the sensor that are valid for all drives (byte size channels). Additional fields appear below. The sensor enters a Warning or Down status when free space limits are undercut or overrun.

Upper Error Limit

This field is only visible if you enable byte limit check above. Specify an upper limit. Use the same unit as shown by the free bytes channels of this sensor (by default this is MByte). If the free disk space of one of your drives overruns this bytes value, the sensor will switch to Down. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Upper Warning Limit

This field is only visible if you enable byte limit check above. Specify an upper limit. Use the same unit as shown by the free bytes channels of this sensor (by default this is MByte). If the free disk space of one of your drives overruns this bytes value, the sensor switches to Warning. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Lower Warning Limit

This field is only visible if you enable byte limit check above. Specify a lower limit. Use the same unit as shown by the free bytes channels of this sensor (by default this is MByte). If the free disk space of one of your drives undercuts this bytes value, the sensor switches to Warning. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Lower Error Limit

This field is only visible if you enable byte limit check above. Specify a lower limit. Use the same unit as shown by the free bytes channels of this sensor (by default this is MByte). If the free disk space of one of your drives undercuts this bytes value, the sensor switches to Down. Please enter an integer value or leave the field empty.

icon-i-round-redThe limits set here are valid for all channels of this sensor. You can additionally set individual limits for each sensor channel in the Sensor Channels Settings. The limits set here and in the channel settings are valid simultaneously!

Alarm on Missing/Removed Disk

If a monitored disk is removed or not found, values are set to zero. Select the alarming approach in this case. Choose between:

  • Deactivate alarm (default): Select this option if you do not want an alarm for a removed disk.
  • Activate alarm: Select this option if you want to be alerted if a monitored disk is removed.

Sensor Display

Primary Channel

Select a channel from the list to define it as the primary channel. In the device tree, the last value of the primary channel will always be displayed below the sensor's name. The available options depend on what channels are available for this sensor.

icon-i-roundYou can set another primary channel later by clicking the pin symbol of a channel in the sensor's Overview tab.

Graph Type

Define how different channels will be shown for this sensor.

  • Show channels independently (default): Show an own graph for each channel.
  • Stack channels on top of each other: Stack channels on top of each other to create a multi-channel graph. This will generate an easy-to-read graph that visualizes the different components of your total traffic.
    icon-i-roundThis option cannot be used in combination with manual Vertical Axis Scaling (available in the Sensor Channels Settings settings).

Stack Unit

This setting is only available if stacked graphs are selected above. Choose a unit from the list. All channels with this unit will be stacked on top of each other. By default, you cannot exclude single channels from stacking if they use the selected unit. However, there is an advanced procedure to do so.

Inherited Settings

By default, all following settings are inherited from objects higher in the hierarchy and should be changed there, if necessary. Often, best practice is to change them centrally in the Root group's settings, see section Inheritance of Settings for more information. To change a setting only for this object, disable inheritance by clicking the button next to inherit from under the corresponding setting name. You will then see the options described below.

Scanning Interval

Click inherited_settings_button to disrupt the inheritance. See section Inheritance of Settings for more information.

Scanning Interval

Select a scanning interval (seconds, minutes, or hours) from the list. The scanning interval determines the time the sensor waits between two scans. You can change the available intervals in the system administration on PRTG on premises installations.

If a Sensor Query Fails

Define the number of scanning intervals that a sensor has time to reach and check a device again in case a sensor query fails. The sensor can try to re-reach and check a device several times, depending on the option you select here, before it will be set to a Down status. This helps you avoid false alarms if the monitored device has only temporary issues. For previous scanning intervals with failed requests, the sensor will show a Warning status. Choose between:

  • Set sensor to "down" immediately: The sensor will show an error immediately after the first failed request.
  • Set sensor to "warning" for 1 interval, then set to "down" (recommended): After the first failed request, the sensor will show a yellow warning status. If the following request also fails, the sensor will show an error.
  • Set sensor to "warning" for 2 intervals, then set to "down": Show an error status only after three consecutively failed requests.
  • Set sensor to "warning" for 3 intervals, then set to "down": Show an error status only after four consecutively failed requests.
  • Set sensor to "warning" for 4 intervals, then set to "down": Show an error status only after five consecutively failed requests.
  • Set sensor to "warning" for 5 intervals, then set to "down": Show an error status only after six consecutively failed requests.

icon-i-roundSensors that monitor via Windows Management Instrumentation (WMI) always wait at least one scanning interval until they show an error. It is not possible to set a WMI sensor to "down" immediately, so the first option will not apply to these sensor types. All other options can apply.

icon-i-roundIf a sensor has defined error limits for channels, it will always show a Down status immediately, so no "wait" option will apply.
 

icon-i-roundIf a channel uses lookup values, it will always show a Down status immediately, so no "wait" options will apply.

Schedules, Dependencies, and Maintenance Window

icon-i-roundInheritance for schedules, dependencies, and maintenance windows cannot be interrupted. The corresponding settings from the parent objects will always be active. However, you can define additional settings here. They will be active at the same time as the parent objects' settings.

Schedule

Select a schedule from the list. Schedules can be used to monitor for a certain time span (days, hours) every week. With the period list option it is also possible to pause monitoring for a specific time span. You can create new schedules and edit existing ones in the account settings.

icon-i-roundSchedules are generally inherited. New schedules will be added to existing ones, so all schedules are active at the same time.

Maintenance Window

Specify if you want to set up a one-time maintenance window. During a "maintenance window" period, this object and all child objects will not be monitored. They will be in a paused state instead. Choose between:

  • Not set (monitor continuously): No maintenance window will be set and monitoring will always be active.
  • Set up a one-time maintenance window: Pause monitoring within a maintenance window. You can define a time span for a monitoring pause below and change it even for a currently running maintenance window.

icon-i-roundTo terminate a current maintenance window before the defined end date, change the time entry in Maintenance Ends field to a date in the past.

Maintenance Begins

This field is only visible if you enabled the maintenance window above. Use the date time picker to enter the start date and time of the maintenance window.

Maintenance Ends

This field is only visible if you enabled the maintenance window above. Use the date time picker to enter the end date and time of the maintenance window.

Dependency Type

Define a dependency type. Dependencies can be used to pause monitoring for an object depending on the status of another. You can choose between:

  • Use parent: Pause the current sensor if the device, where it is created on, is in Down status, or is paused by another dependency.
  • Select object: Pause the current sensor if the device, where it is created on, is in Down status, or is paused by another dependency. Additionally, pause the current sensor if a specific other object in the device tree is in Down status, or is paused by another dependency. Select below.
  • Master object for parent: Make this sensor the master object for its parent device. The sensor will influence the behavior of the device, where it is created on: If the sensor is in Down status, the device will be paused. For example, it is a good idea to make a Ping sensor the master object for its parent device to pause monitoring for all other sensors on the device in case the device cannot even be pinged. Additionally, the sensor will be paused if the parent group of its parent device is in Down status, or if it is paused by another dependency.

icon-i-roundTesting your dependencies is easy! Simply choose Simulate Error Status from the context menu of an object that other objects depend on. A few seconds later all dependent objects should be paused. You can check all dependencies in your PRTG installation by selecting Devices | Dependencies from the main menu bar.

Dependency

This field is only visible if the Select object option is enabled above. Click on the reading-glasses and use the object selector to choose an object on which the current sensor will depend.

Dependency Delay (Sec.)

Define a time span in seconds for a dependency delay. After the master object for this dependency goes back to Up status, PRTG will start monitoring the depending objects after this extra delayed. This can help to avoid false alarms, for example, after a server restart, by giving systems more time for all services to start up. Please enter an integer value.

icon-i-round-redThis setting is not available if you choose this sensor to Use parent or to be the Master object for parent. In this case, please define delays in the parent Device Settings or in the superior Group Settings.

Access Rights

Click inherited_settings_button to disrupt the inheritance. See section Inheritance of Settings for more information.

User Group Access

Define which user group(s) will have access to the object you're editing. A table with user groups and types of access rights is shown: It contains all user groups from your setup. For each user group, you can choose from the following access rights:

  • Inherited: Use the access rights settings of the parent object.
  • None: Users in this group cannot see or edit the object. The object neither shows up in lists nor in the device tree. Exception: If a child object is visible to the user, the object is visible in the device tree, though not accessible.
  • Read: Users in this group can see the object and review its monitoring results.
  • Write: Users in this group can see the object, review its monitoring results, and edit the object's settings. They cannot edit access rights settings.
  • Full: Users in this group can see the object, review its monitoring results, edit the object's settings, and edit access rights settings.

You can create new user groups in the System Administration—User Groups settings. To automatically set all objects further down in the hierarchy to inherit this object's access rights, set a check mark for the Revert children's access rights to inherited option.

icon-book-arrowsFor more details on access rights, see the section User Access Rights.

Channel Unit Configuration

Click inherited_settings_button to disrupt the inheritance. See section Inheritance of Settings for more information.

Channel Unit Types

For each type of sensor channel, define the unit in which data is displayed. If defined on probe, group, or device level, these settings can be inherited to all sensors underneath. You can set units for the following channel types (if available):

  • Bandwidth
  • Memory
  • Disk
  • File
  • Custom

icon-i-roundCustom channel types can be set on sensor level only.

More

Knowledge Base: Why do SSH Disk Free and SNMP Linux Disk Free show different values for my target Linux system?

Knowledge Base: My SNMP sensors don't work. What can I do?

Knowledge Base: Checklist: Setting up SNMP on Linux

Edit Sensor Channels

To change display settings, spike filter, and limits, switch to the sensor's Overview tab and click the gear icon of a specific channel. For detailed information, see the Sensor Channels Settings section.

Notifications

Click the Notifications tab to change notification triggers. For detailed information, see the Sensor Notifications Settings section.

Others

For more general information about settings, see the Object Settings section.

Sensor Settings Overview

For information about sensor settings, see the following sections: