Monitor your old Linux devices

Watching Grampa

© Lead Image © lightwise,

© Lead Image © lightwise,

Article from Issue 236/2020

Create monitoring dashboards with SSH, command-line tools, and Node-RED.

Some excellent technologies and packages are available for monitoring computer hardware. For medium to large systems, the Simple Network Monitoring Protocol (SNMP) approach is usually the preferred solution. However if you have a smaller system with older or low-end servers, some excellent lightweight command-line monitoring utilities can be used instead.

These command-line utilities can be run remotely over Secure Shell (SSH) and the output parsed to return only the key data values, which can then be displayed graphically in a Node-RED web dashboard (Figure 1). In this article, I demonstrate examples that use the iostat utility [1] to monitor CPU utilization and the lm-sensors package [2] and hddtemp utility [3] to monitor temperatures on dashboards.

Figure 1: Sending commands over SSH to a Node-RED dashboard.

CPU Utilitization

The iostat utility is part of the sysstat package and is probably already loaded on your older systems. If not, it can be installed by:

sudo apt-get install sysstat

The iostat utility generates a report for CPU, device, and filesystem utilization. The output from this command can be parsed with some Bash statement to return just the key value of interest.

Listing 1 shows an example of how to grab the fourth line of output with sed (line 7) and parse the %idle value at the end of the line with awk (line 11) to get the sixth string item (line 12).

Listing 1

Parsing iostat Output

01 pete@lubuntu: ~$ iostat -c
02 Linux 4.15.0-72-generic (lubuntu)   2020-05-02  i686    (4 CPU)
03 avg-cpu: %user  %nice %system %iowait  %steal  %idle
04           8.37   0.03  3.33      1.29          86.97
06 # Get 4th line of the iostat output
07 pete@lubuntu : ~$ iostat -c | sed -n 4p
08           8.36   0.03  3.33      1.29  0.00    86.99
10 # Now get the 6th string
11 pete@lubuntu : ~$ iostat -c | sed -n 4p | awk '{print $6}'
12 87.02

Chip-Based Temperature

To install the hardware sensors in the lm-sensors package, enter:

sudo apt-get install lm-sensors

After the package is installed, the software needs to detect which sensors are available for monitoring:

sudo sensors-detect

This step presents a number of prompts about which sensors need to be scanned. Once the scan step is complete, the sensors command returns results for all the hardware it found.

Specific sensors can be shown with the command:

sensors <chip name>

Listing 2 shows an example of the sensors command being used to look at the dell_smm-virtual-0 chipset. The CPU temperature value (in line 5) can be parsed with grep (line 10), which looks for the line that contains "CPU'; then, awk (line 14) outputs the second item of the string (line 15).

Listing 2

Parsing Sensor Data

01 pete@lubuntu: ~$ sensors dell_smm-virtual-0
02 dell_smm-virtual-0
03 Adapter: Virtual device
04 Processor Fan: 2687 RPM
05 CPU:            +40.0°C
06 Ambient:        +34.0°C
07 SODIMM:         +33.0°C
09 # Get the CPU temperature
10 pete@lubuntu: ~$ sensors dell_smm-virtual-0 | grep 'CPU'
11 CPU:            +40.0°C
13 # Return just the temperature
14 pete@lubuntu: ~$ sensors dell_smm-virtual-0 | grep 'CPU' | awk '{print $2}'
15 +40.0°C

Hard Drive Temperature

The hddtemp hard drive temperature monitoring package is installed with:

sudo apt-get install hddtemp

By default, hddtemp requires superuser rights, so to make the results available to non-superusers use:

sudo chmod u+s /usr/sbin/hddtemp

To see the temperature of a hard drive, enter its device name. For example, to see /dev/sda, use:

$ hddtemp /dev/sda
/dev/sda: WDC WD3200BPVT-75JJ5T0: 34°C

Again, you can use the awk command to parse the output to get just the temperature. For this example, the temperature is the fourth item of the string, so the command displays that value as shown here:

$ hddtemp /dev/sda | awk '{print $4}'

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