We can query the value of total disk space usage on GNU/Linux using snmpget tools. The tools can be read SNMP v1 or v2c. On SNMP v1, disk space usage OID defined on UCD-SNMP-MIB with value : 1.3.6.1.4.1.2021.9.1.5. On SNMP v2c, it defined with OID : UCD-SNMP-MIB::dskTotal

To read the total disk space usage using SNMP v1, you can execute command below :

snmpget -v1 -Cf -c heaven localhost 1.3.6.1.4.1.2021.9.1.5.1

To read the total disk space usage using SNMP v1, you can execute command below :

snmpget -v2c -Cf -c heaven localhost UCD-SNMP-MIB::dskTotal.1

Note that : heaven is a community name you set on snmpd.conf