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Semantic Conventions for System Metrics

Status: Experimental

This document describes instruments and attributes for common system level metrics in OpenTelemetry. Consider the general metric semantic conventions when creating instruments not explicitly defined in the specification.

The system.* namespace SHOULD be exclusively used to report hosts' metrics. The system.* namespace SHOULD only be used when the metrics are collected from within the target system. (physical servers, virtual machines etc). Metrics collected from technology-specific, well-defined APIs (e.g. Kubelet's API or container runtimes) should be reported under their respective namespace (e.g. k8s., container.). Resource attributes related to a host, SHOULD be reported under the host.* namespace.

Processor Metrics

Description: System level processor metrics captured under the namespace system.cpu.

Metric: system.cpu.time

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.cpu.time Counter s Seconds each logical CPU spent on each mode
Attribute Type Description Examples Requirement Level
system.cpu.logical_number int The logical CPU number [0..n-1] 1 Recommended
system.cpu.state string The state of the CPU idle; interrupt Recommended

system.cpu.state has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
user user
system system
nice nice
idle idle
iowait iowait
interrupt interrupt
steal steal

Metric: system.cpu.utilization

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.cpu.utilization Gauge 1 Difference in system.cpu.time since the last measurement, divided by the elapsed time and number of logical CPUs
Attribute Type Description Examples Requirement Level
system.cpu.logical_number int The logical CPU number [0..n-1] 1 Recommended
system.cpu.state string The state of the CPU idle; interrupt Recommended

system.cpu.state has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
user user
system system
nice nice
idle idle
iowait iowait
interrupt interrupt
steal steal

Metric: system.cpu.physical.count

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.cpu.physical.count UpDownCounter {cpu} Reports the number of actual physical processor cores on the hardware

Metric: system.cpu.logical.count

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.cpu.logical.count UpDownCounter {cpu} Reports the number of logical (virtual) processor cores created by the operating system to manage multitasking

Metric: system.cpu.frequency

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.cpu.frequency Gauge {Hz} Reports the current frequency of the CPU in Hz
Attribute Type Description Examples Requirement Level
system.cpu.logical_number int The logical CPU number [0..n-1] 1 Recommended

Memory Metrics

Description: System level memory metrics capture under the namespace system.memory. This does not include paging/swap memory.

Metric: system.memory.usage

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.memory.usage UpDownCounter By Reports memory in use by state. [1]

[1]: The sum over all system.memory.state values SHOULD equal the total memory available on the system, that is system.memory.limit.

Attribute Type Description Examples Requirement Level
system.memory.state string The memory state free; cached Recommended

system.memory.state has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
used used
free free
shared shared
buffers buffers
cached cached

Metric: system.memory.limit

This metric is opt-in.

Name Instrument Type Unit (UCUM) Description
system.memory.limit UpDownCounter By Total memory available in the system. [1]

[1]: Its value SHOULD equal the sum of system.memory.state over all states.

Metric: system.memory.utilization

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.memory.utilization Gauge 1
Attribute Type Description Examples Requirement Level
system.memory.state string The memory state free; cached Recommended

system.memory.state has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
used used
free free
shared shared
buffers buffers
cached cached

Paging/Swap Metrics

Description: System level paging/swap memory metrics captured under the namespace system.paging.

Metric: system.paging.usage

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.paging.usage UpDownCounter By Unix swap or windows pagefile usage
Attribute Type Description Examples Requirement Level
system.paging.state string The memory paging state free Recommended

system.paging.state MUST be one of the following:

Value Description
used used
free free

Metric: system.paging.utilization

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.paging.utilization Gauge 1
Attribute Type Description Examples Requirement Level
system.paging.state string The memory paging state free Recommended

system.paging.state MUST be one of the following:

Value Description
used used
free free

Metric: system.paging.faults

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.paging.faults Counter {fault}
Attribute Type Description Examples Requirement Level
system.paging.type string The memory paging type minor Recommended

system.paging.type MUST be one of the following:

Value Description
major major
minor minor

Metric: system.paging.operations

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.paging.operations Counter {operation}
Attribute Type Description Examples Requirement Level
system.paging.direction string The paging access direction in Recommended
system.paging.type string The memory paging type minor Recommended

system.paging.direction MUST be one of the following:

Value Description
in in
out out

system.paging.type MUST be one of the following:

Value Description
major major
minor minor

Disk Controller Metrics

Description: System level disk performance metrics captured under the namespace system.disk.

Metric: system.disk.io

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.disk.io Counter By
Attribute Type Description Examples Requirement Level
disk.io.direction string The disk IO operation direction. read Recommended
system.device string The device identifier (identifier) Recommended

disk.io.direction MUST be one of the following:

Value Description
read read
write write

Metric: system.disk.operations

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.disk.operations Counter {operation}
Attribute Type Description Examples Requirement Level
disk.io.direction string The disk IO operation direction. read Recommended
system.device string The device identifier (identifier) Recommended

disk.io.direction MUST be one of the following:

Value Description
read read
write write

Metric: system.disk.io_time

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.disk.io_time Counter s Time disk spent activated [1]

[1]: The real elapsed time ("wall clock") used in the I/O path (time from operations running in parallel are not counted). Measured as:

Attribute Type Description Examples Requirement Level
system.device string The device identifier (identifier) Recommended

Metric: system.disk.operation_time

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.disk.operation_time Counter s Sum of the time each operation took to complete [1]

[1]: Because it is the sum of time each request took, parallel-issued requests each contribute to make the count grow. Measured as:

  • Linux: Fields 7 & 11 from procfs-diskstats
  • Windows: "Avg. Disk sec/Read" perf counter multiplied by "Disk Reads/sec" perf counter (similar for Writes)
Attribute Type Description Examples Requirement Level
disk.io.direction string The disk IO operation direction. read Recommended
system.device string The device identifier (identifier) Recommended

disk.io.direction MUST be one of the following:

Value Description
read read
write write

Metric: system.disk.merged

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.disk.merged Counter {operation}
Attribute Type Description Examples Requirement Level
disk.io.direction string The disk IO operation direction. read Recommended
system.device string The device identifier (identifier) Recommended

disk.io.direction MUST be one of the following:

Value Description
read read
write write

Filesystem Metrics

Description: System level filesystem metrics captured under the namespace system.filesystem.

Metric: system.filesystem.usage

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.filesystem.usage UpDownCounter By
Attribute Type Description Examples Requirement Level
system.device string The device identifier (identifier) Recommended
system.filesystem.mode string The filesystem mode rw, ro Recommended
system.filesystem.mountpoint string The filesystem mount path /mnt/data Recommended
system.filesystem.state string The filesystem state used Recommended
system.filesystem.type string The filesystem type ext4 Recommended

system.filesystem.state MUST be one of the following:

Value Description
used used
free free
reserved reserved

system.filesystem.type has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
fat32 fat32
exfat exfat
ntfs ntfs
refs refs
hfsplus hfsplus
ext4 ext4

Metric: system.filesystem.utilization

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.filesystem.utilization Gauge 1
Attribute Type Description Examples Requirement Level
system.device string The device identifier (identifier) Recommended
system.filesystem.mode string The filesystem mode rw, ro Recommended
system.filesystem.mountpoint string The filesystem mount path /mnt/data Recommended
system.filesystem.state string The filesystem state used Recommended
system.filesystem.type string The filesystem type ext4 Recommended

system.filesystem.state MUST be one of the following:

Value Description
used used
free free
reserved reserved

system.filesystem.type has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
fat32 fat32
exfat exfat
ntfs ntfs
refs refs
hfsplus hfsplus
ext4 ext4

Network Metrics

Description: System level network metrics captured under the namespace system.network.

Metric: system.network.dropped

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.network.dropped Counter {packet} Count of packets that are dropped or discarded even though there was no error [1]

[1]: Measured as:

Attribute Type Description Examples Requirement Level
network.io.direction string The network IO operation direction. transmit Recommended
system.device string The device identifier (identifier) Recommended

network.io.direction MUST be one of the following:

Value Description
transmit transmit
receive receive

Metric: system.network.packets

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.network.packets Counter {packet}
Attribute Type Description Examples Requirement Level
network.io.direction string The network IO operation direction. transmit Recommended
system.device string The device identifier (identifier) Recommended

network.io.direction MUST be one of the following:

Value Description
transmit transmit
receive receive

Metric: system.network.errors

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.network.errors Counter {error} Count of network errors detected [1]

[1]: Measured as:

Attribute Type Description Examples Requirement Level
network.io.direction string The network IO operation direction. transmit Recommended
system.device string The device identifier (identifier) Recommended

network.io.direction MUST be one of the following:

Value Description
transmit transmit
receive receive

Metric: system.network.io

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.network.io Counter By
Attribute Type Description Examples Requirement Level
network.io.direction string The network IO operation direction. transmit Recommended
system.device string The device identifier (identifier) Recommended

network.io.direction MUST be one of the following:

Value Description
transmit transmit
receive receive

Metric: system.network.connections

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.network.connections UpDownCounter {connection}
Attribute Type Description Examples Requirement Level
network.transport string OSI transport layer or inter-process communication method. [1] tcp; udp Recommended
system.device string The device identifier (identifier) Recommended
system.network.state string A stateless protocol MUST NOT set this attribute close_wait Recommended

[1]: The value SHOULD be normalized to lowercase.

Consider always setting the transport when setting a port number, since a port number is ambiguous without knowing the transport. For example different processes could be listening on TCP port 12345 and UDP port 12345.

network.transport has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
tcp TCP
udp UDP
pipe Named or anonymous pipe.
unix Unix domain socket

system.network.state MUST be one of the following:

Value Description
close close
close_wait close_wait
closing closing
delete delete
established established
fin_wait_1 fin_wait_1
fin_wait_2 fin_wait_2
last_ack last_ack
listen listen
syn_recv syn_recv
syn_sent syn_sent
time_wait time_wait

Aggregate System Process Metrics

Description: System level aggregate process metrics captured under the namespace system.process. For metrics at the individual process level, see process metrics.

Metric: system.processes.count

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.processes.count UpDownCounter {process} Total number of processes in each state
Attribute Type Description Examples Requirement Level
system.processes.status string The process state, e.g., Linux Process State Codes running Recommended

system.processes.status has the following list of well-known values. If one of them applies, then the respective value MUST be used, otherwise a custom value MAY be used.

Value Description
running running
sleeping sleeping
stopped stopped
defunct defunct

Metric: system.processes.created

This metric is recommended.

Name Instrument Type Unit (UCUM) Description
system.processes.created Counter {process} Total number of processes created over uptime of the host

system.{os}. - OS Specific System Metrics

Instrument names for system level metrics that have different and conflicting meaning across multiple OSes should be prefixed with system.{os}. and follow the hierarchies listed above for different entities like CPU, memory, and network.

For example, UNIX load average over a given interval is not well standardized and its value across different UNIX like OSes may vary despite being under similar load:

Without getting into the vagaries of every Unix-like operating system in existence, the load average more or less represents the average number of processes that are in the running (using the CPU) or runnable (waiting for the CPU) states. One notable exception exists: Linux includes processes in uninterruptible sleep states, typically waiting for some I/O activity to complete. This can markedly increase the load average on Linux systems.

(source of quote, linux source code)

An instrument for load average over 1 minute on Linux could be named system.linux.cpu.load_1m, reusing the cpu name proposed above and having an {os} prefix to split this metric across OSes.

Metric: system.linux.memory.available

Name Instrument Type Unit (UCUM) Description
system.linux.memory.available UpDownCounter By An estimate of how much memory is available for starting new applications, without causing swapping [1]

[1]: This is an alternative to system.memory.usage metric with state=free. Linux starting from 3.14 exports "available" memory. It takes "free" memory as a baseline, and then factors in kernel-specific values. This is supposed to be more accurate than just "free" memory. For reference, see the calculations here. See also MemAvailable in /proc/meminfo.