Semantic conventions for system metrics

Status: Development

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.

Warning Existing instrumentations and collector that are using v1.21.0 of this document (or prior):

• SHOULD NOT adopt any breaking changes from document until the system semantic conventions are marked stable. Conventions include, but are not limited to, attributes, metric names, and unit of measure.
• SHOULD introduce a control mechanism to allow users to opt-in to the new conventions once the migration plan is finalized.

General Metrics

Metric: system.uptime

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.uptime	Gauge	s	The time the system has been running [1]

[1]: Instrumentations SHOULD use a gauge with type double and measure uptime in seconds as a floating point number with the highest precision available. The actual accuracy would depend on the instrumentation and operating system.

Processor Metrics

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

Metric: system.cpu.physical.count

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.cpu.physical.count	UpDownCounter	{cpu}	Reports the number of actual physical processor cores on the hardware [1]

[1]: Calculated by multiplying the number of sockets by the number of cores per socket

Metric: system.cpu.logical.count

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.cpu.logical.count	UpDownCounter	{cpu}	Reports the number of logical (virtual) processor cores created by the operating system to manage multitasking [1]

[1]: Calculated by multiplying the number of sockets by the number of cores per socket, and then by the number of threads per core

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	Stability
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	Stability
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	Stability
buffers	buffers
cached	cached
free	free
used	used

Metric: system.memory.limit

This metric is opt-in.

Name	Instrument Type	Unit (UCUM)	Description	Stability
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.shared

This metric is opt-in.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.memory.shared	UpDownCounter	By	Shared memory used (mostly by tmpfs). [1]

[1]: Equivalent of shared from free command or Shmem from /proc/meminfo"

Metric: system.memory.utilization

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.memory.utilization	Gauge	1

Attribute	Type	Description	Examples	Requirement Level	Stability
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	Stability
buffers	buffers
cached	cached
free	free
used	used

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	Stability
system.paging.usage	UpDownCounter	By	Unix swap or windows pagefile usage

Attribute	Type	Description	Examples	Requirement Level	Stability
system.device	string	Unique identifier for the device responsible for managing paging operations.	/dev/dm-0	Recommended
system.paging.state	string	The memory paging state	free	Recommended

system.paging.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	Stability
free	free
used	used

Metric: system.paging.utilization

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.paging.utilization	Gauge	1

Attribute	Type	Description	Examples	Requirement Level	Stability
system.device	string	Unique identifier for the device responsible for managing paging operations.	/dev/dm-0	Recommended
system.paging.state	string	The memory paging state	free	Recommended

system.paging.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	Stability
free	free
used	used

Metric: system.paging.faults

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.paging.faults	Counter	{fault}

Attribute	Type	Description	Examples	Requirement Level	Stability
system.paging.type	string	The memory paging type	minor	Recommended

system.paging.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	Stability
major	major
minor	minor

Metric: system.paging.operations

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.paging.operations	Counter	{operation}

Attribute	Type	Description	Examples	Requirement Level	Stability
system.paging.direction	string	The paging access direction	in	Recommended
system.paging.type	string	The memory paging type	minor	Recommended

system.paging.direction 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	Stability
in	in
out	out

system.paging.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	Stability
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	Stability
system.disk.io	Counter	By

Attribute	Type	Description	Examples	Requirement Level	Stability
disk.io.direction	string	The disk IO operation direction.	read	Recommended
system.device	string	The device identifier	(identifier)	Recommended

disk.io.direction 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	Stability
read	read
write	write

Metric: system.disk.operations

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.disk.operations	Counter	{operation}

Attribute	Type	Description	Examples	Requirement Level	Stability
disk.io.direction	string	The disk IO operation direction.	read	Recommended
system.device	string	The device identifier	(identifier)	Recommended

disk.io.direction 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	Stability
read	read
write	write

Metric: system.disk.io_time

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
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:

• Linux: Field 13 from procfs-diskstats
• Windows: The complement of “Disk% Idle Time” performance counter: uptime * (100 - "Disk\% Idle Time") / 100

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

Metric: system.disk.operation_time

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
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	Stability
disk.io.direction	string	The disk IO operation direction.	read	Recommended
system.device	string	The device identifier	(identifier)	Recommended

disk.io.direction 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	Stability
read	read
write	write

Metric: system.disk.merged

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.disk.merged	Counter	{operation}

Attribute	Type	Description	Examples	Requirement Level	Stability
disk.io.direction	string	The disk IO operation direction.	read	Recommended
system.device	string	The device identifier	(identifier)	Recommended

disk.io.direction 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	Stability
read	read
write	write

Metric: system.disk.limit

This metric is opt-in.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.disk.limit	UpDownCounter	By	The total storage capacity of the disk

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

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	Stability
system.filesystem.usage	UpDownCounter	By	Reports a filesystem’s space usage across different states. [1]

[1]: The sum of all system.filesystem.usage values over the different system.filesystem.state attributes SHOULD equal the total storage capacity of the filesystem, that is system.filesystem.limit.

Attribute	Type	Description	Examples	Requirement Level	Stability
system.device	string	Identifier for the device where the filesystem resides.	/dev/sda; \network-drive	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 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	Stability
free	free
reserved	reserved
used	used

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	Stability
exfat	exfat
ext4	ext4
fat32	fat32
hfsplus	hfsplus
ntfs	ntfs
refs	refs

Metric: system.filesystem.utilization

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.filesystem.utilization	Gauge	1

Attribute	Type	Description	Examples	Requirement Level	Stability
system.device	string	Identifier for the device where the filesystem resides.	/dev/sda; \network-drive	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 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	Stability
free	free
reserved	reserved
used	used

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	Stability
exfat	exfat
ext4	ext4
fat32	fat32
hfsplus	hfsplus
ntfs	ntfs
refs	refs

Metric: system.filesystem.limit

This metric is opt-in.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.filesystem.limit	UpDownCounter	By	The total storage capacity of the filesystem

Attribute	Type	Description	Examples	Requirement Level	Stability
system.device	string	Identifier for the device where the filesystem resides.	/dev/sda; \network-drive	Recommended
system.filesystem.mode	string	The filesystem mode	rw, ro	Recommended
system.filesystem.mountpoint	string	The filesystem mount path	/mnt/data	Recommended
system.filesystem.type	string	The filesystem type	ext4	Recommended

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	Stability
exfat	exfat
ext4	ext4
fat32	fat32
hfsplus	hfsplus
ntfs	ntfs
refs	refs

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	Stability
system.network.dropped	Counter	{packet}	Count of packets that are dropped or discarded even though there was no error [1]

[1]: Measured as:

• Linux: the drop column in /proc/dev/net (source)
• Windows: InDiscards/OutDiscards from GetIfEntry2

Attribute	Type	Description	Examples	Requirement Level	Stability
network.interface.name	string	The network interface name.	lo; eth0	Recommended
network.io.direction	string	The network IO operation direction.	transmit	Recommended

network.io.direction 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	Stability
receive	receive
transmit	transmit

Metric: system.network.packets

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.network.packets	Counter	{packet}

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

network.io.direction 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	Stability
receive	receive
transmit	transmit

Metric: system.network.errors

This metric is recommended.

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

[1]: Measured as:

• Linux: the errs column in /proc/dev/net (source).
• Windows: InErrors/OutErrors from GetIfEntry2.

Attribute	Type	Description	Examples	Requirement Level	Stability
network.interface.name	string	The network interface name.	lo; eth0	Recommended
network.io.direction	string	The network IO operation direction.	transmit	Recommended

network.io.direction 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	Stability
receive	receive
transmit	transmit

Metric: system.network.io

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.network.io	Counter	By

Attribute	Type	Description	Examples	Requirement Level	Stability
network.interface.name	string	The network interface name.	lo; eth0	Recommended
network.io.direction	string	The network IO operation direction.	transmit	Recommended

network.io.direction 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	Stability
receive	receive
transmit	transmit

Metric: system.network.connections

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.network.connections	UpDownCounter	{connection}

Attribute	Type	Description	Examples	Requirement Level	Stability
network.connection.state	string	The state of network connection [1]	close_wait	Recommended
network.interface.name	string	The network interface name.	lo; eth0	Recommended
network.transport	string	OSI transport layer or inter-process communication method. [2]	tcp; udp	Recommended

[1] network.connection.state: Connection states are defined as part of the rfc9293

[2] network.transport: 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.connection.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	Stability
close_wait	close_wait
closed	closed
closing	closing
established	established
fin_wait_1	fin_wait_1
fin_wait_2	fin_wait_2
last_ack	last_ack
listen	listen
syn_received	syn_received
syn_sent	syn_sent
time_wait	time_wait

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	Stability
pipe	Named or anonymous pipe.
quic	QUIC
tcp	TCP
udp	UDP
unix	Unix domain socket

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.process.count

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.process.count	UpDownCounter	{process}	Total number of processes in each state

Attribute	Type	Description	Examples	Requirement Level	Stability
system.process.status	string	The process state, e.g., Linux Process State Codes	running	Recommended

system.process.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	Stability
defunct	defunct
running	running
sleeping	sleeping
stopped	stopped

Metric: system.process.created

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.process.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	Stability
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.

Metric: system.linux.memory.slab.usage

This metric is recommended.

Name	Instrument Type	Unit (UCUM)	Description	Stability
system.linux.memory.slab.usage	UpDownCounter	By	Reports the memory used by the Linux kernel for managing caches of frequently used objects. [1]

[1]: The sum over the reclaimable and unreclaimable state values in linux.memory.slab.usage SHOULD be equal to the total slab memory available on the system. Note that the total slab memory is not constant and may vary over time. See also the Slab allocator and Slab in /proc/meminfo.

Attribute	Type	Description	Examples	Requirement Level	Stability
linux.memory.slab.state	string	The Linux Slab memory state	reclaimable; unreclaimable	Recommended

linux.memory.slab.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	Stability
reclaimable	reclaimable
unreclaimable	unreclaimable