The management subsystem allows remote management of Zephyr-enabled devices. The following management operations are available:

  • Image management

  • File System management

  • OS management

  • Shell management

  • Statistic management

  • Zephyr-basic management

over the following transports:

  • BLE (Bluetooth Low Energy)

  • Serial (UART)

  • UDP over IP

The management subsystem is based on the Simple Management Protocol (SMP) provided by MCUmgr, an open source project that provides a management subsystem that is portable across multiple real-time operating systems.

The management subsystem is located in subsys/mgmt/ inside of the Zephyr tree.

Additionally, there is a sample that provides management functionality over BLE and serial.

Command-line Tool

MCUmgr provides a command-line tool, mcumgr, for managing remote devices. The tool is written in the Go programming language.


This tool is provided for evaluation use only and is not recommended for use in a production environment. It has known issues and will not respect the MCUmgr protocol properly e.g. when an error is received, instead of aborting will, in some circumstances, sit in an endless loop of sending the same command over and over again. A universal replacement for this tool is currently in development and once released, support for the go tool will be dropped entirely.

To install the tool:

go get

Configuring the transport

There are two command-line options that are responsible for setting and configuring the transport layer to use when communicating with managed device:

  • --conntype is used to choose the transport used, and

  • --connstring is used to pass a comma separated list of options in the key=value format, where each valid key depends on the particular conntype.

Valid transports for --conntype are serial, ble and udp. Each transport expects a different set of key/value options:

--connstring accepts the following key values:


the device name for the OS mcumgr is running on (eg, /dev/ttyUSB0, /dev/tty.usbserial, COM1, etc).


the communication speed; must match the baudrate of the server.


aka Maximum Transmission Unit, the maximum protocol packet size.

Saving the connection config

The transport configuration can be managed with the conn sub-command and later used with --conn (or -c) parameter to skip typing both --conntype and --connstring. For example a new config for a serial device that would require typing mcumgr --conntype serial --connstring dev=/dev/ttyACM0,baud=115200,mtu=512 can be saved with:

mcumgr conn add acm0 type="serial" connstring="dev=/dev/ttyACM0,baud=115200,mtu=512"

Accessing this port can now be done with:

mcumgr -c acm0

General options

Some options work for every mcumgr command and might be helpful to debug and fix issues with the communication, among them the following deserve special mention:

-l <log-level>

Configures the log level, which can be one of critical, error, warn, info or debug, from less to most verbose. When there are communication issues, -lDEBUG might be useful to dump the packets for later inspection.

-t <timeout>

Changes the timeout waiting for a response from the default of 10s to a given value. Some commands might take a long time of processing, eg, the erase before an image upload, and might need incrementing the timeout to a larger value.

-r <tries>

Changes the number of retries on timeout from the default of 1 to a given value.

List of Commands

Not all commands defined by mcumgr (and SMP protocol) are currently supported on Zephyr. The ones that are supported are described in the following table:


Running mcumgr with no parameters, or -h will display the list of commands.




Send data to a device and display the echoed back data. This command is part of the OS group, which must be enabled by setting CONFIG_MCUMGR_GRP_OS. The echo command itself can be enabled by setting CONFIG_MCUMGR_GRP_OS_ECHO.


Access files on a device. More info in Filesystem Management.


Manage images on a device. More info in Image Management.


Perform a soft reset of a device. This command is part of the OS group, which must be enabled by setting CONFIG_MCUMGR_GRP_OS. The reset command itself is always enabled and the time taken for a reset to happen can be set with CONFIG_MCUMGR_GRP_OS_RESET_MS (in ms).


Execute a command in the remote shell. This option is disabled by default and can be enabled with CONFIG_MCUMGR_GRP_SHELL = y. To know more about the shell in Zephyr check Shell.


Read statistics from a device. More info in Statistics Management.


Read task statistics from a device. This command is part of the OS group, which must be enabled by setting CONFIG_MCUMGR_GRP_OS. The taskstat command itself can be enabled by setting CONFIG_MCUMGR_GRP_OS_TASKSTAT. CONFIG_THREAD_MONITOR also needs to be enabled otherwise a -8 (MGMT_ERR_ENOTSUP) will be returned.


taskstat has a few options that might require tweaking. The CONFIG_THREAD_NAME must be set to display the task names, otherwise the priority is displayed. Since the taskstat packets are large, they might need increasing the CONFIG_MCUMGR_TRANSPORT_NETBUF_SIZE option.


To display the correct stack size in the taskstat command, the CONFIG_THREAD_STACK_INFO option must be set. To display the correct stack usage in the taskstat command, both CONFIG_THREAD_STACK_INFO and CONFIG_INIT_STACKS options must be set.

Image Management

The image management provided by mcumgr is based on the image format defined by MCUboot. For more details on the internals see MCUboot design and Signing Binaries.

To list available images in a device:

mcumgr <connection-options> image list

This should result in an output similar to this:

$ mcumgr -c acm0 image list
  image=0 slot=0
    version: 1.0.0
    bootable: true
    flags: active confirmed
    hash: 86dca73a3439112b310b5e033d811ec2df728d2264265f2046fced5a9ed00cc7
Split status: N/A (0)

Where image is the number of the image pair in a multi-image system, and slot is the number of the slot where the image is stored, 0 for primary and 1 for secondary. This image being active and confirmed means it will run again on next reset. Also relevant is the hash, which is used by other commands to refer to this specific image when performing operations.

An image can be manually erased using:

mcumgr <connection-options> image erase

The behavior of erase is defined by the server (MCUmgr in the device). The current implementation is limited to erasing the image in the secondary partition.

To upload a new image:

mcumgr <connection-options> image upload [-n] [-e] [-u] [-w] <signed-bin>
  • -n: This option allows uploading a new image to a specific set of images in a multi-image system, and is currently only supported by MCUboot when the CONFIG_MCUBOOT_SERIAL option is enabled.

  • -e: This option avoids performing a full erase of the partition before starting a new upload.


The -e option should always be passed in because the upload command already checks if an erase is required, respecting the CONFIG_IMG_ERASE_PROGRESSIVELY setting.


If the upload command times out while waiting for a response from the device, -t might be used to increase the wait time to something larger than the default of 10s. See general_options.


mcumgr does not understand .hex files, when uploading a new image always use the .bin file.

  • -u: This option allows upgrading only to newer image version.

  • -w: This option allows setting the maximum size for the window of outstanding chunks in transit. It is set to 5 by default.


    If the option is set to a value lower than the default one, for example -w 1, less chunks are transmitted on the window, resulting in lower risk of errors. Conversely, setting a value higher than 5 increases risk of errors and may impact performance.

After an image upload is finished, a new image list would now have an output like this:

$ mcumgr -c acm0 image upload -e build/zephyr/zephyr.signed.bin
  35.69 KiB / 92.92 KiB [==========>---------------]  38.41% 2.97 KiB/s 00m19

Now listing the images again:

$ mcumgr -c acm0 image list
 image=0 slot=0
  version: 1.0.0
  bootable: true
  flags: active confirmed
  hash: 86dca73a3439112b310b5e033d811ec2df728d2264265f2046fced5a9ed00cc7
 image=0 slot=1
  version: 1.1.0
  bootable: true
  hash: e8cf0dcef3ec8addee07e8c4d5dc89e64ba3fae46a2c5267fc4efbea4ca0e9f4
Split status: N/A (0)

To test a new upgrade image the test command is used:

mcumgr <connection-options> image test <hash>

This command should mark a test upgrade, which means that after the next reboot the bootloader will execute the upgrade and jump into the new image. If no other image operations are executed on the newly running image, it will revert back to the image that was previously running on the device on the subsequent reset. When a test is requested, flags will be updated with pending to inform that a new image will be run after a reset:

$ mcumgr -c acm0 image test e8cf0dcef3ec8addee07e8c4d5dc89e64ba3fae46a2c5267fc4efbea4ca0e9f4
 image=0 slot=0
  version: 1.0.0
  bootable: true
  flags: active confirmed
  hash: 86dca73a3439112b310b5e033d811ec2df728d2264265f2046fced5a9ed00cc7
 image=0 slot=1
  version: 1.1.0
  bootable: true
  flags: pending
  hash: e8cf0dcef3ec8addee07e8c4d5dc89e64ba3fae46a2c5267fc4efbea4ca0e9f4
Split status: N/A (0)

After a reset the output with change to:

$ mcumgr -c acm0 image list
 image=0 slot=0
  version: 1.1.0
  bootable: true
  flags: active
  hash: e8cf0dcef3ec8addee07e8c4d5dc89e64ba3fae46a2c5267fc4efbea4ca0e9f4
 image=0 slot=1
  version: 1.0.0
  bootable: true
  flags: confirmed
  hash: 86dca73a3439112b310b5e033d811ec2df728d2264265f2046fced5a9ed00cc7
Split status: N/A (0)


It’s important to mention that an upgrade only ever happens if the image is valid. The first thing MCUboot does when an upgrade is requested is to validate the image, using the SHA-256 and/or the signature (depending on the configuration). So before uploading an image, one way to be sure it is valid is to run imgtool verify -k <your-signature-key> <your-image>, where -k <your-signature-key can be skipped if no signature validation was enabled.

The confirmed flag in the secondary slot tells that after the next reset a revert upgrade will be performed to switch back to the original layout.

The confirm command used to confirm that an image is OK and no revert should happen (empty hash required) is:

mcumgr <connection-options> image confirm ""

The confirm command can also be run passing in a hash so that instead of doing a test/revert procedure, the image in the secondary partition is directly upgraded to, eg:

mcumgr <connection-options> image confirm <hash>


The whole test/revert cycle does not need to be done using only the mcumgr command-line tool. A better alternative is to perform a test and allow the new running image to self-confirm after any checks by calling boot_write_img_confirmed().


Building with CONFIG_MCUMGR_GRP_IMG_VERBOSE_ERR enables better error messages when failures happen (but increases the application size).

Statistics Management

Statistics are used for troubleshooting, maintenance, and usage monitoring; it consists basically of user-defined counters which are tightly connected to mcumgr and can be used to track any information for easy retrieval. The available sub-commands are:

mcumgr <connection-options> stat list
mcumgr <connection-options> stat <section-name>

Statistics are organized in sections (also called groups), and each section can be individually queried. Defining new statistics sections is done by using macros available under zephyr/stats/stats.h. Each section consists of multiple variables (or counters), all with the same size (16, 32 or 64 bits).

To create a new section my_stats:


STATS_SECT_DECL(my_stats) my_stats;

Each entry can be declared with STATS_SECT_ENTRY (or the equivalent STATS_SECT_ENTRY32), STATS_SECT_ENTRY16 or STATS_SECT_ENTRY64. All statistics in a section must be declared with the same size.

The statistics counters can either have names or not, depending on the setting of the CONFIG_STATS_NAMES option. Using names requires an extra declaration step:

  STATS_NAME(my_stats, my_stat_counter1)
  STATS_NAME(my_stats, my_stat_counter2)
  STATS_NAME(my_stats, my_stat_counter3)


Disabling CONFIG_STATS_NAMES will free resources. When this option is disabled the STATS_NAME* macros output nothing, so adding them in the code does not increase the binary size.


CONFIG_MCUMGR_GRP_STAT_MAX_NAME_LEN sets the maximum length of a section name that can can be accepted as parameter for showing the section data, and might require tweaking for long section names.

The final steps to use a statistics section is to initialize and register it:

rc = STATS_INIT_AND_REG(my_stats, STATS_SIZE_32, "my_stats");
assert (rc == 0);

In the running code a statistics counter can be incremented by 1 using STATS_INC, by N using STATS_INCN or reset with STATS_CLEAR.

Let’s suppose we want to increment those counters by 1, 2 and 3 every second. To get a list of stats:

$ mcumgr --conn acm0 stat list
stat groups:

To get the current value of the counters in my_stats:

$ mcumgr --conn acm0 stat my_stats
stat group: my_stats
      13 my_stat_counter1
      26 my_stat_counter2
      39 my_stat_counter3

$ mcumgr --conn acm0 stat my_stats
stat group: my_stats
      16 my_stat_counter1
      32 my_stat_counter2
      48 my_stat_counter3

When CONFIG_STATS_NAMES is disabled the output will look like this:

$ mcumgr --conn acm0 stat my_stats
stat group: my_stats
       8 s0
      16 s1
      24 s2

Filesystem Management

The filesystem module is disabled by default due to security concerns: because of a lack of access control by default, every file in the FS will be accessible, including secrets, etc. To enable it CONFIG_MCUMGR_GRP_FS must be set (y). Once enabled the following sub-commands can be used:

mcumgr <connection-options> fs download <remote-file> <local-file>
mcumgr <connection-options> fs upload <local-file> <remote-file>

Using the fs command, requires CONFIG_FILE_SYSTEM to be enabled, and that some particular filesystem is enabled and properly mounted by the running application, eg for littlefs this would mean enabling CONFIG_FILE_SYSTEM_LITTLEFS, defining a storage partition Flash map and mounting the filesystem in the startup (fs_mount()).

Uploading a new file to a littlefs storage, mounted under /lfs, can be done with:

$ mcumgr -c acm0 fs upload foo.txt /lfs/foo.txt

Where 25 is the size of the file.

For downloading a file, let’s first use the fs command (CONFIG_FILE_SYSTEM_SHELL must be enabled) in a remote shell to create a new file:

uart:~$ fs write /lfs/bar.txt 41 42 43 44 31 32 33 34 0a
uart:~$ fs read /lfs/bar.txt
File size: 9
00000000  41 42 43 44 31 32 33 34 0A                       ABCD1234.

Now it can be downloaded using:

$ mcumgr -c acm0 fs download /lfs/bar.txt bar.txt
$ cat bar.txt

Where 0 is the return code, and 9 is the size of the file.


The commands might exhaust the system workqueue, if its size is not large enough, so increasing CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE might be required for correct behavior.

The size of the stack allocated buffer used to store the blocks, while transferring a file can be adjusted with CONFIG_MCUMGR_GRP_FS_DL_CHUNK_SIZE; this allows saving RAM resources.


CONFIG_MCUMGR_GRP_FS_PATH_LEN sets the maximum PATH accepted for a file name. It might require tweaking for longer file names.


To add security to the filesystem management group, callbacks for MCUmgr hooks can be registered by a user application when the upload/download functions are ran which allows the application to control if access to a file is allowed or denied. See the MCUmgr Callbacks section for details.

Bootloader Integration

The Device Firmware Upgrade subsystem integrates the management subsystem with the bootloader, providing the ability to send and upgrade a Zephyr image to a device.

Currently only the MCUboot bootloader is supported. See MCUboot for more information.

Discord channel

Developers welcome!

API Reference

group mcumgr_mgmt_api

MCUmgr mgmt API.



Used at end of MCUmgr handlers to return an error if the message size limit was reached, or OK if it was not.



typedef void *(*mgmt_alloc_rsp_fn)(const void *src_buf, void *arg)

Allocates a buffer suitable for holding a response.

If a source buf is provided, its user data is copied into the new buffer.

Param src_buf:

An optional source buffer to copy user data from.

Param arg:

Optional streamer argument.


Newly-allocated buffer on success NULL on failure.

typedef void (*mgmt_reset_buf_fn)(void *buf, void *arg)

Resets a buffer to a length of 0.

The buffer’s user data remains, but its payload is cleared.

Param buf:

The buffer to reset.

Param arg:

Optional streamer argument.

typedef int (*mgmt_handler_fn)(struct smp_streamer *ctxt)

Processes a request and writes the corresponding response.

A separate handler is required for each supported op-ID pair.

Param ctxt:

The mcumgr context to use.


0 if a response was successfully encoded, mcumgr_err_t code on failure.


enum mcumgr_op_t

Opcodes; encoded in first byte of header.


enumerator MGMT_OP_READ = 0

Read op-code.

enumerator MGMT_OP_READ_RSP

Read response op-code.

enumerator MGMT_OP_WRITE

Write op-code.

enumerator MGMT_OP_WRITE_RSP

Write response op-code.

enum mcumgr_group_t

MCUmgr groups.

The first 64 groups are reserved for system level mcumgr commands. Per-user commands are then defined after group 64.


enumerator MGMT_GROUP_ID_OS = 0

OS (operating system) group.


Image management group, used for uploading firmware images.


Statistic management group, used for retieving statistics.


Settings management (config) group, used for reading/writing settings.

enumerator MGMT_GROUP_ID_LOG

Log management group (unused)


Crash group (unused)


Split image management group (unused)

enumerator MGMT_GROUP_ID_RUN

Run group (unused)

enumerator MGMT_GROUP_ID_FS

FS (file system) group, used for performing file IO operations.


Shell management group, used for executing shell commands.

enumerator MGMT_GROUP_ID_PERUSER = 64

User groups defined from 64 onwards.


Zephyr-specific groups decrease from PERUSER to avoid collision with upstream and user-defined groups.

Zephyr-specific: Basic group

enum mcumgr_err_t

MCUmgr error codes.


enumerator MGMT_ERR_EOK = 0

No error (success).


Unknown error.

enumerator MGMT_ERR_ENOMEM

Insufficient memory (likely not enough space for CBOR object).

enumerator MGMT_ERR_EINVAL

Error in input value.


Operation timed out.

enumerator MGMT_ERR_ENOENT

No such file/entry.


Current state disallows command.


Response too large.


Command not supported.



enumerator MGMT_ERR_EBUSY

Command blocked by processing of other command.


Access to specific function, command or resource denied.


Requested SMP MCUmgr protocol version is not supported (too old)


Requested SMP MCUmgr protocol version is not supported (too new)

enumerator MGMT_ERR_EPERUSER = 256

User errors defined from 256 onwards.


void mgmt_register_group(struct mgmt_group *group)

Registers a full command group.

  • group – The group to register.

void mgmt_unregister_group(struct mgmt_group *group)

Unregisters a full command group.

  • group – The group to register.

const struct mgmt_handler *mgmt_find_handler(uint16_t group_id, uint16_t command_id)

Finds a registered command handler.

  • group_id – The group of the command to find.

  • command_id – The ID of the command to find.


The requested command handler on success; NULL on failure.

struct mgmt_handler
#include <mgmt.h>

Read handler and write handler for a single command ID.

struct mgmt_group
#include <mgmt.h>

A collection of handlers for an entire command group.

Public Members

sys_snode_t node

Entry list node.

const struct mgmt_handler *mg_handlers

Array of handlers; one entry per command ID.

uint16_t mg_group_id

The numeric ID of this group.