SWUpdate: API for external programs


SWUpdate contains an integrated web-server to allow remote updating. However, which protocols are involved during an update is project specific and differs significantly. Some projects can decide to use FTP to load an image from an external server, or using even a proprietary protocol. The integrated web-server uses this interface.

SWUpdate has a simple interface to let external programs to communicate with the installer. Clients can start an upgrade and stream an image to the installer, querying then for the status and the final result. The API is at the moment very simple, but it can easy be extended in the future if new use cases will arise.

API Description

The communication runs via Unix Domain Socket (UDS). The socket path is determined by

  • the CONFIG_SOCKET_CTRL_PATH compile-time configuration,

  • $RUNTIME_DIRECTORY/sockinstctrl if $RUNTIME_DIRECTORY is set,

  • $TMPDIR/sockinstctrl if $TMPDIR is set, or

  • /tmp/sockinstctrl,

in this order, and taken over from systemd or created by SWUpdate. This socket should, however, not be used directly but instead by the Client Library explained below.

The exchanged packets are described in network_ipc.h

typedef struct {
        int magic;
        int type;
        msgdata data;
} ipc_message;

Where the fields have the meaning:

  • magic : a magic number as simple proof of the packet


  • msgdata : a buffer used by the client to send the image or by SWUpdate to report back notifications and status.

The client sends a REQ_INSTALL packet and waits for an answer. SWUpdate sends back ACK or NACK, if for example an update is already in progress.

After the ACK, the client sends the whole image as a stream. SWUpdate expects that all bytes after the ACK are part of the image to be installed. SWUpdate recognizes the size of the image from the CPIO header. Any error lets SWUpdate to leave the update state, and further packets will be ignored until a new REQ_INSTALL will be received.


It is recommended to use the client library to communicate with SWUpdate. On the lower level with direct socket communication, it cannot be guaranteed that the structures will remain compatible in the future. The client library was affected by this issue, too, and it is changed to accept an opaque interface that will survive API changes. Compatibility layers could be added on-demand in the future due to API changes.

Client Library

Functions to start an update

A library simplifies the usage of the IPC making available a way to start asynchronously an update.

The library consists of one function and several call-backs.

int swupdate_async_start(writedata wr_func, getstatus status_func,
        terminated end_func, void *req, ssize_t size)
typedef int (*writedata)(char **buf, int *size);
typedef int (*getstatus)(ipc_message *msg);
typedef int (*terminated)(RECOVERY_STATUS status);

swupdate_async_start creates a new thread and start the communication with SWUpdate, triggering for a new update. The wr_func is called to get the image to be installed. It is responsibility of the callback to provide the buffer and the size of the chunk of data.

The getstatus call-back is called after the stream was downloaded to check how upgrade is going on. It can be omitted if only the result is required.

The terminated call-back is called when SWUpdate has finished with the result of the upgrade.

Example about using this library is in the examples/client directory.

The req structure is casted to void to ensure API compatibility. Am user should instantiate it as struct swupdate_request. This contains fields that can control the update process:

struct swupdate_request {
        unsigned int apiversion;
        sourcetype source;
        int dry_run;
        size_t len;
        char info[512];
        char software_set[256];
        char running_mode[256];

A user should first call swupdate_prepare_req()

void swupdate_prepare_req(struct swupdate_request *req);

This fills the request structure with default values. After that, the user can fill the other fields as:


  • dry_run : one of RUN_DEFAULT (set from command line), RUN_DRYRUN, RUN_INSTALL.

  • info, len : a variable length data that can be forwarded to the progress interface. The installer in SWUpdate does not evaluate it.

  • software_set and running_mode : this allows one to set the selection for the update, it should be accepted by swupdate (-q, –accepted-select option when swupdate is launched).

Functions to set AES keys

The key for decryption can be set with command line parameter (see -K), but it is possible to set it via IPC. In this way, each update could have a different key.

int swupdate_set_aes(char *key, char *ivt)

The key is for AES-256. The length for key and ivt are then defined by the algorithm amd they are passed as ASCII string, so the length must be 64 bytes for key and 32 bytes for IVT.

Functions to control SWUpdate

int ipc_send_cmd(ipc_message *msg);

ipc_send_cmd is used to send a command to a SWUpdate subprocess (as suricatta). The function is synchron, that means it clocks until the subprocess has answered with ACK or NACK. This function sets type to SWUPDATE_SUBPROCESS. The caller must then set the other fields in message according to the destination. The msgdata field is a structure as:

struct {
   sourcetype source; /* Who triggered the update */
   int     cmd;       /* Optional encoded command */
   int     timeout;     /* timeout in seconds if an aswer is expected */
   unsigned int len;    /* Len of data valid in buf */
   char    buf[2048];   /*
                         * Buffer that each source can fill
                         * with additional information

The caller fills source with the subprocess that acceps the command. Values of cmd are in network_ipc.h.

Messages for suricatta

suricatta accepts messages in JSON format. The message must be formatted in the buf field of the message data.

Setting the polling time

{ "polling" : <value in seconds, range 0..X>}

Setting it to 0 has the special meaning that the polling time is retrieved from the Backend (if this is supported by the server).

Enable / disable Suricatta daemon

{ "enable" : true }
{ "enable" : false }

Set custom device attributes for Suricatta (for Hawkbit implementation)

{ "identify" : [
        "name"  : "customizableAttributeOne",
        "value" : "valueOne"
        "name"  : "customizableAttributeTwo",
        "value" : "valueTwo"

New attributes can be added at runtime, and existing attributes can be modified in the same way. Changes will be reflected on the server in the next poll iteration.

Trigger a check on the server

This is useful in case the device is mostly offline, and when it is online, it should check immediately if an update exists and run it. In fact, after enabling the suricatta daemon, the update follows the usual states, and the daemon waits for a polling time before loading the new software. This command forces an update (if available) without changing the polling time.

{ "trigger" : true }

Activate an already installed Software

After a software was installed, the new software boots and if everything runs fine, an acknowledge should be sent to the hawkBit server. If this feature is used, for example to let the end user decide if the new software is accepted, the parameters used by the installation should be stored during the update process.

{ "id" : <action id>,
  "finished" : "success", "failure", "none",
  "execution" : ["closed", "proceeding", canceled", "rejected", "resumed"]
  "details" : [ ]

Get hawkBit Server Status

To provide the hawkBit server status to other processes, it can be requested by sending an empty message with message type CMD_GET_STATUS.

The response is a JSON object containing the hawkBit server status <status>. <status> is a number representing the value of the channel_op_res_t enum from channel_op_res.h. As the hawkBit server is polled, its status can only be updated when it has been polled. Therefore the response also contains the time <time>, when the hawkBit server has been polled the last time. It is provided as ISO 8601 date and time string. (2021-10-14T13:42:37.000+00)

{ "server" : {
                "status" : <status>
                "time" : <time>

An example application can be found under tools/swupdate-gethawkbitstatus.c

API to the integrated Webserver

The integrated Webserver provides REST resources to push a SWU package and to get inform about the update process. This API is based on HTTP standards. There are to kind of interface:

  • Install API to push a SWU and to restart the device after update.

  • A WebSocket interface to send the status of the update process.

Install API

POST /upload

This initiates an update: the initiator sends the request and start to stream the SWU in the same way as described in API Description. The POST /upload request contains:

  • the SWU file in its body

  • the following header field

    Content-Type: multipart/form-data; boundary...

For example to stream the SWU file and start the update procedure using curl:

curl -F file=@update_file.swu http://host:8080/upload

Restart API

POST /restart

If configured (see post update command), this request will restart the device.

WebSocket API

The integrated Webserver exposes a WebSocket API. The WebSocket protocol specification defines ws (WebSocket) and wss (WebSocket Secure) as two new uniform resource identifier (URI) schemes that are used for unencrypted and encrypted connections, respectively and both of them are supported by SWUpdate. A WebSocket provides full-duplex communication but it is used in SWUpdate to send events to an external host after each change in the update process. The Webserver sends JSON formatted responses as results of internal events.

The response contains the field type, that defines which event is sent.

Event Type


Description of event


Event sent when SWUpdate’s internal state changes


Event to inform from which interface an update is received


Event with custom message to be passed to an external process


Event that contains the error message in case of error


Event to inform about the running update

Status Change Event

This event is sent when the internal SWUpdate status change. Following status are supported:



        "type": "status",
        "status": "SUCCESS"

Source Event

This event informs from which interface a SWU is loaded.

        "type": "source",
        "source": "WEBSERVER"

The field source can have one of the following values:


Info Event

This event forwards all internal logs sent with level=INFO.

        "type": "info",
        "source": < text message >

Message Event

This event contains the error message in case of failure.

Fields for message event






“3” in case of error, “6” as info


Message associated to the event


        "type": "message",
        "level": "3",
        "text" : "[ERROR] : SWUPDATE failed [0] ERROR core/cpio_utils.c : ",

Step event

This event contains which is the current step running and which percentage of this step is currently installed.

Fields for step event




total number of steps N for this update


running step in range [1..N]


filename of artefact to be installed


percentage of the running step


        "type": "step",
        "number": "7",
        "step": "2",
        "name": "rootfs.ext4.gz",
        "percent": "18"