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File system

Mongoose OS implements Virtual File System layer, VFS. That means it can attach (mount) different storage types into a single file system tree. For example, a device can have an SPI flash storage and an SD card storage. For each storage type, a filesystem driver must be implemented. For example, it is possible to write a driver that implements a Dropbox or Google Drive storage type, and a device (e.g. ESP8266 module) can mount a Dropbox folder.

Mongoose OS provides a Filesystem RPC service that allows remote filesystem management - for example, you can edit files remotely.

Adding file system

Let's see how to attach an additional filesystem to Mongoose OS in practice.


On ESP8266, Mongoose OS uses approximately 3MB of flash and default file system is 256K. Most modules (ESP-12F have 4MB), so the last 1MB or so is available. Let's create a 512KB SPIFFS file system in this free space. Note: we cannot use 1MB because at the end of flash there is system params area 16K in size which is used by SDK and SPIFFS requres size to be a power of 2.

First, flash the default firmware and verify that you have at least 4M of SPI flash, watch for the boot message:

$ mos flash esp8266 && mos console
[Jul 28 13:51:11.662] esp_mgos_init2       default 1.0 (20170728-103845/???)
[Jul 28 13:51:11.668] esp_mgos_init2       Mongoose OS 2017072810 (20170728-103845/???)
[Jul 28 13:51:11.675] esp_mgos_init2       SDK 2.1.0(ce90efd); flash: 4M; RAM: 52184 total, 49140 free

flash: 4M means we're good to go. There are modules with even bigger flash chips - WEMOS D1 mini Pro has 16MB, you can have extra 8MB filesystem there.

Now, create the file system:

$ mos call FS.Mkfs '{"dev_type": "sysflash", "fs_type": "SPIFFS", "fs_opts": "{\"addr\": 3145728, \"size\": 524288"}'
Using port /dev/ttyUSB0

addr is the offset from the beginning of the flash chip where to create the filesystem, 3145728 is just after the first 3M.

Mount the newly-created filesystem:

$ mos call FS.Mount '{"dev_type": "sysflash", "fs_type": "SPIFFS", "fs_opts": "{\"addr\": 3145728, \"size\": 524288}", "path": "/mnt"}'
Using port /dev/ttyUSB0

List files on the new FS - it will be empty:

$ mos ls -l /mnt
Using port /dev/ttyUSB0

Let's put a file there

$ mos ls -l /mnt
Using port /dev/ttyUSB0 991

To make the device attach the file system atomatically at boot, let's configure the sys.mount section:

$ mos config-set sys.mount.path=/mnt sys.mount.dev_type=sysflash sys.mount.fs_type=SPIFFS 'sys.mount.fs_opts={"addr": 3145728, "size": 524288}' && mos console
Using port /dev/ttyUSB0
Getting configuration...
Setting new configuration...
Saving and rebooting...
Using port /dev/ttyUSB0
[Jul 28 14:02:32.787] esp_mgos_init2       default 1.0 (20170728-103845/???)
[Jul 28 14:02:32.793] esp_mgos_init2       Mongoose OS 2017072810 (20170728-103845/???)
[Jul 28 14:02:32.801] esp_mgos_init2       SDK 2.1.0(ce90efd); flash: 4M; RAM: 52184 total, 49140 free
[Jul 28 14:02:32.805] esp_print_reset_info Reset cause: 4 (soft reset)
[Jul 28 14:02:32.810] mgos_vfs_dev_open    sysflash () -> 0x3fff0034
[Jul 28 14:02:32.820] mgos_vfs_mount       Mount SPIFFS @ / (dev 0x3fff0034, opts {"addr": 32768, "size": 262144}) -> 0x3fff0044
[Jul 28 14:02:32.883] mgos_vfs_mount       /: size 233681, used: 99647, free: 134034
[Jul 28 14:02:32.970] mgos_sys_config_init MAC: 1AFE34A5930F
[Jul 28 14:02:32.975] mgos_sys_config_init WDT: 30 seconds
[Jul 28 14:02:32.979] mgos_vfs_dev_open    sysflash () -> 0x3fff087c
[Jul 28 14:02:32.989] mgos_vfs_mount       Mount SPIFFS @ /mnt (dev 0x3fff087c, opts {"addr": 3145728, "size": 524288}) -> 0x3fff088c
[Jul 28 14:02:33.120] mgos_vfs_mount       /mnt: size 474641, used: 1255, free: 473386
[Jul 28 14:02:33.125] mgos_mdns_init       Listening on udp://:5353

We can make built-in HTTP server serve from /mnt instead of /:

$ mos config-set http.document_root=/mnt


Typical ESP32 modules have 4M flash. Code size is bigger, there is approximately 400K available after all the system stuff. Let's add a 256K file system.

ESP32 uses partition tables for allocating flash space, we will need to add a partition and recompile firmware. Check out or download the default app, edit the mos.yml file and edit the esp32-specific section:

  - when: mos.platform == "esp32"
      build_vars:                                           # Add these
        ESP_IDF_EXTRA_PARTITION: fs_ext,data,spiffs,,256K   # two lines

Build and flash the firmware:

$ mos build --verbose --arch esp32 --clean && mos flash && mos console
Connecting to, user test
Uploading sources (2878 bytes)
Success, built default/esp32 version 1.0 (20170728-131414/???).
Firmware saved to build/
[Jul 28 14:14:44.990] I (99) boot: Partition Table:
[Jul 28 14:14:44.990] I (110) boot: ## Label            Usage          Type ST Offset   Length   Flags
[Jul 28 14:14:44.990] I (135) boot:  0 nvs              WiFi data        01 02 00009000 00004000 00000000
[Jul 28 14:14:45.012] I (161) boot:  1 otadata          OTA data         01 00 0000d000 00002000 00000000
[Jul 28 14:14:45.012] I (186) boot:  2 app_0            OTA app          00 10 00010000 00180000 00000000
[Jul 28 14:14:45.013] I (212) boot:  3 fs_0             SPIFFS           01 82 00190000 00040000 00000000
[Jul 28 14:14:45.034] I (238) boot:  4 app_1            OTA app          00 11 001d0000 00180000 00000000
[Jul 28 14:14:45.035] I (263) boot:  5 fs_1             SPIFFS           01 82 00350000 00040000 00000000
[Jul 28 14:14:45.052] I (289) boot:  6 fs_ext           SPIFFS           01 82 00390000 00040000 00000000
[Jul 28 14:14:45.053] I (315) boot: End of partition table

Note presence of the extra fs_ext partition at the end. Create the file system:

$ mos call FS.Mkfs '{"dev_type": "esp32part", "dev_opts": "{\"label\": \"fs_ext\"}", "fs_type": "SPIFFS"}'
Using port /dev/ttyUSB0

There is no need to specify size and offset, they are taken from partition information. Mount the file system:

$ mos call FS.Mount '{"dev_type": "esp32part", "dev_opts": "{\"label\": \"fs_ext\"}", "fs_type": "SPIFFS", "path": "/mnt"}'
Using port /dev/ttyUSB0

See ESP8266 section above for how to mount the FS at boot, etc.


There is no space availabe on the CC3200 chip fo extra file system, but extern SPI flash can be attached - see below.

External SPI flash

Mongoose OS has an external SPI flash driver, which can be used to attach. Having attached an SPI flash chip, you will be able to use the spi_flash driver like so:

$ mos call FS.Mkfs '{"dev_type": "spi_flash", "dev_opts": "{\"freq\": 20000000, \"cs\": 0}", "fs_type": "SPIFFS", "fs_opts": "{\"size\": 1048576}"}'