@djsumdog and @Sopalajo de Arrierez Sorry for the delayed response. Things got re-orgonized and stream lined. By unifying those that use the fstab files. Such as the init, vold, and recovery all under /fstab. now. Some of which is managed by vold and just off the top of my head it sounds like a permissions issue because with root it's like an override with its R/W powers. Linux used to have an issue with android when formatting due to this but I do not know if it was fixed.

" DEVICES MAY PROVIDE EXTERNAL STORAGE BY EMULATING A CASE-INSENSITIVE, PERMISSIONLESS FILESYSTEM BACKED BY INTERNAL STORAGE. "

" When configuring a device-specific init.rc script,the EXTERNAL_STORAGE environment variable must be defined as the path to the primary external storage. The /sdcard path must also resolve to the same location, possibly through a symlink. If a device adjusts the location of external storage between platform updates, symlinks should be created so that old paths continue working."

"One possible implementation is provided by the FUSE daemon in system/core/sdcard, which can be added as a device-specific init.rc service":

virtual sdcard daemon running as media_rw (1023) service sdcard /system/bin/sdcard <source_path> <dest_path> 1023 1023 class late_start

"Where source_path is the backing internal storage and dest_path is the target mount point."

Reference

@djsumdog and @Sopalajo de Arrierez Sorry for the delayed response. 

Things got re-orgonized and stream lined. By unifying those that use the fstab files. Such as the init, vold, and recovery all under /fstab.<device> now. Some of which is managed by vold and just off the top of my head it sounds like a permissions issue because with root it's like an override with its R/W powers. Linux used to have an issue with android when formatting due to this but I do not know if it was fixed.

" DEVICES MAY PROVIDE EXTERNAL STORAGE BY EMULATING A CASE-INSENSITIVE, PERMISSIONLESS FILESYSTEM BACKED BY INTERNAL STORAGE. "

" When configuring a device-specific init.rc script,the EXTERNAL_STORAGE environment variable must be defined as the path to the primary external storage. The /sdcard path must also resolve to the same location, possibly through a symlink. If a device adjusts the location of external storage between platform updates, symlinks should be created so that old paths continue working."

"One possible implementation is provided by the FUSE daemon in system/core/sdcard, which can be added as a device-specific init.rc service":

virtual sdcard daemon running as media_rw (1023)
service sdcard /system/bin/sdcard <source_path> <dest_path> 1023 1023
    class late_start

"Where source_path is the backing internal storage and dest_path is the target mount point."

Reference

@djsumdog and @Sopalajo de Arrierez Sorry for the delayed response. Things got re-orgonized and stream lined. By unifying those that use the fstab files. Such as the init, vold, and recovery all under /fstab. now. Some of which is managed by vold and just off the top of my head it sounds like a permissions issue because with root it's like an override with its R/W powers. Linux used to have an issue with android when formatting due to this but I do not know if it was fixed.

DEVICES MAY PROVIDE EXTERNAL STORAGE BY EMULATING A CASE-INSENSITIVE, PERMISSIONLESS FILESYSTEM BACKED BY INTERNAL STORAGE.

When configuring a device-specific init.rc script,the EXTERNAL_STORAGE environment variable must be defined as the path to the primary external storage. The /sdcard path must also resolve to the same location, possibly through a symlink. If a device adjusts the location of external storage between platform updates, symlinks should be created so that old paths continue working.

One possible implementation is provided by the FUSE daemon in system/core/sdcard, which can be added as a device-specific init.rc service:

virtual sdcard daemon running as media_rw (1023) service sdcard /system/bin/sdcard <source_path> <dest_path> 1023 1023 class late_start

Where source_path is the backing internal storage and dest_path is the target mount point.

Reference

@djsumdog and @Sopalajo de Arrierez Sorry for the delayed response. Things got re-orgonized and stream lined. By unifying those that use the fstab files. Such as the init, vold, and recovery all under /fstab. now. Some of which is managed by vold and just off the top of my head it sounds like a permissions issue because with root it's like an override with its R/W powers. Linux used to have an issue with android when formatting due to this but I do not know if it was fixed.

" DEVICES MAY PROVIDE EXTERNAL STORAGE BY EMULATING A CASE-INSENSITIVE, PERMISSIONLESS FILESYSTEM BACKED BY INTERNAL STORAGE. "

" When configuring a device-specific init.rc script,the EXTERNAL_STORAGE environment variable must be defined as the path to the primary external storage. The /sdcard path must also resolve to the same location, possibly through a symlink. If a device adjusts the location of external storage between platform updates, symlinks should be created so that old paths continue working."

"One possible implementation is provided by the FUSE daemon in system/core/sdcard, which can be added as a device-specific init.rc service":

virtual sdcard daemon running as media_rw (1023) service sdcard /system/bin/sdcard <source_path> <dest_path> 1023 1023 class late_start

"Where source_path is the backing internal storage and dest_path is the target mount point."

Reference