First of all thanks to the entire team at Victron for your work on the integration of SignalK! I have a question on using SignalK as part of VenusOS Large on a Cerbo GX: I would like to save log data from SignalK to SD card. However, Venus OS mounts the SD without write permissions for other users meaning that the user which runs the signalk-server process canāt write to it. Any ideas on how to give SignalK plugins write access without messing up VenusOS?
Thanks and best regards,
Johannes
Insert an additional SD-Card into teh Cerbo GX. This is mounted R/W (unless it has errors in which case it is R/O) as it is also used by the VRM logger log file. It is only the root partition that is mounted as R/O.
The SD-Card will be mounted as
/dev/mmcblk0p1 on /run/media/mmcblk0p1 type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
Hi @Bathnm, thank you so much for your fast reply! The mount information you supplied is consistent with what I have on my system (except for my card being exFAT but I have tried FAT32 too)
/dev/mmcblk0p1 on /run/media/mmcblk0p1 type exfat (rw,relatime,fmask=0022,dmask=0022,iocharset=utf8,errors=remount-ro)
However, as fmask and dmask indicate, rwx permission is only allowed for root leading to the following output of ls -l for the cards mount path and changing these permissions is not possible (as it's prohibited by the mask)
drwxr-xr-x 5 root root 32768 Aug 16 10:48 mmcblk0p1
Following the output of ps on my system, I find that signalk-server is run by user signalk and not by root
1384 signalk 247m R node /usr/lib/node_modules/signalk-server/bin/signal
I suspect that it's because of this that my SignalK Plugins can't write to /run/media/mmcblk0p1 even if I supply that precise path, what do you think?
Best regards,
Johannes
@sy.shenandoah yes looks like permissions, create a folder under /run/media/mmcblk0p1, then give that folder permissions and ownership by the user signals and point the plugin to that directory.
Hi, just a quick update on how I solved this: as @Bathnm correctly pointed out, I needed to change permissions on the folder I wanted to write to on the SD. However, this only works with ext3/4 formatted SD cards since FAT does not include permissions and therefore won't let you change rights or ownership. So what I ended up doing was format the SD card to ext4 in the Cerbo
fdisk /dev/mmcblk0 d n w mkfs.ext4 /dev/mmcblk0p1
and then add write permission for other
chmod o+w /run/media/mmcblk0p1/foldername
I guess to use non ext-formatted SD cards you'd still have to change the mount settings of Venus OS.
