Help with how to get info on USB stick

General
1

I am using a USB stick to store data because I have been warned not to do this with the SD card, as this kind of writing to the card is not good for them.

But either way, I am stuck getting how much memory is left on the USB stick. (Or SD card, if I use it)

I know there is the command df -h, but that is more human readable, and it isn't for the specific device.

So say it is a 1 G SD card. How can I get a command that shows me the remaining memory so I can be notified when it gets too low.

2

They both use the same technology: NAND.
The potential problem with both is writing/reading when the device writing/reading crashes, or gets unplugged. And although the risk should be low, it can still happen that you end up with an unusable storage stick/card.

To get the filesystem status for a particular device, first determine its mount point. With df -h you should see something like:

/dev/disk1s1                                  466Gi  295Gi  170Gi    64%     3567807 9223372036851208000    0%   /

Together with a bunch of others, one of which is your SD card/USB stick.

The last part/column in the output shows you where it is 'mounted' on.
Enter df -h /< the mount found in the list >

For use in node-red, you could use the exec node with something like

df -h /< mount found in the list >  | grep / | tr -s ' ' | cut -d " " -f4

which would give you the number in Gigabytes available.

1 Like
3

Thanks very much.

I shall have to "tweak" the output so it is a number, then I can do comparisons of value.

4

Just split and select the data required out of the df command

image
image.png1004Ă—109 6.71 KB 

[{"id":"e9ee1b34.cfb5f8","type":"exec","z":"8376d5c1.273ed8","command":"","addpay":true,"append":"","useSpawn":"false","timer":"","oldrc":false,"name":"","x":670,"y":700,"wires":[["5c3effd9.e932a"],[],[]]},{"id":"c65210d3.f1ccf","type":"inject","z":"8376d5c1.273ed8","name":"","topic":"","payload":"df -h /dev/sda1","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":420,"y":700,"wires":[["e9ee1b34.cfb5f8"]]},{"id":"601069e4.f909b8","type":"debug","z":"8376d5c1.273ed8","name":"","active":true,"tosidebar":true,"console":false,"tostatus":true,"complete":"payload","targetType":"msg","x":1170,"y":680,"wires":[]},{"id":"5c3effd9.e932a","type":"split","z":"8376d5c1.273ed8","name":"","splt":" ","spltType":"str","arraySplt":1,"arraySpltType":"len","stream":false,"addname":"","x":830,"y":680,"wires":[["86f87ffc.c62c6"]]},{"id":"86f87ffc.c62c6","type":"switch","z":"8376d5c1.273ed8","name":"","property":"parts.index","propertyType":"msg","rules":[{"t":"eq","v":"25","vt":"num"}],"checkall":"true","repair":false,"outputs":1,"x":970,"y":680,"wires":[["601069e4.f909b8"]]}]
1 Like
5

Ok, so that is:
looking for the / (Not sure why)
trimming repeat characters (set to a space) So really removing excess spaces.
cutting (not sure about this either) setting delimiter as a space (" ")
returning the 4'th entry.

Ok, so I get back
1007M

So I need to strip the trailing M from there.

I'll mess about with it but if you could help me get through the workings of the grep / and how the last part works: cut -d " " -f4

Ok. What I understand.
cut -d " " -f4
Use a space (" ") as a delimiter and return the 4'th section.

Now all I need to do is "strip" the message.... Or maybe better: Delete the last letter of the message. (M)

Sorry, but what is the command for doing that?
I'll look, but if may be quicker with a bit of help.
:slight_smile:

6

Strange.

When I run the flow I get this back:

/media/pi/9020-9C27

Not the size available.

7

Might have to alter the index number in the split node for your system
Also might have to alter inject string so that it reads your usb drive - it might not be /dev/sda1 on your system

8

It is /dev/sda1

I'm kind of bitten by bakman2's method. I just don't know all the commands to do the tricks to manipulate the string/s.

9

use @bakmans2 method and then add this in a function node to get rid of the letter

msg.payload = msg.payload.substring(0,msg.payload.length-1);
return msg;
1 Like
10

I didn't think of that.

I was thinking of doing it all in the original command.

Oh, bakman2.....

I worked out why you need the grep /. To get the second line which has the information I want.

Moving on.

11

I decided to use your way.

Like this:

msg.payload = msg.payload.substring(0,msg.payload.length-2);
msg.payload = parseInt(msg.payload);
return msg;

That way it is a number and stripped the trailing M.

But it had to be -2 not -1. But no worries.

Now on to the next part of the journey.

12

Because df -h /path outputs 2 lines, the first line shows the columns, we don't need that line so we grep the / which only occurs in the next line.

In one go, to end up with a number:

df -h /dev/sda1 | grep / | tr -s ' ' | cut -d " " -f4 | sed s'/[A-Za-z].$//'

The sed command (stream editor) can manipulate per line. And in this case it is looking for 1 or more uppercase or lowercase characters and replaces it with nothing. (regular expressions are a completely different world in which you can get lost, but extremely powerful).

Use a space (" ") as a delimiter and return the 4'th section.

Read it as "column".

There are many ways to Rome, this could also be done (perhaps simpler) with the awk command. Or just with a flow with split and change nodes like @cymplecy shows.

1 Like
13

Thanks. Really.

awk. I'll look at that.

Though I have got it working as @cymplecy said.

14

That is caused by the operating system, the flow will not be compatible crossplatform, some OS-es output 200MB, while other say 200M, same applies to G vs Gi

15

All good.

Again: Thanks.

16

Just for my curiosity to see the difference - what does df -h output on your system?

17

(Actually I was about to post on that.....)

pi@TelePi:/media/pi/9020-9C27 $ df -h /dev/sda1 | grep / | tr -s ' ' | cut -d " " -f4
1007M
pi@TelePi:/media/pi/9020-9C27 $

I get 1007M. So it is interesting that I need to specify the -2 rather than the -1

But to answer your question fully:

pi@TelePi:/media/pi/9020-9C27 $ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        30G  4.2G   24G  15% /
devtmpfs        181M     0  181M   0% /dev
tmpfs           186M     0  186M   0% /dev/shm
tmpfs           186M   21M  165M  12% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           186M     0  186M   0% /sys/fs/cgroup
/dev/mmcblk0p1   42M   22M   20M  54% /boot
tmpfs            37M     0   37M   0% /run/user/1000
/dev/sda1      1007M  272K 1007M   1% /media/pi/9020-9C27
pi@TelePi:/media/pi/9020-9C27 $
18 
466Gi  295Gi  170Gi

See the difference (-1) character or (-2)

19

Yeah, but if I am getting 1007M why is it I am needing -2 to delete the M?

That would be -1 yeah?

20

Actually (and honestly): I'm missing something I think.
Other than the first has 4 digits and the second and third have only 3 digits.