Everything was going so well

JMac

@sdetweil sorry to be dense how do I know what I’m unmounting?
am I unmounting /dev/mmcblk0p1?? it says thats mounted on /boot.

edit to add,
after re running sudo fdisk -l it would appear the old memory card (with my previous MM setup on) is on Disk /dev/sda

thats classed as Disk Model: storage device (as it’s mounted in the usb drive atm) does this seem correct? is this the one which needs unmounting?

sdetweil

@JMac well mounted means accessible by the filesystem

so it’s /dev/sda
the usb installed sd card

so

sudo unmount /dev/sda
and then run fsck on that

JMac

so I run the command sudo umount /dev/sda
and get
umount: /dev/sda: not mounted.

so should now go,
e2fsck -f -v /dev/sda
not the original
e2fsck -f -v mmcblk0p2

?

sdetweil

@JMac correct… you had to find the disk name

JMac

@sdetweil when i run e2fsck…
I get
e2fsck: permission denied while trying to open /dev/sda
you must have r/w access to the filesystem or be root.

sdetweil

@JMac yes, you must use sudo on both commands unmount and fsck

sorry I was unclear

normal users should not be able to mess with hardware, so one must act as root

JMac

@sdetweil I run sudo umount…
and get
umount:… not mounted,

then run
sudo e2fsck -f -v /dev/sda
and get
e2fsck 1.46.2 (28-feb-2021)
/dev/sda is in use
efsck: connot continue, aborting.

sdetweil

@JMac hm… wonder what is using it?

can you open the disks app on the pi from the dedktop menu

JMac

@sdetweil on the home screen I have 2 drive icons under the wastebasket.
one is boot
the other is rootfs

i then have the option to eject these in the file manager

sdetweil

@JMac there should be that drive on /dev/sda too

JMac

@sdetweil I’m a little confused (I’d imagine thats pretty clear at this point).

i run sudo fdisk -1
and get
Disk /dev/ram0 through to Disk /dev/ram15
the list then has
Disk/dev/mmcblk0: 7.4GiB (my thinking is this is the current/new sd card)

Device
/dev/mmcblk0p1
/dev/mmcblk0p2

Disk /dev/sda:59.69 GiB (I again assume this is the old SD with my original MM setup)

Device
/dev/sda1
/dev/sda/2

end of the list.

does any of that make sense/ is any of it what I’m looking for? I’ve obviously taken out several lines under each of those headers just for space and time typing.

sdetweil

@JMac yes sda has two partitions boot and rootfs

but you need to run e2fsck on /dev/sda2
e2fsck mean extended version 2, file system check

JMac

so should i also run sudo umount /dev/sda2 before running sudo e2fsck -f -v /dev/sda2?

sdetweil

@JMac yes

JMac

@sdetweil so I’ve run sudo umount /dev/sda1 and the same for sda2 and both folders have disappeared off the home screen.

which e2fsck do I run if i had to unmount 2 drives?

sdetweil

@JMac unmount means remove them from normal file system access

the device names still exist

as e2fsck could modify the file system blocks on the drive, you don’t want to do that while you could still copy a file there

so you are passing the hardware name to e2fsck

JMac

@sdetweil so do I run e2fsck -f -v /dev/sda1 or e2fsck -f -v /dev/sda2
or does it not matter?

I’m struggling here to the bigger picture so can’t see the logic of the steps.

sdetweil

@JMac ok bigger picture, in Linux

hardware devices are named. see the output of ls /dev

disk devices are usually named sd??? where xxx is a letter, and partition number
letter a is the first device b the second etc

sometime in the past the type of storage device was also used as part of the name, scsi, atapi …
for this case they are named sd (storage device)

sda is the first storage device
sda1 is the first partition on the sda device

on those partitions are a logical way of storing data. most linux and all windows devices store file data in sectors, 512 byte chunks called sectors. and then the file system (way of organizing those sectors)
applies some data structure on top. it’s a directory or a file. tables in other sectors build trees of data to describe the entire partition.

there are different layouts depending on vendor and intended use
FAT, exFAT, NTFS EXT3, EXT4, and a host of others.

all is wonderful until some sector or more gets damaged… machine was powered off during write, a hardware failure…

now the filesystem code is confused… says read sector 853, and the bits there will tell it where the next sector is for this file. but the bits don’t point to the right place… Oops

some file systems include a duplicate set of bits do there is an alternative way . some use them only for recovery.

sd card hardware is known for being fragile. it was designed for lots of reads,with few writes. camera picture music file. NOT an os that is waiting logs and other stuff constantly.

anyhow.
to check and correct these kinds of problems with the Linux ext file system we need to run thr fsck program on the raw partition. and make sure that moone else is using it.

unmount takes it out of circulation. no users files open

fsck and e2fsck need to read the raw sectors on the partition, but we just unmounted it.
so we need to provide the hardware name for the program to use.

JMac

@sdetweil Wow, that was a bit to take in but makes sense (I think).

So if I unmount it how do I get the information off it?
what are the steps here?

sdetweil

@JMac
unmount it
run fsck against it
remount it (hopefully fixed)

then copy your data first thing, DO NOT WRITE TO THE SD CARD

config.js
custom.css
and a list of all the modules in modules (ls *)

if u WANT to try in each module folder do

git remote -v
```⁷
so we know where it came from

quickest way in each module folder

git remote -v | tail -a ~/module_list 

this will list to github source (git remote -v) and append that info  (tail -a) to a known file in your home folder (~ = home)

this is what my backup script does
IF you have any modules that require authentication (run an auth script) 
ls *.json while you are there,

you could also run my backup script, from the web page copy/paste  with -s  pointing to the mounted folder MagicMirror 
https://github.com/sdetweil/MagicMirror-backup-restore

...MM_backup -s /media/??????/MagicMirror some gobbleygoop name (tab key will fill it in after the 1st letter)

this will create the MM_backup folder in your logged on user home folder..  
and do all the work described above (after the mount)
https://github.com/sdetweil/MagicMirror-backup-restore