How to copy files from an SD in a USB card reader

Question

I have a bunch of files I'd like to send to my rpi. I have them in 2 places: 1. on my mac and 2. on a an SD card for my pi that has corruption in the kernel and won't boot.

I'd like to put the files on my currently running pi that has a different SD card.

ssh'ing the files from my mac is soooo slow, so I'm trying to figure out a faster way. I tried and failed to put them on a USB thumb drive from my mac and connect it to the pi but I couldn't mount the thumb drive. So I had an idea to put the SD with the corrupt kernel in the USB card reader that came in my kit and connect it to the pi.

When I do that, I can see the contents of that card. But I couldn't find the files in there so I tried mounting the 2 imgs I found in it (kernel.img and kernel7.img) using (e.g.) sudo mount -t sysfs kernel7.img /home/pi/mntpt, but I believe that what I'm seeing is the boot drive partition. It's only 35M in size. The pi home folder is nowhere to be found.

Is there a way I can find the files in the SD that's in the USB card reader and copy them out into the card that my pi booted from?

Output of requested commands (while the USB SD card reader is inserted into one of the pi's USB ports:

pi@raspberrypi:/media $ lsblk
NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda           8:0    1 29.8G  0 disk 
├─sda1        8:1    1   57M  0 part /media/usb0
└─sda2        8:2    1  7.4G  0 part 
mmcblk0     179:0    0 29.7G  0 disk 
├─mmcblk0p1 179:1    0  1.2G  0 part 
├─mmcblk0p2 179:2    0    1K  0 part 
├─mmcblk0p5 179:5    0   32M  0 part /media/pi/SETTINGS
├─mmcblk0p6 179:6    0   69M  0 part /boot
└─mmcblk0p7 179:7    0 28.4G  0 part /
pi@raspberrypi:/media $ sudo parted /dev/sda print free
Model: Mass Storage Device (scsi)
Disk /dev/sda: 32.0GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End     Size    Type     File system  Flags
        16.4kB  4194kB  4178kB           Free Space
 1      4194kB  64.0MB  59.8MB  primary  fat16        boot, lba
 2      64.0MB  7969MB  7905MB  primary
        7969MB  32.0GB  24.0GB           Free Space

Answer 1

As far as I understand you are trying to do all copying on your mac. But why not using the Raspberry Pi? Just boot it up and then plug in the USB card reader to it with source SD Card inserted. Then mount the source SD Card and copy the files you want to the RasPis storage (SD Card).

Update:
As I can see from your updated question the "old" corrupted SD Card, plugged in with a card reader onto the RasPi, has two partitions:/dev/sda1 (boot partition, formated with fat filesystem) and /dev/sda2 (root partition, formated with ext4 filesystem). To get access to the files you have to mount the root partition /dev/sda2. But it seems this partition has lost its filesystem ext4 because parted should show it in its output at column File system for Number 2 (/dev/sda2). For Number 1 (/dev/sda1) it shows the correct filesystem fat16.

You can try to mount /dev/sda2 but I'm not very hopeful that you can because of the corrupted filesystem:

rpi ~$ sudo mkdir /mnt/sda2
rpi ~$ sudo mount -t ext4 /dev/sda2 /mnt/sda2

If this fails you could use very low level recovery tools scanning the SD Card for readable data but that is not an easy task. Fortunately you have the files still available on your MAC. The MAC can read fat filesystems so you can format your USB thumb drive on the RasPi and then transfer the files from the MAC to the RasPi with it. Of course you will loose all data on the thumb drive. You have already tried it but I don't know why it fails. Maybe the thumb drive wasn't formated the right way. Here is how to format it with a 4 GB partition. With 4 GB you are on the save side with fat because there are known limits with bigger partitions.

rpi ~$ sudo parted /dev/sda mktable msdos
rpi ~$ sudo parted /dev/sda mkpart primary fat32 0% 3999MB
rpi ~$ sudo mkfs.fat -F32 /dev/sda1

The thumb drive should then look like this:

rpi ~$sudo parted /dev/sda print
Model: General UDisk (scsi)
Disk /dev/sda: 4028MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  3999MB  3998MB  primary  fat32        lba

Try if you can access it:

rpi ~$ sudo mkdir /mnt/sda1
rpi ~$ sudo mount /dev/sda1 /mnt/sda1
rpi ~$ sudo touch /mnt/sda1/USB_thumb_drive
rpi ~$ sudo ls /mnt/sda1
USB_thumb_drive

rpi ~$ sudo umount /mnt/sda1

Now plug the USB thumb drive into the MAC and copy the files.

Answer 2

I find that the easiest way to copy files from a Mac to the Pi is FTP, although I also use rsync and AFP (netatalk on the Pi).

Unless you have a very slow network this is unlikely to be slow - All I/O on the Pi goes through the USB controller (except on-board WiFi and GPIO) so all methods have the same bottleneck.

You can put the old SD Card in a reader and read on the Pi. These will automount on Desktop, and can easily be mounted from the command line.

You have asked many different (and vague) questions. You cannot access ext4 partitions on the Mac (at least not since Apple inflicted SIP on us), although these are readable on any Linux machine.

The kernel.img files are NOT file system images and are not mountable (they are kernel code).

The root partition does not seem to be mounted. The following will mount it if it is OK

sudo mkdir /mnt/SDA2
sudo mount /dev/sda2 /mnt/SDA2

This is a script I use to mount Cards

#!/bin/bash
# 2017-05-06
# 2018-11-18

BOOT_MOUNT='/mnt/SDA1'
ROOT_MOUNT='/mnt/SDA2'

# Check/create Mount Points
if [ ! -e $BOOT_MOUNT ]; then
    mkdir $BOOT_MOUNT
fi
if [ ! -e $ROOT_MOUNT ]; then
    mkdir $ROOT_MOUNT
fi
    echo "mounts " $BOOT_MOUNT  $ROOT_MOUNT
if [ -e /dev/sda ]; then
    SD1='/dev/sda1'
    SD2='/dev/sda2'
else
    SD1='/dev/sdb1'
    SD2='/dev/sdb2'
fi
echo $SD
# Mount Partitions
if ! $(mountpoint -q $BOOT_MOUNT); then
    mount $SD1 $BOOT_MOUNT  # mount partition containing boot files
fi
if ! $(mountpoint -q $ROOT_MOUNT); then
    mount $SD2 $ROOT_MOUNT  # mount root partition containing OS files
fi