Tutorial: Adding a swap file and moving /home to an SD card

[pliablepixels]

I thought it might be useful to document the steps to resolve #5 and #6. I'm not an embedded person by any means, so feel free to correct/suggest improvements:

Here is what I did - I added a 128GB micro SD card to the coral board and wanted to do the following:

a) Migrate my existing /home to my sd card
b) Set up a 1G swap file, but set a low swapiness value, so its only used when really needed

Caveats:
a) Migrating /home and swap to an SD card may reduce the lifespan of the card. Thus it is important to make sure the swap file is only used when really needed. I'm personally not convinced that moving /home to an SD card is bad, but who knows. Don't do it if you don't want to :-)

Start:
I assume you have followed the "Getting Started" instructions and are now at a point where you can successfully mdt shell into your device and can run the demos the page shows (nice demos).

Steps:

1. Insert SD card

2. Now get ID of SD card

sudo fdisk -l
<various disks, snipped>
Disk /dev/mmcblk1: 116.2 GiB, 124721823744 bytes, 243597312 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

So in my case, the SD card is /dev/mmcblk1

3. Format disk

 sudo mkfs.ext4 /dev/mmcblk1

Now wait a while while it formats.

4. Mount newly formatted disk and prepare to migrate existing home

# mount it to /mnt 
sudo mount /dev/mmcblk1 /mnt

# copy everything in current /home to /mnt
# command below does not include encrypted directories
sudo rsync -aXS --exclude='/*/.gvfs' /home  /mnt
 
# make sure your copy went will. Diff should not show anything 
# which means everything is same
sudo diff -r /home /mnt/home -x ".gvfs/*"

# make sure new /home/mendel is RW mendel
sudo chown -R mendel:mendel /mnt/home/mendel

5. Make the home directory remounting permanent

sudo echo " /dev/mmcblk1 /home ext4 defaults 0 1" >> /etc/fstab

6. Reboot your machine from an mdt shell and make sure your home directory is all good. Note if you are unable to mdt shell you did something wrong. In my case, I forgot to change permissions of the copied directory to mendel and also mistakenly moved /home to /home/home in my SD card with the first rsync command. Worry not, you can always use your serial connector and connect to the coral board - you can login with mendel/mendel and rectify things.

7. Assuming now your home directory is migrated and you have validated running the demos etc, lets set up Swap

This sets up a bounded 2G file on your SD card

 # setup swap
 sudo fallocate -l 2G /home/swapfile
 sudo chmod 600 /home/swapfile
 sudo mkswap /home/swapfile
 sudo swapon /home/swapfile

Make sure its set up correctly:

sudo swapon --show
NAME           TYPE  SIZE USED PRIO
/home/swapfile file 2G   0B   -2

Yup.

Now make it permanent

sudo echo "/home/swapfile none swap sw 0 0" >> /etc/fstab

Now make sure you set a low swappiness to the system doesn't use it aggressively

Edit your /etc/sysctl.conf and add:

vm.swappiness=10

to the file, if it doesn't already exists. If that value exists, change it to 10

8. reboot again to make sure all settings are permanent

This is my system after all of that and a fresh reboot

l@red-dog:~$ df
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/root        7294440 1542164   5394784  23% /
devtmpfs          340344       0    340344   0% /dev
tmpfs             504824       0    504824   0% /dev/shm
tmpfs             504824   19388    485436   4% /run
tmpfs               5120       4      5116   1% /run/lock
tmpfs             504824       0    504824   0% /sys/fs/cgroup
/dev/mmcblk0p1    126931   30370     90008  26% /boot
/dev/mmcblk1   119361328 1115052 112139960   1% /home
tmpfs             504824     428    504396   1% /var/log
tmpfs             100964    4708     96256   5% /run/user/1000

mendel@red-dog:~$ sudo swapon -s
Filename				Type		Size	Used	Priority
/home/swapfile                         	file    	1048572	0	-2

mendel@red-dog:~$ cat /proc/sys/vm/swappiness
10

[Ecuashungo]

I followed your instructions, and somehow messed up something. I wanted to connect through the serial port to rectify things, but I have got the following message:
Cannot open access to console, the root account is locked. See sulogin(8) man page for more details.
Any idea how I can remove the line /dev/mmcblk1 /home ext4 defaults 0 1 from /etc/fstab without serial console?

[haithienld]

-bash: /etc/fstab: Permission denied
sudo chmod 666 /etc/fstab

[Namburger]

@pliablepixels Nam from the coral team here, very nice guide, and thanks
Although before making the mkfs.ext4, it's usually standard to create a partition in the sd card first. So something like:

sudo fdisk /dev/mmcblk1
// create new partition
Command (m for help): n
// make this a primary partition, leave default values for first and last sector
Command (m for help): p
// Write it (by default fdisk will make this a ext4 partition)
Command (m for help): w

Then sudo fdisk -l should show something like this:

....
Disk /dev/mmcblk1: 29.7 GiB, 31914983424 bytes, 62333952 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x2aaeb742

Device         Boot Start      End  Sectors  Size Id Type
/dev/mmcblk1p1       2048 62333951 62331904 29.7G 83 Linux

You'll want to make /dev/mmcblk1p1 the ext4:

sudo mkfs.ext4 /dev/mmcblk1p1

And the rest is to follow your tutorial :)

For me personally, I'll just mount it to an sdcard directory without copying $HOME files over:

mendel@queen-zebra:~$ sudo mount /dev/mmcblk1p1 sdcard
mendel@queen-zebra:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root       7.0G  3.9G  2.9G  58% /
devtmpfs        333M     0  333M   0% /dev
tmpfs           493M   20K  493M   1% /dev/shm
tmpfs           493M   13M  481M   3% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           493M     0  493M   0% /sys/fs/cgroup
tmpfs           493M  620K  493M   1% /var/log
/dev/mmcblk0p1  124M   30M   88M  26% /boot
tmpfs            99M   13M   86M  13% /run/user/1000
/dev/mmcblk1p1   30G   45M   28G   1% /home/mendel/sdcard

Cheers!

[slbejaranom]

I always get to the point where you "permanently mount it" but once i reboot the board, it doesn't mount itself, still don't know why, followed the exact steps verifying not damaging fstab, checked thrice, after reboot the file fstab keeps the modification but the SD doesn't mount itself, am I doing something wrong?

[jnnks]

I always get to the point where you "permanently mount it" but once i reboot the board, it doesn't mount itself, still don't know why, followed the exact steps verifying not damaging fstab, checked thrice, after reboot the file fstab keeps the modification but the SD doesn't mount itself, am I doing something wrong?

If anyone has a similar problem, check your /etc/fstab file in a text editor. I already had an entry mounting a partition to /home and the one added manually failed because of that.

The partitions are mounted in the order they appear in /etc/fstab, so your SD Card should be listed after the original mount:

/dev/mmcblk0p4 / ext4 noatime,defaults 0 1
/dev/mmcblk0p1 /boot ext2 noatime,defaults 0 2
tmpfs /var/log tmpfs defaults 0 0
# sd card
/dev/mmcblk1p1 /home ext4 defaults 0 1
# default
/dev/mmcblk0p3 /home ext4 noatime,nosuid,nodev,defaults 0 3

Leave the original mount entry in the config file in case something goes wrong.

[Sruthi-sk]

Is there any way I can merge /dev/mmcblk0p3 with /dev/mmcblk0p4 ?
Currently, /dev/root only has 5 GB, and I want to add the original mount entry's 2 GB to this.

[brianthelion]

@Sruthi-sk Please open a new issue.

[nerbivol]

I always get to the point where you "permanently mount it" but once i reboot the board, it doesn't mount itself, still don't know why, followed the exact steps verifying not damaging fstab, checked thrice, after reboot the file fstab keeps the modification but the SD doesn't mount itself, am I doing something wrong?

If anyone has a similar problem, check your /etc/fstab file in a text editor. I already had an entry mounting a partition to /home and the one added manually failed because of that.

The partitions are mounted in the order they appear in /etc/fstab, so your SD Card should be listed after the original mount:

/dev/mmcblk0p4 / ext4 noatime,defaults 0 1
/dev/mmcblk0p1 /boot ext2 noatime,defaults 0 2
tmpfs /var/log tmpfs defaults 0 0
# sd card
/dev/mmcblk1p1 /home ext4 defaults 0 1
# default
/dev/mmcblk0p3 /home ext4 noatime,nosuid,nodev,defaults 0 3

Leave the original mount entry in the config file in case something goes wrong.

Issue Title

Unable to Mount New Partition to /home Directory

Issue Description

I attempted to add a new partition to the /home directory by modifying the /etc/fstab file. However, after rebooting the system, the new partition does not seem to be mounted as expected. Below are the steps I followed and the current state of my system.

Steps to Reproduce

1. Initial state of /etc/fstab:

   PARTUUID=02f36a4f-4562-46b2-bbec-bfc1682f9e92 / ext4 noatime,defaults 0 1
   PARTUUID=b3c678b9-3004-4e30-87dc-ed33fbf4dbfd /home ext4 noatime,nosuid,nodev,defaults,x-systemd.makefs 0 3
   PARTUUID=0f94c91b-1d90-492f-ab86-6952303b214e /boot ext2 noatime,defaults 0 2
   tmpfs /var/log tmpfs defaults 0 0
   

2. Output of df -h command:

   Filesystem      Size  Used Avail Use% Mounted on
   /dev/root       5.1G  1.7G  3.1G  36% /
   devtmpfs        967M     0  967M   0% /dev
   tmpfs           999M     0  999M   0% /dev/shm
   tmpfs           999M  8.7M  991M   1% /run
   tmpfs           5.0M  4.0K  5.0M   1% /run/lock
   tmpfs           999M     0  999M   0% /sys/fs/cgroup
   /dev/mmcblk0p2  124M   28M   91M  24% /boot
   /dev/mmcblk0p3  2.0G  1.7G  180M  91% /home
   tmpfs           999M  272K  999M   1% /var/log
   tmpfs           200M  8.3M  192M   5% /run/user/1000
   

3. Added the following line to /etc/fstab:

   /dev/mmcblk2p1 /home ext4 defaults 0 1
   

4. New state of /etc/fstab after modification:

   PARTUUID=02f36a4f-4562-46b2-bbec-bfc1682f9e92 / ext4 noatime,defaults 0 1
   PARTUUID=b3c678b9-3004-4e30-87dc-ed33fbf4dbfd /home ext4 noatime,nosuid,nodev,defaults,x-systemd.makefs 0 3
   PARTUUID=0f94c91b-1d90-492f-ab86-6952303b214e /boot ext2 noatime,defaults 0 2
   tmpfs /var/log tmpfs defaults 0 0
   /dev/mmcblk2p1 /home ext4 defaults 0 1
   

5. Rebooted the system.

Expected Behavior

The new partition /dev/mmcblk2p1 should be mounted to the /home directory.

Actual Behavior

The /home directory remains on the original partition:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root       5.1G  1.7G  3.1G  36% /
devtmpfs        967M     0  967M   0% /dev
tmpfs           999M     0  999M   0% /dev/shm
tmpfs           999M  8.7M  991M   1% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           999M     0  999M   0% /sys/fs/cgroup
/dev/mmcblk0p2  124M   28M   91M  24% /boot
/dev/mmcblk0p3  2.0G  1.7G  180M  91% /home
tmpfs           999M  272K  999M   1% /var/log
tmpfs           200M  8.3M  192M   5% /run/user/1000

Possible Suggested Fix

Modification for /etc/fstab:

    PARTUUID=02f36a4f-4562-46b2-bbec-bfc1682f9e92 / ext4 noatime,defaults 0 1
    /dev/mmcblk2p1 /home ext4 defaults 0 1
    PARTUUID=b3c678b9-3004-4e30-87dc-ed33fbf4dbfd /home ext4 noatime,nosuid,nodev,defaults,x-systemd.makefs 0 3
    PARTUUID=0f94c91b-1d90-492f-ab86-6952303b214e /boot ext2 noatime,defaults 0 2
    tmpfs /var/log tmpfs defaults 0 0

Is it supposed to work?