with emmc unmounted

sudo e2fsck -f /dev/mmcblk1p1 # check filesystem
sudo resize2fs -M /dev/mmcblk1p1 # shrink filesystem to minimum size
sudo fdisk /dev/mmcblk1 # shrink partition
sudo resize2fs /dev/mmcblk1p1 # Expand filesystem to fill the new (smaller) partition

execute the following commands:

p – print table (to get start sector of p1)
d – delete partition (I know this is scary but it will be OK)
n – create new primary partition #1
  - Use same start sector
  - Choose a smaller size that is slightly larger than the new filesystem
  - when asked "Partition #1 contains a ext4 signature. Do you want to remove the signature?" answer No
w – write changes

• Start sector was: 8192
• New end sector: something corresponding to ~5.2GB:
  • 1 GiB = 1,073,741,824 bytes
  • 5.2 × 1,073,741,824 = 5,583,457,484.8 bytes
  • 5,583,457,485 / 512 ≈ 10,910,860 sectors
  • end = 8192 + 10,910,860 - 1 = 10,919,051

so that:

• temporary files created by programs go to RAM
• keeps logs/temp writes from wearing out eMMC
• mode=1777: world-writable sticky bit (normal for /tmp)
• limit size of files/logs

inside /etc/fstab

tmpfs /tmp      tmpfs defaults,noatime,mode=1777,size=128M 0 0
tmpfs /var/tmp  tmpfs defaults,noatime,mode=1777,size=64M  0 0
tmpfs /var/log  tmpfs defaults,noatime,mode=0755,size=32M  0 0

• you'll have no logs for boot failures
• inside /etc/systemd/journald.conf

Storage=volatile
RuntimeMaxUse=10M
RuntimeKeepFree=2M
SystemMaxUse=0   # ignored in volatile mode

• in /etc/fstab: /dev/mmcblk1p1 / ext4 noatime,data=writeback,barrier=1,commit=60,errors=remount-ro 0 1
  • noatime: don't update access time every time you read a file
  • data=writeback: lighter journaling (metadata-only)
  • commit=60: group writes once per minute instead of 5 seconds
  • barrier=1: maintain safety
  • data=writeback + sudden power loss = some recently changed files may become garbage inside (but no FS corruption)
• add/change the cmdline in uEnv.txt (otherwise data=writeback will cause kernel to remount partition as Read Only:
  • cmdline=coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100 root=/dev/mmcblk1p1 rw rootfstype=ext4 rootwait

* When a file is deleted trim says to tell the OS to tell the flash controller that those blocks are no longer used. * Unused blocks even in the file system can be used by the controller to help with wear leveling * Continuous trim is apparently a bad idea but for wear leveling a periodic trim of 1x/week is helpful“

sudo systemctl enable fstrim.timer # defaults to 1x/week
sudo systemctl start fstrim.timer

* Zram doesn't help wear leveling directly but helps to maximize RAM availability so it can be helpful if that's an issue:

sudo apt update
sudo apt install zram-tools # or sudo apt install systemd-zram-generator
sudo nano /etc/systemd/zram-generator.conf

inside /etc/systemd/zram-generator.conf

# ===========================
# ZRAM configuration for BBB
# ===========================

[zram0]
# swap zram
type = swap
compression-algorithm = zstd
zram-size = 256M

[zram1]
# /var/log on zram
type = ext4
mount-point = /var/log
zram-size = 64M

[zram2]
# /tmp on zram (optional)
type = ext4
mount-point = /tmp
zram-size = 64M

then

sudo systemctl daemon-reload
sudo systemctl start /dev/zram0 # check if already started
sudo systemctl start /dev/zram1
sudo systemctl start /dev/zram2
# check
lsblk
zramctl
df -h
# disable journaling
tune2fs -O ^has_journal /dev/zram1 # do not do for zram0 Yes do for zram2
mkswap /dev/zram0

If using zram, remove the /tmp and /var/log lines in /etc/fstab or they will override zram mounts.