In order to isolate the changes when compiling and installing a large program, and to extract the (compiled and linked) files needed to install that program on another RPi, an overlay of the root file system was defined. A 32 [GiB] SD card is used to install buster, and after configuration of Raspbian on an RPi, the SD card is modified using gparted. The large partition is halved and another partition (of about the same size) is defined. The RPi starts with this new partitioning of the SD card. The additional partition is mounted on /mnt. A modified version of script overlayRoot.sh (see http://wiki.psuter.ch/doku.php?id=solve ... _partition) is used. The modification is to use the additional partition in stead of tempfs file system(s).
It works, except for swap. In the 'upper dir', file /var/swap has been created with the configured size, but examination of /proc/meminfo shows that there is no swap space available. Various ways of stopping and starting, disabling and enabling dphys-swapfile all result in error message:
swapon: /var/swap: swapon failed: Invalid argument.
The status of the file systems is:
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pi@rpi3r:~ $ lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT mmcblk0 179:0 0 29,7G 0 disk ├─mmcblk0p1 179:1 0 256M 0 part /boot ├─mmcblk0p2 179:2 0 14,6G 0 part /ro └─mmcblk0p3 179:3 0 14,9G 0 part /mnt pi@rpi3r:~ $ df -h Filesystem Size Used Avail Use% Mounted on /dev/mmcblk0p2 15G 9,2G 4,6G 67% /ro overlayfs-root 15G 2,1G 12G 15% / devtmpfs 459M 0 459M 0% /dev tmpfs 464M 0 464M 0% /dev/shm tmpfs 464M 6,4M 457M 2% /run tmpfs 5,0M 4,0K 5,0M 1% /run/lock tmpfs 464M 0 464M 0% /sys/fs/cgroup tmpfs 16M 4,0K 16M 1% /tmp tmpfs 1,0M 32K 992K 4% /overlay/xymon tmpfs 1,0M 4,0K 1020K 1% /var/lib/xymon/tmp /dev/mmcblk0p3 15G 2,1G 12G 15% /mnt /dev/mmcblk0p1 253M 52M 201M 21% /boot overlayfs 1,0M 32K 992K 4% /var/lib/xymon/www tmpfs 93M 0 93M 0% /run/user/1000 pi@rpi3r:~ $cat /proc/meminfo | fgrep Swap SwapCached: 0 kB SwapTotal: 0 kB SwapFree: 0 kB pi@rpi3r:~ $
What is needed to use swap space on the new root file system?