# cat /sys/class/dmi/id/board_serial
# cat /sys/class/dmi/id/product_uuid
root@pecka:/home/bazil# for i in /sys/class/dmi/id/product_*; do echo -n "$i: "; cat $i; done
(/sys/class/dmi/id/*)
ROUT (/sys/class/net/*/address)
ROUT - stable? (/sys/bus/usb/devices/*/serial)

/var/lib/dbus/machine-id (/var/db/dbus/machine-id)
/etc/machine-id

parts from /proc/cpuinfo

ALL - model name

A simple and portable way of computing your own sysid may be to serialize uname(), gethostid() and some inodes like /home or your application homedir (obtained with stat()) etc. in a string and hash It.

hostid (command)
(/etc/hostid)

ROUT-empty blkid

LINUX lsblk -nro SERIAL

dmidecode

lshw

(https://www.baeldung.com/linux/machine-id)

$ echo "$(fdisk --list)$(lshw -short)" | md5sum | cut --delimiter=' ' --fields=1

df /
 -> get disk path (e.g. /dev/sda1)
 -> /dev/disk/by-uuid je linka (e.g. na /dev/sda1)

e.g.: for disk in /dev/disk/by-uuid/*; do 
    basename "$(readlink "$disk")"
    basename "$disk"
    echo
done

e.g. disk=sda1
find /dev/disk/by-uuid -type l -exec sh -c "readlink {} | grep -o $disk && basename {}" \;


---
in general

mac address
some sort of serial no

combinations:
md5sum, sha*sum

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/proc/sys/kernel/random/boot_id - generated one-time on boot (for detecting reboots)
/proc/sys/kernel/hostname