Using Ubuntu 18.04 bash, if I list all files that share the same specific inode 4 with:
sudo find -inum 4 -printf "%D %i %n %pn" 2>/dev/null
I can see different values of the number of hard link for that same specific inode (=4). The same occur if I do it with C code.
For other inodes I get the correct identical hard links values.
What is the problem with that inode 4?
Here is the output:
54 4 2 d ./run/user/1000/systemd 52 4 2 d ./run/user/121/systemd 27 4 1 f ./run/lock/asound.state.lock 23 4 7 d ./run/udev 66305 4 4 d ./boot/efi/EFI 6 4 1 c ./dev/rfkill 8 4 1 f ./sys/kernel/debug/pinctrl/pinctrl-devices 21 4 23 d ./sys/devices 43 4 1 f ./sys/fs/cgroup/devices/cgroup.sane_behavior 42 4 1 f ./sys/fs/cgroup/perf_event/cgroup.sane_behavior 41 4 1 f ./sys/fs/cgroup/hugetlb/cgroup.sane_behavior 40 4 1 f ./sys/fs/cgroup/freezer/cgroup.sane_behavior 39 4 1 f ./sys/fs/cgroup/net_cls,net_prio/cgroup.sane_behavior 38 4 1 f ./sys/fs/cgroup/pids/cgroup.sane_behavior 37 4 1 f ./sys/fs/cgroup/cpuset/cgroup.sane_behavior 36 4 1 f ./sys/fs/cgroup/cpu,cpuacct/cgroup.sane_behavior 35 4 1 f ./sys/fs/cgroup/blkio/cgroup.sane_behavior 34 4 1 f ./sys/fs/cgroup/memory/cgroup.sane_behavior 33 4 1 f ./sys/fs/cgroup/rdma/cgroup.sane_behavior 30 4 1 f ./sys/fs/cgroup/systemd/cgroup.sane_behavior 29 4 1 f ./sys/fs/cgroup/unified/cgroup.controllers 1812 4 1 l ./snap/core18/1074/bin/bzcmp 1797 4 1 l ./snap/core18/1066/bin/bzcmp 1803 4 1 f ./snap/gnome-characters/292/flavor-select 1809 4 1 f ./snap/gnome-characters/296/flavor-select 1810 4 2 d ./snap/gnome-3-28-1804/67/etc/X11/Xreset.d 1794 4 2 d ./snap/gnome-3-28-1804/63/etc/X11/Xreset.d 1796 4 25 d ./snap/gtk-common-themes/1313/share/gtk2 1804 4 15 d ./snap/gtk-common-themes/1198/share/gtk2 1798 4 1 f ./snap/gnome-system-monitor/100/flavor-select 1801 4 1 f ./snap/gnome-system-monitor/95/flavor-select 1807 4 1 l ./snap/core/7169/bin/bzcmp 1808 4 1 l ./snap/core/7270/bin/bzcmp 1806 4 1 f ./snap/gnome-calculator/260/flavor-select 1802 4 1 f ./snap/gnome-calculator/406/flavor-select 1805 4 1 f ./snap/gnome-calculator/352/flavor-select 1793 4 3 d ./snap/gnome-logs/45/etc 1792 4 1 f ./snap/gnome-logs/61/flavor-select 1800 4 1 f ./snap/gnome-logs/57/flavor-select 1799 4 2 d ./snap/gnome-3-26-1604/90/etc/X11/Xreset.d 1795 4 2 d ./snap/gnome-3-26-1604/88/etc/X11/Xreset.d
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Answer
After editing, the output of the modified command shows that the inode number is unique per file system. With different device numbers, the number of hard links is not related to each other.
As expected you see a link count of 1 for normal files (type f) or devices (type c for a character device in this case).
Directories (type d) have a link count of at least 2 for the directory name and the contained .. If the directory contains subdirectories, the link count will be equal to the number of immediate subdirectories + 2, because every subdirectory will contain a .. entry.
For information about /snap see https://snapcraft.io/docs/system-snap-directory
For information about /sys/fs/cgroup see http://man7.org/linux/man-pages/man7/cgroups.7.html