same device mounted on differences mount points

May 30, 2022 - 2 minutes read - 240 words

As in my previous article, I gave the following information of my pod. I still have some time before bed, I couldn’t help to seek the reason of that.

/usr/share/nginx/html # df -h
Filesystem                Size      Used Available Use% Mounted on
overlay                  80.0G     34.5G     45.5G  43% /
tmpfs                    64.0M         0     64.0M   0% /dev
tmpfs                     3.7G         0      3.7G   0% /sys/fs/cgroup
/dev/nvme0n1p1           80.0G     34.5G     45.5G  43% /dev/termination-log
/dev/nvme0n1p1           80.0G     34.5G     45.5G  43% /etc/resolv.conf
/dev/nvme0n1p1           80.0G     34.5G     45.5G  43% /etc/hostname
/dev/nvme0n1p1           80.0G     34.5G     45.5G  43% /etc/hosts
shm                      64.0M         0     64.0M   0% /dev/shm
tmpfs                     3.7G     12.0K      3.7G   0% /run/secrets/kubernetes.io/serviceaccount
tmpfs                     3.7G         0      3.7G   0% /proc/acpi
tmpfs                    64.0M         0     64.0M   0% /proc/kcore
tmpfs                    64.0M         0     64.0M   0% /proc/keys
tmpfs                    64.0M         0     64.0M   0% /proc/latency_stats
tmpfs                    64.0M         0     64.0M   0% /proc/timer_list
tmpfs                    64.0M         0     64.0M   0% /proc/sched_debug
tmpfs                     3.7G         0      3.7G   0% /sys/firmware

Linux: same device mounted on differences mount points gave me the direction to look: bind mount. Since I couldn’t find /dev/nvme0n1p1 in the /etc/mtab of my pod, I continued to look for other information. Later I found that findmnt can list all the mounts including bind mount. Here is the results.

/usr/share/nginx/html # findmnt --real --verbose
TARGET               SOURCE                                                                                                                  FSTYPE OPTIONS
/dev/termination-log /dev/nvme0n1p1[/var/lib/kubelet/pods/c7eb6eb6-951c-43f8-9efe-4869d64a7edf/containers/webclient/af0905e1]                xfs    rw,noatime,attr2,inode64,logbufs=8,logbsize=32k,noquota
/etc/resolv.conf     /dev/nvme0n1p1[/var/lib/docker/containers/7834807dda525874ef8234c9b2f293a953dc2e6a0798387ccf056f7139af04ba/resolv.conf] xfs    rw,noatime,attr2,inode64,logbufs=8,logbsize=32k,noquota
/etc/hostname        /dev/nvme0n1p1[/var/lib/docker/containers/7834807dda525874ef8234c9b2f293a953dc2e6a0798387ccf056f7139af04ba/hostname]    xfs    rw,noatime,attr2,inode64,logbufs=8,logbsize=32k,noquota
/etc/hosts           /dev/nvme0n1p1[/var/lib/kubelet/pods/c7eb6eb6-951c-43f8-9efe-4869d64a7edf/etc-hosts]                                    xfs    rw,noatime,attr2,inode64,logbufs=8,logbsize=32k,noquota

It seems that kubelet and docker do the magic to do bind mounting. Next time, I will dig deeper in this area. It’s time to go bed now.