Modification to /run is not captured

[AkihiroSuda]

Because /run is mounted as tmpfs, unlike Docker.

buildkit/vendor/github.com/containerd/containerd/oci/spec_unix.go

Line 148 in b14fd54

Destination: "/run",

$ docker build -t foo . && docker run -it --rm  foo ls -l /run
Sending build context to Docker daemon  2.048kB
Step 1/2 : FROM busybox
 ---> 8c811b4aec35
Step 2/2 : RUN mkdir -p /run && echo hello > /run/hello
 ---> Running in 6a5b0410c0c8
Removing intermediate container 6a5b0410c0c8
 ---> 26c30d301753
Successfully built 26c30d301753
Successfully tagged foo:latest
total 4
-rw-r--r--    1 root     root             6 Jun  4 14:12 hello

$ sudo build-using-dockerfile -t foo . && docker run -it --rm  foo ls -l /run
[+] Building 3.6s (5/5) FINISHED
 => local://context (.dockerignore)                                                                                                       0.0s
 => => transferring context: 02B                                                                                                          0.0s
 => local://dockerfile (Dockerfile)                                                                                                       0.1s
 => => transferring dockerfile: 101B                                                                                                      0.0s
 => docker-image://docker.io/library/busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47                      0.0s
 => => resolve docker.io/library/busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47                          0.0s
 => => sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47 2.70kB / 2.70kB                                            0.0s
 => => sha256:74f634b1bc1bd74535d5209589734efbd44a25f4e2dc96d78784576a3eb5b335 527B / 527B                                                0.0s
 => => sha256:07a152489297fc2bca20be96fab3527ceac5668328a30fd543a160cd689ee548 723.15kB / 723.15kB                                        0.0s
 => => sha256:8c811b4aec35f259572d0f79207bc0678df4c736eeec50bc9fec37ed936a472a 1.50kB / 1.50kB                                            0.0s
 => => unpacking docker.io/library/busybox@sha256:141c253bc4c3fd0a201d32dc1f493bcf3fff003b6df416dea4f41046e0f37d47                        0.0s
 => /bin/sh -c mkdir -p /run && echo hello > /run/hello                                                                                   0.2s
 => exporting to oci image format                                                                                                         0.4s
 => => exporting layers                                                                                                                   0.3s
 => => exporting manifest sha256:83a9ac75cdfe48de0028a9016b1d72a00d340ccb60133b405111d0621766cfcc                                         0.0s
 => => exporting config sha256:9c539798303e23f5cf22e2c124fab9eea84883c365a67cd5bc8e1216c1e21902                                           0.0s
 => => sending tarball                                                                                                                    0.0s
INFO[0003] Loading the image to Docker as "foo". This may take a while.
0c53f8a6b89d: Loading layer [==================================================>]     179B/179B
The image foo:latest already exists, renaming the old one with ID sha256:26c30d3017532dd1a6bd991e2d6856af2927f61f85454534d9f23e55345d6506 to empty string
Loaded image: foo:latest
INFO[0003] Done
total 0

[kunalkushwaha]

Is there any specific reason to mount /run for buildkit?

[AkihiroSuda]

For buildkit we can safely remove /run mount.