config.json in container and 'Device or resource busy'

[robertkarbowski]

Bug report information

Description

In docker-entrypoint.sh there is a command:

...
    mv config.json.tmp config.json
...

It works fine as long as no-one wants to mount external config.json file (docker run -v $(pwd)/config.json:/usr/src/app/config.json ...). If so "docker" fails with the error:

mv: cannot move 'config.json.tmp' to 'config.json': Device or resource busy

The reason is that Linux does not allow to delete/rename mount points (mv uses actually rename() syscall).

One of the possible solutions is to replace "mv" with 2 commands:

--- old/docker-entrypoint.sh    2021-08-31 07:47:00.832079384 +0000
+++ new/docker-entrypoint.sh    2021-08-31 07:47:30.516815669 +0000
@@ -197,7 +197,8 @@
 
 if [[ $JQ_FILTERS_CONFIG != "." ]]; then
     jq "$JQ_FILTERS_CONFIG" config.json > config.json.tmp
-    mv config.json.tmp config.json
+    cp config.json.tmp config.json
+    rm config.json.tmp
 fi

[yishangru]

We also encountered this problem for kubernetes v1.20. Instead of mounting config.json, we mount .docker directory. In this way, you can change config.json (rewrite, replace, etc.) in container environment.

[sytolk]

duplicate https://github.com/scality/cloudserver/issues/1520#issuecomment-419576769