When activate the plugin, it has load the config file and there are some other issues cause mm try to fix config and persist the readonly config file.
unable to start plugin: mattermost-file-list: failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system
github.com/mattermost/mattermost-server/plugin.(*Environment).Activate /go/src/github.com/mattermost/mattermost-server/plugin/environment.go:251
github.com/mattermost/mattermost-server/app.(*App).SyncPluginsActiveState
/go/src/github.com/mattermost/mattermost-server/app/plugin.go:100
github.com/mattermost/mattermost-server/app.(*App).InitPlugins
/go/src/github.com/mattermost/mattermost-server/app/plugin.go:133
github.com/mattermost/mattermost-server/app.(*Server).RunOldAppInitalization.func6
/go/src/github.com/mattermost/mattermost-server/app/server_app_adapters.go:148
github.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners.func1
/go/src/github.com/mattermost/mattermost-server/config/emitter.go:35
sync.(*Map).Range
/usr/local/go/src/sync/map.go:333
github.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners
/go/src/github.com/mattermost/mattermost-server/config/emitter.go:33
github.com/mattermost/mattermost-server/config.(*commonStore).set
/go/src/github.com/mattermost/mattermost-server/config/common.go:90
github.com/mattermost/mattermost-server/config.(*DatabaseStore).Set
/go/src/github.com/mattermost/mattermost-server/config/database.go:148
github.com/mattermost/mattermost-server/app.(*App).SaveConfig
/go/src/github.com/mattermost/mattermost-server/app/config.go:378
github.com/mattermost/mattermost-server/app.(*App).EnablePlugin
/go/src/github.com/mattermost/mattermost-server/app/plugin.go:333
github.com/mattermost/mattermost-server/api4.enablePlugin
/go/src/github.com/mattermost/mattermost-server/api4/plugin.go:298
github.com/mattermost/mattermost-server/web.Handler.ServeHTTP
/go/src/github.com/mattermost/mattermost-server/web/handlers.go:148
github.com/NYTimes/gziphandler.GzipHandlerWithOpts.func1.1
/go/src/github.com/mattermost/mattermost-server/vendor/github.com/NYTimes/gziphandler/gzip.go:336
net/http.HandlerFunc.ServeHTTP
/usr/local/go/src/net/http/server.go:1995
github.com/gorilla/mux.(*Router).ServeHTTP
/go/src/github.com/mattermost/mattermost-server/vendor/github.com/gorilla/mux/mux.go:212
net/http.serverHandler.ServeHTTP
/usr/local/go/src/net/http/server.go:2774
net/http.(*conn).serve
/usr/local/go/src/net/http/server.go:1878
runtime.goexit
/usr/local/go/src/runtime/asm_amd64.s:1337
{"level":"info","ts":1574415946.239485,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultServerLocale must be one of the supported locales. Setting DefaultServerLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.2395804,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultClientLocale must be one of the supported locales. Setting DefaultClientLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.2396028,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"AvailableLocales must include DefaultClientLocale. Setting AvailableLocales to all locales as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"error","ts":1574415946.2436152,"caller":"mlog/log.go:174","msg":"Unable to activate plugin","plugin_id":"mattermost-file-list","error":"unable to start plugin: mattermost-file-list: failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system","errorVerbose":"failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system\nunable to start plugin: mattermost-file-list\ngithub.com/mattermost/mattermost-server/plugin.(*Environment).Activate\n\t/go/src/github.com/mattermost/mattermost-server/plugin/environment.go:251\ngithub.com/mattermost/mattermost-server/app.(*App).SyncPluginsActiveState\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:100\ngithub.com/mattermost/mattermost-server/app.(*App).InitPlugins\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:133\ngithub.com/mattermost/mattermost-server/app.(*Server).RunOldAppInitalization.func6\n\t/go/src/github.com/mattermost/mattermost-server/app/server_app_adapters.go:148\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners.func1\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:35\nsync.(*Map).Range\n\t/usr/local/go/src/sync/map.go:333\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:33\ngithub.com/mattermost/mattermost-server/config.(*commonStore).set\n\t/go/src/github.com/mattermost/mattermost-server/config/common.go:90\ngithub.com/mattermost/mattermost-server/config.(*DatabaseStore).Set\n\t/go/src/github.com/mattermost/mattermost-server/config/database.go:148\ngithub.com/mattermost/mattermost-server/app.(*Server).UpdateConfig\n\t/go/src/github.com/mattermost/mattermost-server/app/config.go:53\ngithub.com/mattermost/mattermost-server/app.(*App).UpdateConfig\n\t/go/src/github.com/mattermost/mattermost-server/app/config.go:59\ngithub.com/mattermost/mattermost-server/app.(*App).EnablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:328\ngithub.com/mattermost/mattermost-server/api4.enablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/api4/plugin.go:298\ngithub.com/mattermost/mattermost-server/web.Handler.ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/web/handlers.go:148\ngithub.com/NYTimes/gziphandler.GzipHandlerWithOpts.func1.1\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/NYTimes/gziphandler/gzip.go:336\nnet/http.HandlerFunc.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:1995\ngithub.com/gorilla/mux.(*Router).ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/gorilla/mux/mux.go:212\nnet/http.serverHandler.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2774\nnet/http.(*conn).serve\n\t/usr/local/go/src/net/http/server.go:1878\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1337"}
{"level":"info","ts":1574415946.2884111,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultServerLocale must be one of the supported locales. Setting DefaultServerLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.2885144,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultClientLocale must be one of the supported locales. Setting DefaultClientLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.2885332,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"AvailableLocales must include DefaultClientLocale. Setting AvailableLocales to all locales as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"error","ts":1574415946.2925034,"caller":"mlog/log.go:174","msg":"Unable to activate plugin","plugin_id":"mattermost-file-list","error":"unable to start plugin: mattermost-file-list: failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system","errorVerbose":"failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system\nunable to start plugin: mattermost-file-list\ngithub.com/mattermost/mattermost-server/plugin.(*Environment).Activate\n\t/go/src/github.com/mattermost/mattermost-server/plugin/environment.go:251\ngithub.com/mattermost/mattermost-server/app.(*App).SyncPluginsActiveState\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:100\ngithub.com/mattermost/mattermost-server/app.(*App).InitPlugins.func2\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:183\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners.func1\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:35\nsync.(*Map).Range\n\t/usr/local/go/src/sync/map.go:333\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:33\ngithub.com/mattermost/mattermost-server/config.(*commonStore).set\n\t/go/src/github.com/mattermost/mattermost-server/config/common.go:90\ngithub.com/mattermost/mattermost-server/config.(*DatabaseStore).Set\n\t/go/src/github.com/mattermost/mattermost-server/config/database.go:148\ngithub.com/mattermost/mattermost-server/app.(*Server).UpdateConfig\n\t/go/src/github.com/mattermost/mattermost-server/app/config.go:53\ngithub.com/mattermost/mattermost-server/app.(*App).UpdateConfig\n\t/go/src/github.com/mattermost/mattermost-server/app/config.go:59\ngithub.com/mattermost/mattermost-server/app.(*App).EnablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:328\ngithub.com/mattermost/mattermost-server/api4.enablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/api4/plugin.go:298\ngithub.com/mattermost/mattermost-server/web.Handler.ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/web/handlers.go:148\ngithub.com/NYTimes/gziphandler.GzipHandlerWithOpts.func1.1\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/NYTimes/gziphandler/gzip.go:336\nnet/http.HandlerFunc.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:1995\ngithub.com/gorilla/mux.(*Router).ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/gorilla/mux/mux.go:212\nnet/http.serverHandler.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2774\nnet/http.(*conn).serve\n\t/usr/local/go/src/net/http/server.go:1878\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1337"}
{"level":"info","ts":1574415946.3499353,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultServerLocale must be one of the supported locales. Setting DefaultServerLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.3500009,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultClientLocale must be one of the supported locales. Setting DefaultClientLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.3500133,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"AvailableLocales must include DefaultClientLocale. Setting AvailableLocales to all locales as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"error","ts":1574415946.3533194,"caller":"mlog/log.go:174","msg":"Unable to activate plugin","plugin_id":"mattermost-file-list","error":"unable to start plugin: mattermost-file-list: failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system","errorVerbose":"failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system\nunable to start plugin: mattermost-file-list\ngithub.com/mattermost/mattermost-server/plugin.(*Environment).Activate\n\t/go/src/github.com/mattermost/mattermost-server/plugin/environment.go:251\ngithub.com/mattermost/mattermost-server/app.(*App).SyncPluginsActiveState\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:100\ngithub.com/mattermost/mattermost-server/app.(*App).InitPlugins.func2\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:183\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners.func1\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:35\nsync.(*Map).Range\n\t/usr/local/go/src/sync/map.go:333\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:33\ngithub.com/mattermost/mattermost-server/config.(*commonStore).set\n\t/go/src/github.com/mattermost/mattermost-server/config/common.go:90\ngithub.com/mattermost/mattermost-server/config.(*DatabaseStore).Set\n\t/go/src/github.com/mattermost/mattermost-server/config/database.go:148\ngithub.com/mattermost/mattermost-server/app.(*App).SaveConfig\n\t/go/src/github.com/mattermost/mattermost-server/app/config.go:378\ngithub.com/mattermost/mattermost-server/app.(*App).EnablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:333\ngithub.com/mattermost/mattermost-server/api4.enablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/api4/plugin.go:298\ngithub.com/mattermost/mattermost-server/web.Handler.ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/web/handlers.go:148\ngithub.com/NYTimes/gziphandler.GzipHandlerWithOpts.func1.1\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/NYTimes/gziphandler/gzip.go:336\nnet/http.HandlerFunc.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:1995\ngithub.com/gorilla/mux.(*Router).ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/gorilla/mux/mux.go:212\nnet/http.serverHandler.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2774\nnet/http.(*conn).serve\n\t/usr/local/go/src/net/http/server.go:1878\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1337"}
{"level":"info","ts":1574415946.3960114,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultServerLocale must be one of the supported locales. Setting DefaultServerLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.3960712,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"DefaultClientLocale must be one of the supported locales. Setting DefaultClientLocale to en as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"info","ts":1574415946.396083,"caller":"go-plugin/stream.go:15","msg":"{\"level\":\"warn\",\"msg\":\"AvailableLocales must include DefaultClientLocale. Setting AvailableLocales to all locales as default value.\"}","plugin_id":"mattermost-file-list","source":"plugin_stdout"}
{"level":"error","ts":1574415946.399258,"caller":"mlog/log.go:174","msg":"Unable to activate plugin","plugin_id":"mattermost-file-list","error":"unable to start plugin: mattermost-file-list: failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system","errorVerbose":"failed to load: failed to persist required changes after load: failed to write file: open /mattermost/config/config.json: read-only file system\nunable to start plugin: mattermost-file-list\ngithub.com/mattermost/mattermost-server/plugin.(*Environment).Activate\n\t/go/src/github.com/mattermost/mattermost-server/plugin/environment.go:251\ngithub.com/mattermost/mattermost-server/app.(*App).SyncPluginsActiveState\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:100\ngithub.com/mattermost/mattermost-server/app.(*App).InitPlugins\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:133\ngithub.com/mattermost/mattermost-server/app.(*Server).RunOldAppInitalization.func6\n\t/go/src/github.com/mattermost/mattermost-server/app/server_app_adapters.go:148\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners.func1\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:35\nsync.(*Map).Range\n\t/usr/local/go/src/sync/map.go:333\ngithub.com/mattermost/mattermost-server/config.(*emitter).invokeConfigListeners\n\t/go/src/github.com/mattermost/mattermost-server/config/emitter.go:33\ngithub.com/mattermost/mattermost-server/config.(*commonStore).set\n\t/go/src/github.com/mattermost/mattermost-server/config/common.go:90\ngithub.com/mattermost/mattermost-server/config.(*DatabaseStore).Set\n\t/go/src/github.com/mattermost/mattermost-server/config/database.go:148\ngithub.com/mattermost/mattermost-server/app.(*App).SaveConfig\n\t/go/src/github.com/mattermost/mattermost-server/app/config.go:378\ngithub.com/mattermost/mattermost-server/app.(*App).EnablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/app/plugin.go:333\ngithub.com/mattermost/mattermost-server/api4.enablePlugin\n\t/go/src/github.com/mattermost/mattermost-server/api4/plugin.go:298\ngithub.com/mattermost/mattermost-server/web.Handler.ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/web/handlers.go:148\ngithub.com/NYTimes/gziphandler.GzipHandlerWithOpts.func1.1\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/NYTimes/gziphandler/gzip.go:336\nnet/http.HandlerFunc.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:1995\ngithub.com/gorilla/mux.(*Router).ServeHTTP\n\t/go/src/github.com/mattermost/mattermost-server/vendor/github.com/gorilla/mux/mux.go:212\nnet/http.serverHandler.ServeHTTP\n\t/usr/local/go/src/net/http/server.go:2774\nnet/http.(*conn).serve\n\t/usr/local/go/src/net/http/server.go:1878\nruntime.goexit\n\t/usr/local/go/src/runtime/asm_amd64.s:1337"}