Cloud9のディスク容量を減らしたい

Cloud9でRuby on Railsを使用したアプリケーションを作っています。

ディスク容量がもう少しでいっぱいになるという警告が出ました。
ネット検索でherokuのtempファイルが容量を圧迫していることが多いと知り、削除しようと思ったのですが、
tempファイルが見当たりません。

探し方が悪いのでしょうか？
もしtempファイルがない場合、どのファイルを削除すればいいでしょうか？

また、workspaceにrails tutorialで作成したsample_appのフォルダがあったのですべて削除したのですが、
ディスク容量は相変わらずalmost fullのままでした。

できれば有料の容量グレードアップをせずに、このまま使っていきたいです。

アドバイスお願いします！

コマンド

$ du -h -t 50M

結果

53M     ./usr/local/rvm/rubies/ruby-2.4.0/lib
54M     ./usr/local/rvm/rubies/ruby-2.4.0
54M     ./usr/local/rvm/rubies
108M    ./usr/local/rvm/gems/ruby-2.4.0/gems
135M    ./usr/local/rvm/gems/ruby-2.4.0
135M    ./usr/local/rvm/gems
215M    ./usr/local/rvm
59M     ./usr/local/heroku/node_modules
93M     ./usr/local/heroku
308M    ./usr/local
178M    ./usr/bin
154M    ./usr/share/doc
70M     ./usr/share/emacs/24.3
70M     ./usr/share/emacs
576M    ./usr/share
320M    ./usr/lib/x86_64-linux-gnu
93M     ./usr/lib/valgrind
70M     ./usr/lib/python2.7
78M     ./usr/lib/jvm/java-7-openjdk-amd64/jre/lib
78M     ./usr/lib/jvm/java-7-openjdk-amd64/jre
78M     ./usr/lib/jvm/java-7-openjdk-amd64
78M     ./usr/lib/jvm
862M    ./usr/lib
114M    ./usr/include/boost
151M    ./usr/include
2.1G    ./usr
du: cannot read directory ‘./nix/.cache’: Permission denied
55M     ./nix/store/cz8sfjinal66y350ynyz89vihihcn7k6-gcc-4.9.3/libexec/gcc/x86_64-unknown-linux-gnu/4.9.3
55M     ./nix/store/cz8sfjinal66y350ynyz89vihihcn7k6-gcc-4.9.3/libexec/gcc/x86_64-unknown-linux-gnu
55M     ./nix/store/cz8sfjinal66y350ynyz89vihihcn7k6-gcc-4.9.3/libexec/gcc
55M     ./nix/store/cz8sfjinal66y350ynyz89vihihcn7k6-gcc-4.9.3/libexec
99M     ./nix/store/cz8sfjinal66y350ynyz89vihihcn7k6-gcc-4.9.3
68M     ./nix/store/d1prcspbh2qsviipvnaxizcj8l3g7fpw-bootstrap-tools/libexec/gcc/x86_64-unknown-linux-gnu/5.3.0
68M     ./nix/store/d1prcspbh2qsviipvnaxizcj8l3g7fpw-bootstrap-tools/libexec/gcc/x86_64-unknown-linux-gnu
68M     ./nix/store/d1prcspbh2qsviipvnaxizcj8l3g7fpw-bootstrap-tools/libexec/gcc
68M     ./nix/store/d1prcspbh2qsviipvnaxizcj8l3g7fpw-bootstrap-tools/libexec
114M    ./nix/store/d1prcspbh2qsviipvnaxizcj8l3g7fpw-bootstrap-tools
106M    ./nix/store/lrd5wjp4151wmflci68i8vd7a9a4lwmb-glibc-locales-2.23/lib/locale
106M    ./nix/store/lrd5wjp4151wmflci68i8vd7a9a4lwmb-glibc-locales-2.23/lib
106M    ./nix/store/lrd5wjp4151wmflci68i8vd7a9a4lwmb-glibc-locales-2.23
61M     ./nix/store/3fyzfkv0k3d1ymfv25d2k7kqbpibhl1r-gccgo49-4.9.3/libexec/gcc/x86_64-unknown-linux-gnu/4.9.3
61M     ./nix/store/3fyzfkv0k3d1ymfv25d2k7kqbpibhl1r-gccgo49-4.9.3/libexec/gcc/x86_64-unknown-linux-gnu
61M     ./nix/store/3fyzfkv0k3d1ymfv25d2k7kqbpibhl1r-gccgo49-4.9.3/libexec/gcc
61M     ./nix/store/3fyzfkv0k3d1ymfv25d2k7kqbpibhl1r-gccgo49-4.9.3/libexec
67M     ./nix/store/3fyzfkv0k3d1ymfv25d2k7kqbpibhl1r-gccgo49-4.9.3/lib
151M    ./nix/store/3fyzfkv0k3d1ymfv25d2k7kqbpibhl1r-gccgo49-4.9.3
70M     ./nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/share/ri/2.3.0/system
70M     ./nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/share/ri/2.3.0
70M     ./nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/share/ri
70M     ./nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0/share
107M    ./nix/store/zmisxnl63ica4zaviifixamr3xg27kzp-ruby-2.3.1-p0
52M     ./nix/store/adnbhcy51b4x19fmfci6h0qfy5sarwpr-python-2.7.11/lib/python2.7
54M     ./nix/store/adnbhcy51b4x19fmfci6h0qfy5sarwpr-python-2.7.11/lib
55M     ./nix/store/adnbhcy51b4x19fmfci6h0qfy5sarwpr-python-2.7.11
51M     ./nix/store/7nygbmc03nxm24iz59s6gwwh9j1q5ham-nixpkgs/nixpkgs/pkgs/development/haskell-modules
77M     ./nix/store/7nygbmc03nxm24iz59s6gwwh9j1q5ham-nixpkgs/nixpkgs/pkgs/development
128M    ./nix/store/7nygbmc03nxm24iz59s6gwwh9j1q5ham-nixpkgs/nixpkgs/pkgs
134M    ./nix/store/7nygbmc03nxm24iz59s6gwwh9j1q5ham-nixpkgs/nixpkgs
134M    ./nix/store/7nygbmc03nxm24iz59s6gwwh9j1q5ham-nixpkgs
100M    ./nix/store/gphrkb6lzn9bf7db2q1z00ypfdh46lma-node-sources/deps
136M    ./nix/store/gphrkb6lzn9bf7db2q1z00ypfdh46lma-node-sources
69M     ./nix/store/l8y2srrkp5fflwph7vq0gllj1k1ai17w-gcc-5.3.0/libexec/gcc/x86_64-unknown-linux-gnu/5.3.0
69M     ./nix/store/l8y2srrkp5fflwph7vq0gllj1k1ai17w-gcc-5.3.0/libexec/gcc/x86_64-unknown-linux-gnu
69M     ./nix/store/l8y2srrkp5fflwph7vq0gllj1k1ai17w-gcc-5.3.0/libexec/gcc
69M     ./nix/store/l8y2srrkp5fflwph7vq0gllj1k1ai17w-gcc-5.3.0/libexec
116M    ./nix/store/l8y2srrkp5fflwph7vq0gllj1k1ai17w-gcc-5.3.0
68M     ./nix/store/w1vk7050ib5vi1qlqr80s3hfvx4ni5cm-python3-3.5.1/lib/python3.5
71M     ./nix/store/w1vk7050ib5vi1qlqr80s3hfvx4ni5cm-python3-3.5.1/lib
72M     ./nix/store/w1vk7050ib5vi1qlqr80s3hfvx4ni5cm-python3-3.5.1
1.9G    ./nix/store
2.0G    ./nix
64M     ./home/ubuntu/.local/share/heroku/client/node_modules
98M     ./home/ubuntu/.local/share/heroku/client
98M     ./home/ubuntu/.local/share/heroku
98M     ./home/ubuntu/.local/share
98M     ./home/ubuntu/.local
51M     ./home/ubuntu/workspace
51M     ./home/ubuntu/.nvm/versions/node/v6.11.2
51M     ./home/ubuntu/.nvm/versions/node
51M     ./home/ubuntu/.nvm/versions
54M     ./home/ubuntu/.nvm
221M    ./home/ubuntu
221M    ./home
du: cannot read directory ‘./var/lib/php5’: Permission denied
du: cannot read directory ‘./var/lib/mysql’: Permission denied
du: cannot read directory ‘./var/lib/postgresql/9.3/main’: Permission denied
du: cannot read directory ‘./var/lib/sudo’: Permission denied
du: cannot read directory ‘./var/lib/polkit-1’: Permission denied
du: cannot read directory ‘./var/lib/mysql-files’: Permission denied
du: cannot read directory ‘./var/lib/couchdb’: Permission denied
69M     ./var/lib
du: cannot read directory ‘./var/cache/ldconfig’: Permission denied
117M    ./var/cache/apt/apt-file
117M    ./var/cache/apt
124M    ./var/cache
du: cannot read directory ‘./var/log/mysql’: Permission denied
du: cannot read directory ‘./var/log/apache2’: Permission denied
du: cannot read directory ‘./var/log/exim4’: Permission denied
du: cannot read directory ‘./var/log/couchdb’: Permission denied
du: cannot read directory ‘./var/spool/exim4’: Permission denied
du: cannot read directory ‘./var/spool/rsyslog’: Permission denied
du: cannot read directory ‘./var/spool/cron/crontabs’: Permission denied
194M    ./var
du: cannot read directory ‘./lost+found’: Permission denied
du: cannot read directory ‘./run/exim4’: Permission denied
du: cannot read directory ‘./root’: Permission denied
du: cannot read directory ‘./etc/polkit-1/localauthority’: Permission denied
du: cannot read directory ‘./etc/ssl/private’: Permission denied
du: cannot read directory ‘./etc/couchdb/local.d’: Permission denied
52M     ./opt/go/src
87M     ./opt/go/pkg/tool/linux_amd64
87M     ./opt/go/pkg/tool
163M    ./opt/go/pkg
279M    ./opt/go
279M    ./opt
52M     ./mnt/shared/benchmark/go
52M     ./mnt/shared/benchmark
99M     ./mnt/shared/lib/node_modules
51M     ./mnt/shared/lib/python2/lib/python2.7/site-packages/codeintel/codeintel2/stdlibs
68M     ./mnt/shared/lib/python2/lib/python2.7/site-packages/codeintel/codeintel2
87M     ./mnt/shared/lib/python2/lib/python2.7/site-packages/codeintel
109M    ./mnt/shared/lib/python2/lib/python2.7/site-packages
110M    ./mnt/shared/lib/python2/lib/python2.7
110M    ./mnt/shared/lib/python2/lib
110M    ./mnt/shared/lib/python2
258M    ./mnt/shared/lib
52M     ./mnt/shared/plugins/salesforce.sync/kracht/node_modules
56M     ./mnt/shared/plugins/salesforce.sync/kracht
76M     ./mnt/shared/plugins/salesforce.sync
91M     ./mnt/shared/plugins
414M    ./mnt/shared
414M    ./mnt
du: cannot read directory ‘./proc/tty/driver’: Permission denied
du: cannot read directory ‘./proc/1/task/1/fd’: Permission denied
du: cannot read directory ‘./proc/1/task/1/fdinfo’: Permission denied
du: cannot read directory ‘./proc/1/task/1/ns’: Permission denied
du: cannot read directory ‘./proc/1/fd’: Permission denied
du: cannot read directory ‘./proc/1/map_files’: Permission denied
du: cannot read directory ‘./proc/1/fdinfo’: Permission denied
du: cannot read directory ‘./proc/1/ns’: Permission denied
du: cannot read directory ‘./proc/7/task/7/fd’: Permission denied
du: cannot read directory ‘./proc/7/task/7/fdinfo’: Permission denied
du: cannot read directory ‘./proc/7/task/7/ns’: Permission denied
du: cannot read directory ‘./proc/7/fd’: Permission denied
du: cannot read directory ‘./proc/7/map_files’: Permission denied
du: cannot read directory ‘./proc/7/fdinfo’: Permission denied
du: cannot read directory ‘./proc/7/ns’: Permission denied
du: cannot read directory ‘./proc/14192/task/14192/fd’: Permission denied
du: cannot read directory ‘./proc/14192/task/14192/fdinfo’: Permission denied
du: cannot read directory ‘./proc/14192/task/14192/ns’: Permission denied
du: cannot read directory ‘./proc/14192/fd’: Permission denied
du: cannot read directory ‘./proc/14192/map_files’: Permission denied
du: cannot read directory ‘./proc/14192/fdinfo’: Permission denied
du: cannot read directory ‘./proc/14192/ns’: Permission denied
du: cannot access ‘./proc/15072/task/15072/fd/4’: No such file or directory
du: cannot access ‘./proc/15072/task/15072/fdinfo/4’: No such file or directory
du: cannot access ‘./proc/15072/fd/3’: No such file or directory
du: cannot access ‘./proc/15072/fdinfo/3’: No such file or directory
5.1G    .