EC2環境下でrails assets:precompileがうまくいかない

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> Successfully installed Yarn 1.7.0! Please open another terminal where the `yarn` command will now be available.
[ec2-user@ip-172-31-32-152 chat-space]$ rails assets:precompile
Yarn executable was not detected in the system.
Download Yarn at https://yarnpkg.com/en/docs/install
[ec2-user@ip-172-31-32-152 chat-space]$ source ~/.bashrc
[ec2-user@ip-172-31-32-152 chat-space]$ yarn -v
1.7.0
[ec2-user@ip-172-31-32-152 chat-space]$ rails assets:precompile
yarn install v1.7.0
info No lockfile found.
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
[4/4] Building fresh packages...
success Saved lockfile.
Done in 0.16s.
[ec2-user@ip-172-31-32-152 chat-space]$ RAILS_SERVE_STATIC_FILES=1 unicorn_rails -c config/unicorn.rb -E production
[ec2-user@ip-172-31-32-152 chat-space]$ rails assets:precompile
yarn install v1.7.0
[1/4] Resolving packages...
success Already up-to-date.
Done in 0.07s.
[ec2-user@ip-172-31-32-152 chat-space]$ RAILS_SERVE_STATIC_FILES=1 unicorn_rails -c config/unicorn.rb -E production
[ec2-user@ip-172-31-32-152 chat-space]$ git pull origin master
remote: Counting objects: 8, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 8 (delta 2), reused 8 (delta 2), pack-reused 0
Unpacking objects: 100% (8/8), done.
From https://github.com/yu-smc/chat-space
 * branch            master     -> FETCH_HEAD
   c641bdf..b317bd1  master     -> origin/master
Updating c641bdf..b317bd1
Fast-forward
 public/uploads/message/image/13/map_eng.jpg | Bin 0 -> 69871 bytes
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 public/uploads/message/image/13/map_eng.jpg
[ec2-user@ip-172-31-32-152 chat-space]$ rails assets:precompile
yarn install v1.7.0
[1/4] Resolving packages...
success Already up-to-date.
Done in 0.07s.
[ec2-user@ip-172-31-32-152 chat-space]$ git pull origin master
remote: Counting objects: 6, done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 6 (delta 2), reused 6 (delta 2), pack-reused 0
Unpacking objects: 100% (6/6), done.
From https://github.com/yu-smc/chat-space