TL;DR

python2 -c 'import os,sys,fcntl; flags = fcntl.fcntl(sys.stdout, fcntl.F_GETFL); fcntl.fcntl(sys.stdout, fcntl.F_SETFL, flags&~os.O_NONBLOCK);'  

Add the line above at before_install section of your .travis.yml file.
Specifically, add this line before the line in your .travis.yml which causes the error.

This problem won't happen in debug build.

Preface

One of my Travis CI build got tar: write error while installing the gcloud SDK.
I was trying to find the reason in debug build, but got nothing.

Reason

EAGAIN (errno 11) in Linux while dealing with non-blocking operations.

Lots of CLI tools expect stdout is in blocking mode,
but it looks like Travis CI set stdout to non-blocking mode in default.
These CLI tools (tar, make, ...) didn't handle EAGAIN error well. (Should retry when got this error)

Solution

Add the line below before the line in your .travis.yml which causes error.
You can also add it at before_install section of your .travis.yml.

python2 -c 'import os,sys,fcntl; flags = fcntl.fcntl(sys.stdout, fcntl.F_GETFL); fcntl.fcntl(sys.stdout, fcntl.F_SETFL, flags&~os.O_NONBLOCK);'  

For Python 3.5+:

python3 -c 'import os,sys; os.set_blocking(sys.stdout.fileno(), True)'  

This will turn off the non-blocking mode for stdout.

References

• Large writes to stdout sometimes fail with "Resource temporarily unavailable". · Issue #4704 · travis-ci/travis-ci · GitHub
• Linux中的EAGAIN含义 - 桂皮猪 - 博客园
• linux非阻塞的socket EAGAIN的错误处理 - CSDN博客