Require monolog problem

I can't complete require package monolog, the execution is killed. (code below) Someone can help me or give me suggestion? Many thanks

treehouse:~/workspace$ composer require
Search for a package: monolog

Found 15 packages matching monolog

[0] monolog/monolog
[1] kdyby/monolog
[2] mrtnzlml/monolog
[3] stackify/monolog
[4] thinframe/monolog
[5] flowpack/monolog
[6] zoya/monolog
[7] intelogie/monolog
[8] monolog/monolog
[9] amberovsky/zf2-monolog
[10] mero/yii2-monolog
[11] symfony/monolog-bundle
[12] symfony/monolog-bridge
[13] logentries/logentries-monolog-handler
[14] kamisama/monolog-init

Enter package # to add, or the complete package name if it is not listed: 0
Enter the version constraint to require (or leave blank to use the latest version):
Using version ^1.21 for monolog/monolog
Search for a package:
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Killed