composer config --editor --global
显示出的文件路径，就是全局配置文件的路径：
如上：如果当前用户为root，则路径为：/root/.config/composer/config.json
composer 默认的全局配置信息:
[repositories.packagist.org.type] composer
[repositories.packagist.org.url] https://mirrors.aliyun.com/composer/
[process-timeout] 300
[use-include-path] false
[preferred-install] auto
[notify-on-install] true
[github-protocols] [https, ssh]
[vendor-dir] vendor (/root/vendor)
[bin-dir] {$vendor-dir}/bin (/root/vendor/bin)
[cache-dir] /root/.cache/composer
[data-dir] /root/.local/share/composer
[cache-files-dir] {$cache-dir}/files (/root/.cache/composer/files)
[cache-repo-dir] {$cache-dir}/repo (/root/.cache/composer/repo)
[cache-vcs-dir] {$cache-dir}/vcs (/root/.cache/composer/vcs)
[cache-ttl] 15552000
[cache-files-ttl] 15552000
[cache-files-maxsize] 300MiB (314572800)
[bin-compat] auto
[discard-changes] false
[autoloader-suffix]
[sort-packages] false
[optimize-autoloader] false
[classmap-authoritative] false
[apcu-autoloader] false
[prepend-autoloader] true
[github-domains] [github.com]
[bitbucket-expose-hostname] true
[disable-tls] false
[secure-http] true
[cafile]
[capath]
[github-expose-hostname] true
[gitlab-domains] [gitlab.com]
[store-auths] prompt
[archive-format] tar
[archive-dir] .
[htaccess-protect] true
[use-github-api] true
[home] /root/.config/composer
在使用composer 的时候，其cache-dir目录占用磁盘空间过多，修改为其它目录，命令如下：
composer config -g cache-dir /works/.cache/composer