report

$ git --version
git version 2.11.0
$ git commit --amend -S
error: gpg failed to sign the data
fatal: failed to write commit object
$ git config --list
user.name=me
user.email=me@host
credential.helper=osxkeychain
push.default=simple
merge.tool=vimdiff3
core.editor=vim
core.precomposeunicode=true
core.quotepath=false
core.pager=less
status.submodulesummary=true
diff.submodule=log
diff.compactionheuristic=true
color.ui=true
gpg.program=gpg2
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true
core.ignorecase=true