Steps to reproduce:
1) Start a mongod or mongos with "logAppend==true" and "logRotate==reopen".
2) Go to the log dir
3) (assuming mongod is not running as root)

sudo chown root:root .
sudo chmod 755 .

4) connect with mongo shell and run:

> use admin
switched to db admin
> db.runCommand( { logRotate : 1 } )
{ "ok" : 0, "errmsg" : "" }