結論
--logfile
の指定は必須です。
$ sidekiq --daemon --logfile /tmp/foobar.log
補足
ヘルプを見ましょう。ググるよりもまず公式です。
$ sidekiq --help 2018-02-27T05:00:02.740Z 14493 TID-gojqgqogs INFO: sidekiq [options] -c, --concurrency INT processor threads to use -d, --daemon Daemonize process -e, --environment ENV Application environment -g, --tag TAG Process tag for procline -i, --index INT unique process index on this machine -q, --queue QUEUE[,WEIGHT] Queues to process with optional weights -r, --require [PATH|DIR] Location of Rails application with workers or file to require -t, --timeout NUM Shutdown timeout -v, --verbose Print more verbose output -C, --config PATH path to YAML config file -L, --logfile PATH path to writable logfile -P, --pidfile PATH path to pidfile -V, --version Print version and exit -h, --help Show help