Sidekiq をバックグラウンド（daemon）で起動する方法

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