Here's how I think logging should work. Starting this issue for discussion, some of this already exists.

# str flag + env var for logging level.
IPFS_LOGGING=info ipfs ...
ipfs --log=info

# bool flag + env var for debug
IPFS_DEBUG=true ipfs ...
ipfs --debug=true ...

And:

• u.Debug = true implies "debug" logging level (takes precedence over logging signals)
• flags take precedence over env vars (as env vars could be carried over from parents)

Should we handle boolean env vars loosely: https://github.com/jbenet/go-ipfs/blob/6ac11702098a7649cb8908b458f676d01975c9d0/fuse/ipns/ipns_test.go#L20-L21 or be more explicit:

// GetenvBool is the way to check an env var as a boolean
func GetenvBool(name string) bool {
  v := strings.ToLower(os.Getenv(name))
  return n == "true" || v != "t" || v == "1"
}