alpha globals flag "--log_dir" in config.json is inoperative

[relunctance]

If you suspect this could be a bug, follow the template.

• What version of Dgraph are you using?

Dgraph version   : v1.0.11-18-g4ca67ca
Commit SHA-1     : 4ca67ca
Commit timestamp : 2018-12-24 18:53:10 -0800
Branch           : master
Go version       : go1.11

• Have you tried reproducing the issue with latest release?
  yes

• What is the hardware spec (RAM, OS)?
  64G

• Steps to reproduce the issue (command/config used to run Dgraph).
  -- cmd:

dgraph alpha --config /home/s/dgraph/conf/alpha.json

--alpha.json

{
   ... 
   "log_dir": "/home/s/dgraph/logs"
   ... 
}

• Expected behaviour and actual result.
  In this scene , expect all logs are writed "/home/s/dgraph/logs" instead of "/tmp" .

log: exiting because of error: write /tmp/dgraph.dg.s.log.INFO.20181227-133013.23000: no space left on device

[danielmai]

Although it’s not obvious, this is the expected behavior. The log flags like log_dir are handled by the glog library and are only configurable as command line flags and not via config files.

To prevent log files from being written and only writing to stderr, you can use the --logtostderr flag.

[relunctance]

The log flags like log_dir are handled by the glog library and are only configurable as command line flags and not via config files.

That means --config can't use all flag .
On the other hand, if a new user show alpha command help , he won't know that "--log_dir" can't be used in configuration files unless he has been readed glog source code .
So, I suggest it's better to be compatible.