Start logging channel activity to {fname}. When {fname} is an empty string: stop logging. When {mode} is omitted or "a" append to the file. When {mode} is "w" start with an empty file. Use |ch_log()| to write log messages. The file is flushed after every message, on Unix you can use "tail -f" to see what is going on in real time. To enable the log very early, to see what is received from a terminal during startup, use |--cmd|: vim --cmd "call ch_logfile('logfile', 'w')" This function is not available in the |sandbox|. NOTE: the channel communication is stored in the file, be aware that this may contain confidential and privacy sensitive information, e.g. a password you type in a terminal window. Can also be used as a |method|: 'logfile'->ch_logfile('w')