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If a logdriver doesn't register a callback function to validate log options, it won't be usable. Fix the journald driver by adding a dummy validator. Teach the client and the daemon's "logs" logic that the server can also supply "logs" data via the "journald" driver. Update documentation and tests that depend on error messages. Add support for reading log data from the systemd journal to the journald log driver. The internal logic uses a goroutine to scan the journal for matching entries after any specified cutoff time, formats the messages from those entries as JSONLog messages, and stuffs the results down a pipe whose reading end we hand back to the caller. If we are missing any of the 'linux', 'cgo', or 'journald' build tags, however, we don't implement a reader, so the 'logs' endpoint will still return an error. Make the necessary changes to the build setup to ensure that support for reading container logs from the systemd journal is built. Rename the Jmap member of the journald logdriver's struct to "vars" to make it non-public, and to make it easier to tell that it's just there to hold additional variable values that we want journald to record along with log data that we're sending to it. In the client, don't assume that we know which logdrivers the server implements, and remove the check that looks at the server. It's redundant because the server already knows, and the check also makes using older clients with newer servers (which may have new logdrivers in them) unnecessarily hard. When we try to "logs" and have to report that the container's logdriver doesn't support reading, send the error message through the might-be-a-multiplexer so that clients which are expecting multiplexed data will be able to properly display the error, instead of tripping over the data and printing a less helpful "Unrecognized input header" error. Signed-off-by: Nalin Dahyabhai <nalin@redhat.com> (github: nalind)
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% DOCKER(1) Docker User Manuals % Docker Community % JUNE 2014
NAME
docker-logs - Fetch the logs of a container
SYNOPSIS
docker logs [-f|--follow[=false]] [--help] [--since[=SINCE]] [-t|--timestamps[=false]] [--tail[="all"]] CONTAINER
DESCRIPTION
The docker logs command batch-retrieves whatever logs are present for a container at the time of execution. This does not guarantee execution order when combined with a docker run (i.e., your run may not have generated any logs at the time you execute docker logs).
The docker logs --follow command combines commands docker logs and docker attach. It will first return all logs from the beginning and then continue streaming new output from the container’s stdout and stderr.
Warning: This command works only for the json-file or journald logging drivers.
OPTIONS
--help Print usage statement
-f, --follow=true|false Follow log output. The default is false.
--since="" Show logs since timestamp
-t, --timestamps=true|false Show timestamps. The default is false.
--tail="all" Output the specified number of lines at the end of logs (defaults to all logs)
The --since option shows only the container logs generated after
a given date. You can specify the date as an RFC 3339 date, a UNIX
timestamp, or a Go duration string (e.g. 1m30s, 3h). Docker computes
the date relative to the client machine’s time. You can combine
the --since option with either or both of the --follow or --tail options.
HISTORY
April 2014, Originally compiled by William Henry (whenry at redhat dot com) based on docker.com source material and internal work. June 2014, updated by Sven Dowideit SvenDowideit@home.org.au July 2014, updated by Sven Dowideit SvenDowideit@home.org.au April 2015, updated by Ahmet Alp Balkan ahmetalpbalkan@gmail.com