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moby--moby/man/docker-logs.1.md
Nalin Dahyabhai e611a189cb Add log reading to the journald log driver
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)
2015-09-11 16:50:03 -04:00

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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 containers 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 machines 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>