(b) Alternatively, as of docker v1.3 use the docker-exec command to inspect syslog container directlyĭocker exec -t syslog tail -f /var/log/syslog

(a) Inspection Container - Tail them logs:ĭocker run -name seelog -volumes-from syslog ubuntu tail -f /var/log/syslog Log generating container - Start another container to send logs:ĭocker run -name foo -v /tmp/syslogdev/log:/dev/log ubuntu logger -t 'foo says' hello Syslog Container- Run the syslog container, here all the logs will be gathered, when syslog starts it creates /dev/log which will now be in the mounted host dir /tmp/syslogdev:ĭocker run -name syslog -d -v /tmp/syslogdev:/dev syslog He uses 3 containers, but you can dispense with the inspection container if you are using docker v1.3 as you can simply inject a shell in to inspect the /var/log file. Though it might be best to exercise a bit of process hygiene. You can pretty much take your pick of how you now access the container. Or singularly: docker exec -t foo cat /some/log/file Interactively: docker exec -it foo # cat /some/log/file Once a second process is inserted, you can see this with in the container. So it is then possible to attach a process, to access arbitrary log files. While it is not generally considered a good idea to run multi-process containers, from of docker version 1.3, it is possible to insert a secondary process into a container, using docker-exec. #Inject a log monitor process with docker-exec docker run -d -p 80:80 -v :/etc/nginx/sites-enabled -v :/etc/nginx/certs -v :/var/log/nginx ls The alternative would be to mount a host directory as the log folder and then access the log files directly on the host.

#Access the logs on a host mounted directory RUN ln -sf /dev/stderr /var/log/nginx/error.log ngix dockerfile RUN ln -sf /dev/stdout /var/log/nginx/access.log The ngix can write to its logfile, as a file, but as a result the lines will go to stdout & stderr (but can be split see above).Į.g. This way involves creating links /dev/stdout|stderr as /app/log.file. This just tails the log file to stdout or stderr: tail -pid $$ -F /var/log/nginx/access.log & While this is perhaps possible, I don't recommend it. If we were running something in like a webserver docker run -name foo -d -p 80:80 dockerfile/nginx There are a few ways to get at a given application's log files, they either involve either getting these specific log files to the containers stderr|stdout stream or to mount the log file's dir as a volume. Or split stdout and error to host stdout: docker logs foo > docker logs foo 2>. You can then simply split the stdout & stderr of the container by piping the separate streams:Īnd send them to files: docker logs foo > stdout.log cat cat stderr.log Let's create a container named 'foo' docker run -name foo ubuntu /bin/bash -c 'while true do echo 'I am up.' sleep 2 done'ĭocker-logs CLI command merges both stdout and stderr into one stream: docker logs foo Getting logs is still not something perfected in docker, and remains a little clunky. It may look like a json file, it's not.#Some discussions on logging from docker:Ī lot of this boils down to whether you want a single or multi-process (systemd, supervisord etc.) container. In the file **CONTAINER_ID**-json.log in that folder, you'll find a file with all the logs for that container. Under containers/**CONTAINER_ID** you'll find infos about the container. You can specify the date as an RFC 3339 date, a UNIX timestamp, or a Go duration string (e.g. The -since option shows only the container logs generated after a given date. Chances are that directory is in the same place on other systems (can't confirm). The docker logs -details command will add on extra attributes, such as environment variables and labels, provided to -log-opt when creating the container. On systems that use apt/debian style system, the package installed by the docker repository use /var/lib/docker. Location of the fileįind your docker directory. First, I'm using docker 1.1.2 for both client and server, this answer may be obsolete for newer versions of docker as docker evolve quickly.

Docker logs